Detection of Dirofilaria repens and Dirofilaria immitis DNA in mosquitoes from Belarus

Abstract

During the last two decades, Belarus faces an increase of human cases of Dirofilaria (Nematoda, Spirurida, Onchocercidae) infections. However, comprehensive analyses explaining this development and the identification of mosquito vector species are missing. Here, we present results using temperature data from Belarus and show that the annual number of human Dirofilaria cases is significantly correlated with the yearly average temperatures (Spearman's rho = 0.49, p < 0.05) and the average sum of potential Dirofilaria transmission days (Spearman's rho = 0.46, p < 0.05), suggesting that autochthonous transmission is at least in part responsible for the increasing number of clinical Dirofilaria cases in the country. In addition, 467 female mosquitoes were collected from different sampling sites in the regions of Brest and Minsk, which were analyzed by molecular methods for the presence of Dirofilaria repens and Dirofilaria immitis DNA, respectively. Two pools (5.56 %) were tested positive for Dirofilaria (estimated infection rate per 100 specimens = 0.44, 95 % confidence interval = 0.08-1.43), comprising one Anopheles claviger s.l. pool that was positive for D. repens and one Culex pipiens s.l./Culex torrentium pool positive for D. immitis DNA. This, to our knowledge, is the first molecular evidence for the presence of Dirofilaria in mosquitoes from Belarus, suggesting a high probability of autochthonous Dirofilaria transmission in the country.

Circulation of Dirofilaria repens and Dirofilaria immitis in Moldova

“…dorsalis ( D. repens : Hungary [38]), An. claviger ( D. immitis : Belarus [16]), Ae. cinereus / geminus ( D. repens : Hungary [38]).…”

“…infection patterns for the screened mosquitoes, i.e. only D. immitis [41, 42, 46, 50], only D. repens [38, 60–62] or co-circulation as also observed in Moldova [16, 39, 40, 43, 44, 49, 53, 58, 63]. Nevertheless, the incidence of human dirofilariasis in Europe is significantly higher for infections with D. repens than with D. immitis [2].…”

“…However, in this study, the number of days allowing the completion of the extrinsic incubation did not differ between the sites positive for D. repens or D. immitis . One possible explanation of the higher D. repens prevalence in Moldova might be the current spread of D. repens from eastern Europe to central Europe [10–16]. The most likely explanation for this observation is that D. repens infections in dogs are generally asymptomatic, while D. immitis infections cause more severe clinical symptoms and, thus, only the latter is recognized and treated to cure the infection [64, 65].…”

“…Female mosquito specimens were screened for D. repens and D. immitis [16]. Mosquitoes were pooled by sampling site, sampling date and taxon comprising between 1 to 35 specimens per pool (mean = 12.91) and stored in 96% ethanol until further processing.…”

“…infections has been observed in eastern and central Europe, including an increase of human cases [10, 11]. Moreover, autochthonous cases were detected in countries, which were previously regarded as non-endemic: Austria [12], Poland [13], Germany [14], Czech Republic [15] and Belarus [16]). Moldova is bordered to the East and South by the Odessa region of the Ukraine where incidence rates for human dirofilariasis ranged from 2.43 to 3.71 per 100,000 inhabitants between 1997 and 2012 [10].…”