SEPTEMBER1990 As. puncnnn tNo OtHnn Vpctons or CHIK VIRUS 4t5

AEDES FURCIFERAND OTHER MOSQUITOESAS VECTORSOF CHIKUNGUNYAVIRUS AT MICA. NORTHEASTERNTRANSVAAL,

P. G. JUPP ANDB. M. McINTOSH

Arbouirus Ilnit, National lrctitute for Virolagy and, Department of Virolngy, Uniuersity of Witwatersrand, Priuate Bag X4, Sandringham 2131,South Africa

ABSTRACT. From 1977to 1981,studies were conductedon a farm at Mica wherc Aedesfurcifer had. been a vector during an epidemic of virus in 1976to determine whether the virus persisted in this ,the likelihood of vertical transmission, and whether any other Aedesspecies could have been vectors. Aedes furcifer/cord,ellieri was the only prevalent tree hole Aedes which fed readily on monkeysand and occurredthrough the summer until the onset of winter. Virus was not isolated from 7,241females and 4,052 males of this group, which were largely Ae. furcifer and which included a sample of the first post-epidemicpopulation. Five additional Aedes specieswere prevalent in bamboo pots, 3 of which (Ae. aegypti,Ae. fulgens and.Ae. uittatus) were shown to be competentlaboratory vectors. Virus was not isolated from a sample of 13,029such newly emergedmosquitoes representing the first post-epidemicpopulation. It is concludedthat Ae. furcifer is an epidemic-epizooticvector which doesnot maintain the virus at Mica and that no other mosquito speciescould have been important vectors.

