Prevalence and molecular epidemiological data on Dirofilaria immitis in dogs from Northeastern States of India

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.

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.

Heartworm adulticide treatment: a tropical perspective

Dirofilaria immitis (the canine heartworm) is widespread in the tropics, with prevalence surpassing 30% in high-risk areas. In addition to the suitable climatic conditions that favour mosquito abundance and filarial larva development, there is low compliance with the recommended year-round use of preventives in these transmission hotspots. This represents a major concern, considering that melarsomine (first-line heartworm adulticide) is unavailable in several tropical countries, resulting in the so-called slow-kill protocol being the only available adulticide treatment option. In this article, the members of TroCCAP (Tropical Council for Companion Animal Parasites) review the current distribution of heartworm in the tropics and the availability of melarsomine, and discuss alternatives for the management of heartworm infections in dogs.

Filariasis in dogs brought to the Veterinary Teaching Hospital, University of Peradeniya, Sri Lanka

Dirofilariasis is the predominant emerging zoonotic filariasis in the world. The two most frequent filarial worms that infect dogs are Dirofilaria repens and Dirofilaria immitis. This study reports filariasis among dogs brought to the Veterinary Teaching Hospital (VTH) at the University of Peradeniya and signifies the first molecular characterization of D. repens, responsible for an emerging zoonotic filarial disease in Sri Lanka. Blood samples were collected and were morphologically analyzed using Modified Knott's Technique, followed by molecular analyses. The difference in filariasis prevalence among gender, breed, and age categories was analyzed using a chi-square test. Infection intensities were analyzed using the Mann-Whitney U test and the Kruskal Wallis test. The dogs were brought to the clinic for either vaccination and/or for a regular checkup, and most were sick having non-specific clinical signs. Among the 87 dogs tested, 27.6% were positive for Dirofilaria. Conventional PCR and bi-directional sequencing of genomic DNA of microscopically tested positive samples revealed that the species in Sri Lanka was D. repens. The infection was significantly higher in males (39.1%) than in females (14.6%; χ² = 0.447, p = 0.011), though it is not significant between puppies (age < 1 year) and adult dogs. More crossbred dogs were infected compared to older and purebred dogs. There was no difference in intensity of infection based on their gender, age, or breed. Sequences obtained from the current study were unique and were only 63% identical to those of D. repens reported from South India. The high number of Dirofilaria infections in domestic dogs indicates a potential reservoir for emerging human dirofilariasis cases in Sri Lanka. Thus, morphological and molecular diagnosis, along with epidemiological assessment of these zoonoses, is critical for the formulation of effective public health programs and control mechanisms.

Efficacy of ultrasound in diagnosis of dirofilariasis in dogs caused by Dirofilaria immitis

Ultrasonic diagnostics is a modern and effective method of laboratory testing of both animals and humans, used for estimation of overall state, and for detection of different pathologies in organs and systems. The aim of the present study was to establish the efficacy of ultrasonic diagnostics of dog dirofilariasis caused by Dirofilaria immitis parasitism, based on several indexes of invasion intensity. It was established that the number of D. immitis helminths found depended on the intensity indexes of microdirafilariasis invasion: using echocardiography, there were no helminths found under the index lower than 40 larvae/cm3. Under the index higher than that, we visualized 1–10 parasite individuals in the cavity of the right ventricle and right atrium, and at the tricuspid valve leaflets. It was established by the results of echocardiography of dogs invaded by D. immitis that the level of invasion intensity impacts significantly on the animals’ heart structure and function, and on their intracardiac hemodynamics. It was proved that under increase of microfilaria number in the blood, heart function deteriorates. Under the invasion intensity lower than 40 larvae/cm3, the changes were characterized by a slight increase in thickness of the posterior wall of the left ventricle in diastole, aorta diameter, left atrium and pulmonary artery (by 6.2%). Under the invasion intensity of 40–60 larvae/cm3, the deterioration in heart structure and function was followed by thickening of the interventricular septum in diastole, posterior wall of the left ventricle in diastole (by 5.6%), increase in ejection fraction index (by 7.0%), widening of aorta root, pulmonary artery, diameter of the left ventricle (by 21.4%), and with increase in indexes of ratio between diameters of the left ventricle and pulmonary artery, and aorta (by 15.6%). Signs of hemodynamic deterioration were established in sick animals, which was characterized by increase of blood speed in the tricuspid valve (by 33.7%), and its decrease in the pulmonary artery (14.1%). Under the invasion intensity higher than 60 larvae/cm3, the aforementioned indexes changed even more significantly. We observed thickening of the posterior wall of the right ventricle in diastole, decrease of the end-systolic size of the left ventricle (by 13.0%), blood speed increase in the aorta and mitral valve (by 12.2%). The obtained results show the necessity of echocardiographic testing of dogs with cardiac dirofilariasis, which allows effective proof of the diagnosis and also helps to understand the overall state of the animal more deeply and to provide it with the appropriate symptomatic cure.

