Dirofilaria immitis in Bulgaria: the first genetic baseline data and an overview of the current status

Abstract

SummaryDirofilaria immitis, the agent of canine dirofilariosis, is a common parasite of domestic and wild carnivores with zoonotic potential and worldwide distribution, being endemic in many countries. Bulgaria is among European countries recognized as endemic for this heartworm parasite. In the present study, D. immitis adults recovered from pulmonary arteries of domestic dog and golden jackal originating from the Pazardzhik region in southern Bulgaria, and from red fox originating from the Plovdiv region in central-southern Bulgaria, were genetically analyzed in nuclear targets. The first PCR amplification of the internal transcribed region 2 (ITS2) of the ribosomal DNA with previously published D. immitis-specific primers yielded single fragments in size of 302 bp that is characteristic for these heartworms. PCR products of three isolates, resulted from the second amplification of the 5.8S-ITS2 region (235 bp) with pan-filarioid primers, were subjected to direct DNA sequencing. Identical nucleotide composition was detected across the screened target region for these Bulgarian isolates. When the 5.8S-ITS2 sequences were phylogenetically compared to the GenBank-retrieved D. immitis sequences in a worldwide context, the neighbor-joining analysis has shown three discrete clades. The first clade was composed of D. immitis isolates from Europe (including the studied Bulgarian samples), Asia and South America, in the second clade samples from Asia and South America were placed, whereas the third clade was formed by two Brazilian dog isolates originated from the north and southeast part of the country. The purpose of the present study was to verify the taxonomic characterization of D. immitis nematodes from Bulgaria based on morphology and compare their genetic structure with filariae obtained from the different world regions using molecular assays. It also summarizes previous epidemiological and ecological studies on the parasite distribution and prevalences in different hosts and regions undertaken so far in Bulgaria.

Identity of Microfilariae Circulating in Dogs from Western and South-Western Romania in the Last Decade

“…In Europe, infection with Dirofilaria spp. in dogs was identified in many countries including Austria [12], the Baltic countries [23], Bulgaria [24], the Czech Republic and Slovakia [25], France [26], Greece [6,27], Hungary [28], Italy [29][30][31], Serbia [32], and Spain [33], with minor differences among reports [13]. An up-to-date and accurate picture of Dirofilaria infections in central and northern European countries is provided by a study by Fuehrer et al, 2021, which states that, although the number of studies has increased in recent years, epizootiological knowledge is fragmented [34].…”

What Has Happened to Heartworm Disease in Europe in the Last 10 Years?

“…Other studies have reported prevalence between 16.2 and 34.3% in the central-southern region (Stara Zagora) [85,86]. In the city of Sofia (western), the prevalence ranged between 4.8 and 25.8%, while the prevalence rose to 34.7% in the Sofia region [81,83,[86][87][88]. In addition, Iliev et al [80] showed a prevalence of 11.3% in the south and 8.3% in the north, with a mean prevalence of 10.5%.…”

“…In Bulgaria, recent studies reported prevalence between 4.8-34.7%, being higher in the central, eastern, and southern regions and lower in the western and south-western regions [80][81][82]. In the central southern region, prevalence between 15.74 and 17.8% were reported, while prevalence in the south-western region was 5.5% [83,84]. Other studies have reported prevalence between 16.2 and 34.3% in the central-southern region (Stara Zagora) [85,86].…”

“…In Bulgaria, Panayotova-Pencheva et al [82] reported heartworm infection in a golden jackal and a red fox from Pazardzhik and Plovdiv regions, located in southern Bulgaria. In addition, several studies have shown a prevalence of D. immitis antigens between 3-44.4% in red foxes, and 4.4-58.7% in golden jackals; furthermore, isolated cases of infected red foxes and golden jackals were detected by necropsy [83,89,144].…”

Estimated specific antibody-based true sero-prevalences of canine filariosis in dogs in Central Europe and the UK

“…For D. immitis , a trend to spread in north-eastern Europe has been observed in recent decades (Genchi et al 2011 ). The northern border of transmission of D. immitis is not well documented to date, but cases have been identified as north as Central France, Southern Switzerland, Northern Italy, Slovakia, Bulgaria, Hungary and Ukraine (Deplazes et al 1995 ; Farkas et al 2020 ; Hermosilla et al 2006 ; Laidoudi et al 2019 ; Mendoza-Roldan et al 2020 ; Panayotova-Pencheva et al 2020 ; Petruschke et al 2001 ; Sassnau et al 2014a ; Széll et al 2020 ).…”