Haplotypes of Dirofilaria repens from Poland and selected countries of Central, North-Eastern Europe and the Middle East: An evaluation on the relation between the genetic diversity and the geographic distribution of the fast-spreading parasite

Zoonotic dirofilariases: one, no one, or more than one parasite

Dirofilaria spp. are vector-borne filarial nematodes that affect a variety of animal species, including humans. Dirofilaria immitis and Dirofilaria repens are the two main zoonotic species, but also other wildlife-associated Dirofilaria species are occasionally reported as causative agents of human dirofilariasis, including Dirofilaria striata, Dirofilaria tenuis, Dirofilaria ursi, Dirofilaria spectans, and Dirofilaria magnilarvata. Since the etiological identity of most of the species mentioned here is arguable, we summarized and critically discussed data concerning infections in humans, focusing on the reliability of Dirofilaria species identification. We advocate the importance of combined morphological and genomic approaches to provide unequivocal evidence for their zoonotic potential and pathogenicity.

An unexpected case of a dog from Poland co-infected with Dirofilaria repens and Dirofilaria Immitis

BACKGROUND

Dirofilariasis is a vector-borne disease caused by parasitic nematodes of the genus Dirofilaria spp., considered an emerging concern in both veterinary and human medicine. Climate changes and human activities, such as pet travel, contribute to the spread of diseases to new non-endemic regions. Poland is dominated by subcutaneous dirofilariasis caused by D. repens infections. Cardiopulmonary dirofilariasis, also known as a heartworm disease is much more rare with only single autochthonous cases reported so far. Also, imported infections are observed sporadically in dogs traveling to endemic countries. In this study, we report the first case of a dog in Poland, never having traveled abroad, co-infected with Dirofilaria repens and Dirofilaria immitis.

CASE PRESENTATION

A 14-year-old mixed breed, an intact male dog with fever, lightly pale mucosal membranes, moderate abdominal pain, and a mild cough was presented in a veterinary clinic in Warsaw, Poland. The examination of the blood sample collected for complete morphology and biochemistry revealed the presence of live microfilariae. Presence of the DNA of both microfilariae species was detected using Real-Time PCR with species-specific primers.

CONCLUSIONS

Since the remaining diagnostic methods like Knott's test, antigen test or echocardiography did not reveal the presence of D. immitis, we discussed the impact of microfilariae periodicity and low worm burden infections on the limited efficiency of these techniques. We strongly recommend using a mixed diagnostic approach for the most sensitive and specific diagnosis since the ideal diagnostic method does not exist, and several factors may contribute to misdiagnosis. Furthermore, we considered factors that contribute to the uncontrolled spread of dirofilariasis such as climate changes, introduction of new species of mosquitoes competent for the transmission of the disease, and wildlife animals as an important reservoir of this parasitosis. Given that Poland shares borders with countries classified as endemic and pre-endemic for D. immitis, such as Slovakia and Ukraine, it is reasonable to anticipate a rise in autochthonous heartworm infections and shifts in the epidemiological pattern of dirofilariasis in the coming years.

Genetic variability of Dirofilaria repens isolates from humans and dogs in Italy

Dirofilaria repens is a paradigmatic example of an emerging vector-borne pathogen (VBP) in both human and veterinary fields. The spatial expansion and the increasing zoonotic impact of this VBP can be related to several drivers including the genetic structure of parasite populations. Italy is one of the European countries traditionally endemic with the highest incidence of canine and human cases of subcutaneous dirofilariosis. The present study aimed to assess the genetic identity and variability of D. repens isolates of human and canine origin from areas of Central Italy, compared with those isolated from different areas of Europe by sequence analysis of mtDNA genes (i.e., 12 S rDNA and cox1). A total of twenty isolates of D. repens were obtained from biopsies of subcutaneous and ocular cases of dirofilariosis occurring in 10 dogs and 10 humans. The sequence analysis of 12 S rDNA showed that all the sequences obtained clustered as a monophyletic group with a strong nodal support, indicating that all sequence types represented D. repens. The cox1 and the 12 S sequence analysis did not show host-related polymorphisms between human and dog-derived specimens. The sequence analysis of cox1 was performed including 8 additional sequences previously obtained from human and canine isolates in the same areas. Out of the 28 sequences analyzed, 20 were grouped in a haplogroup comprising 15 haplotypes (i.e., DR1, DR2, DR4, DR5, DR7, DR8, DR10-DR18), 2 sequences matched to DR9, reported for the first time in Italy, and 6 showed peculiar polymorphisms that were not previously described. The results obtained have implications for a better understanding of the epidemiology and phylogeography of this emerging vector-borne zoonotic parasite.

Vector-borne parasites in dogs from Ukraine translocated to Poland following Russian invasion in 2022

INTRODUCTION

Since 24 February 2022, the day the Russian aggression against Ukraine began, millions of refugees and thousands of pets crossed the Polish-Ukrainian border. Additionally, an unknown number of shelter and stray dogs and cats were rescued and translocated to Poland by private persons and non-profit organizations. The aim of the present study was to examine rescued dogs and cats for presence of canine vector-borne parasites to determine the role of armed conflict in spreading these parasites.