INTRODUCTION Ae. furcifer was highly susceptibleto infection with the virus and a moderately efficient trans- (CHIK) Chikungunya virus occurs in the mitter (Jupp et al. 1981). tropical region of southern Africa, which in After the epidemic, field observations were South Africa comprises the eastern Transvaal continued at Mica on the farm "Hope," chosen lowveld and coastalnorthern Natal. out- becausethe highest post-epidemicimmune rates breaks of the virus have been infrequent and were recorded there for both the human and always related to ample rains in wooded sa- baboonpopulations. A seriesofmosquito collec- vanna. Infections in man have been recognized tions with monkey and baboonbaits was carried in the easternTransvaal in 1956,1975, 1976 and out in March 1977during the summer following 1977(Gear and Reid 1957, Mclntosh et al. 1977. the outbreak (Mclntosh et al. 1977). The Ae. Morrison 1979). A large epidemic occurred in group, composed mainly of the Zimbabwean lowveld in 1962 (Mclntosh furcifer/cordellieri et Ae. was the predominant speciestaken al. 1963a)and an epizootic among furcifer, vervet mon- on wild primate bait and 8- to lO-fold greater keys (Cercopithccus aethinps) in northern Natal numbers were collected in the understory than in 1964(Mclntosh 1970).Studies done in rela- on the ground. tion to these outbreaks, especiallythe outbreak Further observations were made during the at Mica in the northeastern Transvaal in 1976 summer in 1977, 1978, 1980 and 1981 which (Mclntosh et al. 1977),have shown that vervet were designedto answer 2 questions. The first monkeys and baboons (Papio ursinus) are the was whether the virus remained in the local Ae. primary vertebrate hosts,while the primary vec- population, with this speciesacting as a tor is the Aedes group furcifer furcifer/cordellierir of reservoir vector, or whether it disappeared.Sec- mosquitoes. ond, could other mosquito species have been During the rural epidemic at Mica in March- involved in the transmission of virus during the April 1976,Aedes was furcifer/cordellieri by far outbreak which escapeddetection at the time? the most prevalent speciescollected off human Answers were sought as follows: 1) the mosqui- bait and yielded16 isolations of (Mclntosh virus toes at "Hope" were monitored for virus infec- et aI. 1977).The identification of male mosqui- tion, including post-epidemic survival of virus toes also taken in the catchesindicated that Ae. through the dry winter by vertical transmission, was comprised largely of Ae. furcifer/cordellieri 2) the relative abundance of mosquito species (Edwards) and was probably the princi- furcifer and their feeding preference for man and wild pal speciesin the epidemic. In the laboratory primates were determined, and 3) the vector competenceof the 5 most common tree hole breeding aedine mosquitoesapart from Ae. fur- I Taxonomic examination of the Ae. furcifer gtoup cifer was evaluated. Transmission experiments in South Africa in the light of Huang's (1986)revision had been conductedwith 3 of these speciespre- indicates that Ae. taylori is not present but Ae. cordel- viously but not with the "Hope" mosquito pop- Iieri Huane occursthere. ulations. Furthermore, more tests were needed JounNer, oF THE Avnnrcen Mosqurro CoNrRor, AssocrATroN Vol.6, No.3 on these speciesbefore a 50% infection thresh- the eggs were hatched and adults reared. The old could be determined. pots were alternately flooded and dried twice so that the majority of eggswere hatched. Mosquitoes collected as adults were killed MATERIALS AND METHODS with hydrogencyanide, pooled accordingto spe- cies and stored in liquid nitrogen. Adults reared Human-baited catches:In these collections 2 from pots and bottles were discardedafter iden- volunteers used test tubes to collect mosquitoes tification, except those from the 1976-77 sum- which alighted on their bare legs fot 2-3 h after mer which were stored according to speciesin sunset. At night, flashlights shaded with red liquid nitrogen and selectedspecies which were cloth were used. Forty-nine man-hours of col- kept alive for vector competencestudies. Iecting were done for 12 daysduring March 1977 Attempted uirus isolation from mosquitoes: and February 1978. Mosquito suspensionsprepared from pools of Monkcy-baited surtion traps: In the March eachspecies were inoculated intracerebrally into 1977collection series (Mclntosh et al. 1977),a 1- to 2-day-old mice for attempted virus isola- single anesthetized baboon or monkey was tion. placed on a wire mesh platform with two 12- Vector competencetests: Specimensof the 5 volt, 8-watt fans suspendedbelow. These fans most prevalent Aedes speciesaged 1-14 days, sucked mosquitoes attracted to the bait down- and reared from the bamboo pots, were used for ward into organdie cages (Jupp 1978). Subse- vector competencetests. Experiments were con- quently, the traps differed slightly in that 2 ducted in an insectary where the mosquitoes unanesthetizedvervet monkeys were housed in were maintained at 75-80% RH 24-26'C. The a wire meshcage (60 x 45 x 30 cm) under which virus used was the H817 strain of CHIK virus the 2 suction fans were hung. Traps were sus- at the third mouse-passagelevel. Attempts to pended10 m abovethe ground in the understory infect mosquitoes were made by feeding them of 3 trees for 2 h after sunsetduring March 1977, on vervet monkeys while these monkeys were February 1978and January to June 1980. viremic after inoculation of virus 48 h previ- Carbon dioxide-baited light traps: The light ously. Monkeys were anesthetizedand exposed traps used had a 5-mm wire mesh filter fitted to mosquitoesheld in 10-cmdiam canisterswith over the trap entrance and COz was released mesh-coveredends strapped to the monkey's through 3-mm bore polythene tubing close to chest and abdomen.Immediately before feeding the opening (Jupp et at. 1980).The sourceofthe began, a blood sample was collected from each COz was a tin insulated with corrugated card- to determine the viremia. Virus titra- board containing about 2 kg of dry ice. The traps tions were done in infant mice inoculated intra- were set overnight during February, March and cerebrally and titers refer to logrolDso/ml. The April 1977and February, March and June 1980 infection rate, i.e., the proportion of mosquitoes with a total of 63 trap-nights. feeding which becameinfected, was determined Artificial ouiposition sites in trees: To collect by testing them individually for virus by inocu- tree hole breeding speciesunsampled as adults lation of infant mice. Thesedeterminations were by the 3 collecting methods described above, done 15-16 days after the infective meal and 1- bamboo oviposition pots were exposedso as to 2 days after the transmission feeds. Infected include all or part of 4 summers:November 1976 mosquitoeswere held for 13 or 14 days before to April 1977, December 1977 to April 1978, transmissionswere attempted. These were done February to June 1980, and February to June by feeding groups of potentially infected mos- 1981. During 1980, 560-ml plastic bottles, quitoeson 1 or 2 Syrian hamsters.Transmission painted black on the outside, containing 2 of virus was determined by testing for hemag- wooden paddles ("tongue depressors") for ovi- glutination-inhibition antibodies in the serum position were exposed in addition to the pots. of hamsters 21 days after the transmission was Pots and bottles were suspendedfrom trees at attempted. The titer of virus needed to infect varying heights up to 6 m above the ground. In 50% of the mosquitoeswas estimated from the 1980 and 1981, the openings of about half the infection rates. pots were reduced by closing them partly with "Hope" board. During each visit to a sample of any larvae present in pots or bottles was pre- RESULTS served for subsequent identifrcation and the paddles were changedin the caseof the plastic Adult mosquitocollections: At least 15 species bottles, the exposedones being returned to the were collected off human bait (Table 1) but Ae. laboratory under humidification. At the end of furcifer/ cordellieri represented,84% of the total summer,pots and bottles with their severalsets catch with a high biting late of 40.2mosquitoes ofpaddles were returned to the laboratory where per man-hour. Other specieswhich occurred in SnprnMspn 1990 Ap. punarsn lno Otnnn VEcroRS or CHIK VIRUs 4t7

