Parasitology



Plasmodium falciparum sporozoites increase feeding-associated mortality of their mosquito hosts Anopheles gambiae s.l.


R. A. ANDERSON a1c1, B. G. J. KNOLS a2 and J. C. KOELLA a1
a1 Department of Zoology, University of Aarhus, Universitetsparken B135, 8000 Århus C, Denmark
a2 International Centre of Insect Physiology and Ecology, PO box 30772, Nairobi, Kenya

Abstract

There is some evidence that pathology induced by heavy malaria infections (many oocysts) increases mortality of infected mosquitoes. However, there is little or no published evidence that documented changes in feeding behaviour associated with malaria infection also contribute to higher mortality of infected mosquitoes relative to uninfected individuals. We show here for the first time that, in a natural situation, infection by the sporozoites of the malaria parasite Plasmodium falciparum significantly reduced survival of blood-feeding Anopheles gambiae, the major vector of malaria in sub-Saharan Africa. To estimate feeding-associated mortality of infected mosquitoes, we compared the percentage of sporozoite infection in host-seeking mosquitoes caught before and after feeding. The infection rate was 12% for mosquitoes caught during the night as they were entering a tent to feed; however, only 7·5% of the surviving members of the same cohort caught after they had had the opportunity to feed were infected. Thus, Plasmodium falciparum sporozoites increased the probability of dying during the night-time feeding period by 37·5%. The increase in mortality was probably due to decreased efficiency in obtaining blood and by increased feeding activity of the sporozoite-infected mosquitoes that elicited a greater degree of defensive behaviour of hosts under attack.

(Received June 5 1999)
(Revised September 17 1999)
(Accepted October 23 1999)


Key Words: malaria; virulence; Plasmodium falciparum; Anopheles gambiae.

Correspondence:
c1 Corresponding author: Behavioural Ecology Research Group, Department of Biological Sciences, Simon Fraser University, Burnaby, BC, V5A 1S6, Canada. Tel: +1 604 291 4462. Fax: +1 604 291 3496. E-mail: raa@sfu.ca


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