Laboratory and field studies of mansonia and coquilleitidia mosquitoes in relation to ecology and transmission of filariasis in Malaysia

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Date
1987-04
Authors
Geok Lian, Chiang
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Abstract
A supportive programme to control Mansonia and Coguillettidia vectors awaits formulation till some aspects of ecology of these mosquitoes and parameters associated with the dynamics of 'transmission of filariasis are better understood. It was in response to these needs that the present study was carried out. Included in this study were the following: to establish strong colonies of Mansonia spp. and Coguillettidia crassipes to provide materials for laboratory studies; to study their susceptibility to human and animal filariae; and to conduct field studies on their ecology in relation to transmission of filarial parasites in different ecotypes. Mansonia uniformis, Mansonia indiana, Mansonia bonneae and Cq. crassipes were successfully colonized using liver-yeast and guinea pig dung infusions as larval media and plants and wet strength paper for larval attachment. The new liver yeast medium and paper cultures developed in this study constituted a simplified and convenient technique suitable for rearing the mosquitoes on a large scale for laboratory studies. Findings of the susceptibility study of Mansonia spp. to periodic and subperiodic Brugia malayi and Brugia pahangi concur with those of earlier workers. Strains of Ma. 'uniformis from endemic and non-endemic areas were shown to be equally efficient in supporting the development of subperiodic B. malayi <p > 0.05). Studies on the species composition, seasonal abundance, filarial infection, survivorship, age composition and biting cycles of Mansonia were carried out in two ecotypes in Selangor, Peninsular Malaysia - a swamp forest in Jalan Tanjong Karang and an open swamp rice~ field in Lubuk Pusing. Ma. uniformis was the predominant species in both ecotypes. The seasonal abundance was generally similar in all species. There was an increase in the abundance generally from July to November coinciding with rainfall. Results of~infection indicated that Ma. uniformis and Ma. annulata in Jalan Tanjong Karang and Ma. uniformis and Ma. indiana in.Lubuk Pusing were the probable vectors of ~ malayi. There was no difference in the pattern of biting of nulliparous and parous populations, with a general peak period of activity between 1800-2000 hours in both ec~types. di~cussed. Observed differences between the two study areas were The parous rates coupled with high daily mortality (27.9-43.8%) of the mosquitoes could have been important factors preventing active transmission in the two ecotypes as indicated by the low Annual Infective Biting Rate (AIBR) and Annual Transmission Potential (ATP) estimated for the vectors concerned. The epidemiological importance of these two entomological parameters (AIBR and ATP) was discussed. Mark-release-recapture experiments demonstrated that Ma. uniformis had a mean dispersal distance ranging from 1.45 to 1.71 km in an open swamp ecotype. The longest flight distance recorded was 3.50 km. Based on these findings, the importance of reinvasion must be recognised when control operation is restricted to small areas. The duration of the gonotrophic cycle for Ma. uniformis was estimated to be 3-4 days. Natural and laboratory infection studies indicated that ~ crassipes was capable of transmitting~ malayi. Two ~ crassipes with L3 Brugia in Jalan Tanjong Karang appeared to be the first record in Malaysia. The field studies also provided evidence of similarity in seasonal abundance, biting activity and survivorship of ~ crassipes to the Mansonia vectors in the same study area t where their breeding habitats overlap. In the studies on the surveillance of adult ~ crassipes, IMR traps with bird baits proved to be a convenient and satisfactory method of sampling the mosquitoes. Vertical distribution showed that greater numbers of the mosquitoes were caught at higher than ~~ lower elevations. Based on the morphology of the adult worms recovered and microfilarial stages in naturally and experimentally infected chickens, a bird filarioid Cardiofilaria nilesi was shown to be present in Malaysia. The presence of infective larvae in wild caught mosquitoes indicated th~t ~ crassipes was the principal vector of C. nilesi in birds. Experimental transmission of C. nilesi in chickens and jirds was successfully carried out using laboratory bred ~ crassipes. The results demonstrated for the first time that a filarioid parasite from bird can be transmitted to a mammal. The short prepatent period, prolonged patent period and the nocturnal subperiodic pattern of periodicity observed during the study co~ld contribute to the establishment of an ideal model in the jird for not only basic studies on host- parasite relationship but also for screening potential filaricides.
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Coquilleitidia mosquitoes , Filariasis in Malaysia
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