Mencn. 1985 J. Ar"r.Mosq. CoNrhol Assoc. 93

Beck, S. D. 1980. photopefiodism, 2nd ed. ural history of RVF. In this study we exatnined AcademicPress, New York. 387 pp. 739 blood-fed mosquitoes trapped during and Gallaway,W. J. and R. A. Brust. 1982.The occur- following a period of particularly heavy rainfall rence of hend,ersoniCockerell and Aedes (October-December1982), which did not gen- triseriatus(Say) in Manitoba. MosQ. Syst. 14:262- eratean epizooticof RVF. However,during this 264. Holzapfel,C. M. and W. E. Bradshaw.lg8l. Geogra- period the virus was isolated from mosquitoes phy of larval dormdnci ln the tree-hole , at the trapping sites,and from orle dead calf on Aed,estriseriatus (Say). Can. J. Zool.59:l0l,l-1021. a nearby farm; there were also 4 seroconver. Sims,S. R. 1982.Larval diapauseiir the easterntree- sionsin a group of 80 yearling testedai hole mosquito, Aed.estriseriatui; Latitudinal varia- one of the trapping sites(Davies, unpublished tion in induction and intensity.Ann. Entorhol.Soc. data). The emergenceof mosquito speciesap- Am. 75:195-200. peared to be similar to that occurring during Wood, D. M., P. T. Dang and R. A. Ellis. 1979.The the early stagesof RVF epizootics(Linthicum et insectsand arachnids Part of Canada. 6. The mos- al. 1983,1984a). quitoesof Canada(Diptera: Culicidae).Agric. Can. Publ. 1686.390 pp. Mosquitoeswere trapped with Solid State Zavortink, T. J. 1972. Mosquito studies (Diptera: Army Miniature light traps (John W. Hock, Co., Culicidae)XXUII. The New World speciesfor- Gainesville,FL) at known RVF epizootic sitesin merly placedin Aedrs(Finlaya). Contrib. Am. En- ecologicalzones II (1"14'30'S, 36'50'E; 1700 tomol. Inst. (Ann Arbor) 8(3):l-206. m) and III (l' l2'S, 37"E; 1500m) in the vicin- ity of Nairobi, Kenya. Studiesconcerning the natural history of RVF during epizootics (Davies 1975, Daviesand Highton 1980), the population biology of immature mosquitoesin A BLOOD MEAL ANALYSIS OF dambos(Linthictrm ENGORGED MOSQUITOES FOUND IN et al. 1983, 1984a)and the feeding habits RIFT VALLEY FEVEREPIZOOTICS AREAS of mosquitoesat and calf (Linthicum TN KENYAI bait et al, 1984b) have been con- ducted at these sites. The domestic K. J. LTNTHICUM,H. F. A. KABURIA,'F. G. presentin theseareas were predominantly cattle, DAVIESaNo K. J. LINDQVIST, with a few , horses and . The com- U.S.Army MedicalResearch Unit (WRAIR)Kenya, mon wild animals present were: bushbuck Box 401,APO New York 09675,and Veterinary (Tragelaphus scriptru), eland (Taurotragus oryx), ResearchLiboratoty, P.O. Kabete, Kenya Grant's gazelle(Garclla granti) and Thomson's gazelle (Gazella thomsonii), giraffe (Gira,ffa Epizootic Rift Valley fever (RVF) occurs in camzlopardali;),jackal (Canisrnesamzlzs), ostrich Kenya in grasslandsadjacenr to, within or de- (Struthio carnehu),reedbuck (Reduncaredunca) rived from natural forest. xnd in the bushed and zebra (Equus burchelli). Light traps were and wooded grasslandswith predominantly suspended5G-80 cm above the ground and Combretumor Acacin tree cover (Davies 1975). baited with CO" (2 kg dry ice). The traps were These are in ecological zones II-IV described generally. placed adjacent to emergence sites by Pratt et al. (1966), in their classificationof (flooded dambo formations). Specimenswere EastAfrican habitat. Epizooticsoccur after pe- obtained in 380 rap night collectionsmade riods of prolonged and heavyrainfall (Scottet during the period October 15, 1982 to Febru- al. 1956, Davies 1975, Davies and Highton ary 15, 1983.One to eight rraps were set 4-7 1980, Davies et al., unpublished data). The days a week at