Table 1. Mosouito collectionsusine 3 different baits. Monkey-baited suction Human bait at ground Light traps with CO2at traps 10 m above ground IeveI' ground level" in trees' No. as % No./ No. as % No./trap No. as % No./trap Species No. of total man-hour No. of total hour No. oftotal night Tree hole Aedesspecies Ae. (D ic.) f ur cif er / cordellie ri 1,968 83.9 40.2 3,995 43.6 16.6" r74 4.8 2.8 femalesd Ae. (Dic.) furcifer males 4,825 52.6 20.r 265 7.4 4.2 Ae. (Dic.) cordellieri males 49 0.5 0.2 Ae. (Dic.) adersi 2 Ae. (Dic.) fascipalpis 11 0.3 0.2 Ae. (Adm.) uittatus 2 31 0.9 0.5 Ae. (Stg.)aegypti 2213 0.4 0.2 Ae. (Stg.) Iedgeri Ae. (Stil metallicus 8 0.3 0.2 2 43 t.2 0.7 Ae. (Stg.) unilineatus 2 Other species Cx. (Cux.) poicilipes 28 t.2 0.6 271 3.0 l.l 334 9.3 5.3 Aedes(Adm.) 6 spp. I 20 0.6 0.3 Aed.es(Neom.) 2 spp. 25 0.7 0.4 AnophelesIl spp. JJ4 t4.2 6.8 2,498 69.6 39.7 Cubx ll spp. r t2 0.1 149 4.2 2.4 Mansonia2 spp. I 9 0.3 0.1 Ur anotae nia rnashonaensis 12 0.3 0.2 Total 2,345 9,174 3,590 'Mosquitoes collectedin 49 man hours over 12 days during 2 summers(March 19?7and February 19?8). b Collectedin 240.5trap hours over 36 days in March 1977,February 1978and January-June 1980. "Collected in light traps baited with COz over 26 nights (63 trap nights) in February-April 1977 and February-June 1980. d Proportion of Ae. cordellieri L.0-3.5%based on males attracted to femalesin traps. " No./trap hour varied from 0 to 77.5,depending on the month. significant numberswere Culexpoicilipes (Theo- were larger numbers of Cr. poicilipes andArwph- bold) and severalspecies of. Arwphclcs. elesspecies. No other aedine specieswere taken The use of 2 unanesthetizedmonkeys as bait in the light traps in significantly large numbers. in the understory was the most productive Artificinl ouipositionsites: Table 2 shows the method for collecting Ae. furcifer/cordellieri as frequencyof occurrenceof various mosquitospe- can be seenin Table 1. This modification of the cies, expressedas percentages,as they occurred original trap was much easierto use as eachpair in bamboo pots exposedduring 4 summers and of monkeys were kept in the same cage for the in plastic bottles in the 1980summer. "Hope." A total of duration of a visit to The identification 155 pots were exposed,while 1-34samples were of maleswhich were drawn into the suction traps identified from the bottles. The bottles yielded becausethey had been attracted to females on a high percentageof collections of Ae. ocgypti or near the bait showed that the proportion of (Linn), Ae. ledgeri Huang, Ae. metallicus Ed- Ae. cordellieri Huang varied from 1.0 to 3.5%. wards and Cx. horridus Edwards, while other Aedes furcifer/cordellieri was consistently the species rarely occurred; Ae. furcifer/ cordellieri most prevalent speciesgroup during the 3 years occurring only once. A larger number of differ- of study; Cx.poicilipes also regularly entered the ent specieswere collected at a higher frequency traps but in rather low numbers. The numbers in the pots. These included the 4 speciesthat of Ae. furcifer/cordellieri depended on rainfall were common in the bottles but also Ae. uittatus and in 1980the group was collected throughout (Bigot) (27Vo),Ae. ful.gens(Edwards) (48%) and, the summer but disappearedby the end of May Cx. ncbulastrsTheobold (39%). The mean fre- at the onset ofthe dry winter. quency for Ae. furcifer /cordelli.eri was 167obut a Carbon dioxide baited light traps were also much higher frequencyof 48% occurredin 1981. set to sample other mosquitoeswhose presence Similar figures fot Ae. haworthi (Edwards) were and abundance might not be revealed by the L6% and \tVo, respectively.The plastic bottles human and monkey-baitedcollections (Table 1). with their wooden paddles were less bulky and FewerAe. furcifer / cordellieri werc taken in these easierto use than the pots although they failed traps than in the other collections but there to sample as many different species. 418 JounNll oF THEAunnrcnt Moseuno CoNrnor,Assocrlrrolr Vor,.6. No. B

