The climate of Spain has favourable characteristics for the development of D. immitis in dogs, being an endemic country. Given that vector-borne diseases are spreading rapidly through Europe, due to factors such as climate change, the expansion of vectors and the increased mobility of reservoir animals, the aim was to update the epidemiology of heartworm in dogs and analyse the results based on climate and other epidemiological and geo-environmental factors. To this aim, 9543 blood samples from dogs from all provinces and autonomous cities of Spain were analysed for the detection of antigens of D. immitis, obtaining a prevalence of 6.47%. The northwestern and southern provinces showed the highest prevalences, as well as in the Balearic and Canary Islands. Prevalences were higher in dogs outdoors. Furthermore, most of the positive dogs were found in regions with high humidity and water availability. This study shows, for the first time, positive cases in provinces and islands where no cases had previously been described and demonstrates the continuous expansion and consolidation of heartworm in Spain. Considering its zoonotic character, the implementation of control and awareness programmes for the prevention of D. immitis in pets is necessary.

Dirofilaria immitis causes heartworm disease, a chronic and potentially fatal cardiopulmonary disease which mainly affects dogs and cats. It is present in most of Spain, due to favourable climatic factors. Madrid, located in the centre of the Iberian Peninsula, is the most highly populated city in the country. There is a lack of current data on canine heartworm and there are no published epidemiological data regarding feline heartworm in this region, therefore the aim of this study was to assess the prevalence and current distribution of canine and feline dirofilariosis in the province of Madrid. Serum samples from 1716 dogs and 531 cats, from animals living in the metropolitan area of Madrid and adjacent areas, were studied. All the samples, either from cats and dogs, were tested for circulating D. immitis antigens using a commercial immunochromatographic test kit. Furthermore, to establish the seroprevalence of heartworm infection in cats, serological techniques for anti-D. immitis and anti-Wolbachia antibody detection were used. Prevalence of D. immitis in the canine population of Madrid was 3%, showing an increase in comparison to previous data. The presence of heartworm in the city centre could be influenced by the presence of Urban Heat Islands, while the positive dogs from metropolitan and adjacent areas were mainly located under the influence of rivers. Regarding cats, 0.2% were positive to the antigens test and 7.3% were seropositive to both anti-D. immitis and Wolbachia surface protein antibodies, which demonstrate the presence of feline heartworm in Madrid. Seropositive cats were present in the same areas where positive dogs were found. Indoor/outdoor cats showed the highest seroprevalence whereas the lowest corresponded to indoor cats, demonstrating that prophylactic treatments should be carried out regardless of lifestyle. Infection was found in 2.2% of dogs and 6.7% of the cats < 1 year-old, which indicates that early preventive campaigns in puppies and kittens should be implemented. The results point to the need for adequate prophylactic measures through the administration of macrocyclic lactones in animals living in Madrid. Veterinarians should be aware of the presence of this disease and include heartworm in the differential diagnosis when a pet presents with symptoms compatible with D. immitis.

Pulmonary hypertension (PH) is a frequent and severe phenomenon in heartworm disease caused by Dirofilaria immitis, mainly caused by intimal proliferation of the arteries and pulmonary thromboembolisms. Transthoracic echocardiography is the method of choice for diagnosing PH in dogs although the diagnosis is often based on indirect and subjective parameters. The Right Pulmonary Artery Distensibility Index (RPAD Index) is a method that has been recently validated to estimate the presence and severity of PH in heartworm-infected dogs. This study compared some echocardiographic parameters commonly used to estimate PH in 93 dogs infected by D. immitis and evaluated the impact of the parasite burden, microfilaremia, sex or origin of the dog (client-owned/shelter). None of the studied echocardiographic variables seemed useful in the estimation of the evaluated clinical aspects, except for the PA/Ao ratio for parasite burden. The RPAD Index was determined in 88 of the dogs; of these, 70.4% had PH (mild: 37.5%, moderate: 19.3%, severe: 13.6%). This Index showed non-significant differences according to microfilaremia, sex, origin or parasite burden. Symptomatic dogs showed PH more often and displayed more severe PH, in addition the presence of symptoms was greater among dogs with high burden; on the other hand 64.4% of asymptomatic dogs had some degree of PH according to the RPAD Index. Apart from the PA/Ao ratio, the other evaluated echocardiographic variables were not useful in evaluating of the hypertensive status of the heartworm-infected dog compared to the RPAD Index. The estimation of most common indirect parameters is not useful in predicting PH in heartworm-infected dogs. The results confirm the RPAD Index as an objective and supportive test in the monitoring and evaluation of PH in the heartworm-infected dog, and show a potential diagnostic value for the detection of PH in asymptomatic animals.

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.

Background:Dirofilaria immitis produces proliferative pulmonary endarteritis and pulmonary thromboembolism in infected dogs. The pulmonary vascular lesions lead to irreversible and persistent structural damage and, as a consequence, sustained precapillary pulmonary hypertension (PH). The purpose of this study was to assess the diagnostic value of the pulmonary vein to pulmonary artery ratio (PV:PA ratio) to determine moderate or severe PH (>50 mmHg) in dogs with heartworm disease. Methods: A total of 151 naturally heartworm-infected and 66 healthy dogs were included in the study. The presence/absence of PH was based on the right pulmonary artery distensibility index (RPAD index < 29.5%), and the PV:PA ratio was echocardiographically measured by the time–motion mode (M mode) and two-dimensional mode (2D mode). Other echocardiographic parameters were also assessed (pulmonary trunk to aorta ratio, tricuspid regurgitation pressure gradient, and AT:ET ratio). Results: The results of the PV:PA ratio showed a highly positive correlation between the M and 2D modes (r = 0.928). The PV:PA ratio obtained by the M mode was identified as the strongest predictor for RPAD index (R² 0.628, p < 0.0001) with a good diagnostic accuracy (AUC = 0.99). The results of PV/PA by the 2D mode showed a similar prediction for the RPAD index (R² 0.606, p < 0.0001) with a good diagnostic accuracy (AUC = 0.98). Both of the 2D and M modes’ PV:PA ratios decreased significantly with the presence of PH. A cut-off value of ≤0.845 showed high sensitivity and specificity for the M mode (97% and 94%, respectively) and the 2D mode (96% and 93%, respectively). Conclusions: The PV:PA ratio may be useful as a complementary diagnostic method for the estimation of moderate or severe PH in dogs with heartworm.

The Canary Islands are hyperendemic for canine heartworm and the risk of zoonotic infection is high. Additionally, there is evidence of development of allergies due to nematode infections in animals and humans. Since the population of the Canary Islands presents high prevalence of allergic comorbidities, and previous studies have shown a possible relationship between allergies and seropositivity to heartworm, the aim was to evaluate whether exposure to heartworm may contribute to the development of allergies in the human population. First, an epidemiological study was conducted on 248 owners of dogs with/without heartworm infection in the Canary Islands. Secondly, a serological analysis of the presence of total IgE and specific IgE against heartworm was conducted in 66 samples of inhabitants of the Canary Islands. The survey showed that allergic owners had heartworm-positive dogs more frequently (p < 0.01). Of the analyzed human samples, 43.9% were seropositive to heartworm and Wolbachia. Total IgE concentrations were increased in 34.5% seropositive samples and 8.1% seronegative samples. Specific IgE against heartworm was only found in human seropositive samples (17.2%). Contact with heartworm may be a risk factor for the development of allergic diseases, although further studies to elucidate the relationship between heartworm and allergies should be carried out.