Expansion of Canine Heartworm in Spain

Simple Summary Dirofilaria immitis is a nematode parasite causing heartworm disease worldwide. Spain is one of the southern European countries where the risk of infection in domestic dogs is moderate/high. The aim of this study was to update the epidemiology of canine heartworm and analyse the results based on climate and other geo-environmental factors. For this, 9543 blood samples from dogs from all provinces, autonomous cities and islands that comprise Spain were tested using D. immitis antigen tests. The mean prevalence obtained was 6.47%. Prevalences exceeding 11% were located in the northwestern and southern provinces, in the Balearic and Canary Islands. The presence of positive dogs was described for the first time in provinces and islands where previously no cases of infected dogs had been reported. Considering its zoonotic character, further studies are needed to identify infected animals and to carry out national control programmes for the prevention of heartworm disease. 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.