Abstract
Haemosporidians, a group of vector-borne parasites that include Plasmodium, infect vertebrates including birds. Although mosquitoes are crucial elements in the transmission of avian malaria parasites, little is known of their ecology as vectors. We examined the presence of Plasmodium and Haemoproteus lineages in five mosquito species belonging to the genera Culex and Ochlerotatus to test for the effect of vector species, season and host-feeding source on the transmission dynamics of these pathogens. We analyzed 166 blood-fed individually and 5,579 unfed mosquitoes (grouped in 197 pools) from a locality in southern Spain. In all, 15 Plasmodium and two Haemoproteus lineages were identified on the basis of a fragment of 478 bp of the mitochondrial cytochrome b gene. Infection prevalence of blood parasites in unfed mosquitoes varied between species (range: 0–3.2%) and seasons. The feeding source was identified in 91 mosquitoes where 78% were identified as bird. We found that i) several Plasmodium lineages are shared among different Culex species and one Plasmodium lineage is shared between Culex and Ochlerotatus genera; ii) mosquitoes harboured Haemoproteus parasites; iii) pools of unfed females of mostly ornithophilic Culex species had a higher Plasmodium prevalence than the only mammophylic Culex species studied. However, the mammophylic Ochlerotatus caspius had in pool samples the greatest Plasmodium prevalence. This relative high prevalence may be determined by inter-specific differences in vector survival, susceptibility to infection but also the possibility that this species feeds on birds more frequently than previously thought. Finally, iv) infection rate of mosquitoes varies between seasons and reaches its maximum prevalence during autumn and minimum prevalence in spring.
Highlights
Pathogens are selective factors for micro-evolutionary changes in their hosts and as such play an important role in regulating population dynamics [1]
The four Culex species tested here, Cx. modestus, Cx. perexiguus, Cx. pipiens and Cx. theileri have been previously reported as potential vectors of avian Plasmodium, this is the first report for Oc. caspius as a potential host of avian malaria
Both Cx. theileri and Oc. caspius are presumed to have a preference for biting on mammals [25,50,51] and so we expected a lower prevalence of infection by avian malaria parasites than in species that mainly feed on birds (i.e. Cx. modestus, Cx. perexiguus and Cx. pipiens)
Summary
Pathogens are selective factors for micro-evolutionary changes in their hosts and as such play an important role in regulating population dynamics [1]. Haemosporidian blood parasites include three main genera, Plasmodium, Haemoproteus and Leucocytozoon, all of which are phylogenetically closely related and have similar life cycles, but different life-history traits. Their life cycles require the intervention of insect vectors during sexual and sporogonic phases, along with a vertebrate host for the merogony phase and the development of gametocytes [2]. It is closely related to mammal malaria, avian Plasmodium form a phylogenetically independent clade [5] Despite their high diversity and widespread distribution range [2,6], and contrary to the case of human malaria parasites, little information is available about the population dynamics of avian malaria parasites in natural ecosystems
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