Nodular lesions due to infestation by Dirofilaria repens in dogs from Italy

Zoonotic Dirofilaria sp. "hongkongensis" in subcutaneous nodules from dogs and cats, Hong Kong SAR

BACKGROUND

Dirofilaria sp. "hongkongensis" is a putative Dirofilaria species, initially identified in subcutaneous nodules in humans in Hong Kong and in other South and Southeast Asian regions. While it differs genetically from the better-known zoonotic species, Dirofilaria repens and Dirofilaria immitis, information on the lesions caused by Dirofilaria sp. "hongkongensis" in the hosts as well as on its biology is scarce. This study documents for the first time the presence of this filarioid nematode in subcutaneous nodules in dogs and cats in Hong Kong, where it was originally described in human patients, therefore providing evidence for the zoonotic nature of this parasite.

METHODS

Records of Veterinary Diagnostic Laboratory of City University of Hong Kong were searched between 2019 and 2024 for histological reports of possible filarioid-associated lesions. Tissue samples were collected by excisional surgical biopsy and processed with routine paraffin techniques. Selected slides were stained using various staining techniques [i.e., hematoxylin and eosin, periodic acid-Schiff (PAS), Grocott methenamine silver (GMS) or Ziehl-Neelsen (ZN) and Gram stain]. DNA from formalin-fixed paraffin-embedded tissue were extracted, submitted to conventional polymerase chain reaction (cPCR) and sequencing (i.e., cox1 and 12S rRNA genes) and phylogenetic analyzed.

RESULTS

A total of five subcutaneous nodules from four cats and one from a dog with histopathology suggestive of filariosis were selected. The presence of Dirofilaria sp. "hongkongensis" was morphologically and molecularly confirmed in one dog and one cat. Both histopathological presentation and phylogenetic analysis enabled classification of this species close to D. repens and within the subgenus Nochtiella. In the remaining three cases, one showed histological evidence of aberrant nematode migration, while non-parasitic causes were identified in the other two.

CONCLUSIONS

This study provides the first evidence of Dirofilaria sp. "hongkongensis" in subcutaneous nodules in cats and dogs. The histology of clinical lesions of this filarioid species herein described is closely related to those caused by D. repens. Overall, this species should be considered in differential diagnoses of subcutaneous lesions in both animals and humans in the region.

How frequently Dirofilaria repens localizes in dog testes?

Dirofilaria repens (Spirurida: Onchocercidae) is the causative agent of canine subcutaneous dirofilariosis. Adults of D. repens localize in the subcutaneous tissues and fasciae and most of the infected animals are asymptomatic though dermatological disorders have been described sporadically. In this study, the gonads of 100 male dogs were inspected for D. repens presence from December 2020 to January 2022. All examined dogs were older than 48 months and underwent castration for several reasons. The testes and the superficial layers were examined with the aid of stereomicroscope; in addition, the blood of all included dogs was collected and analysed by Knott's test to assess the presence of microfilariae. Six out of 100 (6 %, CI95%, 2.2-12.6 %) examined dogs were positive for D. repens presence, and in all the cases the parasites were found beneath the tunica vaginalis layers. Microfilariae were found in 15 blood samples including 5 out of those 6 testes positive dogs thus resulting in a final D. repens prevalence of 16 % (CI95%: 9.4-24.7 %). No pathological changes and or lesions due to parasite presence were observed in the testes or in their layers. The present study represents the first survey focusing on the detection of D. repens in dog testes on a large sample size. Adult parasites were found in the testes of 6 out of 16 D. repens infected dogs accounting for 37.5 % of cases and suggesting as testicular localization is not uncommon. The absence of neoplastic or inflammatory lesions in D. repens infected testes suggests as these conditions do not act as attractive stimuli for the parasite localization. Finally, considering the zoonotic potential of D. repens and the large infection prevalence here reported, active surveillance in endemic areas is strongly advocated to limit the presence of reservoir and prevent further infections to animals and humans.

Dirofilaria immitis and Onchocercidae spp. in wild felids from Brazil

Among the species described within the Onchocercidae family, Dirofilaria immitis is regarded as the most common worldwide, causing severe and often fatal conditions in dogs, cats, and occasionally humans. Dirofilaria spp. are vectored by mosquitoes, simulids, and culicoids, with their epidemiology dependent on the geographical distribution of competent vectors. Eight species of Dirofilaria have been reported so far in Brazil, of which six parasitize non-human primates, deer, procyonids, and marsupials. Here, we investigated the occurrence of Onchocercidae in wild felids (i.e., Panthera onca, Puma concolor, Herpailurus yagouaroundi, Leopardus geoffroyi, Leopardus guttulus, Leopardus pardalis, Leopardus wiedii, Leopardus munoai) from different locations in Brazil. Overall, 82 samples (n = 63 blood; n = 19 tissues) were molecularly screened for cytochrome c oxidase subunit-1 (cox1) gene. Four (i.e., 4.8%) wild felid samples were positive, and at BLAST analysis, the obtained sequences showed varying percentage of nucleotide identity with the genera Brugia (i.e., 87-88%), Setaria (i.e., 89%), and D. immitis (i.e., 94.4%). Phylogenetic analyses clustered sequences obtained into three distinct clades, one with D. immitis and the remaining two with other Onchocercidae spp. Data herein obtained highlight the need for a more comprehensive understanding of the diversity and biology of Onchocercidae in South America in order to assess the potential impact that these species may have for domestic and wild animals, as well as humans.

