The prevalence of Dirofilaria immitis in Gran Canaria, Canary Islands, Spain (1994-1996)

Change in the Distribution Pattern of Dirofilaria immitis in Gran Canaria (Hyperendemic Island) between 1994 and 2020

Dirofilariosis is a zoonotic disease that mainly affects dogs and cats, with a high risk to public health. The island of Gran Canaria (Spain) has been shown to be a hyperendemic area of infection and, therefore, a model for studying the evolution of the disease. The objective of this study was to track the prevalence and distribution of heartworm in dogs, cats, and residents of Gran Canaria from 1994 to 2020, using published and unpublished data. Blood samples from 5841 dogs, 1203 cats, and 1604 humans were collected in the years analyzed, considering geographical and isoclimatic factors. In 1994, a prevalence of Dirofilaria immitis of 67.02% in dogs was reported, while in 2020 it was 15.81%. In cats, the seroprevalence in 2010 was 33.03%, compared to 17.20% in 2020. The incidence of D. immitis in humans in 2008 was 18.66%, while in 2020 it was 8.27%. For all study groups, temperate cold zone (TC) and temperate mild zone (TM) climates had the highest prevalence. Throughout these 20 years, the prevalence of heartworm disease has decreased. Despite this, it continues to be a hyperendemic island. This study highlights the importance of using the "One Health" perspective and the risks of contagion of the disease.

Assessment Heartworm Disease in the Canary Islands (Spain): Risk of Transmission in a Hyperendemic Area by Ecological Niche Modeling and Its Future Projection

Heartworm disease is a vector-borne zoonotic disease caused by Dirofilaria immitis. The Canary Islands (Spain), geolocated close to the coast of Western Sahara, is an archipelago considered hyperendemic where the average prevalence in domestic dogs is high, heterogeneous, and non-uniform. In addition, Culex theileri has been reported as a vector of the disease on two of the most populated islands. Our aim was to develop a more accurate transmission risk model for dirofilariosis for the Canary Islands. For this purpose, we used different variables related to parasite transmission; the potential distribution of suitable habitats for Culex spp. was calculated using the ecological niche model (ENM) and the potential number of generations of D. immitis. The resulting model was validated with the geolocation of D. immitis-infected dogs from all islands. In addition, the impact of possible future climatic conditions was estimated. There is a risk of transmission on all islands, being high in coastal areas, moderate in midland areas, and minimal in higher altitude areas. Most of the dogs infected with D. immitis were geolocated in areas with a high risk of transmission. In 2080, the percentage of territory that will have been gained by Culex spp. is small (5.02%), although it will occur toward the midlands from coastal areas. This new model provides a high predictive power for the study of cardiopulmonary dirofilariosis in the Canary Islands, as a hyperendemic area of the disease, and can be used as a tool for its prevention and control.

The seroprevalence of canine dirofilariosis in dogs in the eastern coastal areas of China

Background and objectives

The present study was carried out to assess the presence of canine Dirofilaria immitis infection in pet dogs in China.

Materials and methods

From October 2018 to November 2019, a total of 216 sera were collected from pet hospitals in Shandong, Jiangsu, Shanghai, Zhejiang, and Fujian regions of Eastern China. The sera were tested by using a commercial canine heartworm antibody ELISA test kit.

Results

70.8% of the pets had significant clinical symptoms resembled to heartworm infection; the overall dirofilariosis positivity found was 12.5% (27/216); Significant positive rates differences were observed between symptomatic and asymptomatic dogs (P < 0.05) (i.e. 15.7% and 4.7% respectively).The prevalence of infection in Shandong Province (15.5%) was the highest among the surveyed areas, but the difference among the geographic regions was not statistically significant (P > 0.05). Furthermore, the prevalence detected in summer (28.2%) was significantly higher than in other seasons (P < 0.05). In addition, no significant difference was observed between male and female sex (P > 0.05).

Conclusions

Altogether, these results suggest that an epidemic of dirofilariosis exists in eastern coastal China, as such preventive measures should be taken to control the spread of dirofilariosis to reduce the risk of human and pet infection with heartworm.

New distribution patterns of Dirofilaria immitis in Italy

In recent decades, the number of autochthonous cases and foci of Dirofilaria immitis in dogs from southern regions has increased considerably, suggesting that the distribution of the species is not limited to northern Italian regions. This epidemiological picture emerges from case reports or studies in specific locations where outbreaks of heartworm disease have occasionally been reported together with the presence of mosquito vectors. To obtain a more comprehensive picture of the current distribution of D. immitis in southern Italy, a multicenter cross-sectional survey of canine filariasis was conducted. Owned and sheltered dogs (n = 1,987) were included in the survey regardless their breed, attitude and/or sex. All included dogs were older than 1 year and had no history of chemoprophylactic treatment against filarioses. A blood sample was collected from enrolled dogs and screened by modified Knott's test and, when positive, tested using D. immitis specific ELISA rapid test (SNAP 4DX, IDEXX). The overall microfilaremia prevalence was 17% (n = 338) being single-species infection (92.6%) more common that mixed (7.4%). Remarkably, D. immitis was the most frequent species detected with an overall prevalence of 11.4% (n = 227), followed by Dirofilaria repens (n = 74; 3.7%), and Acanthocheilonema reconditum (n = 12; 0.6%). Sheltered dogs were significantly more infected by D. immitis, as well as mongrel dogs and animals housed in rural areas. Data here reported indicate that D. immitis is largely present in southern Italy, raising awareness about the necessity of proper screening and chemoprophylactic treatments in exposed animals.

