Human dirofilariasis: an emerging zoonosis in India

Knowledge, attitude, and practices of veterinarians towards canine vector-borne pathogens in Sri Lanka

Canine vector-borne pathogens (CVBP) have a worldwide distribution and show a high prevalence in tropical countries such as Sri Lanka. Some CVBP are zoonotic, with dogs identified as reservoir hosts for human subcutaneous dirofilariasis and potentially for spotted fever rickettsioses and re-emergent brugian filariasis in Sri Lanka, making these pathogens emerging public health issues in the country. Veterinarians are crucial in monitoring, preventing, and controlling these pathogens in dogs. Therefore, it is imperative to understand veterinarians' knowledge, attitude, and practices (KAP) regarding CVBP to mitigate their impact. A survey was designed and administered electronically to veterinarians residing and practising in Sri Lanka. Responses were evaluated using descriptive, univariable, and multivariable analyses to investigate associations between demographic factors, knowledge, attitude, and practices related to CVBP. Out of the 170 participating veterinarians, nearly 70% had moderate or high knowledge. However, the awareness of zoonotic pathogens, Brugia spp. (16%) and Rickettsia conorii (18%), was low, and a considerable number of veterinarians were unaware of the zoonotic nature of Dirofilaria repens. Based on multivariable analysis adjusting for experience and self-rated knowledge, new graduates had higher odds of knowledge compared to experienced veterinarians (OR 5.7, 95% CI 1.7-23, p = 0.028). Questions assessing the attitude towards CVBP indicated that most participating veterinarians comprehend and agree with their importance. Nearly all participants agreed that ectoparasite control is the best option to prevent CVBP infections (91%, 153/167) and that for effective treatment of CVBP, a definitive diagnosis is required (81%, 135/167). However, veterinarians recommended suboptimal treatments for some CVBP, like Babesia gibsoni. Better practices were associated with being a companion animal practitioner (OR 2.4, 95% CI 1.1-5.7, p = 0.032) and having a low to moderate canine caseload (OR 3.6, 95% CI 1.3-10.4, p = 0.038). Limited knowledge of zoonotic CVBP among veterinarians, along with suboptimal treatment, might contribute to dogs acting as reservoirs and high prevalence of these pathogens in Sri Lanka. Therefore, continued veterinary education is recommended to improve knowledge and practices, which in turn will help to improve the diagnosis, treatment, and control of these infections in Sri Lanka to ensure the well-being of dogs and humans.

Dirofilariasis of the Nasal Dorsum: A Case Report

Dirofilariasis is an infection caused by the filarial nematode Dirofilaria. Dirofilaria immitis primarily causes pulmonary dirofilariasis, while subcutaneous dirofilariasis is usually caused by Dirofilaria tenuis and Dirofilaria repens but can rarely be caused by Dirofilaria immitis as well. Here we report a rare case where in a 26-year-old with a history of international travel presented with swelling over the nasal dorsum. Following surgical excision, histopathological examination revealed dirofilariasis. Although uncommon, this zoonosis should be taken into consideration as a differential diagnosis of facial swellings.

Subconjunctival Dirofilaria masquerading as nodular scleritis

A man in his late 50s presented with a gradually enlarging, painless, reddish mass on the white portion of his left eye for 2 weeks. His best-corrected visual acuity was 20/20 in both eyes. Slit-lamp examination showed a congested, nodular, elevated lesion on the temporal bulbar conjunctiva with two pustule-like elevations. Anterior segment optical coherence tomography showed a subconjunctival solid mass rather than an abscess or a cyst. Scleral deroofing was performed and a long thread-like object resembling a dead worm was identified. The worm was removed intact, and its histopathology confirmed the diagnosis of Dirofilaria Peripheral blood smear did not show any microfilariae. No recurrences or new lesions were observed during the follow-up examinations at 1 and 5 months post-surgery. This case highlights the importance of considering a parasitic aetiology in cases of nodular or infectious scleritis.

