Bloodmeal Microfilariae Density and the Uptake and Establishment of Wuchereria bancrofti Infections in Culex quinquefasciatus and Aedes aegypti
Vol. 94(5): 591-596
Cleide MR Albuquerque/+, Vânia MS Cavalcanti*, Maria Alice V Melo, Paulo Verçosa, Lêda N Regis*, Hilary Hurd**
Departamento de Zoologia, Centro de Ciências Biológicas, Universidade Federal de Pernambuco, Av. Moraes Rego 1235, 50670-420 Recife, PE, Brasil *Centro de Pesquisas Aggeu Magalhães-Fiocruz, Av. Moraes Rego
s/no, 50670-420 Recife, PE, Brasil **Centre for Applied Entomology and Parasitology, Keele University, Staffordshire, ST5 5BG, UKThe relationship between ingestion of microfilariae (mf), production of infective larvae (L3) and mf density in human blood has been suggested as an important determinant in the transmission dynamics of lymphatic filariasis. Here we assess the role of these factors in determining the competence of a natural vector Culex quinquefasciatus and a non vector Aedes aegypti to transmit Wuchereria bancrofti. Mosquitoes were infected via a membrane feeding procedure. Both mosquito species ingested more than the expected number of microfilariae (concentrating factor was 1.28 and 1.81 for Cx. quinquefasciatus and Ae. aegypti, respectively) but Cx. quinquefasciatus ingested around twice as many mf as Ae. aegypti because its larger blood meal size. Ae. aegypti showed a faster mf migration capacity compared to Cx. quinquefasciatus but did not allow parasite maturation under our experimental conditions. Similar proportions of melanized parasites were observed in Ae. aegypti (2.4%) and Cx. quinquefasciatus (2.1%). However, no relationship between rate of infection and melanization was observed. We conclude that in these conditions physiological factors governing parasite development in the thorax may be more important in limiting vectorial competence than the density of mf ingested.
Key words: Culex quinquefasciatus - Aedes aegypti - Wuchereria bancrofti - vectorial capacity
Lymphatic filariasis is one of the most important human diseases transmitted by mosquitoes. It affects approximately 120 million people worldwide (Otensen & Ramachandran 1995). Understanding of vector/parasite interactions is essential for rational development of filariasis control measures. This is particularly important, considering that vectorial competence, i.e. the ability of mosquitoes to ingest mf and to promote their maturation until the infective stage and the rate of mosquito survival until parasite maturation (Failloux et al. 1995), seem to differ according to geographic mosquito strain (Wharton 1960, Crans 1973, McGreevy et al. 1982). Variation in the density of mf in the blood and parasite behaviour also influence vector/parasite relationships (Tabachnick et al. 1985, Southgate & Bryan 1992, Failloux et al. 1995).
Recife, a Brazilian coastal city (on 8o4'3" south latitude), with approximately 1.4 million people, is an endemic area of Wuchereria bancrofti, transmitted by Culex quinquefasciatus. In 1952, Azevedo and Dobbin registered lymphatic filariasis in a local district with microfilaraemia rate of about 9.7%. A recent survey, of several areas, has shown that W. bancrofti infection now has prevalence rates ranging from 0.64 to 14.95% (Maciel et al. 1996). In addition to increasing incidence of lymphatic filariasis in some areas, the number of breeding places for Cx. quinquefasciatus is rising due to uncontrolled urbanization (Oliveira 1996). Despite these facts, we have a poor understanding of the interactions that occur between the parasite and its vector in Recife.
Ae. aegypti is also abundant in Recife, but it is not regarded as a natural vector of W. bancrofti, however understanding of the relationship mosquito/parasite is relevant to studies concerned to immune mechanism of refractory species. It has been suggested that the relationship between the density of microfilariae (mf) in human blood, the ingestion of mf and production of L3 larvae is an important determinant of transmission dynamics of lymphatic filariasis (Brito et al. 1997, Calheiros et al. 1998). Ingestion may depend upon feeding behaviour and mechanics, whereas, difference in vector physiology will contribute to the success or failure of parasite maturation to L3. Here we report upon a study designed to investigate the relative role of these factors in the development of W. bancrofti in the susceptible Cx. quinquefasciatus and refractory Ae. aegypti and describe our initial observations on the immune response to mf in these two mosquitoes.
ACKNOWLEDGEMENTS
To Dr André Furtado for valuable discussion; to Mrs EHM Rocha for technical assistance.
TABLE I | TABLE II | TABLE III
This work was supported by the Wellcome Trust and CNPq.
+Corresponding author. Fax: +55-81-271.8359. E-mail: Cleide@npd.ufpe.br
Received 24 November 1998
Accepted 23 April 1999
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