Dirofilaria repens: emergence of autochthonous human infections in the Czech Republic (case reports)

Human Dirofilariasis Infection in the Forehead: A Case Report

Human dirofilariasis is currently considered a zoonotic infection, a mosquito-borne disease caused by the filarial nematodes of dogs, mainly Dirofilaria repens and D. immitis. Human dirofilariasis has been reported from many parts of the world, including Africa, Australia, the Americas, Europe, and Asia. The climate of Bandar Abbas in Hormozgan province, Sothern of Iran, has favorable conditions for the growth and reproduction of different types of vector mosquitoes. A 20 yr old woman from Bandar Abbas, visited a surgeon where the presence of a nodule was diagnosed in the forehead. In histopathological examination, cross-sections of a worm surrounded by necrotic tissues were observed. By evaluating the sections, Dirofilaria sp. was the probable diagnosis. To our knowledge, in Iran, this is the first human dirofilariasis occurring in the forehead. Human cases of dirofilariasis need to be reported so that physicians could consider dirofilariasis in their differential diagnoses.

A rare subcutaneous periorbital zoonotic infection in a 42-year-old female patient

Human dirofilariasis represents a zoonotic infectious disorder caused by parasites belonging to the Dirofilaria genus, which includes numerous species with a large variability regarding the host specificity, life cycle, and clinical manifestations. This disease appears to be a vector-borne parasitosis that is spread through insects - intermediate hosts (usually mosquitos) - and affects several carnivores as definitive hosts. Humans represent an unsuitable host for the parasite to complete its life cycle, being unable to release microfilariae in the blood as the inoculated larvae fail to reach sexual maturity. Therefore, humans are unable to transmit the infection to other humans, neither directly nor through an intermediate host. The current case report indicates a rare encounter of a Dirofilaria repens infection in a 42-year-old female patient living in an urban area (Craiova, Romania), who developed intermittent right periorbital edema after a previous trip to Greece. Over the course of one month, the right periorbital edema gradually remitted, and a firm, round lump developed in the external inferior right periorbital region. There were no similar clinical manifestations among other family members. Her medical history showed no other complaints or any serious general health problems. Also, the patient denied having any pets at home. The blood tests did not reveal any abnormalities. The exact source of infection could not be identified, but the chances for this infection to be related to the history of traveling to Greece are high, given that this region is one of the most important endemic areas in Europe.

Further data on the distribution of Dirofilaria spp. in the Czech Republic in dogs

Based on previously published data, the Czech Republic is regarded an endemic country of the onchocercid nematodes Dirofilaria immitis (Leidy, 1856) and Dirofilaria repens Railliet et Henry, 1911. Nevertheless, while cases of D. repens are commonly reported from dogs in South Moravia, no recent records of D. immitis are available. Therefore, the present study was performed to clarify the occurrence of both species of Dirofilaria Railliet et Henry, 1910. Blood samples of 551 dogs sampled during 2015 and 2016 were analysed microscopically for presence of microfilariae and blood sera were examined by IDEXX SNAP® 4Dx® test (IDEXX, USA). DNA from blood of microscopically positive dogs was extracted and PCR protocol amplifying fragment of cytochrome c oxidase I (COI) gene was performed; PCR products were then sequenced. All dogs from the Bohemian part of the Czech Republic were negative. The prevalence of D. repens in the Moravian region was 5.7 % (27/476). BLAST analyses of obtained sequences confirmed the presence of D. repens (99-100% identical to KX265049). All sampled animals showed a negative result for D. immitis antigen in IDEXX SNAP® 4Dx® test. Our study confirmed the previously reported occurrence of D. repens in South Moravia and revealed its spreading from the epicentre to the north and west. PCR with subsequent sequencing together with negative results for D. immitis antigen in IDEXX SNAP® 4Dx® test revealed only D. repens infection. A previously published autochthonous infection of dogs with D. immitis in South Moravia was not confirmed.