Development and validation of a long-read metabarcoding platform for the detection of filarial worm pathogens of animals and humans

BACKGROUND

Filarial worms are important vector-borne pathogens of a large range of animal hosts, including humans, and are responsible for numerous debilitating neglected tropical diseases such as, lymphatic filariasis caused by Wuchereria bancrofti and Brugia spp., as well as loiasis caused by Loa loa. Moreover, some emerging or difficult-to-eliminate filarioid pathogens are zoonotic using animals like canines as reservoir hosts, for example Dirofilaria sp. 'hongkongensis'. Diagnosis of filariasis through commonly available methods, like microscopy, can be challenging as microfilaremia may wane below the limit of detection. In contrast, conventional PCR methods are more sensitive and specific but may show limited ability to detect coinfections as well as emerging and/or novel pathogens. Use of deep-sequencing technologies obviate these challenges, providing sensitive detection of entire parasite communities, whilst also being better suited for the characterisation of rare or novel pathogens. Therefore, we developed a novel long-read metabarcoding assay for deep-sequencing the filarial nematode cytochrome c oxidase subunit I gene on Oxford Nanopore Technologies' (ONT) MinION™ sequencer. We assessed the overall performance of our assay using kappa statistics to compare it to commonly used diagnostic methods for filarial worm detection, such as conventional PCR (cPCR) with Sanger sequencing and the microscopy-based modified Knott's test (MKT).

RESULTS

We confirmed our metabarcoding assay can characterise filarial parasites from a diverse range of genera, including, Breinlia, Brugia, Cercopithifilaria, Dipetalonema, Dirofilaria, Onchocerca, Setaria, Stephanofilaria and Wuchereria. We demonstrated proof-of-concept for this assay by using blood samples from Sri Lankan dogs, whereby we identified infections with the filarioids Acanthocheilonema reconditum, Brugia sp. Sri Lanka genotype and zoonotic Dirofilaria sp. 'hongkongensis'. When compared to traditionally used diagnostics, such as the MKT and cPCR with Sanger sequencing, we identified an additional filarioid species and over 15% more mono- and coinfections.

CONCLUSIONS

Our developed metabarcoding assay may show broad applicability for the metabarcoding and diagnosis of the full spectrum of filarioids from a wide range of animal hosts, including mammals and vectors, whilst the utilisation of ONT' small and portable MinION™ means that such methods could be deployed for field use.

Hematological characteristics of autochthonous hypermicrofilaremic dirofilariosis in dogs in Kannur District of Kerala

This study aimed to determine whether autochthonous high-intensity D. repens microfilaremia leads to haematological changes in companion dogs. Dogs with hypermicrofilaremia presented to the District Veterinary Centre, Kannur were selected for the study. A total of 100 dogs were positive for hypermicrofilariaemia with D. repens based on peripheral blood smear examination and Knott's test. Of these, 3 dogs were concurrently positive for sheathed microfilaria (MF) of Brugia spp. Interestingly, an adult live worm of D. repens approximately eight cm in length was detected on a subcutaneous mass on the hind limb of a hypermicrofilaremic dog in the study. We compared the hematological parameters of 100 autochthonous hypermicrofilaremic dogs and 15 uninfected dogs. The hematological findings in the study are mild to moderate anemia, moderate to severe thrombocytopenia, leucocytosis with granulocytosis, lymphocytosis and monocytosis as compared to the uninfected group of dogs. The pathogenicity of naturally occurring hypermicrofilaremia is poorly studied, and knowledge of its epidemiology, host-parasite relationship and impact on various organs is warranted for better prevention and control, especially in hot-spot areas.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12639-023-01622-6.

Dirofilariasis Presenting as Orbital Abscess Complicating Ethmoid Sinusitis

Dirofilariasis in deep tissue plane is seldom reported in literature. A 58 year old woman presented with right orbital abscess complicating ethmoid sinusitis. She underwent endoscopic ethmoidectomy with abscess drainage where a dirofilaria worm was extracted. Treatment requires surgical removal of the worm without the need for anti-parasitic medications.

