...... e.. ECO 92: Pu6h Hedth1nThAma;zm...... New entomological and virological data on the vectors of sylvatic yellow fever in

NICOLASDÉGALLIER', AMÉLIA P. A. TRAVASSOSDA ROSA^, PEDROE C. VASCONCELOS',ELIZABETH S. TRAVASSOS DA ROSA^, SUELIG. RODRIGW~,GREGÓRIO C. SÁ FILHO^, JORGEE S. TRAVASSOSDA ROSA^

' ORSTOM e Iiistitirto E~~aiidi.~Chagas, Belém, PA 66000, arid 21nstit~4toEvandro CliagaslFNS-MS, Laboratório de Arhovíriis, Belém, PA 66000, Brasil

The present report focuses on recent ecoepidemiological data on yellow fever, obtained recently in two very distinct ecoepidemiological contexts: the Barcarena (PA) area, situated in the dense Amazonian , and the (MS) region, situated in the with gallery forest in central Brazil. In the first region, one strain was isolated from a pool of 6 Haenzagogus janthinomys. In the other region, 2,480 anthropophilous mosquitoes were collected, of which near 40 % were potential YF vectors. These species, classified by decreasing relative abundance, were: Aedes scapularis, Sabethes chloropterus, Hg. jantlzìnomys, Hg. leucocelaenus, Hg. spegazinii, and Sa. soperi. Four strains of YF virus were isolated from Hg. janthinomys, one from Sa. cheoropterrcs (first report for South America) and one from Sa. soperi (first report). The minimal infection rates varied among the three localities of collection but were all high, compared with previous data. The mean daily survival rate was 0.9635 for the populations of Hg. janthinonzys, allowing extrapolation of the value of the infection rate when people were infected most recently. It was deduced that the epizootics were intense and more or less concomitant in the three areas. The main problem that remained to be solved concerns the mode(s) of reintroduction or survival of YF virus in each of the two regions under study.

O presetite trabalho enfati-a resultados recentes sobre eco-epide- Quatro aniostrus de FA foram isoladas a partir de Hg. jantliinomys, niiologia da febre aniurcla. obtidos em (luas localiclades ecolo- irnio de Sa. cliloropterris (primeiro registro na América do Sitl), e rinia gicaniente niiiito diferentes: Barcarena (PA),situada na floresia de Sn. soperi (prinieiro reSistro). As tasas niininlas de infecqão unia-ônica derisa. e a região de Canipo Grarrcle (MS), coberta de i~oriaronisegirnrlo os locais de coleta. nias foram senipre altas eni cerrado atravessado por florestas de galeria na região Cerirro-oeste. coniparapio coni darlos anteriores. A tasa média de sobreisii'ência No primeiro local foi isolada rinia aniostra a parrir de irni lote de 6 diciria do Hg. jantlrinoriiys 4 ;giro1 o 0,9635, perniitindo estimar o seir Hnernagogris jantlrinonrys. Na região de Campo Grande* 2.480 mos- ~wlorna ocosido em que os casos liiiniaiios niais recentes foram m qrriros aiitropófilos foroni coletcidos, dos qirois cerca de 40% erani provawlnierite contaniinados. Dedii-iir-se qite as epirootias forani wtores potenciais íla FA. Essas espécies, classificados por ordeni niirito intensas e niais 011 nienos siniitltûneos nos dois locais com&- =4- decrescente de abirndâncio, erani: Ae. scaprilaris, Sa. cliloropterris. rarlos. O maior problenia a ser resolvido P o modo de re-introdufão do Hg. jairtliinornys, Hg. lericocelaenus, Hg. spegazinii e Sa. soperi. ~~friis,oit siia sobreiviw?ncia. eni cada região soh esriido. l=z Ga ea espite the existence of a good vaccine, yellow fe- in order to define the places and times where and when the sa ver (YF) virus continues to cause, almost every risk of transmission is highest. c-4 year many human deaths in its area of distribution Recent studies in Africa (2,3) and South America (4) (1). The reasons of the failure to control this dis- have shown that diverse ecoepidemiological situations may ease 'are multiple. The main reason is related to the diffi- exist, which are characterized by the nature of man-made g y culty of accessing and vaccinating all people in the risk re- changes of the environment and vector populations. Fur- a gions. Another reason is the lack of the ecological data ther, it became evident that the studies in Brazil must be % W which would be needed for establishing vaccination priori- related to the phytogeographical zones present in the coun- E ties. In other words, it would be necessary to better under- try (1). The present report will focus on data, obtained re- gSb r\- stand the mechanisms of i) the transmission of the virus and cently in two very distinct ecoepidemiological contexts, EB.J ,+ ii) emergence of epizootics, with or without human cases, with a discussion of implications for future studies. u.c The three main phytogeographical zones where YF vi- 9 4.': Correspondence to: Nicolas Degallier, ORSTOM, Caixa Postal 75. Belem, rus is circulating in Brazil are characterized by dense Ama- PA 66000, Brasil zonian rain forest, open rain forest and gallery run- 0 k !!?3 a> "d 6 136 Ciencia e Cultura (Journal of the Brazilian Association for lhe Advancement of Science) Volume 44(2/3) March/June 1992 0" &, 0" i' ...... ECO 92: Pu6& HedthInThe Amm......