Dirofilaria spp. and Angiostrongylus vasorum: Current Risk of Spreading in Central and Northern Europe

In the past few decades, the relevance of Dirofilaria immitis and Dirofilaria repens, causing cardiopulmonary and subcutaneous dirofilariosis in dogs and cats, and of Angiostrongylus vasorum, causing canine angiostrongylosis, has steadily increased in Central and Northern Europe. In this review, a summary of published articles and additional reports dealing with imported or autochthonous cases of these parasites is provided for Central (Austria, Czechia, Germany, Hungary, Luxemburg, Poland, Slovakia, Slovenia, and Switzerland) and Northern (Denmark, Finland, Iceland, Norway, and Sweden) Europe. Research efforts focusing on Dirofilaria spp. and A. vasorum have varied by country, and cross-border studies are few. The housing conditions of dogs, pet movements, the spread of competent vectors, and climate change are important factors in the spread of these nematodes. Dogs kept outside overnight are a major factor for the establishment of Dirofilaria spp. However, the establishment of invasive, diurnal, synanthropic, competent mosquito vectors such as Aedes albopictus may also influence the establishment of Dirofilaria spp. The drivers of the spread of A. vasorum remain not fully understood, but it seems to be influenced by habitats shared with wild canids, dog relocation, and possibly climatic changes; its pattern of spreading appears to be similar in different countries. Both Dirofilaria spp. and A. vasorum merit further monitoring and research focus in Europe.

Dirofilaria repens microfilaremia in humans: Case description and literature review

Introduction

Dirofilaria repens is a vector-borne filaroid helminth of carnivorous animals, primarily domesticated dogs. Humans are considered to be accidental hosts in which D. repens rarely reach sexual maturity but induce local inflammation, mainly in subcutaneous and ocular tissues.

Methods

In the current study, we present the detection of multiple adults of D. repens, endosymbiont Wolbachia sp. and microfilariae by molecular analysis in peripheral tissues and bloodstream of a human host. A subsequent meta-analysis of published literature identified 21 cases of human infection with adult D. repens producing microfilariae.

Results

Within the study population, there were 13 (59.09%) males, eight (36.36%) females and, in one (4.55%) case, sex was not reported. A total of 11 (50.00%) cases had subcutaneous dirofilariasis, six (27.27%) had ocular dirofiliariasis, with single cases (4.55% each) of genital, mammary, lymphatic and a combination of subcutaneous and pulmonary dirofilariasis described. In one (4.55%) case, the primary anatomical site of adult D. repens could not be found. D. repens microfilariae were detected in the local tissue (local microfilariasis) in 11 (50.00%) cases and the peripheral blood (microfilaremia) in 11 (50.50%) cases. Final identification of D. repens microfilariae was based on morphological detection in 14 (63.64%) cases, and molecular detection in eight (36.36%) cases.

Conclusion

The results of this study suggest that humans may act as a final host for D. repens, however its role as a source of D. repens infection is less clear.

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Humans may act as a final host for D. repens

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Immunodeficiency is not a risk factor for human D. repens microfilaremia.

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Surgical extirpation of adult D. repens is a mainstay of treatment.

Human dirofilariosis in Austria: the past, the present, the future

Background

Dirofilariosis is a vector-borne parasitosis caused by filarial nematodes of the genus Dirofilaria. In humans, who represent accidental hosts, dirofilariosis is mostly caused by Dirofilaria repens and Dirofilaria immitis. In Austria, the first reported case occurred in 1978. Since then, several (case) reports have been published.

Methods

A systematic and retrospective review of collected published cases and new, unpublished confirmed cases of human dirofilariosis occurring in Austria was performed. A nematode was extracted from the eyelid of a previously unreported case and subsequently characterized histologically and using molecular biology techniques.

Results

Data on a total of 39 cases of human dirofilariosis in Austria occurring between 1978 and 2020 are summarized. Over the past four decades the incidence has markedly increased, in particular after 1998. Of the 39 patients, men and women were equally affected, and the mean age was 47.1 years. The area most frequently affected was the head (38.5% of cases). Confined ocular involvement was observed in 23.1% of cases, and nematodes were isolated from the neck/trunk, extremities and the genito-inguinal area in 25.6, 15.4 and 15.4% of patients, respectively. Microfilariae were detected in two cases. Of the 39 patients, only 73.9% tested positive for anti-filarial antibodies and 56.3% for eosinophilia, despite successful isolation of a nematode; consequently, these measures did not represent reliable markers for dirofilariosis. Most patients had a travel history to countries endemic for Dirofilaria species. One patient who had not traveled abroad represented the only autochthonous case recorded to date. Dirofilaria repens was the predominant species, identified in 89.7% of cases. In the newly reported case of subcutaneous dirofilariosis, a live non-gravid Dirofilaria repens adult female of 12 cm length was isolated from the eyelid of the patient, and a video of the extraction is provided.