Atypical case of subcutaneous filariosis in a cat caused by Dirofilaria immitis

Subcutaneous dirofilariosis is a well-known disease caused mainly by Dirofilaria repens and described in several mammalian species including humans, dogs, and cats. Additionally, early developing stages of the heartworm Dirofilaria immitis are rarely reported in subcutaneous localization from humans and dogs. To our knowledge, confirmed clinical evidence of this condition has not been described in the cats yet, even if the feline hosts can be affected either by the classic adult-related heartworm form or heartworm-associated respiratory disease (HARD) caused by immature stages. A 2 year old, spayed male cat was presented for three subcutaneous nodules on the head and trunk. The cat lived in Northern Italy and was regularly vaccinated and treated monthly with an antiparasitic spot on formulation containing selamectin. One of the three nodules was surgically excised and examined. Histology showed the presence of a nodular lesion in the subcutis characterized by a severe inflammatory infiltrate composed of macrophages, small lymphocytes, with fewer eosinophils, and mast cells, supported by a proliferation of mature fibroblasts (fibrosis). Inflammatory cells were multifocally surrounding sections of parasites identified as adult nematodes. Microscopic features were compatible with D. immitis, which has been molecularly confirmed (98.2% identity to D. immitis isolate OP107739). The cat tested negative for D. immitis antigenemia and the two remaining nodules disappeared spontaneously in a few months. In region where heartworm is prevalent, aberrant localization of D. immitis should be considered in the differential diagnoses of subcutaneous filarial worms in cats and dogs.

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.

Occurrence of Dirofilaria immitis in Stray Dogs from Nepal

BACKGROUND

Nematodes of the genus Dirofilaria are widespread vector-borne helminths (VBH) of veterinary relevance. Dirofilariosis caused by D. immitis is frequently diagnosed in dogs often showing a severe clinical condition known as heartworm disease. Assessing the distribution pattern of canine dirofilariosis is pivotal to undertake appropriate control measures and define the risk of infection in animals and humans. This study provides original data on the occurrence of D. immitis in naive stray dogs from Nepal.

METHODS

An epidemiological study was performed on stray dogs from Siddharthanagar, Lumbini region, Nepal. Alive animals were blood sampled and examined for microfilariae using direct microscopy, buffy coat centrifugation and modified Knott's method. In addition, hematobiochemical parameters, including packed cell volume (PCV), alanine aminotransferase (SGPT), aspartate aminotransferase (SGOT), alkaline phosphate (ALP), creatinine, blood urea nitrogen (BUN), urea and total protein were analysed, along with a clinical scoring (body temperature and respiratory rate). During the observation period, data on autopsies performed on stray dogs showing canine heartworm disease were also included.

RESULTS

The overall prevalence of D. immitis in both alive and necropsied dogs was 22.49% (38/169). Out of 150 alive dogs, 29 (19.3%) were positive for D. immitis microfilariae. The prevalence of the infection varied according to the technique used, ranging from 16.0 to 19.3% based on direct blood smear microscopy and modified Knott's technique, respectively. The infection rate was significantly higher (p < 0.05) in dogs aging more than 3 years. A positive correlation was observed between SGPT and SGOT and the presence of microfilariae (p < 0.05). Among the 19 dead stray dogs, 9 animals showed adult D. immitis nematodes.

CONCLUSION

Results of this survey account for the presence of D. immitis in stray dogs from Nepal, thus supporting the existence of a local transmission cycle of diroflariosis in the region. Further investigations are warranted to accurately define the prevalence of the infection in the canine population and to undertake appropriate control measures to reduce the burden on the infection in dogs and, accordingly, the risk of transmission to humans.

Case Report: Molecular Detection of Dirofilaria repens in an Italian Patient after a Stay in Tanzania

A 35-year-old man was admitted to a hospital in the south of Italy because of a periocular nodule and subpalpebral edema. The patient reported having been stayed in Tanzania five months before. Hematologic parameters were within the normality range, the Acanthocheilonema viteae ELISA did not detect significant levels of antifilarial IgG, and no further symptoms were described. The surgical inspection of the nodule led to the isolation of two filarioid parasites, identified as Dirofilaria repens by scanning electron microscope (SEM), and then by molecular assays. Knott’s test did not reveal microfilaremia, whereas loop-mediated isothermal amplification and PCR detected D. repens DNA. The patient was treated with doxycycline, and he was found no more positive at the follow-up.

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.

Usual or unusual presentations of Dirofilaria repens in two sibling dogs: a case report

This study describes two different manifestations of Dirofilaria repens infection in sibling dogs with microfilaremia. Dog 1, asymptomatic, harbored a gravid female of D. repens on the parietal layer of tunica vaginalis of one testicle and showed a marked circulating eosinophilia (3.3·103/μL). Both testicles were normal in shape and size without any gross lesions. Dog 2 had a pyotraumatic dermatitis. The cases were confirmed by PCR and sequencing. The sequences obtained showed 100% identity with those of D. repens isolated from human scrotum in Croatia. The treatment with moxidectin 2.5% and imidacloprid 10%/kg was effective in eliminating microfilariae after just one application, as demonstrated by negative modified Knott's tests and PCR analyses of blood samples. This status was maintained during the post-treatment observation period. The classical localization of D. repens in dogs is in subcutaneous tissues, within nodules or free; however, it can also occur with some frequency in testicles, as described in humans. The infection can be associated with circulating eosinophilia or pyotraumatic dermatitis, as reported in this study. Thus, in endemic areas, it is advisable to carefully inspect the removed testicles at neutering since parasite localization can take place without any macroscopic changes. Moreover, in the case of circulating eosinophilia or pyotraumatic dermatitis, investigations should include modified Knott's test and PCR to ensure that D. repens is not the cause of these alterations. Rapid and sensitive tests for the early detection of infected animals would help to prevent or limit the spread of this zoonosis.

