Dncnrvrnnn.1986 Mosqurro-BoRNE ARBovTRUSES 437

CHANGING PATTERNS IN -BORNE ARBOVIRUSES

G. R. DEFOLIARTT. D. M. WATTS' eNo P. R. GRIMSTAD3

ABSTRACT. Researchleading to the current state of knowledge on the epidemiology of La Crossevirus (LACV),JamestownCanyon (JCV) and dengue(DEN) virusesis summarizedin relationto the generally recognizCdcriteria for incriminating vectors.The importance of vector biology and local ecologicalconditions is eriphasized as is the necessityofi good balanceb6tween laboratory and fiIld-based studies.The influence of huinan activity in shaping th'e epidemiologicalpatterns of all three'of these arbovirusesis readily apparent.

INTRODUCTION such,the suddenlyvoluminous research on this virus and its major vector, Aedzstriserintus (Say), Four basiccriteria must be met in incriminat- is relatively condensedin time compared to any ing the mosquito vector(s)of an arbovirus: l) other arbovirus. It illusrates the types of isolation of virus from naturally infected questions raised in investigating a virus known mosquitoes;2) laboratory demonsration of the to be transovarially transmitted in nature. ability of the mosquitoesto become infected by Jamestown Canyon virus appears to be the feeding on a viremic host; 3) laboratory most rapidly emerging "new" arboviral prob- demonstration of the ability of these infected lem of public health importance in North mosquitoes to transmit the virus during America. Although serologicallyclose to LACV, bloodfeeding,and ; 4) evidenceof bloodfeeding its ecological support system (i.e., vectors, contact between the suspectedmosquito vector vertebratehosts, landscape) is completelydif- and suspectedvertebrate hosts under natural ferent. Despite this, these two interface conditions. In a companion review (DeFoliart in intricate ways that carry potentially impor- et al. 1987),the focuswas on the importanceof tant public health implications. Current ques- a host of variables that must be considered in tions relative to JCV typify the formulation of attempting to satisfy these basic criteria and to hypotheses necessaryduring the early phases assesstrue vector comPetence.It was empha- of vector incrimination. Dengue viruses, a sized that a good balance of field- and group of 4 closely related serotypes laboratory-basedstudies must be maintained to (DEN-1,2,3,4),warrant inclusion becauseden- ascertainthe unique combination of ecological gue has greater world-wide public health and behavioral features essentialto survival of importance than any other mosquito-borne a given arbovirus in a given situation. With the arboviral entity. Regardeduntil recently as an input of field-basedstudies, it becomesappar- "there anthroponosis (i.e., transmitted by vectors ent as statedby the above authors that is solelyfrom human to human), it is probably a no aspect of vector ecology or behavior that zoonosiswith an ecologicalvariety of transmis- may not be found to require clarification sion cyclesincluding sylvan,rural, and urban, during the epidemiological investigation of an The DEN virusesvividly portray the difficulties arbovirus." encountered with a public health problem The implications of the preceding statements intimately adapted to the cultural and socio- can best be illustrated by the changing ques- economic environment of human populations tions that arise at progressive stages in the in the tropics. investigationof a specificarbovirus. As exam- ples, we discusshere the 3 viruseswith which we have had our most extensive research LA CROSSEVIRUS experience, La Crosse (LACV), Jamestown Canyon (JCV) and dengue (DEN). Each virus La Crossevirus is a Bunyavirusbelonging to has unique characteristicsthat make its inclu- (CAL) serogroupwhich contains sion appropriate. Lacrosse virus is the most the California virus and variet- recently recognized of the major mosquito- 14 recognized types, subtypes (Calisher 1983). At least 6 of the viruses borne arboviruses in North America, and, as ies cause human illness. La Crosse virus was originally isolated from the brain of a child who died of encephalitisin 1960 in La Crosse, I Department of Entomology, University of Wis- Wisconsin(Thompson et al. 1965).The major- consin,Madison, WI 53706. ity of virus isolations and human clinical cases 2 of Pathogenesisand Immunology, Department have occurred in Ohio, Wisconsin, Minnesota, Divisionof DiseaseAssessment, United StatesArmy MedicalResearch Institute of InfectiousDiseases, Ft. Iowa, Illinois, Indiana and New York, but Detrick. Frederick,MD 21701. there have been serologically confirmed hu- 3 Department of Biology, University of Notre man infections in Nebraskaand the majority of Dame,Notre Dame, IN 46556. statescontiguous with or eastof the Mississippi 438 Jounuel oF THEArunnrceN Mosgurro coNrnor. AssocrerroN vor.. 2, No. 4

River (Calisher 1983, Calisher and Thompson maternal vertical transmission rates (MVTRs) 1983). of up to 70Vo(the MVTR is the product of the It required 7 years after the identification of percentageof infected females passingvirus to LACV before the basic criteria for vector at least some of their progeny and the fitial incrimination had been satisfied. Chipmunks infection rate [FIR], i.e., ttre mean percentaqe and gray squirrels were suspectedas veitebrate of infected progeny from transovarialiy- hosts based on their high prevalence transmitting females). These results led to the in nature (Moulton and Thompson l97l). view that LACV maintenance relies primarily Aedzstriseri,atus, a tree hole breeding mosquito, on this vertical transmission component with becamesuspected as the primary vettor on the horizontal amplification via vertebiates viewed basisof virus isolations from naturally infected as a processfor recruiting enough new vertical mosquitoes (Thompson et al. lli72), and transmitters to maintain a relatively stablevirus demonstration under simulated field condi- prevalencein the vector population. Increasing tions of bloodfeeding contact with the sus- evidence,however, that LA-CV undergoes high p€.J.{ vertebrare amplifying hosts (Wright and attrition at several points during vinebra"te DeFoliart 1970).Also, seasonaland geo[raphic amplification has riised a queition as to compatibility.was shown between peik fopula- whether this horizontal proiess can fully tions of Aa. triseriahts(Loor and Oefolait i9Z0; negate the erosion of virus prevalence that and human clinical cases (Thompson and occurs during maternal vertical transmission Inhorn 1967). This early era of vector incrimi- (DeFoliart 1983). The quesrion was first raised nation^wascapped by thi laboratory demonstra- by Miller et al. (1979) who reported that orallv tion of high ransmission ntes (93% or higher) infected Ac. trkerianu did noi become vertical by Ae. tri.seriatruorally infected on virus doiages transmitters until the second oviposition after as low as 1.8 median tissue culture infectlive the infectious blood meal. Female dailv life (TCIDso)/0.I dose ml (Waus et al. lg72), and expectancies of 80-95Vo have been reported demonstration that chipmunks and gray squir- for Ae. triseriatus(Beier et al. 1982, Hiramis rels developed viremias sufficient to"ini^eciac. and Foster 1983, Sinsko and Craig l9Z9), and (Pantuwatana triseriatus et al. lg72). Other it can be calculated that the orillv infected mosquito speciestested were relatively ineffi- cohort^probably experiencesa mortaiity rate of cient oral ransmitters of the virus, in'dicating about 90% prior to deposition of infected eggs. there were no important secondary vectors ii I hls assumptton was strengthened by the the upper Midwest (Watts et al. lg73a). finding at one endemic site that onlv ?.lVo of Additionally, the early conclusion that chip- bloodseeking Ac. triseriaus females were bipar- munks-and squirrels were amplifying hosis, ous (Porter and DeFoliarr 1985). originally somewhattentative as it was blsed on Overall, there appear to be at least 4 presence of.antibody to undifferentiated CAL sequential points and 7 or 8 factors during the serogroup virus, was substantiatedby isolations vertebrate amplification process that wiii, or of LACV from both of these mammalian may under certain condilions, result in high species(Gauld et al. 1975, Ksiazekand yuill virus attrition: 1977), and by evidenceof high LACV transmis- l) Virus atrrition resulting from bloodfeeding sion activity in areas with good-subsequent chipmunk on non-amplifier species of vertebrates: AeI habitat (Gauld et al. lg74). re- trtseriahr is catholic in its feeding behavior search (discussedbelow) showed 3 additional (Burkot and DeFoliart 1982, Naici l9g2a, types of transmissionand additional vertebrate 1985; Wright and DeFoliart 1970). White- and potential vector species.Also, it became tailed deer are non-amplifiers of LACV (Issel evident that, to explain the transmissiondynam- et al. 1972a, 1972b),buia 3-year studv of blood ics of LACV, information was needed on meal sources at an endemii site in i{isconsin 4T"r! every aspect of vector biology and revealed that 65Voof Ae. triserialru blood meals behavior. were from this vertebrate while only 24Vowete In the early 1970s, Watts et al. (lg?3b) from chipmunks and gray squirrils (Burkot experimentelly demonstratedtransovarial trans- and DeFoliart 1982). A blood meal ratio such mission of LACV by Ae. triseriatusand this as this from deer and amplifier speciesresults breakthrough was followed quickly by the in a nearly l6-fold decrCasein implification finding that the virus overwinteis in the potenrial, because only about 2b'% of the dilpaused eggs of the mosquito (Watts et al. potentially infective bites are delivered to 1974).In endemic areasof Wisconsin,overwinter- amplifier speciesand only 2bVoof the poten- ing virus prevalencewas found to be about 0.4 tially infectable vector population feeds on to0.6% in larvae and adults from overwintered amplifier-species.Although-such dispersion of (Beaty eggs and Thompson 1975, Lisitza et al. bloodfeeding among host speciesmilht not be 1977), and Miller et at. ltSZZy demonsrrared important with a high population density DBcrrusrn,1986 Mosqurro-Bonxe Annovrnusrs 439