Prevalence and molecular characterization of Dirofilaria immitis in road killed canids of northern Iran

Background

Dirofilaria immitis is a mosquito-borne filarial nematode, which infects primarily wild and domestic canids, causing cardiopulmonary dirofilariasis. The aim of the present study was to determine the prevalence and characterize molecular features of D. immitis in road killed canids, northern Iran.

Methods

The carcasses of 53 road killed canids including 18 dogs (Canis familiaris), and 35 golden jackals (C. aureus) were necropsied in both Mazanderan and Guilan provinces, northern Iran. The molecular analyses were conducted based on the cytochrome oxidase (Cox) 1 and 18S ribosomal RNA (rRNA) genes.

Results

The heartworm infection was found in 55.6% of dogs and 22.9% of jackals. Our study revealed significantly higher prevalence of D. immitis in dogs compared to jackals (P = 0.031). The prevalence of D. immitis was no statistically significant between males and females in both dogs and jackal (P > 0.05). Comparison of the Cox1 gene sequences with available data in the GenBank illustrated 100% similarity with D. immitis isolates from different hosts in European, Asian, and South American continents. Moreover, the 18S rRNA gene sequences showed 100% identity with dog isolates from Japan and French Guiana.

Conclusions

This study confirms the high prevalence of D. immitis in dogs and jackals of northern Iran. Developing control programs to prevent transmission of the disease is necessary for dogs and humans in the study areas.

Differential diagnosis of Dirofilaria immitis nematodes (Nematoda, Onchocercidae)

Heartworm disease is a widespread anthropozoonotic disease of carnivorous animals, as well as humans. It is caused by nematodes belonging to the suborder Filariata, family Onchocercidae, genus Dirofilaria. There are about 26 species of heartworms in nature, the most common and pathogenic species in dogs and cats in most countries is Dirofilaria immitis Leidy, 1856. Mature helminths parasitize in the right ventricle and pulmonary arteries, large veins of animals and cause heart and vascular disorders, and death. Therefore, the aim of the study was to investigate the features of morphological and metric structure of adult nematodes of D. immitis isolated from the heart of dogs. Morphological studies have shown that in males the most characteristic differential features are the presence of two unequal spicules, specifically positioned relative to each other, as well as well-defined preanal and less pronounced adanal and postanal papillae. In female heartworms, the characteristic morphological features are the shape and location of the vulva. There is a difference in the structure of the esophagus in males and females. In females, the anterior and posterior parts of the esophagus are well expressed, with enlargements, in males these divisions are not pronounced. To increase the efficiency of species identification of D. immitis nematodes, it is proposed to use metric parameters that characterize the overall body size, body and width of esophagus in different areas, length of esophagus, and the location of the nerve ring. In males, 11 indicators are also suggested that characterize the size of the spicules and the location of the cloaca. In females, seven additional parameters are pointed out that characterize the location of the vulva, anus and body width in these areas. The obtained data expand the already existing data on the peculiarities of the morphological structure of parasitic nematodes of the species D. immitis and their identification.

The global status of Dirofilaria immitis in dogs: a systematic review and meta-analysis based on published articles

Dirofilaria immitis is a parasitic filarial nematode responsible for heartworm disease in domestic as well as wild canines and felines and pulmonary or cutaneous infections in humans. This systematic review and meta-analysis aimed to evaluate the status of D. immitis in dogs based on available literature. Four English language databases (ISI Web of Science, Scopus, PubMed and Science Direct) containing data on D. immitis prevalence in dogs were thoroughly searched resulting in the inclusion of 193 studies. The findings revealed that the pooled and weighted prevalence of D. immitis infection in dog population based on published papers throughout the world was 10.91% (95% CI=10.18-11.65). In addition, subgroup analysis based on meta-regression revealed that a significant difference between the pooled and weighted prevalence of D. immitis in dogs and country (β =0.14, P=0.049). Given the relatively high prevalence of D. immitis infection in dogs and its adverse effects, it is suggested that to perform more research on the prevention and control of dirofilariasis infection in dogs worldwide.