with a very low relative density (0.3 mosquitoes/man X hour), is probably the result of a high sam- pling error. The only other poten- tial vectors which were also col- lected were Ae. scapufuris (1 specimen), Hg. feucocefaenus (4 spec.) and Sa. chforopterus (23 spec.; 1 pool) (7). Two studies, conducted in the same region, from June 21 to 28 and September 20 to 28, 1990, gave mainly the same entomologi- cal pattern (8). More recently, no strains were isolated on a collect- ing trip, made between December 3 and 21, 1991 (9). In ordcr to identify the possi- ble incidence of YF in the human ning through arboreal savannahs. We recently have been population (by sylvatic contacts or vaccination), four able to show active circulation of YF virus in the formcr serological surveys were donc, the positive results of which and latter, thus under very different conditions (5). are reported in Table 1 (IO). Unexpectedly, antibody rates to YF virus were not high among the riverine populations in this region. This may be Isolation of YF virus in due either to a low rate of vaccination or to a lack of con- the absence of human cases tacts between man and sylvatic YF virus, or both. On the other hand, high immunity rates against Mayaro virus, During routine mosquito collecting work, done in Bar- which is transmitted mainly by Hg. janfhinomys (1 l), show carena, Pará (Figs. I to 4) (6), from June 12 to 26, 1991, that the contacts with the vectors actually exist or have ex- one strain of YF virus was isolated from the six mosquitoes isted. In fact, the active circulation of YF virus was de- which constituted the only inoculated pool of Ha. jun- tected in this region or the nearby Abaetetuba county only fhinomys. Such a high infection rate (1 6.66%), associated in 1968 (12) and 1988 (13). YF virus may have circulated

Volume 44(2/3) MarchlJune 1992 Ciëncia e Cultura (Journal of lhe Brazilian Associalion for the Advancement of Science) 137 ...... e. ECO 92: PUL& HedthInThe Amazon......

at a very low rate, and only among the monkey population which is probably diffuse. However, we consider that there is a real risk of sporadic human cases that could occur or even an epizootic to initi- ate if the simian population in- le6 creases. 2 0.8 5 13.8 3 5.1 5 37.4 Isolation of the YF virus o 3.9 during an epizootic with 12 4.7 many human cases

At the end of 1991 and beginning 1.9 1 3.3 o,8 of 1992, a total of 14 human YF cases were confirmed in the region the following surveys, the results of the former of campo~~~~d~ (MS). This re- gion is phytoclimatically very dif-

Figiire 5. Map of do Siil State with divisions of coioities, 1ocali:atiori arid year of repor1 of cases of YF ditring the last 39 years.