mosquito, Ae. trisnians generally is a low virus at a competitive disadvantage insofar as density species. vertical transmission is concerned (Mather and A second factor of similar magnitude may DeFoliart 1983). also be operative at this point. Preliminary data 4) Virus attrition resulting from high vector (Patrican et al. 1985b) indicated that Ae. mortality between the infectious blood meal triseriaau became infected after ingesting white- and the second post-infection oviposition. The tailed deer blood-LACV mixtures containing findings of Miller et al. (1979) were discussed JCV neutralizing antibody, but failed to trans- above. mit LACV. If this inhibitory effect occurs in Possiblycontradictory to the above evidence nature among LACV-infected mosquitoes that for a reduced role for vertebrate amplifiers was imbibeJCV antibody, it could explain the focal failure to isolate LACV from 22,479 Ae. distribution of LACV becauseof the high JCV trisnianu complex mosquitoes collected on the antibody prevalence in many midwestern deer Delmarva Peninsula (and near absence of populations. It appears that LACV could neutralizing antibody in mammalian sera as- eventually become largely restricted to sayed)where chipmunks are scarce(Clark et al. urban/suburban localities where deer abun- 1986). Gray squirrels are present in the area, dance does not present a barrier to virus however, making it likely that factors other dispersion. than scarcity of chipmunks will be found to 2) Virus attrition resulting from bloodfeeding explain the apparent absence or scarcity of on the immune portion of amplifier popula- I-ACV infections. tions. In active transmission areas, chipmunks One aspect of feeding behavior, probing and squirrels sometimesexhibit LACV neutral- without complete engorgement, could be im- izing antibody prevalencesexceeding 40-50% portant in partially negating the atrritional (Gauld et al. 1974, Moulton and Thompson factors discussed above, but "probing" is not l97l). Infective bites delivered to theseanimals well understood despite several recent papers. "wasted" are insofar as virus amplification is A single probe is sufficient for ransmission of concerned. Once again, a second attritional LACV (Grimstad et al. 1980). Such probing factor may be important, as there is prelimi- appearsto be inherentin Ae. triseriahsbehavior nary evidence of reduced transmission of even when the mosquito is attempting to obtain LACV by Ae. triseriaau that have imbibed a blood meal from a non-defensive host. chipmunk blood-LACV mixtures containing Walker and Edman (1985a)found that approx- LACV neutralizing antibody (Patrican et al. imately 55Voof nulliparous Ae. triseriatw (6-16 1985b). It remains to be seen whether this days old) probed only once before beginning to phenomenon occurs in previously infected feed on anesthetized chipmunks and gray mosquitoes;however, reduced transmissionhas squirrels, while 45Vo probed 2 to 6 times. also been observed in Ae. triseriatus that Multiple probing may be more common in engorged on chipmunks with LACV antibody nature than indicated by these results, how- 5-l I days prior to venereal infection (Thompson ever, as the mosquitoes used were in the F1a 1983). generation of colonization, and long-colonized 3) Virus attrition resulting from inefficient Ae. triserinnuevolve toward single-probebehav- transfer from infected mosquito to susceptible ior (Grimstad et al. 1977). In a study of Ae. amplifier animal to susceptible mosquito. Not triseriatw orally infected with LACV, Grimstad all susceptible amplifier hosts fed upon by et al. (1980) found evidence for increased infected Ae. triserians develop high enough transmission by multiple-probing mosquitoes viremia to infect other feeding mosquitoes. of strains with "low" transmission capability, Patrican et al. (1985a,b) found that the virus and somewhat reduced ability by infected titer required to insure high transmission rates mosquitoesto feed to repletion. Patrican et al. (i.e.,90Voor higher) by feeding mosquitoeswas (1985a,1985b) found no significantdifference, approximately 3.4 logro median suckling mouse however, between transovarially infected and inracerebral lethal dose (SMICLDboy0.025 ml uninfected Ae. trisnianu in the proportion of and that only 52Voof chipmunks exposed ro single versusmultiple probes during refeeding. the bite of a single transovarially-infected Ae. Multiple-probers were more successfulin trans- triserianu developed a viremia of this level or mitting LACV and the majority (both "effective higher. The mean duration of transovarially-infected and uninfected) were viremia" was only I day per infective bite successfulin obtaining a complete blood meal delivered to the susceptible portion of the while the majority of single-probers were not chipmunk population. In addition, A e.triseriahs successful. Probing activity was found to be that feed on chipmunks and squirrels have highest among transovarially-infected and. reduced reproductive capacity compared to uninfected mosquitoes after 15 days of age, those feeding on deer, placing orally-acquired indicating a positive correlation between age 440 JounNe,r"oF THEAlrnnrcax Mosqurro CoNrnol AssocrlrroN Vor. 2, No. 4 and probing, but the sample of less-than-15- that the timing of the blood meal relative to day-old mosquitoeswas too small for statistical mating had no effect on the venereal infection confidence. rate. In one cohort ofthose that fed only a few Clearly, probing behavior is complicated and hours before mating, 60Vo and 94Vo of t}lre may be influenced by age, length of coloniza- venereally-infected females transmitted virus tion, and infection status, particularly in the to progeny of their second and third ovarian caseof orally acquired virus. Additional inves- cycles, respectively. Filial infection rates were tigation of this exceedingly important parame- 46Vo and 65Vo, resPectively, but, as in ter is needed. The abovedata were obtained on Thompson's experiments, infection was not immobilized vertebrates. Studies have been detected in progeny of the first ovarian cycle. made of the persistence of attack by Ae. Venereal infection rates were lower when Fa triseriatusagainst defensive hosts (Walker and and F7 females were used. Edman 1985b),but at present the number of In general, this information "infective suggests that contacts" per ovarian cycle com- unless PVT is more efficient in the production pleted by mosquitoes in the field cannot be of infected progeny than currently shown, it estimated with any confidence. makes only a modest compensation for even Thompson and Beaty (1977, 1978) demon- relatively low virus erosion rates during mater- strated paternal venereal transmission (PVT) nal vertical transmission. As SlVo of the of LACV from transovarially-infected Ae. oviposition by Ae. t*eria,l.ruin the field appears triseriatusmales to uninfected females during to be by femalescompleting the first oviposition copulation. Paternal venereal transmission has (S.V. Landry, unpublished data), absenceof appeared to be the most likely alternative or infection in first ovarian cycle progeny of supplement to vertebrate amplification in ne- venereally infected females has the same gating virus erosion during maternal vertical quantitative difficulty as posed by absenceof transmission, but, again, the quantitative con- infection in first ovarian cycle progeny of orally tribution of paternal venereal transmission has infected females. As virus dissemination to not been determined. Paternal transmission ovaries occurs within 3 to 5 days after mating, rates, as measured by the venereal infection however (Kramer and Thompson 1985, rate of females mated with infected males. Thompson and Beaty 1978), investigators were less than 5Vo in early experiments but should be alert to the possible presence of rates up to 49% were obtained when Ae. infection in first ovarian cycle progeny of triseriahu were provided a blood meal 6 to 8 venereally infected females. days prior to mating with transovarially- Recentlydiscovered vertebrate hosts of LACV infected males (Kramer and Thompson 1983, include red and gray fox (Amundson and Yuill Thompson 1979). Little is known- about Ae. l98l) and woodchuck(Amundson et al. l98b). triserians mating behavior but some mating The finding that free-ranging foxes develop occurs on or in the vicinity of the vertebrate viremias sufficient to orally infect Ae. triseriaku host (Loor and DeFoliari tgZO) and once (Amundson and Yuill 1981, Amundson et al. young females have obtained a blood meal, 1985) suggests this mammal may act as a they are immediately willing to accept mates vehicle for transporting and reintroducing (Mather and DeFoliarr 1984b). Thus, it ap- LACV from one woodlot to another. Ol pears that in nature blood engorgement sel- interest is the recent finding (T. E. Amundson, dom precedes mating by the 6 to 8 days personal communication) that the red fox can discussedabove. become infected after ingesting infected chip- In Thompson'sexperiments ( 1979),venereally- munks and suckling mice and develop viremias infected Ae. triseriatw females exhibited oral similar to those of foxes bitten by infected transmission rates to suckling mice of \Vo and mosquitoes.This representsa previously un- 327o,4-7 and 8-17 days, respectively, known mode of arbovirus transmission.Surpris- postmating.No transovarionrransmission (0/23) ingly, in view of the findings on foxes, dogs by venereally-infectedfemales occurred during apparently are lesssusceptible to LACV (M.5. the first ovarian cycle and only 4OVotransovar- Godsey, personal communication) as only I of ian transmission(4/10) in the second ovarian 88 dog sera from the endemic region of cycle with a FIR of 64% in progeny of the 4 Wisconsin had detectableLACV neutralizing ransovarially-transmitting females, an MVTR antibody. Of 6 dogs inoculated intramuscularl| of only 26Vo.L.A. Patrician (unpublished data) and subcutaneously, none developed detect- found venereal infection rates averaging 46% able viremia although 3 exhibited a low in F2 females receiving a blood meal 6-8 hours neutralizing antibody response. before their first opportunity to mate, and 45Vo As happens with many important vector in females given their first blood meal 7 days species, Ae. triseriahu has benefitted enor- after their first opportunity to mate, indicating mously from its interaction with humans. Drcr,Msrn, 1986 Mosqurro-BonNnAnsovrnusrs 441