METHODS

In July 2022 blood samples were collected from two animal shelters in central Poland hosting dogs and cats rescued from Ukraine. Animals were imported from various regions of Ukraine, including eastern and southeastern Ukraine (military conflict area). Fifty-three dogs (51 from two shelters and two owned ones) and one shelter cat were examined by molecular methods (PCR and sequencing) for the presence of Babesia/Theileria spp., Dirofilaria spp. and Hepatozoon spp. DNA.

RESULTS

We detected Dirofilaria immitis, a parasite species non-endemic in Poland, in two dogs translocated from Ukraine (2/53 = 3.8% [95% CI 0.5-13.0%]). One dog had a history of previous heartworm infection. High prevalence of Hepatozoon canis (51% [95% CI 36.8-64.9%]) was noted among translocated dogs. Prevalence of Dirofilaria repens in Ukrainian dogs (18.9% [95% CI 9.4-32.0%) was similar to prevalence in dogs from central Poland (12%). Co-infection of D. repens and D. immitis was found in two dogs and six dogs were co-infected by D. repens and H. canis. Hepatozoon canis infection was also identified in an imported cat.

CONCLUSION

We confirmed that this military conflict has facilitated the spread of canine vector-borne parasites, including zoonotic species.

Genetic diversity and characterization of Wolbachia endosymbiont in canine filariasis

Canine filariasis is caused by nematodes from the family Onchocercidae, which is transmitted by arthropod vectors. The disease is commonly found in Southeast Asia and exists worldwide. Some filarial nematodes are associated with intracellular bacteria of the genus Wolbachia, which plays an important role in embryogenesis, molting, and the long-term survival of adult worms. This study aims to characterize Wolbachia sp. and determine the association between Wolbachia and canine filarial nematode species in Thailand. A total of 46 dog blood samples that were naturally infected with filarial nematodes were obtained to identify filarial nematode species by Giemsa stained under a light microscope and confirmed using the molecular technique. In order to characterize Wolbachia sp., the nested PCR assay targeting the 16S rRNA gene showed that all samples of Dirofilaria immitis and fifteen samples of Candidatus Dirofilaria hongkongensis were grouped into Wolbachia supergroup C. In addition, all samples of Brugia spp. and five samples of Candidatus Dirofilaria hongkongensis were classified into Wolbachia supergroup D. The genetic diversity analysis conducted using the 16S rRNA gene revealed a similar result when analyzed through phylogenetic tree analysis. This is the first genetic diversity study of Wolbachia of Candidatus Dirofilaria hongkongensis in infected dogs in Thailand.

Diversity and geographic distribution of haplotypes of Dirofilaria immitis across European endemic countries

BACKGROUND

Dirofilaria immitis, also known as heartworm, is one of the most important parasitic nematodes of domestic dogs, causing a potentially serious disease, cardiopulmonary dirofilariosis, which can be lethal. This species seems to be less 'expansive' than its sister species Dirofilaria repens, and it is believed that climate change facilitates the spread of this parasite to new non-endemic regions.

METHODS

In total, 122 heartworm isolates were analysed from nine endemic countries in Europe (Portugal, Spain, Italy, Greece, Hungary, Romania, Slovakia, and Ukraine) and a single isolate from Bangladesh by amplification and sequencing of two mitochondrial (mt) DNA markers: cytochrome c oxidase subunit 1 (COI) and dehydrogenase subunit 1 (NADH). The main aim of the current study was to determine the genetic diversity of D. immitis and compare it with D. repens haplotype diversity and distribution. DNA was extracted from adult heartworms or microfilariae in blood. Most isolates originated from dogs (Canis lupus familiaris) while 10 isolates originated from wildlife species from Romania, including eight isolates from golden jackals (Canis aureus), one isolate from a Eurasian otter (Lutra lutra) and one isolate from a red fox (Vulpes vulpes).

RESULTS

Median spanning network analysis was based on the combined sequence (1721 bp) obtained from two mt markers and successfully delineated nine haplotypes (Di1-Di9). Haplotype Di1 was the dominant haplotype encompassing 91 out of the 122 sequences (75%) from all nine countries and four host species. Haplotype Di2 was the second most common haplotype, formed solely by 13 isolates from Italy. The remaining sequences were assigned to Di3-Di9 haplotypes, differing by 1-4 SNPs from the dominant Di1 haplotype. There was evidence for geographical segregation of haplotypes, with three unique haplotypes associated with Italy and four others associated with certain countries (Di4 and Di7 with Slovakia; Di8 with Greece; Di6 with Hungary).

CONCLUSION

Diversity in D. immitis mt haplotypes was lower by half than in D. repens (9 vs. 18 haplotypes in D. immitis and D. repens, respectively), which may be associated with the slower expansion of heartworm in Central and NE Europe. NADH gene appears to be conserved in Dirofilaria sp. by showing lower genetic diversity than the analysed COI gene.