Trypanosomatid parasites in Austrian mosquitoes

Abstract

Trypanosomatid flagellates have not been studied in Austria in any detail. In this study, specific nested PCR, targeted on the ribosomal small subunit, was used to determine the occurrence and diversity of trypanosomatids in wild-caught mosquitoes sampled across Eastern Austria in the years 2014-2015. We collected a total of 29,975 mosquitoes of 19 species divided in 1680 pools. Of these, 298 (17.7%), representing 12 different mosquito species, were positive for trypanosomatid DNA. In total, seven trypanosomatid spp. were identified (three Trypanosoma, three Crithidia and one Herpetomonas species), with the highest parasite species diversity found in the mosquito host Coquillettidia richiardii. The most frequent parasite species belonged to the mammalian Trypanosoma theileri/cervi species complex (found in 105 pools; 6.3%). The avian species T. culicavium (found in 69 pools; 4.1%) was only detected in mosquitoes of the genus Culex, which corresponds to their preference for avian hosts. Monoxenous trypanosomatids of the genus Crithidia and Herpetomonas were found in 20 (1.3%) mosquito pools. One third (n = 98) of the trypanosomatid positive mosquito pools carried more than one parasite species. This is the first large scale study of trypanosomatid parasites in Austrian mosquitoes and our results are valuable in providing an overview of the diversity of these parasites in Austria.

Fig 1. An SSU rDNA-based Bayesian phylogenetic tree representing the most likely new Herpetomonas species obtained from a mosquito collected in Eastern Austria.

Bootstrap values from Bayesian posterior probabilities (5 million generations) and bootstrap percentages for maximum-likelihood (PhyML) analysis (1,000 replicates) are shown at the nodes; dashes indicate <50% bootstrap support or different topology; asterisks mark branches with maximal statistical support; double-crossed branches are 50% of the original length. The tree was rooted with five sequences of Phytomonas spp., the closest relative of the genus Herpetomonas. Parasite names, names of strains or GenBank accession numbers are given; the branch lengths are drawn proportionally to the amount of changes (scale bar).

Fig 2. Number of mosquito pools positive for trypanosomatid DNA (trypanosome species, T. avium, T. culicavium, and T. theileri, are shown separately while Crithidia spp. infections are combined) according to the sampled months in 2014 and 2015 (Vienna and Eastern Austria).

Fig 3. Prevalence of trypanosomatids calculated as minimum infection rate (MIR) (trypanosome species are shown separately while Crithidia spp. infections are combined) in mosquitoes according to the sampled months in 2014 and 2015 (Vienna and Eastern Austria).