Seropositivity of main vector-borne pathogens in dogs across Europe

BACKGROUND

Canine vector-borne disease (CVBD) has been an area of increasing interest in Europe over the last few decades, and there have been changes in the prevalence and distribution of many of these diseases. Monitoring CVBD infections in Europe is often done by individual countries, but aggregated data for the European countries are helpful to understand the distribution of CVBDs.

METHODS

We used an extensive retrospective database of results from point-of-care rapid enzyme-linked immunosorbent assay (ELISA) tests on dogs across Europe to identify distribution and seropositivity in animals tested for selected CVBDs (Anaplasma spp., Ehrlichia spp., Borrelia burgdorferi, Leishmania spp., and Dirofilaria immitis) from 2016 through 2020. Geographic distribution of positive tests and relative percent positive values were mapped by the Nomenclature of Territorial Units for Statistics classification for regions with sufficient test results for reporting.

RESULTS

A total of 404,617 samples corresponding to 1,134,648 canine results were available from dogs tested in 35 countries over the 5-year study period. Over this period the number of test results per year increased whereas test positivity decreased. Leishmania spp. had the largest increase in total test results from 25,000 results in 2016 to over 60,000 results in 2020. Test positivity for Leishmania spp. fell from 13.9% in 2016 to 9.4% in 2020. Test positivity fell for Anaplasma spp. (7.3 to 5.3%), Ehrlichia spp. (4.3 to 3.4%), and Borrelia burgdorferi (3.3 to 2.4%). Dirofilaria immitis test positivity trended down with a high of 2.7% in 2016 and low of 1.8% in 2018. Leishmania spp. test positivity was highest in endemic areas and in several non-endemic countries with low numbers of test results. Co-positivity rates were significantly higher than expected for all pathogen test positive pairs except for Ehrlichia spp. with Borrelia burgdorferi and D. immitis with Borrelia burgdorferi.

CONCLUSIONS

This study represents the largest data set on CVBD seropositivity in Europe to date. The increase in the number of test results and decreasing test positivity over the study period may reflect changes in testing behavior and increased screening of healthy animals. The Europe-wide mapping of CVBD provides expected test positivity that can help inform veterinarians' decisions on screening and improve prevention and identification of these important, sometimes zoonotic, diseases.

Integration of Microscopic, Serologic and Molecular Techniques for Detection of Filarial Parasites in Dogs in Malaysia

PURPOSE

Canine filariosis in domestic dogs caused by several species of filarids is an emerging vector-borne disease and the spread of this disease remains a global veterinary and public health concern. However, information regarding these filarids and their epidemiological patterns remains scarce in Malaysia. The present study aimed to determine the infection rate and associated risk factors of filarial parasites in dogs in Malaysia.

METHODS

A total of 399 dog blood samples were collected from veterinary hospitals and animal shelters in Malaysia to determine the infection rate and associated risk factors via a combination of microscopic, serologic and molecular diagnostic techniques.

RESULTS

Two species of canine filariae identified in this study were Dirofilaria immitis (6.5%) and Brugia pahangi (1.3%), and their infections were associated with cross breed, medium size and short hair (p < 0.05).

CONCLUSIONS

A new pair of primers was developed to complement the recovery of the 12S rRNA gene fragment of filarial parasites. This study represents the first molecular evidence of B. pahangi in dogs in Malaysia.

Updates on the distribution and host spectrum of Dirofilaria repens in the Republic of Uzbekistan

Among the zoonotic mosquito-borne nematodes, Dirofilaria repens and Dirofilaria immitis (Spirurida, Onchocercidae) are highly significant from a public health perspective. While D. immitis is also of major veterinary concern, D. repens is regarded as less pathogenic for carnivores, but is the main causative agent of human dirofilariosis throughout the Old World. In the Republic of Uzbekistan, recent data refer exclusively to D. immitis infection in domestic and wild carnivores, while the current prevalence and distribution of D. repens remain unknown. Between 2015 and 2021, a total of 559 domestic and wild carnivore carcasses were collected and examined by necropsy. All subcutaneous nematodes were collected and identified morphologically. The overall prevalence of D. repens infection was of 11.03% in domestic dogs, Canis familiaris, and 9.29% in wildlife hosts: golden jackals, Canis aureus (11.76%), wolves, Canis lupus (9.09%), red foxes, Vulpes vulpes (9.23%), and jungle cats, Felis chaus (7.14%). Additionally, a human case of subcutaneous D. repens infection was also documented. The present study represents the first recent assessment of the occurrence of the zoonotic filarioid D. repens in the Republic of Uzbekistan. It indicates a wide distribution in domestic dogs and four species of wildlife hosts throughout the country, raising awareness on the public health risks associated with this parasite.

Dirofilariosis caused by Dirofilaria immitis in the south of Kerman province, Iran

BACKGROUND

Dirofilariosis due to Dirofilaria immitis is endemic in various areas of Iran. Domestic dogs are the main reservoirs and represent a major potential infection source for the vector and humans.