Although originally a tree hole breeding will presumably reduce the number of clinical species, research on its vector biology and cases of La Crosse . In fact, this control has centered increasingly on its adapta- appears to have been the result of such a tion to breed in small man-made water contain- program initiated in 1979in La CrosseCounty, ers, especiallydiscarded automobile and truck Wisconsin(Parry 1983).In an ll-county area tires. Tires are estimated to be increasingin the of westcentral Wisconsin, the number of United Statesat the rate of 200 million per serologically confirmed cases of La Crosse year (Beier et al. 1983,Deese et al. l98l), and encephalitisin La CrosseCounty declined from Craig (1983) has emphasized the need for 22Vaof the total casesin 1978and 1979to only technology and legislation for disposing of the 6Vo of the total during the ensuing 3-year steel-belted tire. The associationof tires and period, 1980through 1982.This program and other small water-containerswith human cases reduced number of casesis still being main- of La Crosseencephalitis is well documented tained (J.E. Parry, personalcommunication). (Hedberget al. 1985).When in closeproximity Oligonucleotide mapping of LACV appar- to human residencesor other areas of high ently allows some clarification of the long human activity, thesecontainers becomepartic- uncertain vector status of Aedcs cona.dpruis ularly dangerous and persistent foci of infec- (Theobald).Over the years,there havebeen 4l tion becauseof the vertical transmission capa- isolatesof LACV from Ae. conadensisin Ohio. bility of Ae. triseriatus. Such containers are far more than from any other speciesin that readilv colonized bv Ae. triseriatzrsfrom wooded state although the field infection rate of areas or from other concentrations of such 0.5/1000is lower than the l.l/1000 recorded containers. Although basically a woodland ftom Ae. triserintw (Berry et al. 1986). Early mosquito, Ae. triseriatus is now known to experiments with Ae. canadznsisfrom Wisconsin disperse readily along fencerow "corridors" and a Wisconsin isolate of LACV from Ae. (Mather and DeFoliart 1984a, Nasci 1982b) triseriatus indicated that Ae. canadensissup- and across such open terrain as corn and ported virus replication poorly (Watts et al. alfalfa fields (Mather and DeFoliart 1984a).In 1973a).Klimas et al. (1981), however, de- a surveyof South Bend, Indiana, Leiser (1981) scribed 3 geographic variants of LACV with found Ae. triserianu present throughout the Types A and B occurring in the upper city, except for an industrialized section where midwestern states,while a third type, C, was treesand other vegetationwere sparse.Haramis found in New York and several southern (1984)has shown that, becausewater in tires is states.While LACV isolates from Ae. triseriatw relatively warm, peak pupation of Ae. triseriatus in Ohio are similar to virus strains in Wiscon- occurs 2 to 3 weeks earlier than in tree holes. sin, an Ohio LACV isolate(CDC No. R-15804) and, thus, TO-infected females from tires may from Ae. canadensiswas related to LACV initiate LACV transmission earlier in the strainsfrom New York (Type C) (Klimas et al. season.Means et al. (1977)found femalesfrom l98l). Of the 41 isolates from Ohio Aa. tires in New York to be more aggressivebiters canadensis,39 were from mosquitoes collected than females from tree holes. in the northeastern corner of the state, in close Larvaein tires are dependenton the autumn proximity to New York. Laboratory experi- accumulation of Ieaf litttr as a substratefor the ments with strain R-I5804 showed an infection saprophyticfungi upon which they feed (Fish rate of 7\Vo; 54Voof thesetransmitted virus to and Carpenter 1982).Adults emerging in late suckling mice, a population transmissionrate summer from larvae in tires are smaller and of 40%. fewer, probably becauseof increasedintraspecific Aedeshendersoni Cockerell. a reehole breed- competition resulting from seasonaldepletion ing speciesthat is sympatric with Ae. triseriatw of nutrients (Haramis 1984). Similarly small throughout most of the eastern United States, "Small" females can be produced in tree holes. has been shown to have low LACV transmis- females have higher oral and TOT rates than sion capability, with population rates of only "large" females(Grimstad and Haramis 1984, 0-l4Vo (Grimstadet al. 1985,Watts et al. 1975), Patrican et al. 1985b), although this may be Recent findings by Nasci (1985), however, of offset by lowered fecundity in the smaller heavy utilization of tree squirrels as a blood females (Patrican et al. 1985b). AIso, larger meal source by Ae. hendersoni,and that this females have higher parity rates, indicating speciesoccurred at more than twice the density greater successin bloodfeeding, increased of Ae. triseriatu in an Illinois enzootic area longevity,or both (Haramis 1983). dictate caution in assumingthat this specieshas A thorough, ongoing program involving the no vector role. To date, however, field isolates removal or insecticidal treatment of the small- of LACV have not been obtained from this container and tree hole Ae. triseriatw breeding species,and data from Illinois (Clark et al. sitesnear human habitations in high-risk areas 1985),Indiana (Novak et al. l98l), Wisconsin 442 JounNer oF THEAurnrceu Mosqurro Cournor AssocrerroN Vor_.2, No. 4