First report of Dirofilaria repens infection in a microfilaraemic cat from Romania

The present study describes the first report of Dirofilaria repens infection with the presence of both microfilariae and adult nematodes in a cat from Northeastern Romania. Briefly, a 5-year-old male mixed breed cat was presented to a veterinary clinic in Iasi (Romania), for neutering, in early February 2020. During the surgery, two whitish worms were removed from the internal part of the scrotum. Two adult nematodes, one female and one male, were identified, on the basis of morphological features, as D. repens with whitish, cylindrical bodies, measuring 12.5 cm and 6.5 cm in length, respectively. At histology, the female nematode showed two cavitated structures containing myriads of variably arranged microfilariae. The male had a transversal diameter of 350 μm, a 10 μm thick cuticle and a ridge-period of 10 Μm. multiplex PCR confirmed the diagnosis of D. repens from both nematodes. The Knott's test revealed the presence of microfilariae of D. repens. Routine biochemistry panel was within range with one exception, urea serum level slightly increased. The haematology results revealed an increased number of neutrophils, lymphocytes and eosinophils. The cat had an infection with Otodectes cynotis as well. The cat was discharged with the following therapy recommended: oral doxycycline (10 mg/kg) for 30 days and topical moxidectin, monthly doses. After six months, the Knott's test gave negative results. Further studies should include new insights of D. repens infection in cats concerning its epidemiology, diagnosis and control.

The first case of autochthonous subcutaneous dirofilariasis (Dirofilaria repens) in a dog from Białowieża (NE Poland) and possible threat posed to inhabitants of Białowieża Primeval Forest area

We present the first case of dirofilariasis in a dog from Białowieża village located in the primeval European forest—Białowieża Primeval Forest (NE Poland). Molecular analysis of adult nematode specimens isolated from subcutaneous tissue confirmed the infection with Dirofilaria repens. An adult male dog has not travelled out of the Białowieża village for at least five years; therefore, we assume this is the autochthonous case of the disease. We discuss possible inter- and intra-species transmission routes of dirofilariasis on this territory, which is inhabited by diverse community of wild carnivores, domestic animals, and humans. We also discuss the likely sources of the disease in this, highly biodiverse unique European forest complex. We underline the lack of attention to this problem and its importance for veterinary, wildlife, and human health safety.

New insights into the biology, diagnosis and immune response to Dirofilaria repens in the canine host

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Antibody response to D. repens in dogs develops before the onset of patency.

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Wolbachia and D. repens antibodies had peaks of OD values on Days 220, 245, 281.

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The specificity of IgG ELISA against D. repens and Wolbachia must be evaluated.

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If microfilarial counts are too low, PCR can be considered a sensitive alternative.

Dogs are the primary host for Dirofilaria repens, therefore it is mandatory to accurately diagnose the canine infection and to expand our current knowledge on parasite biology and the immune response of the infected host for a better prevention.Thus, the aim of the present study was to provide new insights from experimental infections of dogs with D. repens, focusing on the evaluation of: 1) the pre-patent period and 2) the antibody response against D. repens somatic antigens and against the Wolbachia endosymbiont. Briefly, on Day 0, twenty purpose-bred Beagle dogs were experimentally infected with 50 infective larvae (L3) of D. repens. Starting from Day 58 until the last day of the study (Day 281), blood samples were collected on a monthly basis for detection of antibodies against D. repens (Dr) and recombinant Wolbachia surface protein (rWSP) by non-commercial IgG-ELISAs. Additional samples were collected on Days 220, 245 and 281 for the detection of microfilariae (mff) using the modified Knott’s test and biomolecular analysis, following two PCR protocols: Gioia et al. (2010; protocol A) and Rishniw et al. (2006- protocol B). The results were analysed by univariate statistical analyses using 2 × 2 contingency tables and K Cohen was calculated to assess the agreement among all the diagnostic techniques. Overall, the outcome of the study revealed that out of the 20 dogs experimentally infected with D. repens, 16 (80 %) were microfilaraemic, 17 (85 %) were positive at DNA detection in the blood, 18 (90 %) had D. repens antibodies and 16 (80 %) had Wolbachia antibodies on the last day of the study. The overall k agreement between Knott’s and PCR protocol B was 0.442 (P = 0.0001) and increased throughout the study, reaching 0.828 (P = 0.0001) on Day 281. To the authors knowledge, this is only the second study reporting antibody response to D. repens somatic antigen in experimentally infected dogs. ELISA results showed that an antibody response develops before the onset of patency, and steadily increases with time. Results would suggest that the development of an immunological response to infection could lead to application in epidemiological studies, risk assessment and as an aid in the diagnostic approach in dogs, in particular for early infections without mff.