Dogs are reservoir hosts of the zoonotic Dirofilaria sp. 'hongkongensis' and potentially of Brugia sp. Sri Lanka genotype in Sri Lanka

In 2016, the World Health Organization declared Sri Lanka as having successfully eliminated lymphatic filariasis as a public health concern. However, in recent decades, several infections with subperiodic filarial species suggestive of zoonotic infections have been recorded across the country. The arthropod-borne filarioids Dirofilaria repens, Brugia malayi, Brugia ceylonensis, and Acanthocheilonema reconditum are historically known to be endemic in dogs in Sri Lanka. Despite this, limited information on the prevalence, diversity, and predictors of filarial infections in dogs in the country has resulted in suboptimal control and prevention of these parasites, some of which are known to be zoonotic. To address this, whole blood and metadata were collected and analysed from 423 pet dogs across three geo-climatic zones within Sri Lanka. Blood samples were screened using the Modified Knott's Test (MKT) and PCR followed by Sanger sequencing. Multivariable logistic regression models were used to assess predictors for canine filarial infections. Dirofilaria sp. 'hongkongensis' (Dirofilaria sp. HK) and Brugia sp. Sri Lanka (SL) genotype were identified infecting dogs. The overall prevalence of filarial infection in pet dogs by PCR was 36.9% (95% CI 32.3-41.7%, n = 156), compared to 18.8% (95% CI 15.2-22.9%, n = 79) detected using the MKT. >80% of filarial-positive dogs were infected by Dirofilaria sp. HK, while the remaining dogs were infected by Brugia sp. SL genotype. Increasing age (p < 0.001) and residing in the low-country wet zone (p < 0.001), which includes regions that were endemic for human filariasis in Sri Lanka, were associated with filarial infections in dogs. No clear pathognomonic signs for filarial infection were identified, indicating that dogs act as reservoirs for these potentially zoonotic pathogens. Given the morphological similarity of Dirofilaria HK and Brugia sp. SL microfilariae with those of D. repens and B. malayi, respectively, it is likely that these species have been misidentified in the past. Prevention and control measures of these potentially zoonotic canine filarial infections are highly advocated to safeguard both canine and human health.

Ocular dirofilariasis: A report from Odisha

We report a case of ocular dirofilariasis in a 68-year-old man manifesting as pre-septal abscess with gradually increasing swelling of the left eyelid and near complete ptosis of eye. A live worm was seen wriggling in the lesion while the abscess was being drained and was extracted carefully. Subsequently, it was identified as an adult female Dirofilaria repens worm. The lid edema and swelling resolved and the patient was discharged without any residual complaints.

Animal and Human Dirofilariasis in India and Sri Lanka: A Systematic Review and Meta-Analysis

Dirofilariasis is an emerging vector-borne tropical disease of public health importance that mainly affects humans and dogs. Dirofilaria immitis and D. repens are the two well-documented dirofilariasis-causing filarioid helminths of both medical and veterinary concerns in India and Sri Lanka. This systematic review and meta-analysis aimed to describe and summarize the current evidence of dirofilariasis prevalence and distribution in India and Sri Lanka. Interestingly, D. repens is reported to circulate in both dogs (prevalence of 35.8% (95% CI: 11.23-60.69)) and humans (97% of published case reports) in India and Sri Lanka, but D. immitis is reported to be present in the dog populations in India (prevalence of 9.7% (95% CI: 8.5-11.0%)), and so far, it has not been reported in Sri Lanka. This peculiar distribution of D. immitis and D. repens in the two neighbouring countries could be due to the interaction between the two parasite species, which could affect the pattern of infection of the two worm species in dogs and thus influence the geographical distribution of these two filarial worms. In medical and veterinary practice, histopathology was the most commonly used diagnostic technique (31.3%; 95% CI 2.5-60.2%). The low specificity of histopathology to speciate the various Dirofilaria spp. may lead to misdiagnosis. It was identified in this study that several regions of India and Sri Lanka have not yet been surveyed for dirofilariasis. This limits our understanding of the geographical distribution and interspecies interactions of the two parasites within these countries. Parasite distribution, disease prevalence, and interspecies interactions between the vectors and the host should be targeted for future research.

Identification of potential vectors of Dirofilaria immitis and Brugia pahangi (Spirurida: Filariidae): First observation of infective third-stage larva of B. pahangi in Culex quinquefasciatus (Diptera: Culicidae)