(Burkot and DeFoliart 1982,Loor and DeFoliart and the initial isolation of LACV from this 1970),and the DelmarvaPeninsula (Clark and speciesin the field. Craig 1985) indicate that Ae. lund,ersoniposes From research to date, it becomes obvious little direct risk to humans as it is either oT low that the urban-suburban environment readily population density or is infrequently encoun- meets the transmission requisites of LACV, tered at ground level. As is often the situation which, evolutionarily, was a disease of the in vector complexes, Ae. hendnsoni creates a deciduous forests of the upper Midwest. As problem in field studies on the vector biology shown by Burkot and DeFoliart (1982),where of Ae. triseriafusbecause adult females of the 2 deer are numerous, they minimize vector- sibling species can be distinguished reliably amplifying host conract,and if JCV antibody only by elecrophoresis (Munstermann et al. prevalence is high, may exerr further inhibi- 1982,Saul et al. 1977). tory effects on LACV transmission (Patrican et _The labor_atory finding that Aedesatropalpus al. 1985b).On the other hand, as shown by (Coquillett) from Indiana is capableof holizon- Nasci (1982a),in the urban-suburbanenviron- tal and vertical transmission of LACV (Freier ment and some rural environments where deer and Beier 1984) adds a potentially important are absent or scarce, contact between vector new dimension to the ecology and distribution and amplifying hosts is greatly increased. ofthe disease.A rock hole breeder in the north Thus, risk of LACV infection in many endemic and east,Ae. atropalpushas rapidly extended its localitiesis directly proportional to the densitv range soutlwestward and, since 1979, been of breedingsites available ro the vector,and thl: found breeding in tires from New york to importance of source reduction becomesobvi- Indiana. These tire-adapted populations, true ous. Ae. atropalpu on the basis of morphology and enzyme phenotype (Munstermann 1980), are JAMESTOWN CANYON VIRUS autogenous for the first ovarian cycle, but . Jamestown Canyon virus, a subtype of Melao similar to the southwesternand closeiyrelated virus of the CAL serogroup, was first isolated Aedzs epadiu Dyar and Knab in the avidity of from Culisaa inornata fiVittiiton; mosquitoesin their biting. WhereasAe. triseria.hnlarvae oicur Coloradoin 196l (Hammon and Sathbr 1966). more abundantly in shaded tires, Ae. atropalpnu-19-83, For the next 2 decades,JCV wasconsidered of prefers tires in the open (Beier et al. minimal public health significance.A 1963 Wis- Berry and Craig 1984),thus potentially further consinstud-y-i{e_ntified 3 young men who expe- increasing the importance of tires as an rienced mild febrile illness that was "California attribuied ecological determinant in the incidence and to a virus" infection(Thompson and spread of LACV infections. Because of its Evans1965) later determinedto havebeen caused oviposition behavior, Ae. atropalpu is also a byJCV (Thompson and Gunderson lg83). These more rapid colonizer than Ae. triseriatus(Berry 3 casesconstituted the only publishedevidence and Craig 1984).On the negativeside relative that JCV infection might causehuman disease to a potential vector role, although Ae.atropalpt$ until 1982, when Grimstad (1982) 'todents" -ttre et al. re- feeds readily on humans and in ported a caseof severeprimary encephalitisthat (Freier laboratory and Beier 1984), limited resultedfrom a JCV inTection'ina ybung Mich- blood meal analyseshave shown engorgement igan girl. Subsequentstudies documented over only on deer, humansand canines(W. J. Berry, 40 clinical casesof central nervous system ill- cited in Freier and Beier 1984) and parity ness and other syndromes caused Uj' ICV ln analysis at the one site for which data are residentsof Ontario (Deibelet al. lg85) ind the available,indicated that only a low percentage NorthwestTerritories in Canada(H. Artsob, per- were successful in obtaining a blood meal sonal communication),and in residentsoflli- (Berry and Craig 1984).In addition, while oral nois, New York (R. Deibel,personal communi- infection and transmissionrates were high and cation), and Ohio in the Uniied States(Deibel et al. 1983, comparable to the Walton (Indiana) and Grimstad et al. 1986).Grimstad et al. (1986) have recently Kerrville (Texas) strains of Ae. triseriatm. and shown that human infec- tion with is widespread in the the vertical FIR was comparable ro the Walton JCV upper Mid- west,(e.9., the statewideneutralizing antibody strain, the FIR of the latter (10.7%) was well prevalencerate in Michigan residentswas28Voi. below that found in Wisconsin populations of The geographic pattern of antibody prevalence Ae. triseriahs (50% or higher). Thus, a more was similar to that of the population distribu- precise definition of the vector role of tire- tion of the white-tailed deer, the primary ver- adapted Ae. atropalpurawaits more information tebrate host of JCV. Similarly, in Indiana, the on the nature and degree of vector-vertebrate geographic pattern of human anribody preva- host contact, the testing of additional popula- lence follows that of the distribution pariern of tions for their vertical transmission capability, deer density (Grimstad 198I. Dncnrr.rsrn.1986 Mosgurro-Bonr.rrAR sovrnusns 443

The lack of human casedetection in the light lower prevalenceof JCV neutralizing antibody of such widespread infection is not surprising in deer fawns compared to yearling (I.5-yr-old) given that only neutralization tests in cell deer (Boromisaand Grimstad 1987,Issel et al. culture with JCV as test anrigen lead to 1972b). At the Houghton Lake (Michigan) recognition of current or past infection (Grimstad Wildlife Research Area, a known JCV focus et al. 1986). Virtually all state diagnostic (Grimstad and Mandracchia 1985), fawns born laboratories that test for CAL group antibody in 1983 had lost maternal antibody by midwin- in clinical central nervous system cases use ter; however, all subsequently seroconverted LACV in complement fixation or hemoglobin during a 6-week period in 1984 (late May to inhibition tests (Calisher and Bailey lg8l). early July). All newborn fawns bled there as Unfortunately, these 2 procedures detect less early as 4 days after birth in 1984 had maternal than l.\Vo of JCV infections (Grimstad et al. antibody to JCV; by late fall all were seronega- 1986). The critical need for a rapid sensitive tiverSeroconversionof the 1984 cohort to JCV diagnostic procedure for JCV is obvious, occurred the following spring within a l0-week especially since its range extends throughout period (Grimstad et al. 1987). Seroconversion temperate North America (Calisher 1983, of year-old deer at Houghton Lake has Grimstad 1987). primarily occurred coincident with spring Extensivestudies in the East and Midwest emergence of snow-melt Aedcs mosquitoes; have demonstrated that the white-tailed deer is seroconversion in deer at Houghton Lake, the primary vertebrate host in the enzootic Kingsbury State Fish and Wildlife Area in cycle (Issel 1973, Issel et al. 1972a, 1972b; northern Indiana, and elsewherehas not been Watts et al. 1979, 1982).The sole isolationof associatedwith blackfly, tabanid or tick biting JCV from a vertebrate was from a sentinel activity (Boromisa and Grimstad 1986). white-tailed deer in Wisconsin (Issel 1973). Three tabanid speciesand numerous mos- Unlike other CAL serogroup viruses in the quito specieshave yieldedJCV isolatesthrough- Midwest, JCV apparently does not produce a out North America (Grimstad 1983). In New detectable viremia in rabbits or squirrels York, JCV has been isolated from 13 mosquito (Seawright et al. 1974, Watts et al. 1979); species,12 of which were (Grayson et al. however, squirrels do seroconvert following 1983). Midwestern workers have shown the JCV infection (Watts et al. 1979). Several marked preference of woodland Aedcsfor d,eet recent studiesdetected |CV antibody in domes- (Nasci 1982a, 1984; Wright and DeFoliart tic livestock (Grimstad lb87;. Crimstad lunpub- 1970). Turell and LeDuc (1983) stated that lished data) found neutralizing antibody prev- Culisetainomata was the primary vector of JCV. alence rates of 4040% in bovine and equine While that may be true in the western United herds in Indiana and Michigan; however, these States, Aedes species, notably Aedes stimulans species do not develop a viremia following (Walker) (Boromisa and Grimstad 1986), and experimental exposure to JCV (M. Godsey, perhaps Ae. cornruunis(DeGeer) group mem- personalcommunication). Thus, neither small bers, are probably the primary regional vectors forest-dwelling mammals nor large domestic in the eastern United States and Canada mammals seem likely to serve as a source for (Grimstad 1987). In the 2 upper Midwestern arthropod infection (Grimstad lg87). JCV foci (Kingsbury [Boromisa and Grimstad Critical to the maintenance of an arbovirus 19861and Houghton Lake), Cs.inornata is quite cycle is the seasonalrecruitment of susceptible rare; however, antibody prevalence to JCV vertebrate hosts. Studies in Michigan and ranges from 70 to l$OVoin yearling and adult Wisconsin have demonstrated a May through deer (Boromisaand Grimstad 1987, Grimstad June period of JCV circulation in older deer et d. 1987). (Grimstadet al. 1987,Issel et al. 1972a,1972b). Evidence is emerging linking multiple spe- Maternal antibody in the colostrum of nursing cies to the JCV transmissioncycle. In northern does protect fawns from a primary infection Indiana, JCV is apparently transovarially trans- with JCV for 8 to 23 weeks (mean of 19 weeks) mitted by Ae. stimulnru; isolations have been following their birth in April through June made from separatepools of teneral males and (Issel 1974). Since most deer seroconversionto females in late May prior to any bloodfeeding JCV presumably occurs by late June in the (Boromisaand Grimstad 1986).At Kingsburya midwesternand northeasternstates, this lengthy minimum field infection rate (MFIR'1of l:1424 period of protection by maternal antibody for male and l:591 for female Ae. stimularcwas provides a large number of susceptibleverte- noted in May 1983; the seasonal MFIR for brate hosts (i.e., the year-old deer) the follow- females was l:1260 (Boromisa and Grimstad ing season. Serologic surveys of deer taken 1986). Bloodmeal precipitin testsindicated that during the fall hunting seasonsin Indiana and free-ranging deer were essentially the only Wisconsin have demonstrated the significantly blood source for Ae. stimularuat this JCV site 444 Jounver oF THE AllnnrceN Mosqurro CoNrnor. AssocrerroN Vor. 2, No. 4