138 Ci&nciae Cultura (Journal of the Brazilian Association for the Advancement of Science) Volume 44(2/3) March/June 1992 ...... ECO 92: Pu6& HedthInTh Amun...... ferent from the Barcarena rc- Table 2 - Anthropophilous mosquitocs collcctcd in thc rcgion of Campo Grandc (MS), bctwccn January 24 and gion (14). Previously de- Fcbruary 14, 1992, according to spccics, placc and Icvcl, with thc potcntial YF vcctors in boldface. scribed collecting and pro- Collnty Juruguuri Sidrolûndiu Cunipo Grunde cessing methods were used (Fazetido nume) (Cub. do Juruguuri) (Águu Encunudu) (Fuz. Rincüo) Tord (5). Three counties, Jara- SpecieslLevel Cunopy Ground Canopy Ground Cuiiopy Ground guari, Campo Grande and Anophelinae Sidrolândia, with fatal hu- Anopheles (AnaU)mediopuncrurus 1 23 24 man cases, were investigated An." (Nys.) triunnulutus 1 14 15 An. (Stli.) iiinrhus 31 31 (Fig. 5) (15). Chugusiu honneue 2 IO 3 15 A total of 986 potential Culicinae vectors of YF were col- Acdini lected, making up near 40% Aedes (How.) sp. 2 2 4 of all mosquitoes (Table 2). Ac. (How.)scprcmstriutus 2 8 IO Ac. {Och.) scapularis 2 85 I6 212 4 88 407 If we consider the rela- Ac. (Ocli.) serrum 9 9 18 tive densities of all spccics Ac. (Pro.) urgvrothorux 12 12 (Table 3), Ac. scapularis Haetnagogus (Hag.)janlhitcohcys 8 29 35 33 II es 184 (Fig. (16) was globally the Hg. (Hag.) spegaziriii 6 6 6) Hg. {Con.) Ieucocelacnus 15 70 II Je 2 17 161 most abundant of the poten- Psoroplroru (Juli.) ulbipcs 13 195 88 271 4 183 754 tial YF vectors, followed by Pu. (Jun.)ferox I 34 2 31 I 69 Sa. chloropterus (Fig. 7), Culicini Culex sp. 4 I 21 26 Hg. janthinomys (Fig. S), Cx. (Cia.) coronutor I 2 3 Hg. leucocelaenus, Sa. so- Cx. (Cu.) decbruror 5 5 IO peri and Hg. spegazinii. Cx. (Mel.) sp. I 2 3 All the above species, Mansoniini Coquillcrtidia (Rhv.) ullx¿mtu 8 8 except for Hg. leucocelaenus Cq. (Rhv.) vene;uelensis 1 I and Sa. soperi, were less and Sabcthini more abundant in the gallery Limulus sp. 2 5 7 Li. durhuniii II II forests of and Suberlies (Sub.) u1biprivii.s 3 51 5 9 I6 67 151 Campo Grande counties, res- Su. (Sah.) belisurioi IO 1 IO 2 8" 31 pectively. Nevertheless, it Su. (Sub.)jiiruttiuii 2 2 was in Sidrolfndia county Su. (Sub.) quusicyuneus 8 2 10 Su. (Sub.)lar.sl~pus 2 2 that the global relative den- Su. (Shir.) interniedius 17 17 sity of anthropophilous mos- Sa. (Sbn.) soperi 19 1 20 quitoes was the highest. The Sa. (Sbo.) cliloroplerus 20 33 46 14 42 53 208 number of different species Su. (Sho.) gluucoduenroii 45 60 55 37 5 8 210 Triclioprosopon obscuruni 7 7 was lower in the ranch Fa- Wyewiiyia sp. 1 17 13 I II 43 zenda Rinciío (Campo Gran- Total" 120 668 271 809 91 521 2480 de county) than in the other No. of spccics II 24 12 23 II 14 33 counties (Table 2). u Thc abbreviations follow thc papcr of Rcincrt (I975 Mrisq Syst 7: 105-1 IO). " A total of 144 pools wcrc inoculatcd, with 50.57 md 37, rcspcctivcly from cach placc orcollcction; among thcsc These differences in thc polcnlial YF vcctorh rcprcscnt 16, 17 and 14 pools, rcspcctivcly. species richness may be re-

(+) Figure 8. Haemagogics janlhiriomys, YF. collected niuinly ut ,yround levcl in /lie tnuiri vector of YF virus iir ßruzil. Plroto: N. Cunip(i Grunde rexion, MS. Plroto: N. D6gullic~r, 1992. (C)Figure 7. Sabethes ciiloropterus, proveii secoirdury vector of YF virus in lhe Cunipo Grunde region. MS. Photo: N. .DCgullier,

~~ ~~

Volume 44(2/3) March/June 1992 Ciëncia e Cultura (Journal of lhe Brazilian Association for the Advancement of Science) = 139 ...... ECO 92: Pu6licHedthInTlieAma;zm......