Giant cutaneous cyst in a dog infected by Cercopithifilaria bainae

Cercopithifilaria bainae is the most prevalent species of filarioids within the genus. This parasite localizes in the skin, sometimes causing erythematous dermatitis. Herein, the authors describe a case of giant cutaneous cyst in a dog infected by Cercopithifilaria bainae. A 9-year-old male mixed-breed dog presented to a veterinary facility in Dourados, Mato Grosso do Sul (Midwest Brazil) with a mass in the lumbosacral region. On clinical examination, the mass was observed to be approximately 15 cm in diameter with a floating consistency and conspicuous presence of viscous fluid; the lesion, however, was non-ulcerated and non-adherent. Cytological examination revealed the presence of moderate lymphocyte cellularity and foamy macrophages, erythrophagocytosis and the presence of numerous microfilariae. After morphological and molecular analysis of the 12S ribosomal RNA gene, the microfilariae were identified as C. bainae, exhibiting 99-100% identity with DNA sequences available from Genbank. Surgery was recommended and after resection of the giant cyst, the dog was treated with ivermectin for two weeks and the clinical condition was completely resolved. Based on the presence of microfilariae in the cyst fluid the role of this filarioid in the determinism of the lesion has been discussed.

Current trends in canine dirofilariosis in Austria-do we face a pre-endemic status?

A retrospective study based on cases of canine dirofilariosis presented to the University of Veterinary Medicine, Vienna or diagnosed by private practitioners throughout Austria, from 1998 to 2018 was conducted to investigate the long-term development and current state of canine dirofilarial infections in Austria. Included in this study were 146 dogs which were tested positive for D. immitis and/or D. repens. The most commonly used diagnostic methods and the probable geographical origins of the infections were evaluated and the treatment protocols applied were compared with each other and with the literature. The results show that most infections were found due to screening for common travel infections using antigen-ELISA or PCR-testing, or by the incidental finding of microfilariae. Remarkably, only 24.3% of all cases presented showed clinical signs indicating canine dirofilariosis. Regarding the origin and travel history of the dogs, thirteen different countries could be identified. The three treatment protocols used showed a similar outcome after 8 months of treatment and minor side effects, which is consistent with the literature. An alarming increase in reported infections with both D. immitis and D. repens in Austria was noted since 2014. The number of documented cases had almost tripled by 2018, raising severe concerns about the threat of it becoming endemic in Austria. Therefore, the existing recommendations in current guidelines regarding canine dirofilariosis should be widely publicised and more strictly enforced. Prophylactic measures for dogs travelling abroad and diagnostic and therapeutic strategies for dogs imported from endemic countries should be obligatorily established throughout Europe, to reduce the risk of further spread of canine filarial infections to non-endemic regions.

Unusual localization of Dirofilaria repens (Spirurida: Onchocercidae) infection in the testicle of a dog

This report describes an uncommon localization of Dirofilaria repens in the testicle of a nine-year-old dog from southern Italy. The dog underwent neutring and three adult nematodes were found in the tunica vaginalis. At gross anatomy, no pathological changes were observed on the tunica, in the testicle or epididymis. The parasites, one female and two males, were morphologically and molecularly identified as D. repens. This is the first report of D. repens in the canine testicle in Italy. This case report highlights the asymptomatic nature of D. repens infection, suggesting that dogs living in endemic areas may act as silent carriers. Careful screening and an effective chemoprophylaxis should be ensured for all animals potentially exposed to D. repens infection in order to reduce the risk of infection to humans in areas where the parasite is endemic.

Occurrence of canine and feline extra-intestinal nematodes in key endemic regions of Italy

Extra-intestinal nematodes of companion animals are of growing concern in veterinary medicine for their pathogenic potential and the current expansion throughout Europe. The present study has evaluated the occurrence of major canine and feline extra-intestinal nematodes in regions of Italy having epidemiological relevance. Associations of various recorded parameters related to the examined animals have been statistically evaluated, along with a comparative analysis with the most recent epidemiological data. Overall, 1055 dogs and 1000 cats were tested. Among extra-intestinal nematodes Angiostrongylus vasorum was the most common in dogs followed by Capillaria aerophila and Dirofilaria spp.; Aelurostrongylus abstrusus was the most recorded parasite in cats, followed by C. aerophila and Troglostrongylus brevior. The statistical analysis revealed that outdoor access is associated with A. vasorum, A. abstrusus and T. brevior infections, that were also more prevalent in animals with cardio-respiratory signs. Moreover, cats aged less than 12 months had more chances to be infected by lungworms. The data herein presented confirm the occurrence and the possible risk of expansion of different extra-intestinal parasitoses of dogs and cats in Italy, underlining the importance of a constant epidemiologic vigilance and of appropriate control methods.

Dirofilaria immitis and D. repens in dog and cat: A questionnaire study in Italy

Dirofilaria immitis and D. repens are vector-borne parasites of dogs and cats, with zoonotic potential, endemic in many parts of Europe, including Italy. Control and prevention of dirofilariosis are essential points to reduce their diffusion in animals and humans and veterinarians are the main subjects involved in this "battle". With the aim to better understand current practice by veterinarians, an online questionnaire on different aspects of D. immitis and D. repens was sent to companion animal veterinary facilities registered with the Italian Veterinary chamber. The overall response rate was 25%. Approximately 47% had diagnosed at least one case of Dirofilaria spp. in dogs in the last year and approximately 6% had diagnosed at least one case of Dirofilaria spp. in cats. Of the 662 facilities surveyed, 83.8% used serology to diagnose heartworm infection. For the diagnosis of D. repens infection in dogs and cats, a high percentage of facilities relied on an external laboratory. Most recommended beginning prevention of canine heartworm disease in April-May. Topical and injectable moxidectin and oral ivermectin were the two most commonly used preventives for D. immitis in dogs. The drug most commonly used for heartworm adulticide treatment in dogs was melarsomine. This study show that veterinary facilities ians working in an endemic area for D. immitis and D. repens are aware of recent developments in adulticide therapy. Results would suggest however that diagnosis is not always carried out according to what is currently recommended by international guidelines and that the timing for starting prevention may not be optimal.