Conclusions

The incidence of human dirofilariosis cases has increased strikingly over the last four decades in Austria. More cases can be expected in the foreseeable future due to changes in human behavior and (travel) activities as well as climate changes and the associated alterations in the availability of the natural reservoir, the vectors and the intrinsic characteristics of the parasite.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-021-04696-4.

A case of inguinal hernia associated with atypical Dirofilaria repens infection in a dog

BACKGROUND

Dirofilaria repens is a filarioid nematode transmitted by mosquitoes. Adult D. repens are typically localized in the subcutaneous tissue of the host, but other, atypical localizations have also been reported. There have been several reports of clinical cases involving an association of parasites and hernias in both animals and humans. However, it is unclear if parasitic infection can act as a triggering factor in the development of hernias.

METHODS

A 12-year-old dog was referred to a private veterinarian clinic in Satu Mare, northwestern Romania due to the presence of a swelling in the lateral side of the penis (inguinal area). The dog underwent hernia repair surgery during which four long nematodes were detected in the peritoneal serosa of the inguinal hernial sac. One female specimen was subjected to genomic DNA extraction to confirm species identification, based on amplification and sequencing of a 670-bp fragment of the cytochrome c oxidase subunit 1 (cox1) gene. Treatment with a single dose of imidacloprid 10% + moxidectin 2.5% (Advocate, Bayer AG) was administered.

RESULTS

The nematodes were morphologically identified as adult D. repens, and the BLAST analyses revealed a 100% nucleotide similarity to a D. repens sequence isolated from a human case in Czech Republic.

CONCLUSIONS

We report a case of an atypical localization of D. repens in the peritoneal cavity of a naturally infected pet dog with inguinal hernia and discuss the associations between hernia and parasitic infections.

The first case of periorbital human dirofilariasis in the Czech Republic

Dirofilaria repens and Dirofilaria immitis are the most common filarial species affecting humans in Europe. Dirofilaria repens causes subcutaneous or ocular infection, whereas D. immitis is responsible mainly for the pulmonary form. In this report, we present the first human case of periorbital dirofilariasis in the Czech Republic. A 58-year-old woman suffered from an eyelid oedema, redness and pain in the left eye. After excising the parasite from her eyelid, all clinical symptoms disappeared. Based on the morphology and cytochrome oxidase I sequencing, the parasite was identified as D. repens. Histology revealed that the excised worm was female with absent microfilariae in uteri. With respect to the length of the incubation period and the sequence identity with a known Czech isolate, we concluded that D. repens was most likely of autochthonous origin.

Different epidemiological pattern of canine dirofilariosis in two neighboring countries in Central Europe-the Czech Republic and Slovakia

The known data resulting from individual surveys of canine dirofilariosis point to the great differences in the epidemiological situation among countries where Dirofilaria parasites emerged approximately at the same time. In this regard, the Czech Republic and Slovakia, neighboring countries situated in Central Europe, could serve as an illustrative example of such a situation. The present study aimed to assess the prevalence of canine dirofilariosis in both countries and to discuss the reasons for potential differences shown. Between October and December 2019, 429 dogs from the Czech Republic and 644 from Slovakia were examined for canine dirofilariosis using the Knott test for microfilariae detection and conventional PCR for the species determination. The results' analyses showed notable differences. While in the Czech Republic autochthonous Dirofilaria repens cases are reported sporadically and Dirofilaria immitis infections have been confirmed only as imported so far, in Slovakia, both Dirofilaria species seem to have become endemic. Concretely, in the Czech Republic, microfilariae were detected in the peripheral blood of 8 dogs (1.86%): in seven, D. repens was confirmed, and in one dog, mixed infection with D. repens and D. immitis was diagnosed. Seven infected animals came from the eastern part of the country neighboring Slovakia. In Slovakia, microfilariae were detected in 68 (10.56%) dogs examined. DNA analysis confirmed D. repens mono-infection in 38 (5.90%) dogs, single D. immitis infection in 21 (3.26%) animals, and both Dirofilaria species were detected in 9 (1.40%) samples. Although we are unable to determine the cause of the differences, our study confirmed that the long-registered low number of canine dirofilariosis cases in the Czech Republic is not due to insufficient investigation (monitoring), but due to a low prevalence of the parasite in this area.

