Experiment in semi-natural conditions did not confirm the influence of malaria infection on bird attractiveness to mosquitoes

Abstract

Background Changes in host phenotype following parasite infection are often considered as host manipulation when they seem advantageous for the parasite. However, putative cases of host manipulation by parasites are rarely tested in field-realistic conditions. Infection-induced phenotypic change cannot be conclusively considered as host manipulation if no evidence shows that this trait is adaptive for the parasite in the wild. Plasmodium sp., the parasites causing malaria in vertebrates, are hypothesized to “manipulate” their host by making their odour more attractive to mosquitoes, their vector and final host. While this is fairly well supported by studies on mice and humans, studies focusing on avian malaria give contradictory results. Methods In the present study, genotyped birds at different stages (uninfected, acute and chronic) of Plasmodium relictum infection were exposed, in a large outdoor aviary, to their natural vector, the mosquito Culex pipiens. Results After genotyping the blood meals of more than 650 mosquitoes, we found that mosquitoes did not bite infected birds more than they bit them before infection, nor more than they bit uninfected hosts. Conclusions Our study highlights the importance of testing ecological behaviours under natural conditions and suggests that different processes might be at play in mammals and birds regarding potential manipulation of attractiveness by malaria parasites. Graphical Abstract

Plasmodium relictum infection in Culex quinquefasciatus (Culicidae) decreases diel flight activity but increases peak dusk flight activity

“…Additionally, a study by Lacroix et al [ 22 ] in the human malaria system found similar results. However, other studies have found that there was no evidence of this alteration, and perhaps a parasite avoidance by these mosquitoes [ 31 , 50 ]. These data support a modulation in flight activity by P. relictum in less overall flight activity and increased flight activity at peak host-seeking times, which could lead to an increase the transmission of this P. relictum parasite.…”

“…The effect of Plasmodium parasites on the behaviour of mosquito hosts has been explored in several studies with conflicting results [ 19 , 30 , 31 ]. Koella et al [ 21 ] demonstrated alterations to Anopheles gambiae mosquito biting behaviour that would improve the transmission of Plasmodium falciparum parasites, including an increase in multiple biting events.…”

Evolutionary consequences of vector-borne transmission: how using vectors shapes host, vector and pathogen evolution

“…This parasite avoidance behaviour has been demonstrated in fewer studies (see Lalubin et al ., 2012 ) when compared to a larger body of studies showing higher vector attraction to infected hosts (Cozzarolo et al ., 2020 ; Santiago-Alarcon and Ferreira, 2020 ). Nonetheless, some earlier studies also suggest the absence of any effect of infection status on vector attraction (Cozzarolo et al ., 2022 ).…”