Vector survival and parasite infection: the effect of Wuchereria bancrofti on its vector Culex quinquefasciatus

• Published in: Parasitology 2004-07, Vol.129 (1), p.43-50
• Main Authors: KRISHNAMOORTHY, K., SUBRAMANIAN, S., VAN OORTMARSSEN, G. J., HABBEMA, J. D. F., DAS, P. K.
• Format: Article
• Language: English
• Subjects: Animals; Aquatic insects; Bancroftian filariasis; Biological and medical sciences; Councils; Culex - growth & development; Culex - parasitology; Culex pipiens; Culex quinquefasciatus; Culicidae; Density; Disease transmission; Engorgement; extrinsic incubation period; Female; Filariasis; Filariasis - parasitology; Filariasis - transmission; Fundamental and applied biological sciences. Psychology; General aspects; General aspects and techniques. Study of several systematic groups. Models; host-parasite relationships; Humans; incubation period; infection; Infections; insect vectors; Invertebrates; Laboratories; Larvae; Likelihood Functions; lymphatic filariasis; Male; Medical research; microfilariae; Mortality; Mosquitoes; nematode larvae; parasite load; parasite-induced vector mortality; Parasitemia - parasitology; Parasites; Parasitology; Public health; Random Allocation; Research centers; Risk analysis; Risk factors; Studies; Survival; Survival Analysis; vector competence; vector mortality; Vector-borne diseases; Weibull model; Wuchereria bancrofti; Wuchereria bancrofti - growth & development; Wuchereria bancrofti - physiology
• ISSN: 0031-1820; 1469-8161
• DOI: 10.1017/S0031182004005153

This paper investigates a cohort of 2187 laboratory reared Culex quinquefasciatus fed on 69 human volunteers, including 59 persons with different levels of Wuchereria bancrofti microfilariae and 10 without microfilaria. Mosquitoes were followed until death. Mosquito survival was analysed in relation to the level of microfilaria in the human and larval count in the dead mosquito. Vector mortality during the extrinsic incubation period (12 days post-engorgement) was significantly higher in mosquitoes fed on microfilaraemic volunteers (50%) than in those fed on amicrofilaraemics (29%). Both the percentage infected and the geometric mean parasite density was significantly higher among mosquitoes which died before 13 days (45% infected and 10 larvae per infected mosquito) than those surviving beyond 13 days (39% and 2·2), suggesting a parasite loss of more than 80% during the extrinsic incubation period. A large proportion (62%) of the mosquitoes that died during the early of phase of parasite development were infected (36% in low, 26% in medium and 90% in high human Mf-density). Survival analysis showed that the parasite load in mosquitoes and the human Mf-density for a given parasite load are independent risk factors of vector survival. Overall, the hazard of dying was found to be 11–15 times higher among mosquitoes fed on microfilaraemic volunteers than those fed on amicrofilaraemics. The hazard doubles for every increase of about 60–70 parasites in the vector. As a consequence of the parasite-induced reduction in vector survival, the transmission success of the parasite is reduced. The implication of the results on control/elimination of lymphatic filariasis using mass-drug administration is discussed.