(Boromisa and Grimstad 1986). Laboratory had onsetduring August to October, and SlVo transmissiontrials with field-collectedmembrane- ( I 3/39) in September-October(Grimstad I 987). fed Ae. stimulansresulted in a 44% population Sincetransmission to deer in this area occurs in infection rate and a l2Vo population transmis- the spring, and univoltine Aed,esdo not persist sion rate. All Ae. stitnulansfemales with dissem- much beyond July, other mosquito vectors inated infections (detected by head-squash must be primarily responsible for late summer immunofluorescence)transmitted JCV to suck- human infections. ling mice (Boromisa and Grimstad 1986). Evidence gained through the deer and These data suggest that a midgut barrier to human epidemiologic studies support a work- JCV exists in Ae. stimulans, but there is ing hypothesis(P. R. Grimstad)that anopheline apparently no salivary gland barrier. Unfortu- mosquitoes,notably Anophclzspunctipnnis (Say) nately, Ae. stimulanshas not been colonized; one and/or Anophelesqwdrimaculntus Say, are poten- difficulty in rearing this speciesis the obligate tial vector candidates.This "anopheline vector" 180-day egg incubation at 4oC necessaryro hypothesis is based on 3 main considerations. break diapause(Horsfall 1974). First, isolationsofJCV have been made in Ohio IsolationsofJCV have been obtained from from An. punctipennisin July and September Aedesuexarc (Meigen) in Connecticut,New York (MFIRs of l:128 and l:733 in different years and Wisconsin(Grimstad 1983).In New York, and localities;R. L. Berry, personalcommuni- Grayson et al. (1983) reported a l:160,811 cation) and from An. qua.drimacul.atusin July MFIR for JCV in Ae. aexans.No JCV isolates (MFIR of l:274) (Berryet al. 1983;R. L. Berry, were obtained at Kingsbury in Indiana from personal communication),and in New York more than 83,000 Ae. vexanscollected over 3 from An. punctipennis during rhe summer years; spring and early summer collections (Graysonet al. 1983). Second,in 1983 in the were made at the same time that isolateswere upper Midwest (including the Chicago area) a obtained from Ae. stirnul,ans(Boromisa and drought summer drastically reduced mosquito Grimstad 1986). In the laboratory,Ae. aexaru populations to record low levels in most areas. showed a 35% population infection rate; However, populations of An. punctipennisand however, infection remained localized in the An. quadrimaculattnwere above averageduring midgut, thus precluding virus transmissionto late August and September; the only potential suckling mice (Boromisaand Grimstad 1986). vectors that might have ftansmitted JCV in late The dose of virus ingested was equivalent to September to the south Chicago youth men- peak titers (3.5 logro/0.025m1)demonstrated in tioned above were An. punctipenn'isor An. experimentally viremic deer (Issel 1972a). quadrimacul.atus- no Ae. triseria.tusfemales were Berry et al. (1977) isolatedJCV from adult collected that month (K. K. Liem, personal Ae. triserinhsreared from field-collectedeggs in communicarion). Third, at Houghton Lake, Ohio and subsequentfield studies have led to one-third of the adult does showed serologic additional JCV isolates from eggs of this evidence of very recent JCV infection in late species(R. L. Berry, personalcommunication). March and early April of 1984and 1985,as did These multiple isolations from overwintering a l-year-old doe in 1985; one other adult eggs strongly suggesta regional vector role for doe (of 3 bled biweekly in 1984) showed Ae. triseriatus.However, laboratory transmission evidenceof reinfectionin late September1984. trials with 8 geographic strains of Ae. triseriatus All other deer showedanamnestic responses or failed to demonstrate oral transmission to seroconverted coincident with the emergence suckling mice (P. R. Grimstad, unpublished of snow-melt Aedes(Grimstad et al. 1987). data). Thus, the vector srarusof this species These early spring seroconversions and remains uncertain until additional populations anamnestic responses were detected I to 3 can be tested for transmission capability. weeks after a warm period each year during Human infection with JCV occurs bimodally which conservationworkers reported mosquito in the upper Midwest and New York State, biting activity;in 1985,workers noted biting by "spotted-winged" with onset of clinical casesin 2 distinct periods: mosquitoes,presumably An. May-June and August-September (in contrast punctipennisas no other potential vectors were to LACV clinical cases which show a single present. At Houghton Lake, collections of peak in August-September)(Grimstad 1987). biting mosquitoesin late March, 1986, were all Clinical casesdocumented to date in New York An. puncti,pennis.lf JCV is transmitted by have had onset from May 14 to October 3 (R. anophelines in the early spring, it must persist Deibel, personal communication);one clinical overwinter in bloodfed adult females. encephalitis casein a south Chicago youth had It must be emphasized that anopheline onset of September30, 1983 (Grimstad et al. involvementis a working hypothesis.It appears 1986).Of the 39 serologicallyconfirmed JCV to offer the best explanation, however, for the casesdocumented through 1984, 62Vo(24139) persistenceof JCV in the field from the time Drcrrrrern. 1986 Mosqurro-BonNeAnnovrnusns 445

transmissionto deer ceasesand snow-meltAedes aegypti (Linnaeus), was incriminated as the females die, until human cases increase in primary vector, and only man and subhuman August-September. Anophelespunctipmrcis has pnmates were recognized as natural hosts. not been colonized per se and difficulties Primary infection of man following the bite of abound in maintaining and infecting field- an infected Ae. acgypti produces a viremia collected specimens and in. stimulating an lasting 4 to 5 days during the acute phase, overwintering cycle to test the hypothesis. beginning a few days after exposure. After Preliminary laboratory trials with a long- ingesting an infectious bloodmeal from a establishedcolony of An. quadrimaculatusindi- viremic human, Ae. aegypti arrains a lifelong cate that this strain is readily infected with JCV vector status following a suitable extrinsic (P. R. Grimstad,unpublished data). incubationperiod. Transmissionoccurs during MaintenanceofJCV in the field in the upper refeeding on a susceptiblehuman, thus allow- Midwest thus appears to be by at least two ing for the endemic persistenceof these viruses mechanisms.Given a) the probable involve- in urban foci. ment of a number of species (representing An enormous amount of historical and severalgenera of mosquitoes)in multiple JCV scientific literature provides the basis for our transmissioncycles throughout temperate North knowledge of the DEN viruses, and only the America, and b) the widespread infection of more recent publications,primarily thosesince humans, domestic livestock, and white-tailed 1983,will be alluded to here. The picture that deer, JCV is the most epidemiologically com- has emerged of Ae. aegypti over the past 4 plex of the North American CAL group decadesof dengue researchis that of an ideal viruses. At the turn of the century, deer urban vector (Halstead 1984). Where urban populations had been extirpated in many transmissionoccurs, Ae. acgyptibreeds predom- midwestern and eastern states: herds were inantly in a variety of artificial containers such rebuilt in the 1920-40 era and rapidly ex- as household water containers. discarded auto- panded only in the past 3 decades (see mobile tires, tin cans,and plasticpails inside of references cited in Grimstad et al. 1986). or in close proximity to human dwellings. It Canyon virus encephalitisis thus an feeds predominantly on man, primarily inside Jamestown"emerging" disease,probably expanding with houses,and commonly takes multiple blood- the exploding deer populations in many mealsduring a single gonotrophic cycle (Klowden regionsof North America. and Lea 1978, Watts et al. 1985, Yasuno and Tonn 1970). DENGUE VIRUSES Although DEN virus transmission in urban areas is continuous, the rate varies, normally Dengue viruses consist of an antigenic peaking during the wet seasonsand decreasing subgroup of 4 closelyrelated, yet antigenically markedly with onset of the dry seasonand its distinct viruses, DEN-I, 2, 3, 4, within the accompanying reduced temperature (Halstead genusFlaviains, family (Westaway 1984).The determinants of this reduction in et al. 1985). All produce human disease, DEN transmissionare not well understood,but ranging from the relatively mild , it has been atributed primarily to fluctuations a selfJimiting acute febrile illness,to rhe severe in Ae. aeglpti population density. However, dengue hemorrhagic fever (DHF) character- temperature was implicated as a strong deter- ized by hemorrhaging with or without a fatal minant in a recent study in Bangkok, Thailand shock syndrome (Halstead 1984). Dengue (Watts et al. 1986),wheie Ae. ac{yptibreedingis hemorrhagic fever is a major causeof morbid- primarily in stored water and slight seasonal ity and mortality among children in many changes in mosquito density are independent countries of southeast Asia and has recently of the wet season(Sheppard et al. 1969).Biting assumedconsiderable public health importance rates peaked during the hot and rainy seasons in the Pacific islands (Rosen 1984) and the (Yasuno and Tonn 1970) when the extrinsic Americas (Guzman et al. 1984).The growing incubation period for DEN-2 virus was less importance of DHF and the recent resurgence than 7 days.During the cool seasons,however, of dengue epidemics(Gratz 1985),parricularly biting rates showed a marked decline and the in the Americas, have led to the recognition of extrinsic incubation period exceeded25 days. DEN virusesas the most important arboviruses Vertical transmissionmay contribute to the transmitted to man. maintenance of DEN viruses in urban areas, Although dengue was recognized as a hu. but the low rates so far observed seem to man disease much earlier, the 4 virus types preclude a significant role. Dengue-2 virus was were originally isolated from both man and transmitted vertically by 4 of 5 experimentally mosquitoesbetween 1943 and 1960 (Johnson infected strains of Ae. aegypti,but filial infection et al. 1967). The domestic mosquiro, Aedcs rates (FIR) were only 0.3 to 1.27o (Jousset 446 Jounnal oF THEAunnrceN Mosqurro Cournol AssocrarroN Vor.. 2, No. 4

