Anopheles stephensi Feeding, Flight Behavior, and Infection With Malaria Parasites are Altered by Ingestion of Serotonin

Abstract

Approximately 3.4 billion people are at risk of malaria, a disease caused by infection with Plasmodium spp. parasites, which are transmitted by Anopheles mosquitoes. Individuals with severe falciparum malaria often exhibit changes in circulating blood levels of biogenic amines, including reduced serotonin or 5-hydroxytryptamine (5-HT), and these changes are associated with disease pathology. In insects, 5-HT functions as an important neurotransmitter for many behaviors and biological functions. In Anopheles stephensi, we show that 5-HT is localized to innervation in the head, thorax, and midgut, suggesting a gut-to-brain signaling axis that could support the effects of ingested 5-HT on mosquito biology and behavioral responses. Given the changes in blood levels of 5-HT associated with severe malaria and the key roles that 5-HT plays in insect neurophysiology, we investigated the impact of ingesting blood with healthy levels of 5-HT (1.5 µM) or malaria-associated levels of 5-HT (0.15 µM) on various aspects of A. stephensi biology. In these studies, we provisioned 5-HT and monitored fecundity, lifespan, flight behavior, and blood feeding of A. stephensi. We also assessed the impact of 5-HT ingestion on infection of A. stephensi with the mouse malaria parasite Plasmodium yoelii yoelii 17XNL and the human malaria parasite Plasmodium falciparum. Our data show that ingestion of 5-HT associated with severe malaria increased mosquito flight velocity and investigation of visual objects in response to host odor (CO2). 5-HT ingestion in blood at levels associated with severe malaria also increased the tendency to take a second blood meal 4 days later in uninfected A. stephensi. In mosquitoes infected with P. y. yoelii 17XNL, feeding tendency was decreased when midgut oocysts were present but increased when sporozoites were present. In addition to these effects, treatment of A. stephensi with 5-HT associated with severe malaria increased infection success with P. y. yoelii 17XNL compared to control, while treatment with healthy levels of 5-HT decreased infection success with P. falciparum. These changes in mosquito behavior and infection success could be used as a basis to manipulate 5-HT signaling in vector mosquitoes for improved control of malaria parasite transmission.

Ingested histamine and serotonin interact to alter Anopheles stephensi feeding and flight behavior and infection with Plasmodium parasites

“…Indian wild-type strain A. stephensi were maintained as previously described ( Rodriguez et al, 2021 ; Briggs et al, 2022 ). All mosquito life stages were maintained at 28°C, 80% humidity, and under 12 h light–dark cycles (0800–2000).…”

“…As described previously, ( Rodriguez et al, 2021 ; Briggs et al, 2022 ), a blood meal consisting of washed human red blood cells (RBCs) and heat inactivated human serum (1:1, vol:vol) was provided via glass bell feeders to A. stephensi for 15 min. Time of blood feeding has been shown to alter some reproductive variables, but infection success is not impacted ( O’Donnell et al, 2019 ), so blood meals were offered between 0800–1,100 to maintain consistency across all studies.…”

“…The treatments described in Section 2.2 were provisioned to mosquitoes by delivery of treatment-soaked cotton balls prior to the first blood meal, previously described as priming ( Rodriguez et al, 2021 ; Briggs et al, 2022 ). Priming was used to provision treatments prior to feeding on infected mice.…”

“…Each treatment ( Section 2.2 ) was offered in a blood meal to groups of 120 female mosquitoes as described in Section 2.4 . Following feeding, 40 blood-fed mosquitoes from each treatment group were placed into individual housing (50 mL conical tubes) for 48 h to oviposit as described ( Rodriguez et al, 2021 ; Briggs et al, 2022 ). Following oviposition, female mosquitoes were transferred back to group housing and eggs were counted and recorded.…”

“…The mouse malaria parasite P. y. yoelii 17XNL (hereafter, P. yoelii ) was maintained in 9–11-week-old CD-1 mice (Envigo, Indianapolis, IN) as previously described ( Rodriguez et al, 2021 ; Briggs et al, 2022 ). All procedures were approved by the Institutional Animal Care and Use Committee of the University of Idaho (protocol IACUC-2023-8, renewed 2/27/2023).…”