Filarial worms: a systematic review and meta-analysis of diversity in animals from Iran with emphasis on human cases

Current systematic review and meta-analysis demonstrate the prevalence reports of filariasis in animals in Iran along with human cases. Studies were screened, relevant papers were selected and the random-effect model was used by forest plot with 95% confidence interval (CI). Of 17 records of human case-reports, particularly from Khuzestan province (5 cases), Dirofilaria repens was the most detected parasite (10 cases) with higher involvement of the right eye (7 cases) than other organs. Eleven animal species were reported to be parasitised by filarioids in Iran. The prevalence of Dirofilaria immitis in canids was 14.69% (95% CI: 10.33-19.67), with highest rates (20.92%; 95% CI: 13.84-29.03) in free-ranging dogs. Male (10.07%; 95% CI: 5.10-16.47) and more than 1-year old (20.77%; 95% CI: 8.66-36.42) dogs were more likely to be found infected. The frequency of other filarioids of zoonotic interest was: Acanthocheilonema reconditum in dogs 2.15% (95% CI: 0.71-4.33), Dipetalonema evansi in camels 10.16% (95% CI: 4.73-17.34), Onchocerca cervicalis in horses 3.63% (95% CI: 1.44-6.75%) and Onchocerca fasciata 16.57% (95% CI: 10.12-24.24%) in camels. Still, our knowledge on parasitic filariae in Iran is limited and more investigation is needed in both human and animal populations.

Detection of Dirofilaria immitis using microscopic, serological and molecular techniques among dogs in Cabo Frio, RJ, Brazil

Abstract Heartworm disease is a health problem for dogs and cats, especially in tropical and subtropical coastal regions of the world. Some studies have compared the efficacy of the diagnostic techniques used to detect this parasitosis. Therefore, the aim of this study was to compare parasitological optical microscopy (POM), serological and molecular techniques for diagnosing canine heartworm infection. Samples were collected between July 2015 and April 2016 from 103 dogs in Cabo Frio, RJ, Brazil. The wet fresh blood, thick smears, thin smears and modified Knott’s test were used to detect microfilariae. ELISA (Snap™ 4Dx ® IDEXX) was used to detect antigens and the polymerase chain reaction (PCR) was used to detect DNA and enable sequencing for species differentiation and confirmation. 19.4% of samples were positive according to microscopy. Through PCR, 15.5% of the total were positive. Using ELISA, the positivity rate was 29.1%. Occult heartworm infection was detected in 11.6% of the samples. ELISA sensitivity was shown to be higher than PCR or microscopy (P = 0.001). Sequencing of samples confirmed the presence of Dirofilaria immitis and Acanthocheilonema reconditum . ELISA was more effective for serological diagnosis canine heartworm and should be used in clinical and epidemiological studies.

Morphological Description, Phylogenetic and Molecular Analysis of Dirofilaria immitis Isolated from Dogs in the Northwest of Iran

BACKGROUND

Dirofilariasis is a globally distributed arthropod-borne parasitic disease of mainly canids and felids. We evaluated to extend the knowledge of morpho-molecular characteristics and outer ultrastructure of Dirofilaria immitis isolated from Northwest of Iran.

METHODS

Overall, 67 filarial worms including 41 females and 26 males parasites were collected from the cardiovascular system of the 43 stray dogs in Meshkinshar, Ardebil Province, Northwest of Iran in 2017, and subjected to light and scanning electron microscopy (SEM) as well as carmine alum staining for morpho-molecular and identification. Molecular methods were used for confirmation of morphological findings by sequencing of Cyto-chrome c oxidase subunit I (cox1) gene.

RESULTS

The partial DNA sequencing of cox1 gene of adult parasites showed considerable homology and close proximity to the previously isolated from Kerman and Meshkinshahr, Iran. The lowest genetic variation and the highest intra-species variability was found in D. immitis and Dirofilaria repens, respectively. No similarity was identified between D. immitis nucleotide sequence and Wolbachia species as its endosymbiont bacteria.