Mosquitoes tested for uirus; Neither CHIK virus to hamsters.Aedes ledgeri and.Ae. metal- virus, nor any other virus, was isolated from licu,swere poorly susceptibleto the virus, with a either Ae. furcifer/cord.ellierior any of the other 50% infection threshold of > 7.2 logl6lDse/ml, speciescollected at Mica sincethe 1gZ6epidemic and large groupsof mosquitoesfailed to transmit (Table 3). to more than half the hamstersexposed to them Vector competencetests: Table 4 shows the indicating a lower transmission efficiency. results of vector competencetests with 5 species. The 50Vo infection thresholds were 6.7 DISCUSSION IogrolDso/ml. (Ae. aegypti) and < 6.7 logrolDm/ mI (Ae. fulgens and. Ae. uittatus), and small The results of the man-baited catches were groupsof eachof these 3 speciestransmitted the very similar to those obtained during the epi-

Table 2. Frequenciesof occurrenceof different speciesin bamboopots or plastic bottles expressedas percentagesof total collections. Bamboo pots Bottles r976-77 t977-78 1980 1981 Mean 1980 Species (47)" (30) (4e) (2e) (155) (134)b Ae. (Adm.) cumm.insi 2 0 0 0 I 0 Ae. (AIb) haworthi t) 10 18 16 0 Ae. (AIb.) marshalli 10 4 0 ^ 0 Ae. (Adm.) uexans t) 0 0 0 2 0 Ae. (Adm.) uittatus 15 Jd 45 27 I Ae. (Dic.) furcifer / cordellieri 4 o t4 48 16 1 I Ae. (Fin.) fulgens 64 o, 62 48 Ae. (Fin.) nyasae 0 6 0 3 0 Ae. (Stg.) aegypti 98 93 100 90 96 78 Ae. (Stg.) ledgeri 89 97 100 100 96 87 Ae. (Stil metallictn 96 67 7l 62 76 46 Ae. (Stg) simpsoni 2 0 0 0 1 0 Ae. (Stil subargenteus 4 0 0 0 0 Ae. (Ste.) unilineatus 0 6 7 4 2 Cx. (Cui.) cinereus 27 ND ND 1n I Cx. (Cui.) nebulosu.s 57 ND T4 ND 39 1 Cx. (Eum.) horridus 2l ND 67 ND 40 23 Cx. (Lut.) tigripes 0 ND ND I 0 Tx. (Tox.) breuipalpis 0 ND 8 ND I ND : larval collections of these speciesnot done. 'No. ofpots exposed. b No. of pairs of woodenpaddles removed from bottles and larval samples.

Table 3. Number of mosquitoes"tested for virus: wild caught as adults and reared from bamboo pots. Wild caught Bamboopots

],!'7b Q8') 1978(7) 1980(31) t977 No. No. No. No. No. No. No. No. Species mosq. pools mosq. pools mosq. pools mosq, pools Ae. f urcifer / cord.ellierife- 3,522 149 2,068 82 r,643 75 81 males q Ae. f urcife r I cordellier i 2,136 89 L,725 187 2 81 males Ae. aelypti 29 4 a 1 5,413d 66 Ae. fulEens 1 1,1?5d 20 Other Aedesspp. 484 26 383 6,44f 81 Culex spp. 545 18 434 15 Anoph.elesspp. 3,631 74 702 13

Totals r0,347 360 3,794 92 3,007 109 13,045 169 'AII mosquitoeswere femalesexcept where indicated otherwise. b Includes catch in Feb-March after first rains. " Number of collecting days. d Males and females. SEPTEMBER1990 AE. FURCTFERnxo Ornnn Vncrons or CHIK VIRUs 4r9

