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Mosquitoborne diseases are a growing threat to public health worldwide. Human dirofilariasis, caused by the nematode Dirofilaria repens and transmitted by mosquitoes from various genera, has recently expanded into new areas of Europe. In this article, we report molecularly confirmed autochthonous human D. repens infections in Estonia.

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 immitis is a parasite related to pulmonary dirofilariasis in humans, its accidental hosts. We detected an autochthonous case of D. immitis infection in a woman from Slovakia. The emergence and spread of this parasite in Europe indicates a critical need for proper diagnosis of infection.

Background Dirofilaria immitis is a mosquito-transmitted filarial parasite causing heartworm disease in dogs. The parasite may cause a significant disease burden to the dog population in high prevalence areas and is mainly managed through prophylactic treatments. Methods In this modelling study, the effect of a prophylactic treatment with moxidectin and sarolaner on heartworm disease dynamics was investigated in dogs. A compartmental model was developed to investigate different epidemiological settings considering different values for prevalence and host preference. Results When the mosquito host preference to dogs is low, a treatment compliance of only 40% decreases the proportion of infectious dogs. When the host preference of the mosquitoes however increases, an exponential increase in infectious dogs was observed, and a higher treatment compliance is required. In high transmission environments, with a high prevalence and a high mosquito host preference, a high treatment compliance (up to 100%) is required to have an impact on the number of infected animals. Notably, in scenarios with higher host preference towards dogs, more mosquitoes are exposed to sarolaner through the blood meal, leading to higher mortality of these mosquitoes and resulting in fewer infected and infectious dogs. Conclusions The preventive efficacy, as measured by the number of non-infected dogs, increases with increasing treatment compliance, but the extent of the treatment effect differs with the epidemiological setting. Adding sarolaner to a heartworm prevention has a complimentary impact on mosquito survival and heartworm disease transmission, although this effect depends on the epidemiological settings, emphasizing the true complexity of disease dynamics of a vector-borne disease. Graphical abstract

Background Human pulmonary dirofilariasis (HPD) is rare in Hungary, and it stems from Dirofilaria immitis , mainly transmitted through mosquito bites, with dogs as primary hosts. Despite its prevalence in veterinary settings, human cases are infrequent. Historically, Mediterranean countries report most HPD cases, but sporadic cases occur in temperate European regions. Radiologically, HPD often manifests in a non-specific manner, resembling pulmonary neoplasms, leading to unnecessary surgery and patient distress. Methods This study presents a notable case series from Hungary, encompassing a 12-year period, documenting 5 instances of HPD with the aim to provide baseline estimate of occurrence for future comparison. Results Among the patients studied, all were of middle age (median: 52 years, range: 37–69) and exhibited tumor-like lesions, primarily localized to the right lung, necessitating lobectomy or wedge resection. Histological examination consistently revealed a necrotizing granulomatous response characterized by remnants of helminths, without the presence of ovules. Furthermore, rigorous diagnostic procedures excluded other potential infectious agents through specialized staining techniques. Polymerase chain reaction analysis definitively confirmed the diagnosis of HPD in each case. Conclusions This case series highlights HPD as a seldom zoonosis, with a probable escalation in its occurrence within temperate regions. Therefore, clinicians should maintain a heightened awareness of HPD in the differential diagnosis of pulmonary coin lesions. Early recognition and diagnosis are paramount for appropriate management and prevention of potential complications associated with this increasingly recognized infectious entity.

Background This is the first case of triple co-infection with vector-borne diseases confirmed by blood smear results and molecular confirmation of the anaplasmosis and dirofilariosis in a dog from North-Eastern Poland. Case presentation A 4-year-old, uncastrated male Central Asian Shepherd Dog with symptoms of apathy and lack of appetite was diagnosed with triple vector disease infection. Microscopic examination of a blood smear revealed the presence of Babesia spp., Anaplasma phagocytophilum and microfilariae. PCR confirmed the presence of A. phagocytophilum and Dirofilaria repens . Clinical examination revealed elevated core body temperature and thrombocytopenia. Treatment for the identified pathogens was initiated. Complete improvement of clinical condition was observed on the second day of treatment. Conclusion The detection of three different pathogens in a blood smear is not often reported, but it can significantly speed up the diagnosis and initiation of targeted treatment. It should be confirmed using molecular methods, which are commonly used in companion animals, especially for diagnosing co-infections.

We describe a case of imported ocular dirofilariasis in Australia, linked to the Hong Kong genotype of Dirofilaria sp., in a migrant from Sri Lanka. Surgical extraction and mitochondrial sequences analyses confirmed this filarioid nematode as the causative agent and a Dirofilaria sp. not previously reported in Australia.