l98l). A comparablerate wasnoted for DEN-I Ae. rotumaz Belkin (Suizuki and Hirshman transmitted vertically by I of 5 strains of Aa. 1977) have been suspected of transmitting azgypti.(Rosen et al. 1983), but attempts to DEN viruses to man in some of the South demonstrate vertical transmissionof DEN-2, 3, Pacific islands. Experimental studies have sup- and 4 by these 5 strains were unsuccessful.In ported a vector role for most of these species, Rangoon, Burma, DEN-2 was obtained from but field evidence is based solely on their field-collected larvae at MFIRs of l:2067 for temporal and spatial association with human larvae, l:3865 for males. and 0:8528 for infections (Rosen et al. 1985). females (Khin and Than 1983). In Trinidad, Aedcsmedtiouittahu (Coquillett) a peridomestic DEN-4 was obtained from a mixed pool of man-biting mosquito, may be a potential vector male and female Ae. azffiti reared from eggs of DEN viruses in Puerto Rico (Gubler et al. collected on the premises of residences with 1985).This speciesbreeds in suburban and ru- recent human DEN virus infections (Hull et al. ral areas and frequently shares larval habitats 1984). The MFIR was l:1855. By conrasr, with Ae.azffii. Laboratorystudies revealed that DEN viruseswere not isolated from 5,766 Ae. Ae.rnedioaittahuwas readily infected with DEN-l aegyptilawae collected in houses in Bangkok, and DEN-2, that both viruseswere transmitted Thailand, in which one or more personChad horizontally, while DEN-l was ransmitted ver- recent DEN virus infection, despite DEN-2 tically. The latter route of transmissionwas sug- isolations from 14 of 268 female Ae. aegypti gested as a possible mechanism for mainti- collected from some of the same housesw[-ere nanceof DEN virusesin rural areaswhere human negative larvae were obtained (Watts et al. population densities are insufficient to sustain le85). theseviruses via an Ae. aegypti-mancycle. There _The peridomestic mosquito, Aedcsalbopictus is no direct field evidence as yet, however, to (Skuse),indigenous to tropical Asia but with a support a vector role for Ae. medioaittatw. range extending from Africa pacific to the ltlqo.ugh a sylvan maintenance cycle for islands, fills a vector role secondary to that of DEN viruses, involving subhuman primates, Ae. acgypti.Except for the recent iiolations of has long been suspected,evidence was lacking DEN-4 and DEN-2 from Ae. albopictusin the until recently when extensiveecological studiei absenceof Ae. aegyptiduring massiveepidemics in the Malaysian Peninsula revealed that all 4 in southern China (Qui et al. lg8l)-and the DEN viruses were enzootic in a cycle involvine SeychellesIslands (Metselaar et al. lg80), several speciesof monkeys and Aedesmosquil respectively,prior evidence for Ae. albopirtu,sas toes (Rudnick 1984). Previous DEN viius a vector has been limited to inteimittent infection was demonstrable in a high -presbytispercent- e.pidemicsin which Ae. aegpti was identified as age -of 4- species of Macaca aid the principal vector. The secondaryvector role monkeys, but more conclusivewas isolatior of of Ae. albopictusis dictated by is breeding DEN-I, 2 and, 4, and serological evidence of habitat and behavior (Wisseman and Sweei recent infections by DEN-I, 2 and 3. These 196l) which allow lessintense interaction with data were obtained in studies using monkeys as humans than for the highly domesticated Ae. virus sentinelsin the forest canopy; in contrast, azgpti. Aedzsalbopirtus breeds in urban, rural DEN virus infections were not demonstrated in and forested areas in water retained bv Macaca rwmzstrina used as sentinels on the artificial containers and natural vegetation, bul forest floor. DEN-4 was isolated from an Aedas it is exophilic and prefers to breed ourside (Fink2a) niaew (Ludlow) group species col- human dwellings. It feeds on both man and lected in a monkey-baited foiest &n6py trap. It domestic animals with relative utilization gov- is not known which of the I I species'iirthi aa. erned by host availability (Sullivan et al. l9?l;. niaeu group yielded the isolaie, but the most Diversion to non-human vertebrate blood common speciesof the group in the area were sources and the fact that its adult activity is Aedzspseudonizeres (Theobald) and,Aed.es suhniaetu generally interrupted by the dry seasonsmay Edwards. Monkeys were considered the pre- reduce its role as an endemic vector and largely ferred hosts of these species.At ground level, preclude the likelihood of a continuous cycle Ae. albopictttswas prevalent but mbre common involving this speciesand man. Experimental-DEN at the forest edge and in adjacent agricultural studies have demonstrated that all virus areas and villages. Virus transmission to hu- types are transmitted vertically by Ae. albopirtus mans_apparendy occurred mainly in rubber (Rosen et d. 1983), but there have been few tree-forest transitional areas where both Aa. attempts to obtain isolationsthat would demon- albopictusand, Ae. niueus group mosquitoes were strate this route of transmissionin nature. abundant, suggestingspillover from the sylvan Qther peridomestic Aedzs(Stcgomyio) species, cycle. Further studies will be necessaryto'fully including Ae. scutellaris(Walkei), Ae. polyrusi- incriminate the species that serve as vectors, ansrSMarks, Ae.psatdoscutellaras (Theobald) and but Ae. aegyptiwas not observed in the study Drcrlrsrn. 1986 Mosqurro-Bonwr Antovrnusrs 447