Table 3 - Relotive densities (No./mnn x hour) of tinthropophilous moscpitocs collected in the region of Campo Criinde (MS), between Jnnunry 24 and February 14, 1092, :IC- cording to spccies and county, with the potcnli:il YF vectors in boltlliicc. SprcieslPluces Juruwuri Sidriilindiu Cun~iioGrunde Tolu1 (Meti .Y I-I~w:~) (18i.S) (183) i127.5) (492 J Anophelinae Anoplirli~s(Ano.") mcdi~iprtnctutus 0.13 0.049 An:' (Nys.) triutinirlutus 0.08 0.03 An. (Sth) nimbus 0.17 0.063 Clrugusiu h~itineue 0.07 0.02 0.03 Culicin:le Acdini Aedes (Ilow.) sp. 0.0 I 0.0 I 0.OOX Ac. (How.) septrmstriutirs 0.0 I 0.06 0.02 ne. (Ocli.) scapu1ari.s 0.48 1.26 O. 72 0.827 Ar. (Oclr.) serrutrts 0.05 0.05 0.037 Ar. (Pro.) ur~yvratlror~~x 0.07 0.024 Ilnentagogns (Hag.) jnntlrinomys 0.20 u.37 0.62 0.374 Hg. (Hag.) spegazinii 0.03 0.012 Hg. (Con.) Ieircocelueniis 0.47 0.31 0.15 0.327 Psnroplr~iru(Jun.) ulbipes 1.15 I .96 I .47 I .533 Ps. (Jun.) ferox 0.19 0.18 0.0 I 0.14 Culicini Cule.r sp. 0.02 0.12 0.053 Cx. (Cux.) c~ir~inut~r 0.01 0.0 I 0.006 Cx. (Cux.) declurutor 0.03 0.03 0.02 Figure 9. Remains of u deud Howler monkey (Alountta Cx. (Mel)sp. 0.0 1 0.0 1 0.006 caraya),fbund in the gullcry fiiresr uper the 1992 epizootic Mansoniini in the Cumpo Grunde region. Plroto: Sr. José Mendes, 1992. Coqirillettidiu (Rlrv.) ulhico.stu 0.04 0.016 Cq. (Rkv.) venezuclensis 0.0 I 0.002 from sylvatic vectors in Mato Grosso do Sul Sabethini Limutrrs sp. 0.0 I 0.04 0.014 State, despite attempts made during previous sur- Li. ditrllumii 0.06 0.022 veys. Suhetlirs (Sub.) ulhiprivus 0.30 0.08 0.65 0.307 It is noteworthy that the infection rates of the Su. (Soh.) helisuririi 0.06 0.05 0.08 0.063 main vector, janthinomys (Table 4), are Su. (Sub.)jiiruttinii 0.02 0.004 Hg. Su. (Sub.) quusicyuneiis 0.04 0.0 I 0.02 higher in the localities with more recent human su. (Sah.) tur.sopus 0.02 0.004 cases, perhaps indicating the progressive de- Su. (Shti.) interniedius 0.09 0.035 crease of the virus in the mosquito population, Sa. {Sbn.) sopen 0.1 o 0.01 0.041 Sa. (Sbo.) cliloropterus 0.29 0.33 O. 75 0.423 because of the immunization of susceptible mon- Su. (Sho.) gluucoduemon 0.58 0.50 0.10 0.427 keys. This hypothesis will be discussed in the Triclroprosoipon ohscarrrm 0.04 0.014 next section. Wyeomyiu sp. 0.10 0.07 0.09 0.087 The species Sa. soperi was encountered Total 4.34 5.90 4.80 5.04 I naturally infected for the first time but its actual "The abbreviations follow the paper of Reinert (1975 Mosq Syst 7: 105-1 IO). role in the transmission of YF needs to be further studied (20). It may be more omithophilous than Table 4 - Minimal infection rates (%) of each positive species for YF virus, according to the place of collection in the region of Campo Grande, MS; the dates of the most re- primatophilous, because the arbovirus Macaua, ccnl human cases in each locality give an indication of the end of the epizootics. for which it is probably a natural host, has been SpecirslPluce Jurqyuuri Cumpo Grunde Sidrolûndiu Tiitul isolated from (21). To date, the Sa. Most recent luimun case Dec. 20,'9/ Dec. 3/,'9/ Feh. 3,'92 chloropterus has been found naturally infected Huemugogus (Hug.)junthinomy.s 1.27 4.41 2.1 7 by YF virus only in Central America (22,231 and Suhctfres (Sho.) clrloropterus 1.67 0.48 recently in Trinidad island (24). Thus, here is the Suhcthes (Shn.) soperi 5.26 5.00 first time that it was found naturally infected in continental South America (25). Contrary to the lated to ecological (man-made?) disturbance of the environ- I-laemagogus spp., these mosquitoes are known to survive ment. during the dry season (26,27), therefore being good candi- The relative density is not the only important factor dates for supporting a short-term maintenance of YF virus related to vector competence of mosquito populations. Of during the unfavorable season. prime importance is also the value of the parous rate (1 7, 18), which allows us to estimate the mean daily survival The role of Hg. jmthinomys as the principal vector of rate. A global proportion of 57.31% of the 164 dissected sylvatic YF in Brazil and responsible for most human Hg.juntlzirzomys were determined as parous. With a 15-day contaminations has been confirmed once more. The rela- long gonotrophic cycle (4), the global survival rate is thus tive densities and infection rates have been compared with 0.9635 (Table 5). those estimated from previous studies in Brazil (Table 5; ref. Three species were found to be infected by the YF vi- 28). The high densities and infection rates, together with the rus (19) and this is the first time that YF virus was isolated presence of infected Suhethes, may suggest that our field work