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-An etiological factor or an incidental finding in cytologic and histopathologic biopsies from dogs

Dirofilaria repens is an endemic, zoonotic parasite of carnivores, causing subcutaneous dirofilariasis, which is mostly asymptomatic. The aim of this study was to describe 22 cases of canine subcutaneous dirofilariasis. The cytologic and histopathologic samples were collected from dogs, which presented with various clinical signs such as cutaneous/subcutaneous nodules, hydropericardium, ascites, and lymphadenomegaly. The cytologic or histopathologic examination revealed purulent, pyogranulomatous, granulomatous or eosinophilic dermatitis/panniculitis, and the presence of D repens microfilariae or adults. The microfilariae or adults were also found incidentally in neoplastic cutaneous or subcutaneous tumors and in a sialocele. For the first time, microfilariae were also detected and described in pericardial and abdominal effusions and in enlarged reactive lymph nodes. Although it is well known that D repens can cause dermatitis and panniculitis in dogs, no previous reports of D repens microfilariae in body cavity fluids were found. The role of this parasite in the accumulation of body cavity fluid or in reactive lymphadenomegaly requires further investigation. Due to its zoonotic potential, and apparently underestimated pathogenicity, each case of canine subcutaneous dirofilariasis should be treated.

Subcutaneous dirofilariosis (Dirofilaria repens): an infection spreading throughout the old world

Background

Two main Dirofilaria species infect dogs: D. immitis and D. repens. While D. immitis has a worldwide distribution, D. repens is currently found only in Europe, Asia, and Africa. Adult D. repens are located in subcutaneous tissues of natural hosts where they survive for long periods of time. First-stage larvae, microfilariae, circulate in the peripheral bloodstream, where they are taken up by the mosquito intermediate hosts. Infected mosquitoes then transmit infective third-stage (L3) larvae to new hosts through the blood meal. In dogs, most infections are asymptomatic, although cutaneous disorders such as pruritus, dermal swelling, subcutaneous nodules, and ocular conjunctivitis can be observed. Currently, two factors have increased the concerns about this parasitic infection 1) its spread throughout the European countries and to other continents and its prevalence in dog populations, where in some cases it has overcome D. immitis; and 2) its zoonotic potential, which is much greater than that of D. immitis.

Results

Different hypotheses can be put forward to explain these concerns. First, climate change has allowed more favorable conditions for survival of culicid vectors. Second, accidental hosts such as humans may have a less efficient immune reaction against a parasite that is located in subcutaneous tissues, and thus less exposed to the host’s immune response than, for instance, D. immitis. Furthermore, the absence of clinical signs in the majority of canine infections and the difficulty in diagnosing the infection, due to the lack of serologic tests and thus the reliance on the identification of microfilariae and differentiation from D. immitis to confirm the presence of the parasite, favor the further spread of this species. Finally, among the macrocyclic lactones currently used to prevent heartworm infection, only moxidectin has been found to be fully effective against the infective larvae transmitted by mosquitoes and partially effective (efficacy 96%) against adult D. repens in experimental studies.

Conclusions

Dirofilaria repens infection is much more difficult than D. immitis to diagnose and control in the reservoir population (microfilaremic dogs). In addition, lack of familiarity with D. repens infection could lead to lack of vigilance underestimation for this parasite. The number of human cases in Europe and Asia is currently a serious public health concern. Medical doctors and veterinarians must collaborate closely for better control and surveillance of D. repens infection.

Aberrant peritoneal localization of Dirofilaria repens in a dog

Subcutaneous dirofilariosis is a widely spread vector-borne zoonotic disease caused by Dirofilaria repens. In the last years, a rise of human and animal cases of infection by D. repens has been reported in different European countries. The disease may be subclinical or characterized by different skin conditions. This report describes an unusual ectopic localization of D. repens in a naturally infected dog. The six-year old Pit Bull mixed breed dog presented dysorexia, exercise intolerance, orchialgia and moderate abdominal effusion. The abdominal ultrasound examination revealed multiple linear tubular structures with writhing and undulating movements within the peritoneal effusion. The microscopic examination of the peritoneal effusion revealed many larvae microscopically and molecularly identified as D. repens. This is the first case of peritoneal localization of D. repens in a dog. Epidemiological implications are discussed.

Filarioid infections in wild carnivores: a multispecies survey in Romania

BACKGROUND

Filarioids are vector-borne parasitic nematodes of vertebrates. In Europe, eight species of filarioids, including zoonotic species, have been reported mainly in domestic dogs, and occasionally in wild carnivores. In Romania, infections with Dirofilaria spp. and Acanthocheilonema reconditum are endemic in domestic dogs. Despite the abundant populations of wild carnivores in the country, their role in the epidemiology of filarioid parasites remains largely unknown. The aim of the present study was to assess the host range, prevalence and distribution of filarioid infections in wild carnivores present in Romania.