villages, thus demonstrating that DEN viruses studies. Finally, critical epidemic precursors were being maintained and transmitted to man such as cultural and socio-economicfactors that in the absence of this mosquito. permit the perperuation of Ae. aegyptiremain Recent field studies in forested areas of West gn{ereqphasized, at least by most public Africa have also provided evidence of a sylvan health funding sources. cycle for DEN-2 involving Aades mosquitoes and monkeys. Mosquitoes collected ir l98l and 1982 in forests of the Upper Volta, Senegal and the Ivory Coast yielded more than THE IMPACT OF HUMAN ACTIVITY 200 strains of DEN-2 virus isolated from b mosquito species (Cordellier et al. 1983, Roche The utilization of small water containers of et al. 1983). These included. Aedes (Stegomyia) all types, including drinking-water containers opok Corbet and Van Someren, Ae. (Stg.) in-sidehouses by Ae. ozgypti,and the adaptarion luuocephalw (Newstead), Ae. (Stg.) afrimmts ot'Ae. triserinlrerto old tires which are accumu- (Theobald), Ae. (Diceromyia) furctfer (Edwards), lating in the Untied States at the rate of 200 and, Ae. (Dic.) taflori Edwards, all associated million per year, show how pervasively vector with the forest canopy. In addition, an isolate speciescan root themselveswithin the cultural of DEN-2 was obtained from a pool of male Ae. fabric of their human hosts. Jamestown Can- taylori and Ae. furcifn collected in a forested yon virgs, in a less obvious manner, is also area of the Ivory Coast and from male Ae. subjecl to the influence of human activity. taylori in Senegal. Monkeys were implicated as Wildlife managemenr programs designed to hosts on the basis of an isolation of DEN-2 increasedeer populations, while making condi- from Erythrocebus patas, and serological evi- tions less favorable for LACV, can improve dence of recent infections in a high percentage conditions forJCV, as well as for Lyme disease, of wild monkeys (Cornet et al. 1984). These the spirochaeteof which is transmitted by ticks observations provide convincing evidence in that utilize deer as hosts. support of the emerging concept that DEN Mitchell (1977),Smith (1975),Surtees (1971), viruses are maintained in sylvan cvcles analo- Ward (1977) and others have listed human gous to those of jungle virus. cultural factors that influence patterns of While a horizontal cycle involving mosquitoes disease.Some factors of greatest relevance to and monkeys may not allow indefinite persis- specific arbovirus vectors include the develop- tence of DEN viruses because of relatively ment of irrigation agriculture, e.g., utilization short viremia in monkeys and slow population of rice fields and irrigation waste water by turnover which would not sustain an adequate Cuhx tarsalis Coquillett and Culex tritaeni- number of non-immune hosrs (Rosen 1984), orhynehtu Giles; the proliferation of small the isolation of DEN-2 from male mosquitoes man-made water containers, e.g., Ae. aegyptt implies that vertical transmission may serve as and,Ae. triseriahu; and inadequate disposal of an enzootic maintenance mechanism. polluted water resulting from burgeoning Although the public health importance of urbanization and industrialization, e.g., Cul.ex dengue and DHF has long been recognized, quinquefascintusSay. Other factors of impor- efforts to combat these diseases have been tance, some of them interacting, include the largely unsuccessful. Vaccines have been devel- development of faster transportation (increas- oped, but none is currently considered satisfac- ing the frequency of introduction of new tory for general (Halstead use 1984). Vector vector species, infected vectors and infected surveillance and control, or attempted eradica- persons); human population movements;changes tion, have provided the most effective strate- in human behavior; modification of vertebrate gies (Halstead 1984), but, except where en- faunas; deforestation; wars and political insta- forced such as in Singapore and, to a lesser bility; insecticides;vector resistance extent, Cuba, these approaches have not been to insecti- cides (often resulting successful in permanently interrupting DEN from agricultural insect control virus transmission to man. Despite an enor- rather than from vector control); mous amount of investigation of the ecology developmentof vaccines,introduction of vec- and epidemiology of DEN viruses, their en- tors to unexploited habitats,etc. Some influenc- demic persistence remains poorly understood, ing factors are quite subtle. Gahlinger et al. as are the implications of enzootic cycles such (1986) found that encephalitis casesin Califor- as those recently discovered in Malaysia and nia were negatively associatedwith television Africa. Recent emphasis on laboratory studies, ownership. It was found that television and air particularly on the potential vector and reser- conditioner utilization timescorresponded closely voir role of mosquitoes, has not been paralleled to the feeding period of Cx. tarsalis,the vector with critically needed multidisciplinary field of St. Louis encephalitis (SLE) and western 448 JounNel oF THEAurnrceN Mosqurro Coxrnol AssocrarroN Vor. 2, No. 4 equine encephalomyelitis(WEE) viruses in on patterns of mosquito-borne disease. Den- California. gue, with the closeassociation of its vector with A factor of special importance in today's man. seemsmade to order for effective control fast-paced and problem-plagued world, and based largely on source reduction and public which is no doubt of great benefit to vector education.But dengue, more than any other species,is public complacencyresulting from mosquito-borne virus diseaseappears to bene- competing societal concerns and priorities. fit from competing societal priorities. There Competing priorities and complacencyresult seems to be no other explanation that the in vector control budgets that are inadequate diseaseflourishes and appearsto have a very for the task. Based on data by Challet and bright future. Consider the scenario that Keller (1981),Beams (1985) stated that, while presentlyexists in the Western Hemisphere: the annual expendituresof 106 U.S. mosquito l) Following the near eradication of its control agenciesincreased an average of only vector during the early 1960s, hundreds of 5.47oper year during the 5-year period from thousandsofcases of denguehave occurred in 1976 through 1980,the consumerprice index the Caribbean Basin in the past 2 decades (a measure of inflation) increased an average (Gratz1985, Tonn et al. 1982). of 8.9% per year. Vector control budgets in 2) Its vector, Ae. aegypti, not only thrives developingcountries are frequently even more under the socio-economicconditions that exist hard pressed (Knudsen 1983 and others). in much of the region (Watermanet al. lg85), From 193 responsesto a questionnairemailed but it moves freely within the region, having to U.S. mosquito control agencies, Beams now reclaimed much of its former territory (1985) found that although 50Vo of the (Chadee1984, Cookman and LeBrun 1986. respondentsconsidered public educationto be Knudsen 1983, LeMaitt" a.td Chadee "as 1983, important as chemical, biological and Mayers 1983, Tonn et al. 1982, Wallis et al. "more physicalcontrol" and l0% consideredir 1984).According to the most recent informa- important," 97% of the agenciesallocated l07o tion (for the years 1982 and 1983) (Anony- or less of their budget to education and the mous 1985, Knudsen 1983),only 4 Caribbean averagewas only l.7Vo. countries (Barbados, Cuba, Grenada and The sheer increase of activity in a more Guyana)had larval houseindices under 5. the populous world and increased technological infestation level generally considered by the complexity in all fields of endeavor exacerbates Centersfor DiseaseControl (CDC) (1979)and problems in vector control and surveillance. others to be that below which epidemic Chadee (1984), for example, reported the transmissionis unlikely to occur. resultsof inspecting46,892 boats entering the 3) Basedon the 1977Puerto Rico epidemic, harbor of Port-of-Spain,Trinidad, W.I. from there is a minimum lagtime of 20-35 days 1972 to 1982. The yearly average derivable between the onset of epidemic activity and the from this total, 4,689, comparesto 727 boats implementation of control measureseven in inspectedby port health officers in 1934.And localities with a good health system, high the boats were smaller in 1934. Reiter and awarenessof dengue and efficient arbovirus Darsie (1984) discussedtwo modern innova- responsecapability (Morens et al. 1986). In tions in shipping, containerization and the general in the Caribbean, however, few coun- Lighter Aboard Ship (LASH) system, that tries have sufficient insecticide reserves on shorten considerably cargo delivery time and hand to mount an immediate wide-scalere- involve docksidehandling methods that make sponse to a dengue or yellow fever outbreak; inspection of the cargo difficult. They noted few have relevant health education programs, that, relativeto shippingvolume, exports ro rhe which are essentialfor enlisting support in United States from the South-East Asian source reduction at the community level; only Trading Nations (ASEAN) increasedby more about half of the countries have adequate than 1,200%in the past decade. vehicles for an emergency campaign; and in No other mosquito vector specieshas inter- some countries inadequate government sup- twined its destiny so intimately with human port reduces program efficiency (Knudsen society as has Ae. aegypti.McClelland (1973) 1983). and Rodhain (1983) have traced the sequence 4) The costsof an epidemic are high. Von of human socio-economicdevelopments, from Allmen et al. (1979) esiimatedthe cos-tof the the beginnings of primitive agriculture ro the 1977 Puerto Rico epidemic at between $6.0 rise of modern urbanization,that encouraged and $15.6 million including direct costs(medi- evolution of the intimate associationof this cal care and epidemic control measures)and specieswith man. As the vector of dengue and indirect costs (lost production of ill workers yellow fever viruses, no other mosquito species and of parentsof ill children). These estimates illustrates so well the impact of human activity did not include costsof schoolabsenteeism nor Drcnnrsrn, 1986 Mosqumo-BonNnAnnovrnusns u9