OBJECTIVE

This study aimed to explore the prevalence of dirofilariosis due to D.immitis and its public health importance in domestic dogs in the Jiroft district, south of Kerman province, Iran, by serological and parasitological methods.

METHODS

This descriptive study was carried out as a cross-sectional investigation. A questionnaire was completed for 100 domestic dogs from May 2017 to February 2018 and recorded their age, sex, and clinical features. Also, we used enzyme-linked immunosorbent assay (ELISA) to identify antigens of heartworms in the bloodstream, with 98% sensitivity and 100% specificity, and parasitological techniques (Knott's test) to detect microfilariae in canine blood in Jiroft district, south of Kerman province, Iran.

RESULTS

Overall, 10 (10%) and 4 (4%) domestic dogs were infected as confirmed by ELISA and modified Knott's tests, respectively. The rate of occult infections in the ELISA test than Knott's test was 60%. No significant difference was found between dirofilariosis and gender. In contrast, there was a significant difference between dirofilariosis infection and age (P < 0.05).

CONCLUSION

The present findings could help understand the epidemiological aspects of D. immitis for future control programs and take appropriate preventive and therapeutic strategies against the disease.

Hyperendemic Dirofilaria immitis infection in a sheltered dog population: an expanding threat in the Mediterranean region

A study on the occurrence of Dirofilaria immitis and its vectors was carried out in order to assess the prevalence of the disease in dogs in previously non-endemic areas of southern Italy. Blood samples (n = 385) and mosquitoes (n = 1540) were collected in two dog shelters and analysed by Knott's test and duplex real-time PCR, respectively. Dirofilaria immitis was the most prevalent filarioid (44.2%), while Culex pipiens was the most prevalent mosquito species (68.8%). This high prevalence of D. immitis infection confirms this location as one of the most hyperendemic foci of dirofilariosis in Europe.

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.

Cross-sectional survey of health management and prevalence of vector-borne diseases, endoparasites and ectoparasites in Samoan dogs

OBJECTIVE

To determine the prevalence of selected canine vector-borne diseases (Leishmania infantum, Anaplasma spp., Ehrlichia canis, Borrelia burgdorferi and Dirofilaria immitis) and endo- and ectoparasites in Samoan dogs presenting for surgical sterilisation and to report on the general health management of the dogs.

METHODS

This study was a prospective serological cross-sectional survey. Management data were obtained for 242 dogs by interview with their owners. Blood samples were collected from 237 dogs and screened for the canine vector-borne diseases using point-of-care qualitative ELISA assays. Anaplasma spp. positive samples were screened by PCR and sequenced for species identification. Rectal faecal samples were collected from 204 dogs for faecal flotation and immunofluorescent antibody tests were performed for Giardia and Cryptosporidium spp. on a subset of 93 faecal samples. The skin and coat of 221 dogs were examined for presence of ectoparasites.

RESULTS

The D. immitis antigen was detected in 46.8% (111/237) of dogs. Seroprevalence of Anaplasma spp. was 8.4% (20/237); A. platys was confirmed by PCR. Prevalence of hookworm was 92.6% (185/205) and Giardia was 29.0% (27/93). Ectoparasites were detected on 210/221 (95.0%) of dogs examined and 228/242 dogs (94.2%) had previously never received any preventative medication.

CONCLUSIONS

There was a very high prevalence of D. immitis, hookworm and external parasites in Samoan dogs, and prophylactic medication is rarely administered. This is the first report confirming A. platys in Samoa and the South Pacific islands. The public health implications of poor management of the dogs should be considered and investigated further.

Seroprevalence of Dirofilaria immitis in Cats from Liaoning Province, Northeastern China

The present study was performed to investigate the seroprevalence and risk factors for Dirofilaria immitis infection in cats from Liaoning province, northeastern China. From October 2014 to September 2016, sera of 651 cats, including 364 domestic cats and 287 feral cats (332 females and 319 males) were assessed. They were tested for the presence of D. immitis antigen using SNAP Heartworm RT test kit. In this population, the average prevalence was 4.5%. Age and rearing conditions (feral or domestic) were found to be associated with the prevalence of D. immitis. The prevalence was significantly higher in feral cats compared with domestic cats (8.4% vs 1.4%, P<0.01). There was no significant difference between males and females (4.7% vs 4.2%, P>0.05), but older cats (≥3 years old) showed a statistically higher prevalence compared with younger cats (<3 years old) in feral populations (16.8 vs 2.4%, P<0.01), while the difference between the age groups was not statistically significant in domestic cats (2.4% vs 0.51%, P>0.05), all these results suggest that outdoor exposure time may be one of the most important factors for D. immitis prevalence in cats. Results reveal that D. immitis are prevalence in domestic and feral cats in northeastern China, which indicates that appropriate preventive measures should be taken to decrease the incidence of feline heartworm disease in Liaoning province, northeastern China.