METHODS

Between May 2014 and February 2016, 432 spleen samples originating from 14 species of wild carnivores have been tested for the presence of DNA of three species of filarioids (D. immitis, D. repens and A. reconditum).

RESULTS

Overall 14 samples (3.24%) were molecularly positive. The most prevalent species was D. immitis (1.62%), accounting for 50% (n = 7) of the positive animals. The prevalence of D. repens was 1.39%, while that of A. reconditum was 0.23%. No co-infections were detected. Dirofilaria immitis DNA was detected in five golden jackals, Canis aureus (7.58%), one red fox, Vulpes vulpes (0.33%), and one wildcat, Felis silvestris (10%). The presence of D. repens DNA was detected in two red foxes (0.66%), two golden jackals (3.03%), one grey wolf (7.14%), and one least weasel, Mustela nivalis (33.33%). Acanthocheilonema reconditum DNA was found only in one red fox (0.33%).

CONCLUSION

The present study provides molecular evidence of filarial infections in wild carnivore species in Romania, suggesting their potential epidemiological role and reports a new host species for D. repens.

Dirofilaria immitis and D. repens show circadian co-periodicity in naturally co-infected dogs

Background

Dirofilaria immitis and Dirofilaria repens are mosquito-borne zoonotic filarioids typically infecting dogs, causing a potentially fatal cardiopulmonary disease and dermatological conditions, respectively. The females are larviparous, releasing the larvae (microfilariae) into the bloodstream, which further develop in mosquito vectors. However, microfilaremia greatly fluctuates during a 24-h period. As the sampling time can greatly influence the accuracy of diagnosis, the aim of the present study was to assess the circadian periodicity of D. immitis and D. repens in naturally co-infected dogs in an endemic area of Romania and to investigate possible differences of periodicity between these two species.

Methods

Overall, four dogs harbouring natural co-infection with D. immitis and D. repens were selected and sampled every two hours for two consecutive days: two dogs in July 2014 and two in July 2015. At each sampling time, a 0.7 ml blood sample was taken. Modified Knott’s test was performed on 0.5 ml, and the remaining 0.2 ml were used for DNA extraction and molecular amplification, both in single and duplex PCR reactions. Microfilariae of both species were morphologically identified and counted in each collected sample, microfilaremia was calculated, and fluctuation was charted.

Results

The dynamics of microfilaremia showed similar patterns for both Dirofilaria species. In all four dogs, D. immitis was present at all sampling times, with several peak values of microfilaremia, of which one was common for all dogs (1 am), while minimum counts occurred between 5 and 9 am. Similarly, for D. repens, one of the peak values was recorded in all dogs at 1 am, while minimum counts (including zero) occurred at 9 and 11 am. Single species-specific PCR reactions were positive for both D. immitis and D. repens in all collected samples, while duplex PCR failed to amplify D. repens DNA in many cases.

Conclusions

Both Dirofilaria immitis and D. repens microfilariae are subperiodic, following a similar variation pattern, with peak values of microfilaremia registered during the night in Romania. Duplex PCR fails to identify the infection with D. repens in co-infected dogs when the ratio of microfilaremia is in favour of D. immitis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-017-2055-2) contains supplementary material, which is available to authorized users.

Clinical and pathological effects of Dirofilaria repens and Dirofilaria immitis in a dog with a natural co-infection

Canine dirofilarioses are mosquito-borne zoonotic diseases with a continuous expansion of their geographical distribution, as a consequence of different climatic and ecological factors. Dirofilaria immitis, the aetiological agent of heartworm disease, has gained a major veterinary interest, mainly due to its severe clinical implication. In the last decades, D. repens, despite of being regarded as a less pathogenic species, regained attention due to its recognized zoonotic potential. Romania has been traditionally regarded as a non-endemic country, but recent epidemiological surveys are highlighting the presence of both D. repens and D. immitis. The present case report describes the clinical and pathological features of a natural co-infection with D. repens and D. immitis in 5year old male Boxer from north-western Romania. Based on clinical and laboratory investigations, a diagnosis of kidney failure and chronical cystitis was established. The parasites were identified by morphology and confirmed by PCR and sequencing. To the best of our knowledge this is the first worldwide report of the ectopic presence of D. repens adults in the pelvic cavity and mesentery by natural infection and first report of the ocular localization of this parasite for Romania. The clinical and paraclinical findings suggest the implication of D. repens microfilariae in the aetiology of histopathological lesions. Further investigations are needed in order to establish the actual pathogenic potential of D. repens, a frequently neglected parasite.

Marked subcutaneous mast cell and eosinophilic infiltration associated with the presence of multiple Dirofilaria repens microfilariae in 4 dogs

Dirofilaria repens is a parasitic nematode in the subcutaneous tissue of carnivores, including dogs and cats, transmitted by mosquitoes. Human beings may be accidental hosts. Infection of a dog with D repens was first reported in Palestine in 1934, and 2 additional cases were reported in dogs in Israel to date. This report describes D repens infection in 4 dogs in Israel that presented with subcutaneous masses, which were cytologically characterized by marked mast cell and eosinophil infiltration. In 3 cases, multiple microfilariae were present in the lesions; rare microfilariae were present in the 4^th case. In all 4 dogs, PCR of fine-needle aspirates from the lesions were positive for D repens. The mast cells observed in all lesions were uniform and highly granulated, and with the presence of the microfilariae, a mast cell tumor was considered less likely. This report suggests that D repens infection-associated subcutaneous lesions, characterized cytologically by massive mast cell and eosinophil infiltration, should be considered a differential diagnosis for mast cell tumor, especially in geographic locations endemic for this nematode. Notably, all 4 dogs were infected with D repens despite a routine prophylactic doramectin therapy administered every 3 months, probably due to the relatively long time interval between treatments.

