Abstract
Whether malaria parasites can manipulate mosquito host choice in ways that enhance parasite transmission toward suitable hosts and/or reduce mosquito attraction to unsuitable hosts (i.e. specific manipulation) is unknown. To address this question, we experimentally infected three species of mosquito vectors with wild isolates of the human malaria parasite Plasmodium falciparum, and examined the effects of immature and mature infections on mosquito behavioural responses to combinations of calf odour, human odour and outdoor air using a dual-port olfactometer. Regardless of parasite developmental stage and mosquito species, P. falciparum infection did not alter mosquito activation rate or their choice for human odours. The overall expression pattern of host choice of all three mosquito species was consistent with a high degree of anthropophily, with infected and uninfected individuals showing higher attraction toward human odour over calf odour, human odour over outdoor air, and outdoor air over calf odour. Our results suggest that, in this system, the parasite may not be able to manipulate the early long-range behavioural steps involved in the mosquito host-feeding process. Future studies are required to test whether malaria parasites can modify their mosquito host choice at a shorter range to enhance transmission.
Highlights
Less likely to attempt to feed[24, 27, 28]
We explored the first possibility using the natural association between Plasmodium falciparum, which causes the most severe form of human malaria, the mosquito species Anopheles coluzzii, Anopheles gambiae and Anopheles arabiensis, three major vectors of P. falciparum in Africa, and calves and human, two common mosquito vertebrate hosts
We found a significant effect of odour combination (χ22 = 6.61, P = 0.04), such that mosquitoes were more activated in the human vs. outdoor air (H-O) combination compared to the two other combinations
Summary
Since biting is risky (e.g., host defensive behaviours can kill the vector and its parasite), reduced feeding attempts seems beneficial to the parasite[32] In natural conditions, these “stage-dependent” behavioural changes presumably increase the rate at which a mosquito will feed on a vertebrate blood-source, not all of which are suitable hosts for the parasite. While some malaria vectors can display propensity to feed on different vertebrate species (i.e. generalist or opportunistic feeding behaviour)[36], the parasites they transmit are often highly host-specific, infecting only one or a few vertebrate species[37]. We experimentally challenged local colonies of three mosquito species with sympatric field isolates of P. falciparum using direct membrane feeding assays in Burkina Faso, and examined the effects of immature (oocyst) and mature (sporozoite) infections on mosquito choice between human and calf odours using a dual-port olfactometer
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