140 Ciencia e Cultura (Journal of the Brazilian Association lor lhe Advancemenl 01 Science) Volume 44(2/3) MarchlJune 1992 ...... e ECO 92: Pub& Hedth In The Amazm, , . . . , . . , ......

MIR (6.54%) when fitting a line with the values Table 5 - Relative densities (Nr./man x h) and minimum infection rates (Nr. of strainsmr. of mosquitoes) for YF (%) of potential vectors of sylvatic YF in Brazil, estimated at 17,41 and 52 days after the last human 1954-1992. contamination. As for the MIR, the relative density Suecies Place (Stute) Densit\f Infecriori rule index seems to decrease linearly with time (Table Hg. spegainii Ilhéus (BA) 1.6 0.01 (1/9119) 6). On the other hand, the parity rate does not seem Hg. species Belém-Brasilia km 87 (PA) ‘ - 1.00 (1/222) to vary linearly with time. No hypothesis is yet Hg. species Belém-Brasília km 94 (PA) - 5.00 (1/20) Ac. fichvis Serrado Navio (AP) - 0.60 (1/165) available to explain these phenomena. Hg. species Barcarena (PA) - 0.29 (1/335) Various other ecoepidemiological aspects re- Hg. species Rio Jaburu (II. Gurupa) (PA) - 0.75 (1/132) main to be studied in relation to the maintenance Hg. species Alenquer (PA) - 1.19 (3/252) of the YF virus in its area of endemicity. In the Hg. capricorciif’ Belterra (PA) - 0.27 (2/732) Hg. species Uruaçu-Niquelândia (GO) 3.2 0.86 (4/461) southern part of this area, it is not known if the Hg. jant/iinoniys ? Formosa (GO) 2.3 0.57 (2/347) virus is periodically reintroduced from the north Hg. juntkinoniys ? (GO) 2.7 0.78 (7/891) (the permanent endemic focus of the French au- Hg. jarirhirioniys Faro (PA) 0.8 0.22 (1/448) Hg. alhoniucfrlatus Monte Alegre (PA) 3.5 0.11 (2/1798) thors (2)) or if it is able to persist during the dry Hg. junr. + Hg. alhoni. Monte Alegre (PA) 0.22 (1/436) and cold season, either .in the drought-resistant Hg. juntliinoniys SI0 Domingos do Capim (PA) 15.0 0.34 (3/858) eggs of the Haetiiagogirs species, or in the more re- Hg. junthinoni-ss Sinop (MT) 1.0 0.47 (1/209) sistant Saberl~esadults, or in both. Whatever the Hg. jurithiuotiiys Ilha Japichaua (PA) 0.6 1.40 (2/142) Hg. jandiinoniys Barcarena (PA) 0.3 16.66 (1/6) case, the “purpose” (32) may not be the same. The Hs. jutithinoniys Campo Grande (MS) 0.6 1.27 (1/79) long-term survival of the virus in the eggs would Hg. junthinoniys Sidrolrindia (MS) 0.37 4.41 (3/68) necessarily have to wait for the reconstitution of Su. chloroprer~ts Sidrolândia (MS) 0.33 1.67 (1/60) the local population of susceptible monkeys (Fig. Su. soueri Jaraeuari (MS) 0.1 5.26 (1119) 9). On the other hand, a shorter-term survival in As this species is not known from Amazonia, and its females are undistinguishable from those of Hg. jun/liinoniys,it was probably the latter which has been collected adult mosquitoes may be a possibility of initiating (see Amell 1973 ConfrAiner Ent Inst 10: 174 p) another epizootic in the case of new vertebrate hosts entering the area. The data obtained in the Barcarena Table 6 - Summary of ecoepidemiological parameters for the Haentugogirs jmtlntioniys mos- quito population, collected in the region of Campo Grande, MS, by county, from January 24 to area were not sufficient to conclude if February 14, 1992. there was an epizootic or not, before the ~uroptaricutnpo Grande SidroMridia Estiniote# recent isolation of YF virus from mosqui- No, of days since the toes. However, the low rate of HI anti- last human case 52 41 17 O bodies in the human population and the MIR (%) O 1.27 4*41 6*54(r2=0*99) absence of recent human cases, despite a Relative density 0.20 0.37 0.62 0.83 (r2=0.99) Parity rate (%) 57.5 53.62 61.81 63.45(&0,48) close contact of these people with the Daily survival rate (%)” 96.37 95.93 96.84 forest, suggest a nonepizootic mode of Surviving infected mosquitoes (%Y 14.62 18.20 57.93 transmission. MIR at time of epizootics ? 6.97 7.6 I