Dirofilaria in Humans, Dogs, and Vectors in Austria (1978-2014)-From Imported Pathogens to the Endemicity of Dirofilaria repens

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.

Role of golden jackals (Canis aureus) as natural reservoirs of Dirofilaria spp. in Romania

BACKGROUND

Dirofilaria immitis and Dirofilaria repens are mosquito-transmitted zoonotic nematodes, causing heartworm disease and skin lesions, respectively, in carnivores. In Europe, the domestic dog is apparently the main definitive host, but patent infections occur also in other species of carnivores. The rapid spread of the golden jackals (Canis aureus) throughout Europe opens a question of involvement of this species in the sylvatic cycle of pathogens in the colonised territories, including Dirofilaria spp.

METHODS

Between January 2014 and May 2015, 54 golden jackals from 18 localities in Romania were examined by full necropsy for the presence of adult filarioid nematodes and blood samples from all animals were screened for the presence of microfilariae of D. immitis, D. repens and Acanthocheilonema reconditum by multiplex PCR DNA amplification.

RESULTS

Nematodes morphologically identified as D. immitis were found in 18.52% of the animals, originating from the southern part of Romania. No D. repens or A. reconditum were found at necropsy. The molecular prevalence in blood samples from the same animals was 9.26% for D. immitis and 1.85% for D. repens. All samples were negative by PCR for A. reconditum.

CONCLUSION

The relatively high prevalence of Dirofilaria spp. infections in golden jackals from Romania together with the increasing density of the jackal populations highlight their potential role in the transmission of these zoonotic parasites and in the maintenance of natural disease foci.

The Increase of Exotic Zoonotic Helminth Infections: The Impact of Urbanization, Climate Change and Globalization

Zoonotic parasitic diseases are increasingly impacting human populations due to the effects of globalization, urbanization and climate change. Here we review the recent literature on the most important helminth zoonoses, including reports of incidence and prevalence. We discuss those helminth diseases which are increasing in endemic areas and consider their geographical spread into new regions within the framework of globalization, urbanization and climate change to determine the effect these variables are having on disease incidence, transmission and the associated challenges presented for public health initiatives, including control and elimination.

[Dirofilaria repens-infection in a dog in central Germany without any history of travel]

A mixed breed dog was presented with dyspnoea and fever. In the purulent thorax aspirate, a nematode larva was found during the cytological examination. Subsequent diagnostic tests revealed an infection with Dirofilaria repens, which was probably acquired autochthonously in central Germany. Moxidectin was administered every 4 weeks for 6 months and shown to be effective as indicated by subsequent blood examinations. This case report shows that infection with Dirofilaria repens is possible in Germany and can be treated successfully.

Current surveys on the prevalence and distribution of Dirofilaria spp. and Acanthocheilonema reconditum infections in dogs in Romania

During the last decades, Dirofilaria spp. infection in European dogs has rapidly spread from historically endemic areas towards eastern and northeastern countries, but little or no information is available from these geographical regions. The present study provides a picture of filarial infections in dogs from Romania and compares two tests for the diagnosis of Dirofilaria immitis. From July 2010 to March 2011, blood samples were collected from 390 dogs from nine counties of Romania and serological SNAP tests were performed for the detection of D. immitis antigen. The remaining blood clots were subsequently used for DNA extraction followed by multiplex PCR for assessing filarioid species diversity (i.e. D. immitis, Dirofilaria repens and Acanthocheilonema reconditum). Based on molecular detection, an overall prevalence of 6.92 % (n = 27; 95 % confidence interval (CI) 4.70-10.03 %) for D. repens, 6.15 % (n = 24; 95 % CI 4.07-9.14 %) for D. immitis and 2.05 % (n = 8; 95 % CI 0.96-4.16 %) for A. reconditum was recorded, with significant variations according to sampling areas. Coinfections of D. immitis and D. repens were recorded in 23.91 % (n = 11) positive dogs. A slightly higher prevalence for D. immitis was detected at the SNAP test (n = 28, 7.17 %; 95 % CI 4.91-10.33 %), but this difference was not statistically significant (p = 0.66). However, only 53.57 % (n = 15) of antigen-positive dogs were confirmed by PCR, while other dogs (n = 9) PCR positive for D. immitis were negative at the serology. The present study shows that Dirofilaria species are endemic in the southern and southeastern areas of Romania, This article also provides, for the first time, an epidemiological picture of the distribution of A. reconditum in Romania.

Subcutaneous Dirofilaria repens infestation in non-descript canines

Dirofilaria repens is a filarial nematode which cause subcutaneous dirofilariosis. Dogs, foxes and cats are the definitive hosts and principal reservoirs of the parasite. We report cases of D. repens infestation in non-descript canines from Goa, India. The nematodes were enclosed within fibrous capsule or freely present in the tunica vaginalis of the testes, in sub-cutaneous tissue of foreleg and body cavity. The parasite showed well-developed thick multilayered cuticular ridges in the outermost layer, followed by transverse smooth muscles striations.