A case of human Dirofilaria repens infection, causing an asymptomatic subcutaneous nodule

We present a case of subcutaneous dirofilariasis, a vector-borne zoonotic disease, in a young woman from Austria. The diagnosis was confirmed by ultrasound and histology of the excised subcutaneous nodule. The parasite species was identified as Dirofilaria repens by polymerase chain reaction. We expect to see more cases of human dirofilariasis also due to climate change and associated increase of the spectrum of suitable mosquito vectors.

Analysis of the Metaphase Chromosome Karyotypes in Imaginal Discs of Aedes communis, Ae. punctor, Ae. intrudens, and Ae. rossicus (Diptera: Culicidae) Mosquitoes

In this study, cytogenetic analysis of the metaphase chromosomes from imaginal discs of Aedes (Diptera: Culicidae) mosquitoes-Aedes communis, Ae. punctor, Ae. intrudens, and Ae. rossicus-was performed. The patterns of C-banding and DAPI staining of the heteroсhromatin and the length of the chromosomes demonstrate species specificity. In particular, the Ae. punctor chromosomes are the shortest compared with Ae. communis, Ae. intrudens, and Ae. rossicus, and they also carry additional C and DAPI bands in intercalary regions. The Ae. intrudens chromosomes are the longest, they have pericentromeric C bands, and they almost lack any DAPI bands near the centromere of chromosome 3 versus Ae. communis, which has the largest pericentromeric DAPI blocks in all three chromosome pairs. Ae. rossicus also possesses DAPI bands in the centromeric regions of all chromosomes, but their staining is weaker compared with those of Ae. communis. Therefore, the analysis of karyotypes is a tool for species-level identification of these mosquitoes.

Encapsulated living worms due to periorbital dirofilariasis: detection with high-resolution sonography

Sonography (US) is commonly required when a superficial lump appears. We present the case of a patient for whom US was highly suggestive of living worms causing a recurrent periorbital mass. After surgery, the final diagnosis was a nodule composed of dirofilariasis larva.

Subcutaneous Dirofilariasis in Female Pubic Region - Case Report

BACKGROUND:

Number of reported cases of human dirofilariasis in the last couple of decades has been increasing. Dogs are the main reservoir hosts, while various mosquito species represent/serve as vectors. Human infections are caused by two different parasites: Dirofilaria immitis and Dirofilaria repens. Dirofilaria repens is currently considered to be one of the most rapidly-spreading human and animal parasite species in Europe. Clinical features are characterised by subcutaneous or ocular lesions which can persist for months without any symptoms. The disease is considered to be endemic in Mediterranean countries, central Asia, Israel, and Sri Lanka with increased incidence in Central and East Europe. Apart from the local population, tourists are also susceptible to this disease. Export of domestic animals can transfer parasites between different countries. This disease is rare in Croatia.

CASE PRESENTATION:

We are presenting a case of a 58-year-old female patient with dirofilariasis of the genital region caused by Dirofilaria repens, confirmed with PCR and sequencing.

CONCLUSION:

From the clinician point of view, subcutaneous dirofilariasis should be considered as a differential diagnosis in cases of long-lasting subcutaneous swellings.