Heterogeneous distribution of Dirofilaria immitis in dogs in St. Kitts, West Indies, 2014-2015

In the Caribbean region, Dirofilaria immitis (heartworm) has been detected on almost all of the islands. While it is assumed to be endemic throughout the region, there is a lack of baseline data from the Leeward Islands (north-east of the Caribbean region). The objective of this study was to estimate the prevalence and the spatial distribution of heartworm disease in dogs on St. Kitts, a small 174km² island which is part of the Leeward Islands. A cross-sectional study was conducted in 2014 with 100 dogs tested using a commercial antigen test. Dogs were from all regions of the island except the southeastern region, which differs socio-economically from the rest of the island. Heartworm was not detected in these 100 dogs. To complete the survey, in 2015, fifteen dogs from the southeast region were tested, eight of which were positive for heartworm. Prevalence was estimated at 7.0% (95% confidence interval: 4.6-11.6). Data from two other sources were added to complete the report: data from dogs enrolled in a free spay and neuter program and tested against heartworm (164 dogs with 3 positive for heartworm), and the data from positive dogs diagnosed at the Ross University Veterinary Clinic in 2014 and 2015 (3 dogs). Most of the heartworm positive dogs (10/14) lived in a delimited area in the southeast of the island. These results indicate an overall low prevalence of Dirofilaria immitis in St. Kitts, lower than that observed in the other Caribbean islands. Heterogeneity in the spatial distribution of the parasite was observed, with the majority of cases residing in the southeast of the island. Previous spatial models focused on the spread of the parasite over large geographical areas and long distances, but not within a restricted area. Our results indicate the presence of local factors which may have limited spread of the disease over short distances. Further studies are needed to understand this markedly heterogeneous distribution.

Molecular survey of Dirofilaria immitis and Dirofilaria repens by new real-time TaqMan® PCR assay in dogs and mosquitoes (Diptera: Culicidae) in Corsica (France)

Dirofilaria immitis and D. repens are filarioid nematodes of animals and humans, transmitted by the bite of infected mosquitoes. Domestic and wild canids are a major natural host and reservoir for these parasites. In this study, we designed a duplex real-time PCR protocol targeting the mitochondrial cytochrome c oxidase subunit I (COI) gene, detecting both D. immitis and D. repens using two primer pairs and two Dirofilaria-specific hydrolysable probes. The sensitivity and specificity of the primers and probes were tested in both experimental and naturally infected samples. The detection limits of this assay were evaluated using plasmid DNA from D. immitis and D. repens. No cross-reaction was observed when testing this system against DNA from other filarial nematodes. The detection limit of the real-time PCR system was one copy per reaction mixture containing 5μl of template DNA. Field application of the new duplex real-time assay was conducted in Corsica. The prevalence rate of D. immitis was 21.3% (20/94) in dogs. In a locality where most dogs with Dirofilaria spp. infection were found, D. immitis and D. repens were detected in 5% (20/389) and 1.5% (6/389) of the Aedes albopictus population, respectively. These results suggest that this sensitive assay is a powerful tool for monitoring dirofilariosis in endemic or high risk areas.

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

The aim of the present study was to determine the prevalence of Dirofilaria immitis in stray, pet, and working dogs (n = 413, 266, and 103, resp.) from Guwahati (Assam) and Aizawl (Mizoram), areas located in two Northeastern States of India. Diagnostic methods applied were microscopy (wet film and Knott's concentration technique), immunological test (Ag ELISA by SNAP 4Dx ELISA kit), and molecular tools (polymerase chain reaction and sequencing), which evidenced 11.38, 18.03, and 13.93% of positive animals, respectively. No significant differences were observed by area (18.23% versus 17.68%) nor by sex (18.1% versus 17.9%), whereas stray dogs proved more infected than other groups (P < 0.05). ELISA test evidenced an overall 22.69% of occult infections, mainly in working dogs (60%), and molecular techniques detected Dirofilaria (Nochtiella) repens in 4 stray dogs from Guwahati. Characterization of D. immitis isolates for ITS-2 region showed close identity with South Asian isolates.

Prevalence of canine heartworm (Dirofilaria immitis) disease in dogs of central Portugal

The aim of the present study was to determine the prevalence and risk factors concerning Dirofilaria immitis infection in dogs from Figueira da Foz, located in the central region of Portugal. In the period between November 2009 and January 2011, 304 blood samples were obtained from dogs over 1 year of age, with no previous history of heartworm prevention or diagnosis. Every blood sample was analyzed using varied laboratory techniques (direct microscopic evaluation of a fresh blood sample, the modified Knott technique, and the ELISA antigen detection test - IDEXX Snapp®). In the samples in which microfilaremia was detected, a histochemical technique using acid phosphatase staining was applied to identify the species of microfilariae. A total prevalence of 27.3% (83 out of 304) was found. We also found that 73.5% of all positive cases (61 out of 83) were microfilaremic, and 26.5% were occult infections (22 out of 83). By means of a histochemical technique Dirofilaria immitis was identified in 96.7% of microfilaremic samples. A multivariate model allowed us to identify the following risk factors for the presence of heartworm disease: age between 4 and 9 years, dogs living in a rural environment, large breed dogs, and living outdoors. This study shows for the first time the high prevalence of heartworm disease in a central area of Portugal and emphasizes the importance of systematic screening for this disease, as well as the need to prevent it in dogs in this area.