Dirofilaria repens infection in a dog imported to Norway

Dirofilaria repens infection was diagnosed in a dog that had been imported to Norway from Hungary three years previously. The dog was a four-year-old castrated male mixed-breed dog and presented for examination of two masses on the right thoracic wall. Fine needle sampling from the subcutaneous nodules and subsequent cytological examination revealed a high number of microfilariae and a pyogranulomatous inflammation. At re-examination approximately 3 weeks later, both masses had apparently disappeared spontaneously, based on both inspection and palpation. However, examination of peripheral blood by a modified Knott's test revealed a high number of unsheathed microfilariae with mean length of 360 μm and mean width of 6-7 μm, often with the classic umbrella handle appearance of D. repens. Polymerase chain reaction and sequencing confirmed the D. repens diagnosis. Subcutaneous dirofilariosis caused by D. repens is probably the most common cause of human zoonotic dirofilariosis in Europe, but currently is rarely encountered in northern countries such as Norway. However, travelling, import and relocation of dogs have increased, and thus the geographical range of these parasites is likely to increase from traditionally endemic southern regions. Increasing numbers of autochthonous cases of D. repens infections in dogs have been reported in eastern and central Europe. Although infection with D. repens often induces only mild signs or subclinical infections in dogs, they nevertheless represent a reservoir for zoonotic transmission and thus a public health concern, and, in addition, due to the long prepatent period and the high frequency of subclinical infections or infections with unspecific clinical signs, could easily be missed. Lack of experience and expectation of these parasites may mean that infection is underdiagnosed in veterinary clinics in northern countries. Also, predicted climate changes suggest that conditions in some countries where this infection is currently not endemic are likely to become more suitable for development in the intermediate host, and thus the establishment of the infection in new areas.

Adult of Dirofilaria repens in a dog with recurrent multiple subcutaneous nodular lesions

Subcutaneous dirofilariosis is a zoonosis parasitizing the dog, transmitted by Culicidae mosquitoes. An increasing number of new cases have been reported both in dogs and in humans all over the world. The aim of this work was to describe an uncommon case of recurrent multiple subcutaneous nodules by Dirofilaria repens in a 2-year-old dog. Surgical excision of two nodules on both hind limbs revealed a single thread-like live nematode and multiple parasite fragments, respectively. The parasite was morphologically identified as an adult female of D. repens. Haematoxylin-eosin tissue sections of nodules revealed a diffuse pyogranulomatous angiocentric dermatitis with an intense eosinophilic infiltrate throughout the dermis. One month post-surgery, a new nodular lesion was detected on the right thigh and resolved spontaneously in a few weeks. During the following 3 months, two other nodules were briefly noted both on the right hip and on the left side of the chest. The dog was periodically treated with milbemycin oxime and praziquantel, starting a week before the appearance of the first nodule. Microfilariae were not detected neither in the bloodstream nor in fine-needle aspirates at any time, and the diagnosis was made only after surgery. Practitioners should consider dirofilariosis in the differential diagnosis of subcutaneous swellings, especially if they have a recurrent behaviour, previously described in humans but not in dogs.

Microfilarial periodicity of Dirofilaria repens in naturally infested dogs

In the past years, canine and human cases of infestation by Dirofilaria repens (Spirurida, Onchocercidae) have been increasingly reported in several European countries. Subcutaneous dirofilariosis by D. repens may either be asymptomatic in dogs or may be characterized by subcutaneous nodules and other symptoms. Information on the periodicity of D. repens microfilariae in naturally infested animals is scant, and this might impair the accurate diagnosis of subcutaneous dirofilariosis and appropriate control plans. In the present study, eight dogs infested with D. repens were sampled twice daily at 12-h intervals for ten consecutive days, and the dog with the highest mean value of microfilariaemia was further sampled every 4 h for four consecutive days. The blood was microscopically and molecularly examined for microfilariae, and, additionally, negative samples were also subjected to a real-time PCR to evaluate the level of circulating DNA. The results demonstrated significant variations in circadian rhythms of D. repens larvae, with higher values of microfilariae per milliliter in the evening samples. A significant variation was also found at the individual level for the dogs with the highest values of microfilariaemia. All samples which were negative at the light microscopy and positive at the real-time PCR displayed levels of circulating parasite DNA <1 microfilaria per milliliter. Biological and clinical implications have been here discussed.

Treatment of Dirofilaria repens microfilariaemia with a combination of doxycycline hyclate and ivermectin

Dirofilaria repens is one of the most widespread mosquito-borne filarioid responsible for infestations in dogs, usually characterized by nodules and other skin lesions. Additionally, the zoonotic potential of this nematode is of public health concern, given that D. repens has been often associated to human dirofilariosis in the Old World. In the present study, the therapeutic efficacy against D. repens microfilariae of a protocol based on doxycycline hyclate (Ronaxan(®), Merial), 10mg/kg every day for 30 days, and ivermectin (Cardotek 30(®), Merial), 6 μg/kg every 15 days for 6 months, was preliminarily investigated in two naturally infested dogs. Blood samples were collected every 30 days during 6 months of treatment and examined by a Knott's modified test and a duplex real-time PCR. The results here presented indicate that this therapeutic protocol, applied monthly, could be effective for treating microfilariaemia in dogs affected by subcutaneous dirofilariosis.