Recent advances on Dirofilaria repens in dogs and humans in Europe

Dirofilaria repens is a nematode affecting domestic and wild canids, transmitted by several species of mosquitoes. It usually causes a non-pathogenic subcutaneous infection in dogs and is the principal agent of human dirofilariosis in the Old World. In the last decades, D. repens has increased in prevalence in areas where it has already been reported and its distribution range has expanded into new areas of Europe, representing a paradigmatic example of an emergent pathogen. Despite its emergence and zoonotic impact, D. repens has received less attention by scientists compared to Dirofilaria immitis. In this review we report the recent advances of D. repens infection in dogs and humans, and transmission by vectors, and discuss possible factors that influence the spread and increase of this zoonotic parasite in Europe. There is evidence that D. repens has spread faster than D. immitis from the endemic areas of southern Europe to northern Europe. Climate change affecting mosquito vectors and the facilitation of pet travel seem to have contributed to this expansion; however, in the authors' opinion, the major factor is likely the rate of undiagnosed dogs continuing to perpetuate the life-cycle of D. repens. Many infected dogs remain undetected due to the subclinical nature of the disease, the lack of rapid and reliable diagnostic tools and the poor knowledge and still low awareness of D. repens in non-endemic areas. Improved diagnostic tools are warranted to bring D. repens diagnosis to the state of D. immitis diagnosis, as well as improved screening of imported dogs and promotion of preventative measures among veterinarians and dog owners. For vector-borne diseases involving pets, veterinarians play a significant role in prevention and should be more aware of their responsibility in reducing the impact of the zoonotic agents. In addition, they should enhance multisectorial collaboration with medical entomologists and the public health experts, under the concept and the actions of One Health-One Medicine.

Dirofilaria repens infection as a cause of intensive peripheral microfilariemia in a Polish patient: process description and cases review

Dirofilariasis is a parasitic disease of dogs and other carnivores transmitted mainly by the mosquitoes of the genera Culex, Aedes, Anopheles. Full life cycle of the Dirofilaria nematodes in humans is extremely rarely observed, usually lacking species determination at the molecular level. We report fully documented unusual clinical manifestation of subcutaneous dirofilariasis with intensive microfilariemia in peripheral blood revealed by the Knott's concentration technique. The identification of the Dirofilaria repens nematode was based on typical morphological findings for adult gravid female nematode found in the histopathological preparations. The morphology of microfilariae obtained from patient's peripheral blood was also typical for D. repens. The final identification was confirmed by the molecular analysis of microfilariae collected from the blood.

Xenomonitoring of Mosquitoes (Diptera: Culicidae) for the Presence of Filarioid Helminths in Eastern Austria

Information on mosquito-borne filarioid helminths in Austria is scarce, but recent discoveries of Dirofilaria repens indicate autochthonous distribution of this parasite in Eastern Austria. In the current xenomonitoring study, more than 48,000 mosquitoes were collected in Eastern Austria between 2013 and 2015, using different sampling techniques and storage conditions, and were analysed in pools with molecular tools for the presence of filarioid helminth DNA. Overall, DNA of D. repens, Setaria tundra, and two unknown filarioid helminths were documented in twenty mosquito pools within the mitochondrial cox1 gene (barcode region). These results indicate that S. tundra, with roe deer as definite hosts, is common in Eastern Austria, with most occurrences in floodplain mosquitoes (e.g., Aedes vexans). Moreover, DNA of D. repens was found in an Anopheles plumbeus mosquito close to the Slovakian border, indicating that D. repens is endemic in low prevalence in Eastern Austria. This study shows that xenomonitoring is an adequate tool to analyse the presence of filarioid helminths, but results are influenced by mosquito sampling techniques, storage conditions, and molecular protocols.

Dirofilaria repens transmission in southeastern Finland

BACKGROUND

The spread of vector-borne diseases to new regions has become a global threat due to climate change, increasing traffic, and movement of people and animals. Dirofilaria repens, the canine subcutaneous filarioid nematode, has expanded its distribution range northward during the last decades. The northernmost European locations, where the parasite life-cycle has been confirmed, are Estonia and the Novgorod Region in Russia.

RESULTS

Herein, we describe an autochthonous D. repens infection in a Finnish woman. We also present two cases of D. repens infection in imported dogs indicating the life-cycle in the Russian Vyborg and St Petersburg areas, close to the Finnish border.

CONCLUSIONS

The most obvious limiting factor of the northern distribution of D. repens is the summer temperature, due to the temperature-dependent development of larvae in vectors. With continuing climate change, further spread of D. repens in Fennoscandia can be expected.

