Seidl, C. M. | bioRxiv Science

bioRxiv2024

Transinfection of Wolbachia wAlbB into Culex quinquefasciatus mosquitoes does not alter vector competence for Hawaiian avian malaria (Plasmodium relictum GRW4)

Avian malaria is expanding upslope with warmer temperatures and driving multiple species of Hawaiian birds towards extinction. Methods to reduce malaria transmission are urgently needed to prevent further declines. Releasing Wolbachia-infected incompatible male mosquitoes suppress mosquito populations and releasing Wolbachia-infected female mosquitoes could reduce pathogen transmission if the Wolbachia strain reduced vector competence. We cleared Culex quinquefasciatus of their natural Wolbachia pipientis wPip infection and transinfected them with Wolbachia wAlbB isolated from Aedes albopictus. We show that wAlbB infection was transmitted transovarially, and demonstrate cytoplasmic incompatibility with wild-type mosquitoes infected with wPip from Oahu and Maui, Hawaii. We measured vector competence for avian malaria, Plasmodium relictum, lineage GRW4, of seven mosquito lines (two with wAlbB; three with natural wPip infection, and two cleared of Wolbachia infection) by allowing them to feed on canaries infected with recently collected field isolates of Hawaiian P. relictum. We tested 73 groups (Ntotal = 1176) of mosquitoes for P. relictum infection in abdomens and disseminated (thorax) infections 6-14 days after feeding across a range of parasitemias from 0.028% to 2.49%, and a smaller subset of salivary glands. We found no measurable effect of Wolbachia on any endpoint, but strong effects of parasitemia, days post feeding, and mosquito strain on both abdomen infection prevalence and disseminated infection prevalence. These results suggest that releasing male wAlbB-infected C. quinquefasciatus mosquitoes could suppress wPip-infected mosquito populations, but would have little positive or negative impact on mosquito vector competence for P. relictum if wAlbB became established in local mosquito populations. More broadly, the lack of Wolbachia effects on vector competence we observed highlights the variable impacts of both native and transfected Wolbachia infections in mosquitoes.

ecology↗

bioRxiv2022

Transcriptional response of individual Hawaiian Culex quinquefasciatus mosquitoes to the avian malaria parasite Plasmodium relictum

Culex quinquefasciatus, the mosquito vector of avian malaria in Hawai{square}i, became established in the islands in the 1820s and the deadly effects of malaria on endemic bird species have been documented for many decades. To evaluate the gene expression response of the mosquito to the parasite, we let the offspring of wild-collected Hawaiian Cx. quinquefasciatus feed on a domestic canary infected with Plasmodium relictum GRW4 freshly isolated from a wild-caught Hawaiian honeycreeper. Control mosquitoes were fed on an uninfected canary. We sequenced the individual transcriptomes of five infected and three uninfected individual mosquitoes at three different stages of the parasite life cycle: 24 h post feeding (hpf) during ookinete invasion; 5 days post feeding (dpf) when oocysts are developing; 10 dpf when sporozoites are released and invade the salivary glands. Differential gene expression analyses showed that during ookinete invasion (24 hpf), genes related to oxidoreductase activity and galactose catabolism had lower expression levels in infected mosquitoes compared to controls. Oocyst development (5 dpf) was associated with reduced expression of a gene with a predicted innate immune function. At 10 dpf, infected mosquitoes had reduced expression levels of a serine protease inhibitor. Overall, the gene expression response of Hawaiian Culex exposed to a Plasmodium infection intensity that occur naturally in Hawaii was low, but more pronounced during ookinete invasion. The low fitness costs often documented in Culex infected with avian Plasmodium likely reflect the relatively small transcriptional changes observed in mosquito genes related to immune response and nutrient metabolism.

microbiology↗