Blood Parasites (Haemosporida, Trypanosomatida) in Culex pipiens: A Study and Review of Hibernating and Active Mosquitoes

Culex pipiens mosquitoes (Diptera: Culicidae) are widespread during warm periods and actively feed on blood while serving as vectors for various human and animal pathogens. Culex mosquitoes overwinter as adults in temperate zones, raising the question of whether hibernating Cx. pipiens can act as pathogen reservoirs. In this study, hibernating mosquitoes and mosquitoes collected during the warm season were tested for the presence of trypanosomatids and avian haemosporidian parasites using PCR. Midgut preparations were made from Cx. pipiens females in order to search for trypanosomatids morphologically. In total, 1037 Cx. pipiens mosquitoes (556 collected during the warm season and 481 overwintering mosquitos) were investigated. The parasite prevalence differed for mosquitoes collected during the warm season and hibernating ones for both Haemosporida (2.9% in warm-season and no infections in overwintering mosquitoes) and Trypanosomatida (1.6% and 0.4%, respectively) parasites. A phylogenetic analysis confirmed that the trypanosomatids found in hibernating mosquitoes were monoxenous and were not parasites of vertebrates. The peak prevalence of Haemosporida parasites was detected in July (4.9%) and August (2.8%), and for Trypanosomatida, it was detected in May (3.5%). The results of the present study show that overwintering Cx. pipiens mosquitoes are questionable reservoirs for avian haemosporidian parasites, but some monoxenous trypanosomatids can be found in overwintering females.