Is molecular xenomonitoring of mosquitoes for Dirofilaria repens suitable for dirofilariosis surveillance in endemic regions?

Dirofilaria repens is a parasite of animals and humans, transferred by mosquitoes. The assessment of the presence of D. repens-infected vertebrate hosts in the investigated area can be performed by xenomonitoring—detection of the parasite in blood-feeding arthropods. Our study aimed to evaluate PCR xenomonitoring of mosquitoes as a tool for dirofilariosis surveillance in Poland. We were also interested whether inter-study comparisons at the international level would be possible. Mosquitoes were collected in a single locality in Mazowsze province in Poland, in which between 12 and 20% of dogs were infected with D. repens and autochthonous human dirofilariosis was confirmed. All captured female mosquitoes were divided into pools; alternatively, single mosquitoes were analyzed; DNA was isolated and subjected to PCR and real-time PCR for detection of D. repens. The estimations of infection rates of mosquitoes with D. repens, based on PCR results, varied from 0 to 1.57% even between assays for detection of distinct fragments of the same marker—cytochrome oxidase subunit one gene. Polymorphisms of the DNA sequence within binding sites of the primers used in D. repens xenomonitoring assays, applied in European studies, were identified. Non-specific amplification of Setaria tundra (Nematoda: Onchocercidae) DNA occurred. Surveillance of dirofilariosis by PCR mosquito xenomonitoring is possible; however, the efficiency of the approach on territories where the prevalence of the disease among definitive hosts is lower than 12% remains unknown. Furthermore, mosquito infection rate estimations can be PCR assay dependent, which makes inter-study comparisons difficult. The results obtained in independent European xenomonitoring studies were contradictory. International collaboration would be required to establish a standardized set of assays for sensitive and specific xenomonitoring-based dirofilariosis surveillance.