Geo-environmental model for the prediction of potential transmission risk of Dirofilaria in an area with dry climate and extensive irrigated crops. The case of Spain

Zoonotic filarioses caused by Dirofilaria immitis and Dirofilaria repens are transmitted by culicid mosquitoes. Therefore Dirofilaria transmission depends on climatic factors like temperature and humidity. In spite of the dry climate of most of the Spanish territory, there are extensive irrigated crops areas providing moist habitats favourable for mosquito breeding. A GIS model to predict the risk of Dirofilaria transmission in Spain, based on temperatures and rainfall data as well as in the distribution of irrigated crops areas, is constructed. The model predicts that potential risk of Dirofilaria transmission exists in all the Spanish territory. Highest transmission risk exists in several areas of Andalucía, Extremadura, Castilla-La Mancha, Murcia, Valencia, Aragón and Cataluña, where moderate/high temperatures coincide with extensive irrigated crops. High risk in Balearic Islands and in some points of Canary Islands, is also predicted. The lowest risk is predicted in Northern cold and scarcely or non-irrigated dry Southeastern areas. The existence of irrigations locally increases transmission risk in low rainfall areas of the Spanish territory. The model can contribute to implement rational preventive therapy guidelines in accordance with the transmission characteristics of each local area. Moreover, the use of humidity-related factors could be of interest in future predictions to be performed in countries with similar environmental characteristics.

Seropositivity rates for agents of canine vector-borne diseases in Spain: a multicentre study

Background

Controlling canine vector-borne diseases (CVBD) is a major concern, since some of these diseases are serious zoonoses. This study was designed to determine seropositivity rates in Spain for agents causing the following five CVBD: leishmaniosis (Leishmania infantum: Li), heartworm (Dirofilaria immitis: Di), ehrlichiosis (Ehrlichia canis: Ec), anaplasmosis (Anaplasma phagocytophilum/Anaplasma platys: An) and Lyme disease (Borrelia burgdorferi: Bb).

Methods

Anti-An, -Bb, and -Ec antibodies and the Di antigen were determined using the 4DX SNAP® Test (IDEXX Laboratories) and anti-L. infantum (Li) antibodies using the Leishmania SNAP® Test (IDEXX Laboratories) in blood and/or serum samples.

Results

Among 1100 dogs examined, overall seropositivity rates were: Li (15.7%), Ec (5%), An (3.1%), Di (1.25%) and Bb (0.4%). While seropositivity towards Bb and Di was similar in all geographic regions, rates were significantly higher in the east of Spain (8.3%) for An, significantly higher in the north (20%) for Ec, and significantly higher in the Southeast (46.6%) and South (27.4%), and significantly lower in the north (0%) for Li.

No statistical associations were observed between sex and the CVBD analyzed (p ≥ 0.05) while the following associations with other variables were detected: a higher seropositivity to Ec (40%) and Bb (6.7%) in dogs under one year of age compared with adults (p < 0.05); and a higher seropositivity to An and Li in dogs that lived outdoors versus indoors (p = 0.01; p < 0.001, respectively). Seropositivity rates of 2.1%, 0%, 1.7%, 0.5% and 4.2% were recorded respectively for An, Bb, Ec, Di and Li in dogs with no clinical signs (n = 556) versus 3.8%, 0.6%, 7.5%, 1.8% and 25.9% for those with signs (n = 507) suggestive of a CVBD.

Conclusion

The data obtained indicate a risk for dogs in Spain of acquiring any of the five CVBD examined. Veterinarians in the different regions should include these diseases in their differential diagnoses and recommend the use of repellents and other prophylactic measures to prevent disease transmission by arthropod vectors. Public health authorities also need to become more involved in the problem, since some of the CVBD examined here also affect humans.

Human and animal dirofilariasis: the emergence of a zoonotic mosaic

Dirofilariasis represents a zoonotic mosaic, which includes two main filarial species (Dirofilaria immitis and D. repens) that have adapted to canine, feline, and human hosts with distinct biological and clinical implications. At the same time, both D. immitis and D. repens are themselves hosts to symbiotic bacteria of the genus Wolbachia, the study of which has resulted in a profound shift in the understanding of filarial biology, the mechanisms of the pathologies that they produce in their hosts, and issues related to dirofilariasis treatment. Moreover, because dirofilariasis is a vector-borne transmitted disease, their distribution and infection rates have undergone significant modifications influenced by global climate change. Despite advances in our knowledge of D. immitis and D. repens and the pathologies that they inflict on different hosts, there are still many unknown aspects of dirofilariasis. This review is focused on human and animal dirofilariasis, including the basic morphology, biology, protein composition, and metabolism of Dirofilaria species; the climate and human behavioral factors that influence distribution dynamics; the disease pathology; the host-parasite relationship; the mechanisms involved in parasite survival; the immune response and pathogenesis; and the clinical management of human and animal infections.

Heartworm Disease (Dirofilaria immitis) and Their Vectors in Europe - New Distribution Trends

Cardiopulmonary dirofilariasis is a cosmopolitan disease caused by Dirofilaria immitis, which affects mainly canids and felids. Moreover, it causes zoonotic infections, producing pulmonary dirofilariasis in humans. Heartworm disease is a vector-borne transmitted disease, thus transmission depends on the presence of competent mosquito species, which is directly related to favorable climate conditions for its development and survival. Cardiopulmonary dirofilariasis is mainly located in countries with temperate and tropical climates. Europe is one of the continents where animal dirofilariasis has been studied more extensively. In this article we review the current prevalence of canine and feline cardiopulmonary dirofilariasis in the European continent, the transmission vectors, the current changes in the distribution and the possible causes, though the analysis of the epidemiological studies carried out until 2001 and between 2002 and 2011. The highest prevalences have been observed in the southern European countries, which are considered historically endemic/hyperendemic countries. Studies carried out in the last 10 years suggest an expansion of cardiopulmonary dirofilariasis in dogs toward central and northern Europe. Several factors can exert an influence on the spreading of the disease, such as movement of infected animals, the introduction of new species of mosquitoes able to act as vectors, the climate change caused by the global warming, and development of human activity in new areas. Veterinary controls to prevent the spreading of this disease, programs of control of vectors, and adequate protocols of prevention of dirofilariasis in the susceptible species should be carried out.