Table 4. Results ofvector competencetests with chikungunya virus and 5 tree hole breeding mosquitoes collectedat Mica. Mosquito infection Transmission to hamsters Titer of infective feed 50% infection Days after No. No. (logroLDoo/ thresholdb infective hamsters mosquitoes Species ml) Rate' (logrolDso/ml) meal exposed feeding Results Ae. acgypti 7.2 L0/r6(63%) 6.7 L4 I 16+ 6.7 6/12(50%) I4 I 12+ Ae. Ledgeri 7.2 1/27(4%) >7.2 T4 2" 1A +.- 6.7 r/r7 (6%) 14 2" 10 +;- Ae. metallicus 7.2 1,2/34(35%) >7.2 I4 2" 37 +;- 6.7 4/22(r8%) L4 2" 23 -;- Ae. uittatus 6.7 10/10 <6.7 13 I 12+ Ae. fulgens 6.7 4/6 (67%) <6.?'t 13 I 4+ u Numerator : no. mosquitoesinfected; denominator : no. mosquitoestested 15 days after their infective meal. b The titer of virus neededto infect 50% of the mosquitoes. '2 hamstersexposed simultaneously in the samecage of mosquitoes. dlnaprevioustest(Juppetal. 1981)29/33(88%) of thisspecieswasinfectedafteraviremicmealof?.4 log1eLD56/ml.