each study site. The catcheswere virus is transmlttedby mosquitoesduring RVF taken to the laboratory live, frozen at - 70oCfor epizootics(Daubney and Hudson 1933, McIn- 30 min and then examined. All blood-fed tosh 1972,Davies and Highton 1980).A knowl- specimenswere removed and their abdomens edge of the mosquitoesfound in such areas smearedonto filter paper) labelledand stored during epizootic and interepizooricperiods is in a desiccatorjar. The smeared area of the relevantto a greater understandingof the nat- filter paper waslater cut out and placedin 0.5 ml of a phosphatebuffered saline which con- tinued 0.1% M sodium preservative. t azideas a This wcirk was supported by Research Grant No. Blood meal identificationwas carried out by DAMDIT-83-c-9517 from the U.S. Army Medical an enzyme immunoassaysystem developed by Research and Development Command, Ft. Detrick, Lindqvist,Gathuma and Kaburia (1982)for use MD 21701 and by a Research Grant for Project No. 3792 by the Overseas Development Administration, in EastAfrica, and many conjugateshad been United Kingdom. prepared againstthe domesticand wild rumi- 2 Department of Public Health, Pharmacology and nants found in this region. The antispecies- Toxicology, Faculty of Veterinary Medicine, Univer- antisera were produced in rabbits, goats or sity of Nairobi, P. O. Box 29053 Nairobi, Kenya. sheep by weekly inoculationsof the different 94 J. Ar. Mosq. CoNrRoLAssoc. Vou l, No. I

species globulin with Freud's adjuvant, these 92.3%, respectively, positive ro the specific continued for severalmonths. The sera were anti-cattle conjugate (Table l). Comparatively subjected to repeated absorption cycles to few Culex specimens were obtained, but of these achievespecies specificity. This wasconsidered 93.3Vo of the haemoglobin positive Culex antm- completewhen serum samplesfrom other spe- natus (Becker) had taken cattle blood meals. ciesgave reactionssimilar to the buffer controls One specimen of Ae. lineanpmnis had taken a in double immunodiffusion tests.Enzyme con- human and one a rabbit blood meal. A single jugates were prepared from either IgG or im- Ae. dmntus had fed upon a giraffe and one A?. munoglobulins with horse-radish peroxidase. cumminsii upon a or jackal and 2 on a rabbit. Testswere carried out directly with speciesspe- The anti-rabbit reactions were weak, suggesting cific conjugates, or indirectly using antisera that they were not due to the closely related produced in rabbits and a conjugated anti- Lepus or Pronolagus species. Pedetes capensis rabbit globulin prepared in a . This method (Rodentia, Pedetidae), the jumping hare, was regularly detected dilutions of test blood be- commonly encountered at the sites and may yond 10-6.The test thus givesa high degreeof have been the host causing the weak reactions. sensitivity and specificity, and is particularly Four specimens of Aa. circurnluteohu (Theobald) suitable for this type of investigation. The and one Ae. qtas'iuniaittatus (Theobald) were eluants were first examined for the presence strongly positive with the anti-horse or -zebra of haemoglobin by oxidizing reduced phe- conjugate. Of the 104 specimens which con- nophthalein in the presenceof FIrO, in alka- tained haemoglobin but were not identified by line solution. Those positive for haemoglo- the l3 specific conjugates, 8 reacted strongly bin were then tested against the following en- when tested later with the broad spectrum zyme conjugates: goat anti-cattle, -human, anti-bovidae conjugate. These 8 may have fed -sheep, -rabbit (Oryctogalus),-bushbuck, on a less abundant wild ruminant at