a Values at origin estimated by linear regression of the known values; the values of the coefficients of regression are indicated between parenthesis. Assuming a 15-day long gonotrophic cycle. Conclusions L. This value represents the proportion of infected mosquitoes surviving at the end of the period = (daily survival rate) (No. of days since the last human cases). Further studies are needed in both types of phytoclimatical zones, in order to de- in Mato Grosso do Sul was done only a short time after a termine what are the means of reintroduction or survival of YF epizootic (29). In the case of the Barcarena isolation, it the YF virus between the successive epizootics. Eggs of is not known if there was a previous epizootic during the Haemagogirs would be collected with ovitraps, and sentinel first half of 1991. monkeys would be maintained to detect any early seasonal An interesting exercise would be to compare some circulation of YF virus. The seasonal variations of the rela- ecoepidemiological parameters of the Hg. jantlzinonzys tive densities and survival rate of the vectors, and the re- populations (infected or not) from the three places of study constitution of the monkey populations would be the sub- in the Campo Grande region. As shown in Table 6, the time jects of other very interesting studies. Finally, the survey of lags between the last human contaminations and our col- susceptible (nonvaccinated) people would be of prime im- lecting of infected mosquitoes (30) would be 41 and 17 portance in relation to the risks of sporadic cases days for Fazenda Rindo and Sidrolsndia, respectively (31). emergences. When all these aspects are better known with With survival rates equal to 0.9593 and 0.9684, the infected fresh data, it would be possible to attempt some modeling mosquitoes would represent 18.20% and 57.93% of those work (33). infected during the epizootics in the respective areas. Thus, the infection rates at the respective times of human con- References and notes taininations would be estimated to be at least equal to 6.97% and 7.61% (Table 6). Therefore, these are of the 1. Dégallier N, APA Travassos da Rosa, JP HervC, JFS Travassos da same order. We have 0btained.a similar value for the initial Rosa, PFC Vasconcelos, VLRS de Barros, LB Dias, ES Travassos

Volume 44(2/3) MarchlJune 1992 Ciencia e Cultura (Journal of the Brazilian Association for the Advancement 01 Science) 141