losses of tourism revenue which, although it has been found capable of oral transmission potentially important, may not have been an of LACV to suckling mice at a rate of 40-50Vo important factor in this epidemic. on days 14 and 2l following the infective blood 5) Although some vector breeding occurs in meal (P.R. Grimstad, unpublished data). Oral g5% sylvan habitats,well over occurs in or in transmissionof JCV to suckling mice was less close proximity to human dwellings, and than lOTaon postinfection days 14 and 21. mostly in manmade containers(Chadee et al. 9) Aedcstriseriatru has been found to be a 1984,Knudsen 1983,Moore 1983,Moore et al. capableoral transmitter of DEN-I virus (Freier 1978,Tonn et al. 1982). and Grimstad 1983). Two good research 6) Despite efforts of national governments questions are: Can Ae, triseriatustransmit DEN and the Panamerican Health Organization viruses transovarially, and, if so, can the virus (PAHO), dengue not only flourishes south of survive northern winters in the egg of the the United Statesbut threatens increasingly to mosquito? spread northward. Several dozen cases are l0) In addition to other man-madecontain- imported to the U.S.A. annually,mostly travel- ers, all 3 of these speciesreadily utilize auto ers returning from the Caribbean region tires for breeding, and as stated earlier, used (Knudsen 1983,Malison and Waterman 1983), auto tires are accumulating at the rate of 200 and after an absenceofmore than 30 years,the million per year in the United States(Deese et virus has again been transmitted endemically al. 1981). within the United States(Texas) (Hafkin et al. Researchwill yield no magic bullet solutions 1982). Mass movements of people pose an to the problem of dengue. Experienced work- additional avenue for entry of dengue, such as ers are increasingly emphasizing that effective the thousandsof Vietnameserefugees entering control of dengue must be based largely on Florida in 1975 and the thousandsof Haitians source reduction, with strong public education and Cubansentering the statein 1980(Breeland and participation, and sufficient resources in and Mulrennan 1983). the form of trained personnel to tailor manage- 7) Aedcsaegpti is again widespread in the ment programs to individual situations (Beams cities and rural areas of the southern United 1985,Gratz 1985,Halstead 1984, Morens et al. States (Fochs et al. 1981, Tabachnick 1982, 1986). Increasingly, there is a call for the Welch and Long 1984). Fochs et al. (1981) imposition of reasonable penalties against reported a houseindex of 35 in a substandard citizenswho fail or refuse to eliminate breeding residentialarea of New Orleans. sites on their own property. These 4 factors, 8) Aedes albopicttu, indigenous to tropical source reduction, public education, trained Asia, and an important secondary vector of personnel and legal sanctions were strong dengue viruses, has recently been introduced ingredientsin the intensivecampaign launched to the United States and is now known from during the Cuban epidemic of l98l (Tonn et Texas (Sprenger and Wuithiranyagool 1986), al. 1982).They were alsogiven prominenceon all of the Gulf Coast stateseastward to Florida a more general policy statement adopted in and Georgia (Centers for Disease Control 1979 by the American Mosquito Control [CDC] 1986), Tennessee(Reiter and Darsie Association(R. A. Hart, cited by Beams 1985). 1984),Ohio (M.A. Parsons,personal communi- Knudsen (1983) sumrnarizedthe outlook for cation), Indiana, Illinois and Missouri (C. G. dengue as follows: Moore, personal communication).(It has also "Thus, one can predict Ae. aegypti been found in Rio de and two will Janeiro continue to live in neighboring statesin Brazil 1986]). In closeassociation with man [CDC in the Caribbean long traditional Harris County, Texas, Ae. albopictruwas the as as water storage habits persist, lip service is given most abundant speciesfound breeding in used to control programs, source reduction tires and other water-filled containers(Sprenger is ig- nored, community participation is and Wuithiranyagool 1986) and it was abun- not ap- plied and researchis treated superficially. As dant and aggressivelybiting humans in many a result, we will other Gulf statessites (CDC 1986). According continue to be faced with the consequencesof Ae. aegypti-borne to the CDC report, the presenceof Ae. aegypti diseases." has not appeared to interfere with establish- As discussedin this paper and by DeFoliart ment of Ae. albopictru,and, in fact, the latter has et al. (1987),"changing patterns" of mosquito- replaced Ae. aegypti in many localities. The borne arboviruses result both from the steady Harris County, Texas population has been accumulation of new research findings and shown to resemble populations from northern from continuing change in the ecology of the Asia that are capableof diapause,indicating vectors and their human and non-human that the species will be capable of surviving vertebrate hosts. Unexpected happenings such northern winterson this continent.In addition. as the 1984 occurrence of 25 casesof St. Louis 450 JounNer-or rHE ArunnrceNMosgurro Corrnor AssocrerroN Vor,. 2, No. 4

encephalitis in southern California remind us Berry, W. J. and G. B. Craig, Jr. 1984. Bionomics of that our knowledge is quite incomplete and Aedzsatrofulpu breeding in scrap tires in northern much is yet to be learned even about aiboviruses lndiana. Mosq. News 44:476484. that have been extensivelystudied. As statedbv Berry, R. L., B.J. Lalonde-Weigen, C. H. Calisher, M. Reeves(1986) in reference to the Los Angeles A. Parsonsand G. T. Bear. 1977. Evidence for Fansovarial transmission area epidemic, "the heart of Jamestown Canyon of research is the virus in Ohio. Mosq. News 37:494-496. reexamination of accepted concepts on the Berry, R. L,, M. A. Parsons,B. Lalonde-Weigert, basisof new facts." The current situation with J. J. Lebio, H. Stegmiller, and G. T. Bear. 1986.Aedzs dengue reemphasizes the fact that research canadensis,a vector of La Crosse virus (California alone does not alleviate public health problems serogroup) in Ohio. J. Am. Mosq. Conrrol Assoc. and is a reminder to investigators, funding 2:78-78. agenciesand governments that research find- Berry, R. L., M. A. Parsons, R. A. Restifo, E. D. ings are uselessuntil they are applied. Peterson, S. W. Gordon, M. R. Reed, C. H. Calisher, G. T.' Bear and T. J. Halpin. 1983. California serogroup virus infections in Ohio: An ACKNOWLEDGMENTS l8-year retrospective survey, pp. 215-223. In: C. H. Calisher and W. H. Thompson (eds.). Partial support Califor- of research conducted in the nia serogroup viruses. A. R. Liss, New York. Iaboratories of G. R. DeFoliart and P. R. Boromisa, R. D. and P. R. Grimstad. 1986. Virus- Grimstad,- and partial support during the vector-host relationships of Aedesstimularc and writing of the manuscripr, was provided by Jamestown Canyon virus in a northern Indiana NIH grants AI 07458 and AI 19679, resp€c- focus.Am. J. Trop. Med. Hyg. 35:1285-129b tively. We thank Dr. Gary G. Clark, Centers for Boromisa,R. D. and P. R. Grimstad. 1987.Seroconver- Disease Control, San Laboratory, San sion_rates 1o Jamestown Canyon virus among six Juan Indiana white-tailed (Odocoilzus Juan, P. R.; Dr. Thomas M. Yuill, School of deer virginiams) populations.J.Wildl. Dis. Veterinary Medicine, University of Wisconsin- 23:(in press). Breeland,S. G. and A. Mulrennln, Madison; and Dr. Ronald A.-Ward, J. Jr. lg83. An Walter overview of organized mosquito control in Florida. Reed Army Institute of Research,Washington, Mosq. News 43:278-280. DC, for critically reading rhe manuscripti We Burkot, T. R. and G. R. DeFoliart. 1982. Bloodmeal thank Kim Viney for her expert secietarial sources of Aedcs triseriatus and, Aedcs acxans in a assrstance. southern Wisconsin forest endemic for La Crosse 91c9p!ali1i-s virus. Am. J. Trop. Med. Hyg. 3l:37G-381. ReferenccsCited Calisher, C. H. 1983. Taxonomy, classification,and geographic Amundson,T. E. andT. M. Yuill. lg8l. NaturalLa distribution of California serogroup Crossevirus infectionin the red fox (Vulpes bunyaviruses,pp. l-16. In: C. H. Calisherana W. fulaa), H. Thompson (eds.) gray fox (Uroqon cincreoargcntctu),raccoon (procyon California serogroup viruses. A. R. Liss, New York. Iator), and opossum (Didclph;t virginianal. Am-. l. Trop. Med. Hyg. 30:?06-714. Calisher,C. H. and R. E. Bailey. lg8l. Serodiacnosis of I.a Crosse virus Amundson, T. E., T, M. Yuill and G. R. DeFoliart. infections in humans. j.'Ctin. Microbiol. l3 :34,f.-50. 1985. Experimental La Crosse virus infection of Calisher, C. H. and W. red fox (Vulpes raccoon (procron tator), H. Thompson, (eds.) fulua), California serogroup viruses. opossum (Didtwit uirgininu), and woodchuck A. R. Liss, New York. 399 pp. (Marmgta monax). A-. J. Trop. Med. Hyg. 34:58L595. Centers for Disease Control. 1986. Aedcs ahopitnts infestation-United States, Anonymous. 1985. Communicable diseasesin the Brazil. Morb. Mort. Wkly. Rep.35:493-495. 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