these -reedbuck, -Grant's and Thomson's gazelle trapping sites, most likely impala (Aepyceros IgG; sheep anti-goat, -dog (ackal) lgG; and melampus) or kongoni (Alcelaphus buselaphus rabbit anti-ostrich, -chicken, -horse (donkey, cokii). There was a residue of 96 (l3Vo) blood- zebra), -mouse (rat), -giraffe whole serum; and fed mosquitoes that have not been identified. an anti-bovidae conjugate which detects all Over 50% of the mosquitoes containing un- membersof this family. identified haemoglobin were Ae. lineatopennis. The results of the haemoglobin screening Aefus lineatopennis does feed on birds (Chandler and blood meal identification testsare shown in et al. 1976). The anti-chicken conjugate may Table l. Of 800 specimensexamined, 6l did have failed to react with the many diverse bird not give a reaction for haemoglobin. The most species encountered at the site. It remains pos- common mosquito species collected over the sible that some of the unidentified specimens trapping period was Aedeslineatopennis (Lud- were avian feeds. low), which comprised more than half the The most abundant mosquitoes obtained in blood-fed specimensexamined. Of the 389 this study after heavy rains in RVF epizootic specimensshown to contain haemoglobin 333 areas were Aedes spp. Cattle were the blood (85.6Vo)had taken cattle blood meals. Three meal source for most of the Aedes spp. which other common Aedesspecies, Ae. dentatus were collected. They were also the most com- (Theobald),Ae. cummircii(Theobald), and Ae. mon large species in the study areas. su.danens'is(Theobald) were 90.7%, 79.2Voand Cattle are considered to be the major amplify-

Table l. Results of haemoglobin screening and blood meal identification tests of engorged mosquitoes collected from October 15" 1982 to February 15, 1983 in Rift Valley fever epizootic areas in Kenya. Uniden- Unknown tified Rabbit Horse/ Species Hb+ Bovidae Cattle Human Canine (Oryctalagus)Giraffe Zebra Total Ae. li,neatoPennis 50 + 333 (85.6Vo)* I 389 Ae, circumluteolus 8 I 27 (67.5Vo) 40 Ae. cumminsii 25 9 lr4 (79.2Vo) 9 t44 Ae. sudanmsis J 36 (92.3Vo) 39 Ae. dzntatru I 88 (90.7Va') 97 Ae. quasiunivittatus 2 6 I Cx, antennatus I l4 l5 Cx. spp. 6 6 Total 96 624 739

* Percentage of total number of blood fed specimens. MencH. 1985 J. Av. Mosq. CoNrnol Assoc, 95 ing and diseasehosts for RVF in many parts of Mclntosh, B. M, 1972. Rift Valley fever I. Vector (Davies 1975), although local farming studiesin the field. J. S. Afr. Vet. Assoc.43:391- practices often dictate whether sheep assume 395. G. I. dos Santos and this role in some areas (Davies, unpublished Mclntosh, B. M., P. Jupp, B.J. H. Barnard, 1980.Vector studies on Rift Valley data). These results suggest that Aedes mos- fever virus in South Africa. S. Afr. Med. J' quitoes, in this ecosystem Ae. lineatopennis, could 58:127-132. play some role in the generation of epizootics of Pratt, D. J., P.J. Greenwayand M. D. Gwynne.1966. RVF. Rift Valley Fever virus has been isolated A classificationof East African rangeland, with an from Ae. kneatopennis in epizootics of RVF in appendix on terminology.J. Appl. Ecol. 3:36$- Africa (Mclntosh 1972, Davies and Highton 382. 