Information on the mosquito species that transmit canine filariosis is scanty. Hence, an experimental study was conducted to identify the potential vectors responsible for the transmission of D. immitis Leidy and B. pahangi Buckley & Edeson. A total of 367 mosquitoes belonging to six species containing both laboratory and field strains (i.e. Aedes togoi Theobald, Aedes aegypti Linnaeus, Aedes albopictus Skuse, Culex quinquefasciatus Say, Culex vishnui Theobald and Anopheles dirus Peyton & Harrison) were used in this study. All mosquitoes were artificially fed on either D. immitis or B. pahangi microfilariae (mfs) infected blood by using the Hemotek™ membrane feeding system. Out of 367 mosquitoes, 228 (64.9%) were fully engorged. After feeding on D. immitis (20%) and B. pahangi (33%) mfs positive blood, the mortality rates for Cx. quinquefasciatus were found to be slightly lower than that of other species of mosquitoes. On the other hand, majority of An. dirus were found to be incapable to withstand the infection of mfs as the mortality rates were relatively high (D. immitis = 71.4%; B. pahangi = 100.0%). Brugia pahangi was detected in Ae. togoi and Cx. quinquefasciatus with infection rates of 50% and 25%, respectively. Aedes togoi was the only species infected with D. immitis with an infection rate of 69%. Our results showed that Ae. togoi was an excellent experimental vector for both D. immitis and B. pahangi. This study also documented the observation of B. pahangi, for the first time in the head region of Cx. quinquefasciatus under a laboratory setting.

Human Dirofilariasis Caused by Dirofilaria repens in Sri Lanka from 1962 to 2020

PURPOSE

Sri Lanka has reported the highest prevalence of human dirofilariasis cases in Asia. Thus far, Dirofilaria repens is the only reported Dirofilaria species that affect humans, dogs, and cats in Sri Lanka. Therefore, this systematic review was carried out to analyse the studies performed on dirofilariasis in Sri Lanka.

METHODS

Peer-reviewed articles were searched on dirofilariasis published on Google Scholar, PubMed, Cochrane, and ResearchGate from January to March 2021. Articles were selected using inclusion and exclusion criteria. Three reviewers assessed the studies and extracted data independently to minimize the risk of bias. Extracted data were compiled, and then the results were compared and discussed in this systematic review.

RESULTS

Twenty-five studies performed in Sri Lanka were analysed, and high prevalence areas, frequent clinical presentations, diagnostic methods, reservoir hosts, and treatment were identified. More than 173 cases of human dirofilariasis caused by D. repens were reported from 1962 to 2020 in 20 districts among 25 investigated. The highest number of cases (n = 80) was recorded during 2010-2012 period. Canine and feline dirofilariasis are reported countrywide, and a large number of potential mosquito breeding sites could be seen in Sri Lanka.

CONCLUSIONS

The number of reported cases of human dirofilariasis has been varied from 1962 to 2020. The highest number of cases has reported in 2010-2012, and then the number of cases has dropped. This may be due to underreporting. Thus, awareness of Dirofilaria repens infection in humans, control measures in endemic areas and further research on dirofilariasis in other districts of Sri Lanka are crucial.

New cases of human dirofilariosis on the Balkan Peninsula - "Masked intruders" uncovered by a surgeon

Dirofilaria spp. nematodes are accidental parasites of humans causing mild to serious, superficial or visceral infections. Superficial dirofilariosis is rather common in Europe and is typically manifested as subcutaneous form. Herein we report 46 new cases of human dirofilariosis (19 patients with subcutaneous, 18 patients with ocular, 4 patients wih genital, 2 patients with submucosal, 2 patients with pulmonary and 1 patient with intramuscular form of infection) that were recorded from the beginning of 2015 to May 2021 on the Balkan Peninsula with a goal to update the prevalence of this parasitosis and point out potential problems in diagnosis and treatment. Besides, given the high possibility of misinterpretation as tumor, our second aim was to encourage the inclusion of this pathogen in the differential diagnosis of subcutaneous nodules. Although quite common forms, subcutaneous and ocular dirofilariosis can be very often misdiagnosed in clinical practice due to the absence of specific clinical manifestations. Therefore, raising awareness of clinicians about this zoonosis is needed as well as closer collaboration between physicians and veterinarians.

Candidatus Dirofilaria Hongkongensis Infections in Humans During 2005 to 2020, in Kerala, India

We tried to determine the epidemiology and species of human dirofilariasis observed at two tertiary care hospitals in Kerala. We searched the hospital database to identify cases of dirofilariosis from January 2005 to March 2020. Along with human isolates, one dog Dirofilaria isolate was also subjected to PCR and sequencing of pan filarial primers cytochrome oxidase subunits 1 and 12S rDNA. We documented 78 cases of human dirofilariosis. The orbit, eyelid, and conjunctiva were the most commonly affected sites. Molecular characterization identified one dog and five human isolates as Candidatus Dirofilaria Hongkongensis. A rare case of subconjunctival infestation by B. malayi was also documented. Human dirofilariosis is a public health problem in the state of Kerala in India, and it is mostly caused by Candidatus Dirofilaria Hongkongensis. We propose that all diroifilaria isolates are subjected to sequencing for identification.