The occurrence of Dirofilaria immitis, Borrelia burgdorferi, Ehrlichia canis and Anaplasma phagocytophium in dogs in China

A survey of the occurrence of Dirofilaria immitis, Borrelia burgdorferi, Ehrlichia canis and Anaplasma phagocytophium in dogs was undertaken in the People's Republic of China between October 2008 and October 2009. A total of 600 blood samples were taken from dogs in four cities in China: 300 in Beijing, 150 in Shenzhen, 30 in Shanghai and 120 in Zhengzhou. All samples were tested for the heartworm antigen and antibodies of canine B. burgdorferi, E. canis and A. phagocytophium by using the canine SNAP® 4Dx® test kit. The occurrence of D. immitis, B. burgdorferi, E. canis and A. phagocytophium was 1.17% (7/600), 0.17% (1/600), 2.17% (13/600) and 0.5% (3/600), respectively. In Shenzhen city 2% (3/150), 8.67% (13/150) and 2% (3/150) of samples were positive for D. immitis, E. canis and A. phagocytophium, respectively. The occurrence of heartworm antigen was 0.33% (1/300) in Beijing, 2.00% (3/150) in Shenzhen, 3.33% (1/30) in Shanghai and 1.67% (2/120) in Zhengzhou. We found E. canis and A. phagocytophium only at one site, Shenzhen, while the only occurrence of B. burgdorferi was at Beijing. In conclusion, the dog population in China is at potential risk for D. immitis, B. burgdorferi, E. canis and A. phagocytophium infection, the risk being especially high in southern China.

Current prevalence of Dirofilaria immitis in dogs, cats and humans from the island of Gran Canaria, Spain

The island of Gran Canaria is a hyperendemic area for canine dirofilariasis. The aim of the present study was to provide data on Dirofilaria immitis in dogs, cats, and humans on this island in 2010. The data confirms the prevalence in the overall canine population (19%), with a considerably higher prevalence (43%) in the autochthonous breed of Canarian Warren hound. The prevalence in the feline population (33%) is higher than that of the canine population, and the existence of specific D. immitis antibodies in the inhabitants of the island of Gran Canaria (12%) is confirmed. In both cats and humans, the prevalence, according to the different climate areas on the island, is related to the prevalence of D. immitis in dogs in the same area, which shows the key epidemiological role played by the canine host with regard to the transmission to other hosts of D. immitis.

A Survey on Dirofilaria immitis Occurence in Stray Dogs of Tabriz (Iran)

To determine the prevalence of microfilariae Dirofilaria immitis (canine heart worm) infection in Tabriz (East-Azarbaijan province, Iran), blood samples from 63 male and 37 female stray dogs of six age groups (< 1 years, 1-3 years, 3-5 years, 5-7 years, 7-9 years and > 9 years) were analyzed by means of the Knott method. Dirofilaria immitis infection was found in 30 of 100 tested dogs (30%). Male dogs (33.3%) were more infected than females (24.3%), but this difference was not significant. Higher prevalence was found in > 9 years old dogs than in other age groups, but this difference was not statistically significant. It would be useful to apply prevention measures to control Dirofilaria immitis infection in the canine population of Tabriz.

Canine and feline cardiopulmonary parasitic nematodes in Europe: emerging and underestimated

Cardiopulmonary nematodes of dogs and cats cause parasitic diseases of central relevance in current veterinary practice. In the recent past the distribution of canine and feline heartworms and lungworms has increased in various geographical areas, including Europe. This is true especially for the metastrongyloids Aelurostrongylus abstrusus, Angiostrongylus vasorum and Crenosoma vulpis, the filarioid Dirofilaria immitis and the trichuroid Eucoleus aerophilus (syn. Capillaria aerophila). The reasons of this emergence are little known but many drivers such as global warming, changes in vector epidemiology and movements in animal populations, may be taken into account. The purpose of this article is to review the knowledge of the most important heartworm and lungworm infections of dogs and cats in Europe. In particular recent advances in epidemiology, clinical and control are described and discussed.

Prevalence of Dirofilaria immitis in dogs from Hatay province, Turkey

The present study was conducted to determine the prevalence of canine dirofilariosis in Hatay province, south of Turkey. A total of 269 blood samples were collected from owned dogs in this multi-centre survey between March and July 2006. Blood samples were examined by modified Knott and enzyme-linked immunosorbent assay (ELISA) techniques to detect circulating microfilariae and antigens of Dirofilaria immitis, respectively. Seventy out of 269 dogs (26.0%) were positive for D. immitis. However, 61.4% of positive dogs had occult infection. The prevalence of canine dirofilariosis was heterogeneous in Hatay province, with higher values in shoreline (33.0%) and riverside (30.9%) areas followed by the lowland (25.5%) or mountainous (15.2%) areas. No statistically significant differences were observed in relation to sex (females, 33.3%; males, 24.4%, P>0.05). When evaluating the prevalence of D. immitis by age, the highest prevalence was observed in dogs older than 4 years of age. Large breeds (29.6%) and the dogs living outdoors (30.2%) showed a higher prevalence in comparison to small breeds (21.4%) and the dogs living indoors (10.5%), respectively. In conclusion, according to the results of this study canine dirofilariosis had a high prevalence in Hatay province. Therefore, prophylaxis against heartworm is advisable to decrease the incidence of canine dirofilariosis.