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da Rosa, SG Rodrigues 1991 A febre amarela na África e na 15. Field collecting of mosquitoes was done between January 24 and America do Sul. Virológica 91 - I1 Sinipósio internaciorial sobre February IO; between January 26 and February 5; and from Febru- Arhoiirirs dos Trópicos e Febres Hentorrcígicas. Centur (Fundaçio ary 6 to 14 i! the three ranches, Fazendas Cabeceira do Jaraguari, Cultural Tancredo Neves), 17-23 November 1991, Beltm, Pari. Rinciío and Agua Encanada, respectively Round table on “Yellow fever” 16. Other authors are considering this species as only a “possible poten- 2. Cordellier R 1991 L’tpidtmioiogie de la fièvre jaune en Afrique de tial vector” and not a ”proven potential vector”, because it has never I”0uest. Bir// Org Mond Sariti 69: 73-84 been encountered riaticrally iifected by YF virus 3. Cordellier R, N Dtgallier 1992 Environment, arboviruses transmis- 17. Dtgallier N, JP Hervt, APA Travassos da Rosa, GC Si Filho 1988 sion and control of epidemics. Rio 92: Conferência interiinciorid de Aedes aegypti (LJ: importance de sa biotcologie dans la transmis- riieio awhiente, desemolviniento e salirle. Cimades - Fundação sion de la Dengue et des autres arbovirus. Premiere partie. &cl1 Soc Oswaldo Cruz, Campus de Manguinhos, 20-24 Abril 1992, Rio de Patliol 8 1 : 97- 1 I O. Idem Deuxième partie: 1 1 I - I24 Janeiro, RJ 18. The mean daily survival rate may be estimated when the duration of 4. Digallier N, APA Travassos da Rosa, PFC Vasconcelos, SC the gonotrophic cycle and the parous rate of the population are Guerreiro, JFS Travassos da Rosa, JP Hervt 1991 Estimation du known. The ovaries of the mosquitoes were dissected, left to dry at taux de survie, de la densite relative et du taux d’infection d’une room temperature, and examined under the microscope. Their population d’Haeniagogus jan/hinoniys Dyar (Diptera: Culicidae) nulliparouslparous state is inferred from the presencehbsence of ayant fourni des souches de fièvre jaune en Amazonie brtsilienne. coiled tracheoles Bir// Soc Patliol 84: 386-397 19. Hg. (Haeniogogirs) janthinoniys: Sidroldndia, 3 strains, Campo 5. Material arid nietliods: Anthropophilous mosquitoes were collected Grande, 1 strain; Sa. (Saherlioides) chloropterrts: Sidroldndia, 1 from human bait (all individuals were volunteers and with protect- strain: Sa. (Sahetliinirs) soperi, Jaraguari, 1 strain ing antibodies), at canopy and ground levels, during the midday 20. The very high infection rate is probably due to a sampling error as hours (the maximum biting activity of the potential vectors of YF in was the case for the strain isolated from Barcarena South America extends between 1O:OO and 15:OO h). The mosqui- 21. Karabatsos N I985 hiternatioiial catalogue of arhoidritses irielitdiitg toes were anesthetized with cold and immediately put in liquid ni- certain orlier iirirses of ivrtebrates, 3rd ed, American Society of trogen. In the laboratory, monospecific pools were done above a Tropical Medicine and Hygiene, San Antonio, Texas chilling table (-2OoC). Thorax and heads of the potential vectors of 22. Galindo P 1978 Los arbovirus de Panama. Rev Med Pananta 3: 1-41 YF were simultaneously inoculated into suckling mice and C6/36 23. Hervt JP, APA Travassos da Rosa 1983 Ecologia da febre amarela Aedes albopictits cells, without refreezing and on the same day. no Brasil. Rev Fioid SESP 28: 11-19 Their abdomens were dissected for estimation of the mean parous 24. Rawlins SC, B Hull, DD Chadee, R Martinez, A LeMaitre. F James, L rate of the population Webb 1990 Sylvatic yellow fever activity in Trinidad, 1988-1989. 6. Barcarena (lo 31’ S; 480 40’ W, alt. < 100 m) is a little town of 46.082 Trans R Soc Trop Merl Hyg 84: 142-143 inhabitants (source IBGE, “Sinopse preliminar do Censo de 1991 p 25. Strains of YF virus have been isolated by the IEC once from a pool of 44‘7, who are mostly employed by the Albras Company for extrac- unidentified Saberlies mosquitoes and once from a mixed pool of tion of bauxite and manufacture of aluminum. The mean annual Aedes sp. and Sohetlies sp. rainfall is between 2,500 and 3,000 mm, with 180-240 rainy days. 26. Galindo P 1958 Bionomics of Saherlies rhlnropterirs Humbolt, a Drier and wetter seasons extend from September to November and vector of sylvan yellow fever in middle America. Am J Trop Med February to April, respectively. The wetter months are also the Hy,? 