Human dirofilariosis of buccal mucosa - First molecularly confirmed case and literature review

When presented in unusual manner, human dirofilariosis is hard to recognize and often leads to misdiagnosis and unjustified use of various medications. Herein, we report a rare case of Dirofilaria infection localized in buccal mucosa. A 45-year-old male, residing in the Central Serbia, developed striking edema of buccal mucosa followed by leucocytosis, with both neutrophylia and eosinophylia. Thirty days after first symptoms occurred, nodule was formed along the lateral edge of right maxilla. Therefore, patient underwent surgical extirpation and subsequent histopathological analysis of the specimen revealed the presence of a nematode. Based on morphological characteristics of detected parasite, the diagnosis of submucosal Dirofilaria repens-like infection was made. The diagnosis was confirmed, being the first case in the world analyzed by molecular methods. So far, only 13 such cases have been reported worldwide and our paper brings attention to rare form of this zoonosis and updates the data about human dirofilariosis in buccal mucosa.

Imaging Findings of Subcutaneous Human Dirofilariasis

Dirofilariasis is an emerging helminthic zoonosis seldom reported. Humans are accidental hosts and rarely affected. We report a case of dirofilariasis presenting as a subcutaneous nodule in the uncommon location in the thigh with concealed history of dog meat handler. Of the cases published in literature, imaging findings of this disease have been few and far between. In this article, we describe multimodality imaging findings of dirofilariasis in the thigh.

The Diversity of Human Dirofilariasis in Western Sri Lanka

BACKGROUND

Human dirofilariasis is an emerging zoonosis in many countries. Dirofilariasis caused by Dirofilaria repens may present with diverse clinical manifestations in humans due to aberrant localization of worm lesions causing diagnostic dilemmas. The aim of this retrospective study was to describe and update the demography and clinical spectrum of human dirofilariasis in western Sri Lanka. Nematode or nematode fragments isolated from excision biopsies that were confirmed as D. repens at the Department of Parasitology, Faculty of Medicine, University of Kelaniya, Sri Lanka, between 2012 and 2018 were included. Data on age, gender, and clinical details were obtained from case files. Identity of worms was established by morphometry and cuticle characteristics on wet-mount preparation. Specimens from unusual case presentations were further analyzed by PCR with specific primers for internal transcribed spacer region 2 (ITS2) of the ribosomal DNA.

RESULTS

Sixteen nematode specimens isolated from subconjunctiva (n=2), subcutaneous (n=13) and intramuscular (n=1) locations were identified as D. repens by morphometry (average length 11.5 cm) and the characteristic longitudinal striations on cuticle visualized by microscopy. The age distribution of cases ranged from 1 to 65 years with a mean of 21.5. Females were more frequently affected (n=10, 62.5%) and worm locations were commonest in the orbital region (5/16) and scrotum (3/16). Imaging techniques were of use in detecting infections in deeper tissue levels. PCR analysis of DNA extracted from a worm in an intramuscular granuloma of the temporal region elicited the expected band at 484bp for D. repens.

CONCLUSIONS

Human dirofilariasis is on an upward trend in incidence. Imaging techniques were of use in clinical diagnosis and molecular speciation in establishing the species identity in unusual case presentations. We suggest a more conservative approach in the management of human dirofilariasis and recommend a one health approach for control.

Human oral dirofilariasis

Zoonotic filarial infections particularly dirofilariasis have been reported worldwide. The route of transmission to human beings is vector-borne through mosquitoes. Increased mosquito activity subsequent to global warming has influenced the transmission of dirofilarial infection in many geographic regions, including Asia. Dirofilariasis presents as mucocutaneous and pulmonary infections. Dirofilarial infections rarely manifest in the oral and perioral region and can pose to be a diagnostic challenge to clinicians. We report the first case of oral dirofilariasis in Goa, India.