Heartworm disease in animals and humans

Heartworm disease due to Dirofilaria immitis continues to cause severe disease and even death in dogs and other animals in many parts of the world, even though safe, highly effective and convenient preventatives have been available for the past two decades. Moreover, the parasite and vector mosquitoes continue to spread into areas where they have not been reported previously. Heartworm societies have been established in the USA and Japan and the First European Dirofilaria Days (FEDD) Conference was held in Zagreb, Croatia, in February of 2007. These organizations promote awareness, encourage research and provide updated guidelines for the diagnosis, treatment and prevention of heartworm disease. The chapter begins with a review of the biology and life cycle of the parasite. It continues with the prevalence and distribution of the disease in domestic and wild animals, with emphasis on more recent data on the spreading of the disease and the use of molecular biology techniques in vector studies. The section on pathogenesis and immunology also includes a discussion of the current knowledge of the potential role of the Wolbachia endosymbiont in inflammatory and immune responses to D. immitis infection, diagnostic use of specific immune responses to the bacteria, immunomodulatory activity and antibiotic treatment of infected animals. Canine, feline and ferret heartworm disease are updated with regard to the clinical presentation, diagnosis, prevention, therapy and management of the disease, with special emphasis on the recently described Heartworm Associated Respiratory Disease (HARD) Syndrome in cats. The section devoted to heartworm infection in humans also includes notes on other epizootic filariae, particularly D. repens in humans in Europe. The chapter concludes with a discussion on emerging strategies in heartworm treatment and control, highlighting the potential role of tetracycline antibiotics in adulticidal therapy.

Serological and molecular studies on Dirofilaria immitis in dogs from Turkey

We estimated the prevalence of Dirofilaria immitis infection in domestic dogs in five Turkish provinces – Sakarya, Kocaeli, Ankara, Elazig and Mersin – using a commercial ELISA kit for detecting circulating antigen and a PCR test for detecting circulating microfilarial DNA. A total of 211 whole-blood and serum samples were collected from dogs of various breeds, ages and life status (owned or stray). Sample population characteristics were recorded and examined for differences in prevalence. Additionally, we collected 15 blood samples from cats (14 owned and 1 stray) from Ankara province and used PCR to detect D. immitis infection. Twenty-seven (12.8%) of 211 dog samples were positive for D. immitis antigen by ELISA. No differences in prevalence were observed by sex (female: 14.4%; male: 10.7%; P>0.05). The prevalence of D. immitis infection varied with age: 11.8% in younger dogs (0.5–2 years) and 17.5% in older dogs (3–5 years). Prevalence between stray dogs (15.2%) and owned dogs (9.3%) did not differ (P>0.05). Prevalence rates were highest in Kocaeli province (18.3%), followed by Ankara (14.8%), Sakarya (12.3%) and Mersin (10.5%) provinces. Prevalence in Elazig province was 0%. No dogs or cats had microfilarial DNA detectable by PCR.

[Frequency of antibodies anti-Ehrlichia canis, Borrelia burgdorferi and Dirofilaria immitis antigens in dogs from microrregion Ilhéus-Itabuna, State of Bahia, Brazil]

In order to detect the positivity to antigens of Dirofilaria immitis, antibodies anti-Borrelia burgdorferi and anti-Ehrlichia canis, 200 canine blood samples were collected as followed: 100 from the municipality of Ilhéus and 100 from Itabuna, State of Bahia. The kit Snap 3DX (IDEXX Laboratories) was used to performe serology. None of the tested animalswere positive for antigens of D. immitis. Only two dogs of them were positive for antibodies anti-B. burgdorferi. From all the samples analyzed, 72 (36%) were positive for antibodies anti-E. canis, 43 from Ilhéus and 29 from Itabuna (p=0.027).

Prevalence of the Dirofilaria immitis infection in dogs from Merida, Yucatan, Mexico

The aim of the present study was to estimate the prevalence of Dirofilaria immitis infection, and to examine the relationship between host factors (gender, age and breed) and D. immitis infection in dogs. The study was designed as a cross-sectional study. A total of 676 dogs were examined for D. immitis infection. Adult worms (necropsy) and blood samples were collected from all animals for diagnosis of D. immitis. Blood samples were examined using a modified Knott's and thick drop techniques. Fifty-six of 676 dogs were diagnosed infected with D. immitis. The odds of infection were 2.85 times higher in female dogs, compared to male dogs (OR = 2.85, 95% CI = 1.5-5.5, P = 0.01). In addition, the odds of infection were 2.11 times higher in > or =3 years old dogs, compared with younger dogs (OR = 2.11, 95% CI = 1.1-4.2, P = 0.03). This information is important for a better understanding of the epidemiology of D. immitis in dogs in Yucatan, Mexico.