1980) and from Ae. circumluteolus (Gear et al. Scott.G. R., I. W. Weddel and D. Reid, 1956. Pre- 1955). Mclntosh et al. (1980) have demon- liminary findings on the prevalenceof Rift Valley strated that Ae. lineatopennis transmitted RVF fever in Kenya cattle, Bull. Epizoot. Dis. Afr. 4:17-26. virus under laboratory conditions. The authors with to thank Drs. C. L. Bailey, L. D. Hendricks, M. J. Reardon, D. R. Roberts and R. A. Ward for review of the manuscript and to the staff of the Veterinary Research Laboratorv. Kabete for technical assistance. The results are published with the approval of Dr. A. R. Njogu, Director, Kenya Trypano- GENETIC ANALYSIS OF A LINKAGE somiasis Institute, Government of Kenya and GROUP III MUTANT IN the Director of Veterinary Services, Kenya. ANOPHELES STEPHENSI KANEEZ AKHTART enn R. K. SAKAIT'2 ReferencesCited A new mutant short, curved palpus/proboscis Chandler,J.A., P. F. L. Boreham,R. B. Highton and (scp)was discovered during routine handling of M. N. Hill. 1976. A study of the host selection a translocation strain, T(2R,3R)4 (Sakai et al. patterns of the mosquitoesof the Kisumu area of Kenya. Trans. R. Soc.Trop. Med. Hyg. 64:415- 1983), of Anophelzsstephensi Liston. The mutant 425. is characterized by shortened (213-314 normal Daubney, R. and J. R. Hudson. 1933. Rift Valley length) palpi and proboscis, both of which Fever.E. Afr. Med.J. l0:2-19. curve upward toward the dorsum of the adult. Davies,F. G. 1975.Observations on the epidemiology There is some variability in expression but pen- of Rift Vafleyfever in Kenya.J. Hyg.75:219-23O. etrance is complete and both sexes express the Davies,F. G. and R. B. Highton. 1980.Possible vec- mutation. A true-breeding scp strain, free of the Trans. R. Soc. tors of Rift Valley fever in Kenya. translocation, was isolated and crosses were Trop. Med. Hyg. 74:81&-816. made to study the mode of inheritance of this Gear,J., B. de Meillon, A. F. Le Roux, R. Kofsky, mutation. R. RoseInnes, J. J. Steyn,W. D. Oliff and K. H. Schulz.1955. Rift Valley Feverin South Africa. A Preliminary crosses indicated that the muta- study of the 1953 outbreak in the Orange Free tion was recessive and autosomal as reciprocal State,with specialreference to the vectorsand pos- crosseswith a wild type (+) strain gave all + Fl sible reservoirhosts. S. Afr. Med. J. 29:51's.-518. progeny whereas a sex-linked mutation in this Lindqvist,K.J.,J. M.Gathumaand H. F. A. Kaburia. species in which females are XX and males XY 1982.Analysis of blood mealsof haematophagous (Aslamkhan 1973) would have resulted in + I insectsby haemagglutinationinhibition and en- andscp d F, progeny in one of the crosses (scpI zyme immunoassay.pp. 122-133. /n.' Current + Moreover, medical researchin easternAfrica with emphasis x d ). crosses with the chromo- on zoonosesand waterbornediseases. Proceedings some 2 mutant marker, mar (Mahmood and of the third annual medical scientificconference, Sakai 1982), indicated that mnr and scp segre- Nairobi, Kenya,1982. P. M. Tukei and A. R. Njogu gated independently of each other. Therefore, (Ed.) AfricascienceInternational, Nairobi. a series of crosseswere initiated between the sc| Linthicum, K. J., F. G .Davies,C. L. Bailey and and, Bl (black larva, a chromosome 3 mutant, A. Kairo. 1983. Mosquito speciessuccession in a Akhtar et al. 1982) strains. Table I summarizes dambo in an East African forest. Mosq. News the results and also contains the observed re- 43:464-470. combination frequencies between scp and Bl. Linthicum, K. J., F. G. Davies,C. L. Bailey and A. Kairo. 1984a.Mosquito species encountered in a flooded grasslanddambo in Kenya. Mosq. News I International Center for Medical Research and 44:228-232. Training,6, A. R. Chughtai Road, Lahore 3, Pakistan. Linthicum,K.J., F. G. Daviesand A. Kairo 1984b. 2 International Health Program, University of Observationsof the biting activity of mosquitoesat Maryland School of Medicine, l0 S. Pine Street, Bal- a floodeddambo in Kenya.Mosq. News 44:595-598. timore, MD 21201.