A preliminary survey of filarial parasites in dogs and cats in Sri Lanka

Human brugian filariasis has re-emerged in Sri Lanka after a quiescent period of four decades. This study investigated the prevalence of canine and feline filarial parasites in three localities with human sub-periodic brugian filariasis, in order to determine their potential reservoir status. All reachable dogs and cats, both stray and domestic, within a 350m radius of an index case of brugian filariasis in three locations (Madampe, Wattala and Weliweriya) were screened for microfilariae using Giemsa stained thick blood smears. A representative sample of canine and feline blood samples positive for Brugia spp. microfilariae by microscopy, from each of the three locations, were further analyzed by PCR with specific primers for internal transcribed spacer region 2 (ITS2) of the ribosomal DNA. A total of 250 dogs and 134 cats were screened. The overall microfilaraemia rates were high among both dogs (68.8%) and cats (47.8%). The prevalence of microfilaraemia was significantly higher among dogs than cats (p<0.05). Two filarial species were identified based on morphology of microfilariae: Dirofilaria (Nochtiella) repens (dogs, 54.4% and cats, 34.3%) and Brugia spp. (dogs, 51.6% and cats, 30.6%). PCR analysis of canine (n = 53) and feline (n = 24) samples elicited bands in the region of 615bp, which confirmed Brugia malayi infection. Co-infection with D.(N.) repens was detected by PCR with an additional band at 484bp, in 36 canine and 17 feline samples. Overall microfilaraemia rates of dogs (81.8%) and cats (75%) in Madampe (rural) were significantly higher than in urbanized Wattala (dogs, 62.4% and cats, 26.0%) (p<0.05). High rates of zoonotic filarial infections strongly implicate dogs and cats as potential reservoirs for human dirofilariasis and brugian filariasis in Sri Lanka.

A case of orbital dirofilariasis in New York

A 39-year-old female presented with a 5-day history of left inferonasal periocular swelling and associated intermittent itching. Ophthalmologic examination demonstrated a 4 × 8 mm subcutaneous painless mass localized anterior to the medial left lower orbital rim. An excision of the mass was performed, and pathology revealed Dirofilaria. The patient improved over the 3 months of postoperative follow-up. Although several human cases of pulmonary dirofilariasis have been reported in the United States, periocular dirofilariasis has been rarely reported in the United States. The case report is in compliance with the Health Insurance Portability and Accountability Act.

The Complexity of Zoonotic Filariasis Episystem and Its Consequences: A Multidisciplinary View

Vector-borne transmitted helminthic zoonosis affects the health and economy of both developing and developed countries. The concept of episystem includes the set of biological, environmental, and epidemiological elements of these diseases in defined geographic and temporal scales. Dirofilariasis caused by different species of the genus Dirofilaria is a disease affecting domestic and wild canines and felines and man, transmitted by different species of culicid mosquitoes. This complexity is increased because Dirofilaria species harbor intracellular symbiont Wolbachia bacteriae, which play a key role in the embryogenesis and development of dirofilariae and in the inflammatory pathology of the disease. In addition, the vector transmission makes the dirofilariasis susceptible to the influence of the climate and its variations. The present review addresses the analysis of dirofilariasis from the point of view of the episystem, analyzing the complex network of interactions established between biological components, climate, and factors related to human activity, as well as the different problems they pose. The progress of knowledge on human and animal dirofilariasis is largely due to the multidisciplinary approach. Nevertheless, different aspects of the disease need to continue being investigated and cooperation between countries and specialists involved should be intensified.

The Mitochondrial Genomes of the Zoonotic Canine Filarial Parasites Dirofilaria (Nochtiella) repens and Candidatus Dirofilaria (Nochtiella) hongkongensis Provide Evidence for Presence of Cryptic Species

Background

Cutaneous dirofilariosis is a canine mosquito-borne zoonosis that can cause larva migrans disease in humans. Dirofilaria repens is considered an emerging pathogen occurring with high prevalence in Mediterranean areas and many parts of tropical Asia. In Hong Kong, a second species, Candidatus Dirofilaria hongkongensis, has been reported. The present study aimed to compare mitochondrial genomes from these parasites and to obtain population genetic information.