CONCLUSION

The SEM technique is an excellent tool for differential recognition of the parasite surface morphology and molecular techniques could differentiate and identify Dirofilaria spp.

The prevalence of Dirofilaria immitis and D. repens in the Old World

Dirofilaria immitis and D. repens are endemic throughout Europe and southern eastern regions of Asia and reported with increasing frequency in Africa. Nevertheless, the increased awareness of veterinary practitioners, even in countries where the prevalence is low, has led to a decrease D. immitis prevalence in dogs, especially in previously endemic/hyper-endemic areas. Prevalence has significantly increased, however, in areas where heartworm has apparently spread more recently, such as Central and North Eastern Europe. Furthermore, autochthonous cases have been observed in Siberia. Low seroprevalence has been reported in Croatia, while in Romania it has reached 14%. In Greece, the prevalence ranges between 0.7% and 25% whilst in Turkey is 0-18%. Data for canine dirofilariosis in Africa is scarce, and most are case reports. Overall, the dominant species is Achanthocheilonema dracunculoides, although both D. immitis and D. repens have been reported from some countries. In the Far East, the prevalence ranges from 2% to 15% in northeastern of China. In Hong Kong a novel species has been found in dogs and humans (Candidatus Dirofilaria hongkongensis). In India, the prevalence ranges from 4.7%-29.5% in Northeastern states. The main factors that have influenced the spreading of Dirofilaria infections are the climate changes and the introduction of new, invasive, competent mosquito species such as Aedes albopictus and Ae. koreicus. Other factors include relocation and insufficient prevention in dogs, manly in the new areas of colonization. Feline heartworm infection has been diagnosed in every European country when diagnosed either by the Knott test or by serology for circulating antibodies and antigens of the parasite. However, prevalence is much lower than in dogs. In spite of the continuing spreading of heartworm infection, D. repens is the main concern in Europe, mostly for physicians, while the infection is nearly always asymptomatic in dogs. The infection is spreading from Portugal to the Southeastern regions of Finland and Siberia, and in some areas its prevalence overlaps that of D. immitis. Many reasons make more difficult the control of D. repens than D. immitis: the frequent lack of clinical symptoms of suspicion, the specific diagnosis being possible only by blood examination and the inefficacy of some macrocyclic lactones.

Dirofilaria hongkongensis - A first report of potential zoonotic dirofilariosis infection in dogs from Tamil Nadu

Dirofilariosisis, is a mosquito borne anthropo-zoonotic disease caused by the filarial nematodes of the genus Dirofilaria. The current paper reports a species of Dirofilaria, which has not been recorded in Tamil Nadu, in addition to differentiating it from the existing species of Dirofilaria spp. through morphological and molecular techniques. Micrometry of the microfilaria detected by Knott's technique as well as in Giemsa stained blood smears revealed that the length was on an average 280 μm to 310 μm whereas the width was 5 to 8 μm. The microfilariae were unsheathed with blunt heads and tapering tails. For molecular confirmation, the blood sample was subjected to genomic DNA isolation. PCR amplification using specific primers for D. hongkongensis was carried out using thermal cycler with the isolated genomic DNA as template. Molecular analyses revealed the band size of about 230 bp which confirmed the presence of D. hongkongensis. Phylogenetic analysis was done using UPGMA and MLM method. Dirofilaria is recognized as a zoonotic entity throughout the world, and dirofilariasis should be considered an emerging zoonosis in southern India. The control of ubiquitous mosquito population is essential to prevent the transmission of microfilaria from animals to arthropods and from arthropods to humans.

Molecular investigation of vector-borne parasitic infections in dogs in Northeast India

BACKGROUND

Information on the status of vector-borne pathogens among canines in Northeast India is lacking, particularly for the states of Mizoram and Tripura close to the Myanmar border. Blood samples collected from 130 dogs, 80 from Mizoram and 50 from Tripura, were examined in this study.

METHODS

Polymerase chain reaction (PCR) was performed for filariid worms, Babesia, Hepatozoon, Ehrlichia and Anaplasma spp. and DNA sequencing was then carried out to identify pathogens at the species level.