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

Human dirofilariosis is currently considered to be an emerging zoonosis of Central Europe with climate change and globalization playing a key role in its spreading. Additionally, the occurrence of Dirofilaria spp. is strongly subject to a certain number of microfilaremic dogs and the presence of the mosquito vectors. Both conditions are fulfilled in Slovakia. The first human case of autochthonous dirofilariosis in Slovakia was diagnosed in 2007, 2 years after the infection had been observed in the Slovak dog population. Since then, a total of 12 human cases caused by Dirofilaria repens have been registered at the Institute of Parasitology, Slovak Academy of Sciences, 7 subcutaneous, 4 ocular and 1 pulmonary; however, it is likely that some cases remain undiagnosed, seeing that this infection is still missed by physicians. Of the patients 9 were male and 3 were female and their age varied between 15 and 72 years (mean 49 years). The majority of those affected came from the southern regions of the country, bordering Austria and Hungary, which are considered to be endemic areas for canine dirofilariosis. In this paper all published and unpublished cases are reviewed, with a special emphasis on the rare pulmonary form of D. repens infection.

Clinical and laboratory features of human dirofilariasis in Russia

The article presents the results of the prospective study of 266 patients with dirofilariasis who received medical and diagnostic assistance in Rostov Scientific Research Institute of Microbiology and Parasitology in Rostov-on-Don, Russia from 2000 to 2016. We have assessed the features of the dynamics of epidemiology of this infection in several territories of the Russian Federation, depending on the social structure of patients. Immature females of dirofilaria were found most commonly in humans (82.9 ± 2.6%), the proportion of maturity females and adult males of worms respectively was 10.5 ± 2.1% and 0.9 ± 0.6%. All mature worms were localized inside a capsule. Peripheral blood eosinophilia was detected only in patients with the migration of helminths (19 of 116 persons – 16.4%). Blood samples of patients examined by the method of concentration in 3% acetic acid for detection of microfilariae, showed negative result in all patients.

Our data are consistent with the opinion of KI Skriabin about that human as «dual facultative host» for dirofiliaria. It is rare that parasite in human body is able to develop to the imago stage (according to our observations – 11.4%). The immune response to invasion by dirofiliaria in human is manifested as dense connective tissue which forms a capsule. According to our study the rare cases (22) of detection the sexual mature D. repens (10.4%) were localized inside the capsule. Observations of patients with D. repens infection allowed concluding that human for this helminth is «a biological deadend».

Circulation of Dirofilaria repens and Dirofilaria immitis in Moldova

BACKGROUND

Over the last two decades, a significant spread of dirofilariasis has been observed in eastern and central Europe. However, data on the circulation of Dirofilaria spp. in Moldova were absent although direct neighbor states reported high incidence rates of human dirofilariasis.

METHODS

Daily mean temperature data were used to calculate Dirofilaria spp. development units, which were used to estimate the potential for complete extrinsic development in the mosquitoes (= sum of potential Dirofilaria spp. transmission days). In addition, 4,481 adult female mosquitoes were collected from 25 trapping sites. From 2010 to 2015, sampling was conducted with Centers for Disease Control miniature light traps, indoor resting mosquito collections as well as human landing catches in urban, rural and natural areas. Mosquitoes were analyzed for the presence of D. repens and D. immitis DNA using a duplex real-time PCR assay targeting nucleotide differences within the cytochrome c oxidase subunit 1 (D. repens) and 16S rRNA gene fragment (D. immitis).

RESULTS

The average of the yearly sum of potential Dirofilaria spp. transmission days between 2010 and 2015 ranged from 90 to 140 days with an increasing gradient from the North to the South of Moldova. Positive mosquito pools for D. repens were found countrywide at 13 of the 25 trapping sites and in 17 of the 22 screened mosquito taxa (26.51% of all 347 tested pools), while D. immitis was detected only at 4 of the trapping sites (Center and South) in 4 different mosquito species (8.65% of all 347 tested pools). Highest infection rates (EIR) per 100 specimens for both Dirofilaria species were found in An. maculipennis (s.l.) (D. repens: EIR = 4.91; D. immitis: EIR = 2.01), whereas the most frequent mosquito taxon Cx. pipiens (s.l.)/torrentium had significantly lower infections rates (D. repens: EIR = 0.88; D. immitis: EIR = 0.47).

CONCLUSIONS

The temperature conditions in Moldova are suitable for transmission of Dirofilaria spp. within the entire country, which is supported by a wide distribution of Dirofilaria spp.-positive mosquitoes with high infection rates. The low number of reported human cases most likely does not reflect the current epidemiological situation of dirofilariasis in Moldova.