7: 429-440 coldest. The during the driest month are more than 60 mm 27. Dtgallier et al, unpublished data 7. 674 individuals of at least 20 different species of other mosquitoes 28. The mean relative density and infection rate are 3.1 mosq./man h and were also collected from human bait during the same period 0.2 1 % (35h 6,573), respectively 8. In June, 1990, 17 YF potential vectors were collected, of which 15 29. We were able to see remains of dead Howler monkeys (Alorratto were Hg. jaiitliirioniys (relative density rate = 0.36). The other caraya) in the Jaraguari and SidrolSndia counties (see Fig. 9) anthropophilous mosquitoes were 634 in number, with at leasf 16 30. A mean incubation period of five days is assumed (see note no. 4) different species. In September of the same year, only 5 YF poten- 31. In the Jaraguari county no strain was isolated from Hg.jarithinoniys tial vectors were collected, 3 of which were Hg. jaiirhiiioniys (rela- 52 days after the time the last human patient was theoretically in- tive density rate = 0.06): the other anthropophilous mosquitoes were fected. As the sensibility of suckling mice is sufficient to allow iso- 446 in number, with at least 15 different species lation at very low rates (around O.Ol%), it is reasonable to consider 9. 22 YF potential vectors were collected, of which 7 were Hg. that the YF virus has vanished from the adult population of this spe- jmitliinon?ys (relative density rate for canopy collecting only = cies, at this time 0.02). The other anthropophilous mosquitoes were 200 in number, 32. From the virus point of view! with at least 12 different species 33. Ackiio~~Ied,~nients:We are much indebted to the technical staff of the I o. The sera were tested for HI antibodies against the most prevalent Evandro Chagas Institute who has collected material in the field pathogenic virus species. The sera were considered positive when (Francisco C. Castro, Htlio A.C. Saraiva, Jonas R. dos S. Moraes, reacting with only one virus, or when the titer of antibodies was at Orlando V. da Silva, Raimundo B. da Silva, Roberto C.F. Brandlo) least two-fold higher than the higher titer of other cross-reacting and processed it in the laboratory (Armando de S. Pereira, Basilio S. ones. Rates (%) are indicated in boldface Buna, Hamilton A. de O. Monteiro, Ivan C. Alves, heraldo F. da 1 I, Travassos da Rosa APA, N DCgallier, JP Hervt. GC Si Filho 1987 Silva, Luiz R.O. da Costa, Maria R.C. Freitas, Maxwell F. de Lima, La recherche sur les arbovirus en Amazonie, p 223-247. Ir1 Osvaldo V. da Silva, Raimundo F. do Nascimento) with much com- Connaissance dir niilierc ania:oriie/i Actes drc sin~inaire,id., petence and responsibility. We sincerely acknowledge the Albras Orstom, col1 Colloques et SCminaires, 15 et 16 octobre, Paris Company which gave us the opportunity to work in the Barcarena 12. One, two and four strains were isolated from mosquitoes, man and area. The studies conducted in the Campo Grande region would not monkeys, respectively have been possible without the logistic help of the Regional Direc- 13. One human case was confirmed serologically tion of National Health Foundation in Mato Grosso do Sul (Director 14. Despite some dispersion of the cases around the Campo Grande Dr. Aroldo Ferreira Galvão) and the special dedication of field ento- county, the latter will be considered as representative of the general mology staff of this institution (under the responsability of Dr. Ari climate of the region. The following data concern the Campo Alves Ribeiro). All meteorological and a part of epidemiological Grande station (20” 27‘ S: 540 37’ W; alt. 556 m) for the period data used in this report were provided by Dr. Carlos J. Mangabeira 1931-1960. Mean annual rainfall is 1,442 mm, with the drier and da Silva (Cenapihlinistry of Health, Brasília, DF). This study was wetter seasons in June to August and December to February, respec- funded by the National Health Foundation, CNPq, Orstom (France) tively. The wetter months are also the hottest. The rains during each and the Albras Company, Pari State, Brazil. of the three drier months are less than 60 mm

142 Ci&nciae Cultura (Journal of the Brazilian Association for the Advancement of Science) Volume 44(2/3) MarchlJune 1992