RESULTS

Vector-borne pathogens were detected in 52% (68/130) of the sampled dogs. The most prevalent pathogen was Babesia gibsoni detected in 56/130 (43%) dogs, followed by Hepatozoon canis in 50/130 (38%), Anaplasma platys in 4/130 (3%), B. vogeli in 4/130 (3%), Acanthochelionema reconditum in 3/130 (2%) and Dirofilaria immitis in 2/130 (2%). Forty-four dogs (34%) were co-infected with two or more pathogens. The most common co-infection observed was with B. gibsoni + H. canis (34%) followed by triple-infection with B. gibsoni + H. canis + A. platys (3%), and B. gibsoni + B. vogeli + H. canis (3%). The infection rate was higher in Mizoram (58%) than in Tripura (44%).

CONCLUSIONS

The high prevalence of infection in the studied dog population, especially with B. gibsoni and H. canis, indicates that vector-borne diseases pose a serious threat to the health of dogs in this area of Northeast India. Prevention of vector-borne diseases by using topical acaricides and heartworm preventative treatment would be of great benefit for reducing the threat of vector-borne diseases in the study area.

Whether Dirofilaria repens parasites from South India belong to zoonotic Candidatus Dirofilaria hongkongensis (Dirofilaria sp. hongkongensis)?

The canine and zoonotic dirofilarioses are arthropod-borne parasitic infections caused by nematodes of the genus Dirofilaria, infecting canines, felines and humans throughout the world. Dirofilaria repens was considered as the most common cause of human dirofilariosis in Kerala. In the present study, molecular characterization of Dirofilaria isolates causing dirofilariosis in humans, dogs and jackal from Kerala, South India was undertaken by performing sequence and phylogenetic analysis based on cytochrome oxidase subunit I (COI) gene. The live worms from swellings/ nodules in subconjunctiva or subcutaneous tissue or scrotum were recovered from humans (n = 3), dogs (n = 4) and one jackal. The PCRs targeting a repetitive fragment, 18S rRNA and COI genes yielded products of ~246 bp, ~875 bp and ~350 bp respectively in all the samples. The sequence analysis of 18S rRNA gene revealed the closest identity (98 to 99%) with an already published sequence of D. repens isolated from a human in Japan. However, based on the sequence and phylogenetic analysis of partial sequences of COI gene, the Dirofilaria infecting both animals (dogs, jackal) and humans native to Kerala, South India were identified as genetically conserved and closely related to Dirofilaria sp. hongkongensis. Hence, the results of the present study suggested the existence of Candidatus Dirofilaria hongkongensis (Dirofilaria sp. hongkongensis) in Kerala, South India causing zoonotic filariosis in canines and humans.

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.

Canine vector-borne pathogens in semi-domesticated dogs residing in northern Cambodia

Background

In Southeast Asia, the canine vector-borne pathogens Babesia spp., Ehrlichia canis, Anaplasma platys, Hepatozoon canis, haemotropic mycoplasmas and Dirofilaria immitis cause significant morbidity and mortality in dogs. Moreover, dogs have also been implicated as natural reservoirs for Rickettsia felis, the agent of flea-borne spotted fever, increasingly implicated as a cause of undifferentiated fever in humans in Southeast Asia. The objective of this study was to determine the prevalence and diversity of canine vector-borne pathogens in 101 semi-domesticated dogs from rural Cambodia using molecular diagnostic techniques.

Results

The most common canine vector-borne pathogens found infecting dogs in this study were Babesia vogeli (32.7 %) followed by Ehrlichia canis (21.8 %), Dirofilaria immitis (15.8 %), Hepatozoon canis (10.9 %), Mycoplasma haemocanis (9.9 %) and “Candidatus Mycoplasma haematoparvum” (2.9 %). A high level of co-infection with CVBD agents (23.8 %) was present, most commonly B. vogeli and E. canis. Naturally occurring R. felis infection was also detected in 10.9 % of dogs in support of their role as a natural mammalian reservoir for flea-borne spotted fever in humans.

Conclusions

This study reports for the first time, the prevalence and diversity of CVBD pathogens in dogs in Cambodia. In total, five species of CVBD pathogens were found infecting semi-domesticated dogs and many were co-infected with two or more pathogens. This study supports the role of dogs as natural mammalian reservoirs for R. felis, the agent of flea-borne spotted fever in humans.