Dirofilaria immitis infection in dogs: unusually located and unusual findings

Clinical, blood, serum biochemistry, and parasitological assessments were performed on four hospitalized dogs, not in good general condition, in a study carried out to determine the prevalence of general parasitic infections. Hematological and biochemical parameters and electrocardiographic recording of the animals were determined during the general clinical examinations. Four dogs were indicated to have been infected with Dirofilaria immitis by using modified Knott's method, and the microfilarial density was determined. Mild to moderate anemia and decrease in sedimentation velocity were established in dogs. Differences in other hematological and biochemical values between the dogs were determined. Right axis deviation was determined in a dog. D. immitis was encountered in the right ventricle, bronchus, and the pericardial sac at the end of the necropsy. On the other hand, in the histopathological examinations, pulmonary adenocarcinoma deriving from bronchial epithelium was identified in a dog, and microfilaria was encountered in bronchial and bronchiolar lumens, interstitium of the lungs, and bile ducts. D. immitis has not been considered in the diagnosis of dogs with pneumonia and tumors. The requirement of parasitological examination with respect to D. immitis in the diagnosis of dogs with tumor or pneumonia has been considered vital.

Prevalence and epidemiological aspects of Dirofilaria immitis in dogs from Kayseri Province, Turkey

This study was conducted to determine the prevalence of Dirofilaria immitis infection and to investigate the risk factors related to heartworm disease in dogs from Kayseri, Turkey. Blood samples were collected from 280 dogs from May 2005 to March 2006 and were examined by membrane filtration-acid phosphatase histochemical staining and antigen Elisa techniques to detect circulating microfilariae and antigens of D. immitis, respectively. Of the total of 280 dogs, 27 were positive for D. immitis with a prevalence value of 9.6%. In addition 29.6% of positive dogs determined to have occult D. immitis infections. D. immitis was the only canine filarial parasite present in the study area. The mean number of microfilariae in infected dogs was 4730+/-5479 per ml of blood. The highest heartworm prevalence were observed in 7-10 age group (28.6%) followed by 4-6 (17.1%) and 0.5-3 (4.8%) age groups. The differences between 0.5-3 and other age groups were found significant, whereas no statistically significant difference was observed between 4-6 and 7-10 age groups. The infection was more prevalent in males, larger breeds and the dogs not on prophylaxis. No statistically significant difference was observed between stray and owned dogs. Our results suggest that heartworm treatment and prophylaxis should be considered in Kayseri Province.

Seroprevalence of canine heartworm disease (Dirofilaria immitis) on Tenerife Island: an epidemiological update

Blood samples from 823 dogs were tested for circulating Dirofilaria immitis antigen during a 1-year period (May 2002 to May 2003) on Tenerife Island, Canary Islands, Spain. Seroprevalence of heartworm infection was 21%. Heartworm infection was similar in males and females and was more common in dogs aged >6 years. Distribution of infection in varying climatic zones was not statistically different.

Is heartworm disease really spreading in Europe?

Based on recently published surveys and newly acquired data, a study was conducted to verify the distribution of filarial worm (Filarioidea) infections in Europe, with particular emphasis on canine heartworm infection (Dirofilaria immitis). A Geographic Information System based on thermal regimen was constructed as a means to identify areas potentially suitable for heartworm transmission, taking into account that the development of D. immitis larvae in the mosquito does not occur below the threshold temperature of approximately 14 degrees C. Furthermore, a bionomic model of D. immitis in its mosquito vectors, which calculates the moving cumulative heartworm development unit parameter, was applied using the available temperature data to assess the theoretic transmission timing of heartworm in Europe. The results show that the earliest infection risk occurs in Spain on March 21 and the latest risk occurs in Spain on September 11. The longest risk period occurs in Spain (Murcia station: March 21-November 11), and the shortest risk period occurs in northeastern Europe. The study also provides the first risk assessment maps for Europe and suggests that if the actual climatic trend continues, filarial infection should spread into previously infection-free areas.

Specific IgG antibody response against antigens of Dirofilaria immitis and its Wolbachia endosymbiont bacterium in cats with natural and experimental infections

Sera from three groups of cats under different experimental conditions were studied by ELISA to assess the host's immune response against synthetic peptides derived from Dirofilaria immitis (Dipp) and against the surface protein of its endosymbiont, Wolbachia (WSPr). In experimentally infected cats (Group 1), an increase of IgG antibody against both Dipp and WSPr was observed from 2 months post-infection until the end of the study, 6 months post-infection. In experimentally infected cats, treated against infective larvae (Group 2), anti-Dipp IgG decreased dramatically from 4 months post-infection (3 months post treatment), showing very low values till the end of the study (6.5 months from infection, 5.5 months from treatment), while anti-WSP IgG increased constantly till the end of the study. Of 49 outdoor, asymptomatic cats exposed to a high risk of natural infection (Group 3), 9 were positive for anti-Dipp IgG and for a validated, in-clinic commercial antibody diagnostic kit for cats. Two cats were also found positive for circulating antigens of adult female worm. Anti-WSPr IgG were found in five of nine anti-Dipp IgG-positive sera and from eight ELISADipp-negative sera. Our results confirm the strong IgG response in heartworm infected cats and demonstrate the involvement of the Wolbachia endosymbiont in the immune reaction to the parasite both in experimentally infected cats and in cats exposed to a high risk of natural infection.