Detection of circulating antigen of Dirofilaria immitis has been a mainstay of identifying heartworm infection in clinical practice for the past three decades. Several validated commercial antigen tests have very good sensitivity, specificity, and positive predictive values, especially when used in patients for which heartworm infection is likely. In some dogs and cats infected with heartworm, antigen may not be available for detection although present in the patient sample; heat pretreatment of these samples reveals the antigen, changing the false negative to positive. This phenomenon was documented in the literature in the 1980s but subsequently overlooked by the heartworm research community for many years. In this review, we provide a summary of the current understanding of the role of heat reversal in diagnosing heartworm infection. This additional diagnostic step is most important for patients in which heartworm infection is likely, such as dogs or cats in an endemic area with an inconsistent history of heartworm preventive use, or dogs with a prior diagnosis of heartworm infection that were recently treated. To illustrate the concept, we share a summary of results from canine samples tested at the state veterinary diagnostic laboratory in Oklahoma, USA in 2017 by modified Knott test and by commercial antigen test before and after heat treatment of samples; in this sample set, heat treatment changed all D. immitis microfilaria-positive but antigen-negative samples to antigen-positive. Pet dogs with a history of consistent preventive use are unlikely to become positive with heat pretreatment; for that reason, routine pretreatment of all samples tested in a veterinary practice is not recommended. We also review known causes of false negative and false positive results on heartworm antigen tests that, although uncommon, can complicate accurate diagnosis in individual patients. Together, this review provides a primer to aid understanding of strategies that can enhance accurate diagnosis of heartworm infection in veterinary practice and clinical research.

Background A recent American Heartworm Society (AHS) survey on the incidence of adult heartworm infections in dogs in the United States of America showed a 21.7% increase in the average cases per veterinary clinic from 2013 to 2016. The analysis reported here was performed to see if heartworm testing results available via the Companion Animal Parasite Council (CAPC) aligned with the AHS survey and whether changes in heartworm preventive dispensing accounts for the increased incidence. The resistance of Dirofilaria immitis to macrocyclic lactones (MLs) has been previously reported. Methods An analysis of 7–9 million heartworm antigen tests reported annually to the Companion Animal Parasite Council (CAPC) from 2013 to 2016 was conducted and compared to the 2016 AHS survey. A state-by-state analysis across the southeastern USA was also performed. National heartworm preventive dispensing data were obtained from Vetstreet LLC and analyzed. All oral, topical and injectable heartworm preventives were included in this analysis, with injectable moxidectin counting as six doses. Results Positive antigen tests increased by 15.28% from 2013 to 2016, similar to the 21.7% increase reported by the AHS survey. Incidence in the southeastern USA increased by17.9% while the rest of USA incidence increased by 11.4%. State-by-state analysis across the southeastern USA revealed an increased positive test frequency greater than 10% in 9 of 12 states evaluated. During this time, the overall proportion of dogs receiving heartworm prophylaxis remained relatively unchanged. Approximately 2/3 of the dogs in the USA received no heartworm prevention each year. Conclusion These CAPC data show the rate of positive heartworm tests increasing significantly ( P  <  0.0001) in the USA from 2013 to 2016, with a higher rate of increase in the southeastern USA than nationally. Only 1/3 of dogs in the USA were dispensed one or more doses of heartworm prevention annually by veterinarians, averaging 8.6 monthly doses/year. Veterinarians and pet owners should work together to follow CAPC and AHS guidelines to protect dogs from infection with D. immitis . Lack of preventive use and the emergence of heartworm resistance to MLs could both be impacting the increased rate of positive heartworm tests in dogs.

Leishmaniasis and dirofilariasis are significant emerging zoonotic diseases. This study aimed to assess the prevalence of single and co-infections involving Leishmania donovani , Dirofilaria sp. “hongkongensis”, and Wolbachia spp. among dogs from the Kani tribal settlements of Western Ghats, Kerala. In July 2023, blood samples from 75 dogs were collected and analyzed using microscopy, serology, and molecular diagnostics. Molecular analysis using kDNA-PCR and ITS1 PCR identified leishmaniasis in 39 out of 75 dog samples (52.0% [95% CI, 40.2 to 63.7], with phylogenetic analysis confirming the species as L. donovani . Additionally, 19 out of 75 dog samples (25.3% [95% CI, 16.0 to 36.7]) produced a ~ 720 bp band for nematode-specific COI amplification, which was confirmed as Dirofilaria sp. “hongkongensis”. Among the 19 Dirofilaria -positive samples, 14 (73.7% [95% CI, 48.8 to 90.9]) tested positive for Wolbachia using the wsp primer. Among the 75 dogs screened, 12 (16% [95% CI, 08.6 to 26.3]) were co-infected with Leishmania and Dirofilaria , while 9 (12% [95% CI, 05.6 to 21.6]) were co-infected with all three parasites: L. donovani , Dirofilaria sp. “hongkongensis”, and Wolbachia spp. The findings suggest that Kerala is gradually becoming more vulnerable to zoonoses like leishmaniasis and dirofilariasis emphasizing the need for prompt intervention and prevention measures. These results underscore the critical need for continued development of multi-pathogen detection methods, not only in regions where multiple diseases are endemic but also in areas where such diseases may emerge.