Do not let your guard down! Prevalence of Dirofilaria immitis and Dirofilaria repens in dogs entering shelters in northern Italy

Background: In Italy, the area of highest prevalence for canine heartworm disease (CHWD) has historically been along the Po River Valley in the northern area of the country, where prevalence in the mid-nineties ranged from 31% to 98%. Currently, increased awareness among practitioners and the availability of preventives have led to a dramatic decrease in prevalence in the area, although cases of CHWD continue to be diagnosed, suggesting the presence of canine reservoirs, including unowned dogs. Methods: The aim of the present study was to determine the prevalence of Dirofilaria spp. in stray dogs entering shelters located in the Po River Valley of northern Italy by using the modified Knott's test and by antigenic testing. Results: Out of the 510 dogs tested, 173 (33.9%) were positive for circulating microfilariae: 15.7% (80/510) with D. immitis, 6.9% (35/510) with D. repens, and 11.4% (58/510) with a mixed infection. Conclusions: Unowned dog populations represent an important reservoir for the parasite, allowing D. immitis to remain in a given geographical area and increasing the risk of exposure to all dogs.