High temperatures and low humidity promote the occurrence of microsporidians (Microsporidia) in mosquitoes (Culicidae).

BACKGROUND: In the context of climate change, a growing concern is that vector-pathogen or host-parasite interactions may be correlated with climatic factors, especially increasing temperatures. In the present study, we used a mosquito-microsporidian model to determine the impact of environmental factors such as temperature, humidity, wind and rainfall on the occurrence rates of opportunistic obligate microparasites (Microsporidia) in hosts from a family that includes important disease vectors (Culicidae). METHODS: In our study, 3000 adult mosquitoes collected from the field over 3 years were analysed. Mosquitoes and microsporidia were identified using PCR and sequencing of the hypervariable V5 region of the small subunit ribosomal RNA gene and a shortened fragment of the cytochrome c oxidase subunit I gene, respectively. RESULTS: DNA metabarcoding was used to identify nine mosquito species, all of which were hosts of 12 microsporidian species. The prevalence of microsporidian DNA across all mosquito samples was 34.6%. Microsporidian prevalence in mosquitoes was more frequent during warm months (> 19 °C; humidity < 65%), as was the co-occurrence of two or three microsporidian species in a single host individual. During warm months, microsporidian occurrence was noted 1.6-fold more often than during the cold periods. Among the microsporidians found in the mosquitoes, five (representing the genera Enterocytospora, Vairimorpha and Microsporidium) were positively correlated with an increase in temperature, whereas one (Hazardia sp.) was significantly correlated with a decrease in temperature. Threefold more microsporidian co-occurrences were recorded in the warm months than in the cold months. CONCLUSIONS: These results suggest that the susceptibility of mosquitoes to parasite occurrence is primarily determined by environmental conditions, such as, for example, temperatures > 19 °C and humidity not exceeding 62%. Collectively, our data provide a better understanding of the effects of the environment on microsporidian-mosquito interactions.

Differences in the proliferation trend of 'Microsporidium' sp. PL03 in Culex pipiens and C. torrentium larvae.

Our study aimed to examine whether there are differences in the proliferation trend of microsporidia in mosquito larvae of the same genus (Culex spp.). DNA-barcoding and quantitative analyses were used to determine microsporidian rDNA copies in 'early' (L1 + L2) and 'late' (L3 + L4) Culex larvae in a natural population. In the study area, C. pipiens and C. torrentium larvae were infected by 'Microsporidium' sp. PL03 at similar levels. Infection by this microsporidian species probably elicits a notable immune response in C. pipiens, whereas in C. torrentium, it may evade or suppress the host immune response.