Human Dirofilaria repens infections diagnosed in Slovakia in the last 10 years (2007–2017)

Canine dirofilariasis caused by Dirofilaria immitis is usually diagnosed by specific antigen testing and/or identification of microfilariae. However, D. immitis and at least six other filariae can produce canine microfilaremias with negative heartworm antigen tests. Discriminating these can be of clinical importance. To resolve discordant diagnoses by two diagnostic laboratories in an antigen-negative, microfilaremic dog recently imported into the US from Europe we developed a simple molecular method of identifying different microfilariae, and subsequently validated our method against six different filariae known to infect dogs by amplifying ribosomal DNA spacer sequences by polymerase chain reaction using common and species-specific primers, and sequencing the products to confirm the genotype of the filariae. We identified the filaria in this dog as D. repens. This is the first case of D. repens infection in the United States. Additionally, we examined microfilariae from five additional antigen-negative, microfilaremic dogs and successfully identified the infecting parasite in each case. Our diagnoses differed from the initial morphological diagnosis in three of these cases, demonstrating the inaccuracy of morphological diagnosis. In each case, microfilariae identified morphologically as A. reconditum were identified as D. immitis by molecular methods. Finally, we demonstrated that our PCR method should amplify DNA from at least two additional filariae (Onchocerca and Mansonella), suggesting that this method may be suitable for genotyping all members of the family Onchocercidae.

The filarial nematode Dirofilaria repens is currently considered to be one of the most extensively spreading human and animal parasites in Europe. In Ukraine, reporting cases of dirofilariasis has been mandatory since 1975, and the disease was included in the national surveillance system for notifiable diseases. Up until December 31st 2012, a total of 1533 cases have been registered, with 1465 cases occurring within the previous 16 years. Most of the cases of dirofilariasis were registered in 6 regions: Kyiv, and the Donetsk, Zaporizhzhya, Dnipropetrovsk, Kherson and Chernihiv oblasts. In the years 1997-2002 the highest incidence rate was noted in the Kherson oblast in the south of the country (9.79 per 100 000 people), and the lowest in western Ukraine (0.07-1.68 per 100 000 people). D. repens infections were registered in all oblasts. Parasitic lesions were most often located in the head, the subconjunctival tissue and around the eyes. D. repens lesions were also found in the limbs, torso, male sexual organs, and female mammary glands. Dirofilariasis was diagnosed in persons aged from 11 months to 90 years old, most often among people between 21-40 years of age. Most patients had only one parasitic skin lesion; the majority of isolated nematodes were female. The results of our analysis point to a constant increase in D. repens dirofilariasis incidence in humans in Ukraine. Despite educational efforts, infections have become more frequent and the territory in which the disease occurs has enlarged to encompass the whole of Ukraine. Nevertheless, the Ukrainian sanitary-epidemiological services managed to achieve some measure of success, e.g. by creating a registration system for D. repens infections and establishing proper diagnostics for the disease.

Background Dirofilaria repens and D. immitis are filarioid helminths with domestic and wild canids as main hosts and mosquitoes as vectors. Both species are known to cause zoonotic diseases, primarily pulmonary (D. immitis), ocular (D. repens), and subcutaneous (D. repens) dirofilariosis. Both D. immitis and D. repens are known as invasive species, and their distribution seems associated with climate change. Until very recently, both species were known to be nonendemic in Austria. Methodology and Principal Findings Metadata on introduced and possibly autochthonous cases of infection with Dirofilaria sp. in dogs and humans in Austria are analysed, together with analyses of mosquito populations from Austria in ongoing studies. In Austria, most cases of Dirofilaria sp. in humans (30 cases of D. repens—six ocular and 24 subcutaneous) and dogs (approximately 50 cases—both D. immitis and D. repens) were most likely imported. However, occasionally infections with D. repens were discussed to be autochthonous (one human case and seven in dogs). The introduction of D. repens to Austria was confirmed very recently, as the parasite was detected in Burgenland (eastern Austria) for the first time in mosquito vectors during a surveillance program. For D. immitis, this could not be confirmed yet, but data from Germany suggest that the successful establishment of this nematode species in Austria is a credible scenario for the near future. Conclusions The first findings of D. repens in mosquito vectors indicate that D. repens presumably invaded in eastern Austria. Climate analyses from central Europe indicate that D. immitis also has the capacity to establish itself in the lowland regions of Austria, given that both canid and culicid hosts are present.