demic except that Cx. poicilipes and,Anophelcs are the only aedine mosquitoesfeeding on man specieswere more prevalent than in the earlier and wild primates at "Hope" to any appreciable collections (Mclntosh et al. L977). The most extent. It is possiblethat other potential aedine successfulmethod for sampling the Ae. furcifer/ vectors which were present but not sampled cordellieri population was the monkey-baited during the actual epidemic were absent during trap in the tree understory, followed by the this study although this is consideredunlikely. ground level man-baited catch and light-carbon The exposureof bamboopots and plastic bottles dioxide suction trap, in that order. All 3 meth- showedthat 13 other tree hole Aedesspecies also ods, especially the light-carbon dioxide traps, occurred, with Ae. aegypti,Ae. ledgeri,Ae. me- collected significant numbers of. Cx. poicilipes, tallicus, Ae. fulgens and Ae. uittatus present at but were ineffective in collecting species of significant frequencies. None of these species Aedes other than Ae. furcifer / cordellieri. The low appearedto be daytime man-biters sinceperson- frequency at which Ae. furcifer/cordelli,eri usu- nel who campedand worked throughout the day "Hope" ally oviposited in the pots appearedto be due to on were rarely bitten. Three of these 5 the wide openingsofthe pots. In 1980and 1981 species,uiz Ae. aegypti,Ae. fulgens and,Ae. uit- about half the pots exposedhad their openings tatus, were shown to be competent laboratory made smaller which may account for the higher vectors of CHIK virus in the present study, (14 frequency and 48%) of this species group while Ae. aegypti and.Ae. fulgens had also been ovipositing during those summers.This concurs incriminated previously (Mclntosh and Jupp with the observationsof Raymond and cowork- 1970,Jupp et al. 1981).Since vervet monkeys ers (1976)who found that Ae. furcifer/cordellieri circulate the virus at titers of 3.5-7.0 logrolDso/ in preferred to oviposit in tree holes ml and baboons 4.6-8.2 log16lD6e/ml,respec- with small openings. tively (Mclntosh et al. 1963b),on the basis of Virus isolation studies in Africa as a whole their infection thresholds of 6.7 or < 6.? have indicated that tree hole breeding Aedes IogrolDso/ml,these 3 speciescould becomein- speciesare the main vectors of CHIK virus to fected after feeding on wild primates. However, wild primates and humans. No isolations have becausethey failed to feed on humans or mon- been made from Anopheles species and only keys, it is concluded that only Ae. furcifer/cor- occasionalisolations ftom Culex species(Jupp dellieri were involved in the epidemic. and Mclntosh 1988). Culex poicilipesis almosl Viral assay of mosquitoes indicated that refractory to infection (Mclntosh and Jupp CHIK virus was no longer present in the local "Hope" 1970).Thus the tree hole breeding aedine mos- Ae. furcifer population at after the epi- quitoes which are prevalent at Mica and which demic. Infected mosquitoes were not detected primates feed on wild and humans are the onlv among the first Ae. furcifer/cordellicri mosqui- mosquitoesthat qualify as candidatevectors. Ail toes to emergeafter the epidemic following the 3 types of bait collections failed to collect sig- rains in February/March 1977 nor among the nificant numbers of any aedine speciesexcept Ae. furcifer/cordellieri collected in the 19?8 and Ae. furcifer/cordellieri. This indicates that these 1979summers. Hence it is unlikelv that trans- 420 JouRNer,oF THEArr,rrnrcaN Moseurro CoNrnol Assocrluon VoL.6,No.3 ovarial transmission occurs in Ae. furcifer/cor- furcifer group, with a description of a new species dellieri,Additionalevidence supporting this con- (Diptera: Culicidae). Proc. Entomol. Soc. Wash. clusion is our failure to demonstrate vertical 88:634-649. transmission experimentally in other studies Jupp, P. G. 1978.A trap to collect mosquitoesattracted to monkeys and baboons.Mosq. News (Jupp al. 1981; 38:288-289. et Jupp and Mclntosh, unpub- Jupp, P. G., B. M. Mclntosh and E. M. Nevill. 1980. lished data). It also seems unlikely that any A survey of the mosquito and.Culicoides faunas at other tree hole breedingAedes is responsiblefor two localities in the Karoo region of South Africa vertical transmission as no virus isolation was with some observations on bionomics. Onderste- made from 13,029male and female mosquitoes poort J. Vet. Res.47:1-6. which emergedfrom the bamboo pots exposed Jupp, P. G., B. M. Mclntosh and I. dos Santos.1981. on "Hope" from November 1976to April 1977 Laboratory vector studies on six mosquito and one tick specieswith immediately following the epidemic. chikungunya virus. Trans. R. Soc. Trop. Med. Hyg. 75:15-19. It is concluded that Ae. furcifer/cordellieri, Jupp, P. G. and B. M. Mclntosh. 1988.Chikungunya predominantly Ae. furcifer, was the principal virus disease,pp. 137-157./n; T. Monath (ed.),The mosquito vector of CHIK virus at Mica during arboviruses: epidemiology and ecology, vol. IL the 1976 outbreak and that other Aedes species C.R.C.Press, Boca Raton,FL. would have at least only played a very minor Mclntosh, B. M. 1970.Antibody against chikungunya vectorial rcle. Aedesfurcifer is not thought to be virus in wild primates in southern Africa. S. Afr. J. a reservoir vector for overwintering of the virus Med. Sci. 35;65-74. unless the virus enters a dormant state in the Mclntosh, B. M., R. M. Harwin, H. E. Pattersonand M. L. Westwater.1963a. An epidemicof chikun- vector undetectable by usual viral assay meth- gunya in south-eastern Southern Rhodesia. Cent. ods. Afr. J. Med. 9:351-359. Mclntosh, B. M., H. E. Paterson, J. M. Donaldson and J. de Sousa. 1963b. Chikungunya virus; viral ACKNOWLEDGMENTS susceptibility and transmission studies with some vertebrates.S. Afr. J. Med. Sci. 28:45-52. We wish to thank J. H. McDonald for allowing "Hope" Mclntosh, B. M. and P. G. Jupp. 1970. Attempts to us to work on and T. Smit, J. Molola transmit chikungunya virus with six speciesof mos- and D. Tigedi for assistancein the freld. Tech- quito. J. Med. Entomol. 7:615-618. nical assistancein the laboratory from I. Dos Mclntosh, B. M., P. G. Jupp and I. dos Santos. 1977. Santos, M. Meenehan and E. Chauke is grate- Rural epidemicof chikungunya in South Africa with (F,d' fully acknowledged. involvement of Aedes (Diceromyia\ furcifer wards) andbaboons. S. Afr. J. Sci. 73:267-269. Morrison, J. G. L. 1979. Chikungunya fever. Int. J. Derm. 18:628-629. REFERENCES CITED Raymond,H. L., M. Cornet and P. Y. Dieng' 1976' Gear,J. and F. P. Reid.1957. The occurrenceof a Etudes sur les vecteurssylvatiques du virus amaril. dengue-like fever in the northeastern Transvaal. 1. Inventaire provisoire des habitats lawaires d'une Clinical features and isolation of virus. S. Afr. Med. for6t-galerie dans le foyer endimique du Senegal J.3I:253-257. oriental. Cah. O.R.S.T.O.M.Ser. Entomol. Med. Huang, Y.-M. 1986. Notes on the Aedes (Diceromyia) Parasitol.14:301-306.