Methods and Findings

Complete mitochondrial genomes were obtained by PCR and Sanger sequencing or ILLUMINA sequencing for four worms. Cytochrome oxidase subunit 1 sequences identified three as D. repens (all from Europe) and one as C. D. hongkongensis (from India). Mitochondrial genomes have the same organization as in other spirurid nematodes but a higher preference for thymine in the coding strand. Phylogenetic analysis was in contradiction to current taxonomy of the Onchocercidae but in agreement with a recent multi-locus phylogenetic analysis using both mitochondrial and nuclear markers. D. repens and C. D. hongkongensis sequences clustered together and were the common sister group to Dirofilaria immitis. Analysis of a 2.5 kb mitochondrial genome fragment from macrofilaria or canine blood samples from Europe (42), Thailand (2), India (1) and Vietnam (1) revealed only small genetic differences in the D. repens samples including all European and the Vietnam sample. The Indian C. D. hongkongensis and the two Thai samples formed separate clusters and differences were comparatively large.

Conclusion

Genetic differences between Dirofilaria spp. causing cutaneous disease can be considerable whereas D. repens itself was genetically quite homogenous. C. D. hongkongensis was identified for the first time from the Indian subcontinent. The full mitochondrial genome sequence strengthens the hypothesis that it represents an independent species and the Thai samples might represent another cryptic species, Candidatus Dirofilaria sp. ‘Thailand II’, or a quite divergent population of C. D. hongkongensis.

The mitochondrial genomes of the zoonotic parasite species Dirofilaria repens and Candidatus Dirofilaria hongkongensis were characterized and compared to the genomes of other filariae. The resulting phylogeny is largely in agreement with recent molecular data. C. D. hongkongensis was placed as a sister group to D. repens and both as a common sister to D. immitis. The large genetic difference between D. repens and C. D. hongkongensis further supports the hypothesis that both are distinct valid species. Two canine samples from Thailand that were diagnosed as D. repens are either from a C. D. hongkongensis population that is quite divergent from the Indian population or might represent another currently unrecognized species in the genus.

Development and Application of a Loop-Mediated Isothermal Amplification (LAMP) Approach for the Rapid Detection of Dirofilaria repens from Biological Samples

Dirofilariasis by Dirofilaria repens is an important mosquito vector borne parasitosis, and the dog represents the natural host and reservoir of the parasite. This filarial nematode can also induce disease in humans, and in the last decades an increasing number of cases have been being reported. The present study describes the first loop mediated isothermal amplification (LAMP) assay to detect D. repens DNA in blood and mosquitoes. Two versions of the technique have been developed and described: in the first, the amplification is followed point by point through a real time PCR instrument (ReT-LAMP); in the second, the amplification is visualized by checking UV fluorescence of the reaction mixture after addition of propidium iodide (PI-LAMP). The two variants use the same set of 4 primers targeting the D. repens cytochrome oxidase subunit I (COI) gene. To assess the specificity of the method, reactions were carried out by using DNA from the major zoonotic parasites of the family of Onchocercidae, and no amplification was observed. The lower limit of detection of the ReT-LAMP assay was 0.15 fg/μl (corresponding to about 50 copy of COI gene per μl). Results suggest that the described assay is specific, and its sensitivity is higher than the conventional PCR based on the same gene. It is also provide a rapid and cost-effective molecular detection of D. repens, mainly when PI-LAMP is applied, and it should be performed in areas where this emerging parasitosis is endemic.

Dirofilaria repens is a filarial nematode which mainly infests the dog, but humans may be occasionally infested, too. The spread of the parasite is mediated by a number of mosquitoes species, which are well recognized as vectors of D. repens. The majority of reports of the disease come from the European Countries, especially those along the Mediterranean basin, but in the last decade several cases have been recorded also from Asian and African Countries, and this led the scientific community to consider such parasitosis an emerging disease. To date, diagnosis is based the morphologic analysis of microfilariae, isolated from the blood of infected hosts, but this may be time-consuming and the identification of parasite requires specialized parasitologists. The here described approach, based on the loop-mediated isothermal amplification (LAMP), allows the detection of D. repens genomic DNA directly from the biological samples, and it may be easily and rapidly performed, producing unequivocal results in less than a hour. We also presented two versions of the assays. The first, a real-time LAMP, is characterized by a very high sensitivity but it requires an expensive real time PCR instrument, while the second, performed with the addition of propidium iodide, does not need such equipment, therefore being very affordable. This makes it suitable to be carried out in field and whenever expensive equipment or specialized personnel lacks.