Birago Project - What has happened thirty years after the introduction of macrocyclic lactones in a historically endemic area for Dirofilaria immitis? Preliminary data

Introduction: The first observation of Dirofilaria immitis in dogs was made by Birago in 1626, a nobleman living in Northern Italy. Since the 1980s, scientific studies have identified Northern Italy, particularly the area around the Po River, as a highly endemic region for heartworm disease, with prevalences ranging from 31% to 98% (Martini et al., 1996). After the introduction of ivermectin in 1988 and other macrocyclic lactones in the following years, parasitic pressure gradually decreased, leading to a reduction in the prevalence and incidence of heartworm disease in this area. However, in recent years, this reduction has led to some practitioners to pay less attention to the disease, including in terms of diagnosis and prevention. Objectives: The aim of the study was to assess, approximately 30 years after the introduction of macrocyclic lactones preventives, the prevalence and distribution of D. immitis in Northern Italy, a historically endemic region for heartworm disease. Materials & methods: The study population consisted of 500 dogs. The inclusion criteria were stray dogs or those without microchips referred to shelters or veterinary facilities, older than 10 months of any breed, and untreated with macrocyclic lactones for heartworm prevention. Approximately 2 ml of blood was collected from each dog and stored at +4°C in tubes with anticoagulant. An identification form was completed for each animal, including the location of recovery, age, breed, sex, weight, and the presence of any clinical signs. Each blood sample was analyzed using Knott's test (Genchi et al., 2021) and a antigen test (Idexx 4DX). Results: Preliminary data from 328 dogs examined with Knott"s test, from 10 provinces of Lombardy and Emilia-Romagna, showed a D. immitis prevalence of 25% (fig.1). In particular, 14% were positive for D. immitis, 8% for D. repens and 11% mixed infection. The antigen prevalence was 29%, 9 dogs were antigen- positive but microfilariae negative, while 2 dogs were antigen-negative but microfilaremic. Conclusion: The data show that even 40 years after the introduction of chemoprophylaxis, in a historically endemic area such as Northern Italy, parasitic pressure has remained high. These data underline the importance of continuing to make a correct diagnosis and prevention not only for D. immitis but also for D. repens and how practitioners must not lower their attention towards these parasites. Birago F. Trattato cinegetico, overo della caccia. Milano: GB Bidelli, 1626:59 Genchi M, Ciuca L, Vismarra A, Ciccone E, Cringoli G, Kramer L, Rinaldi L. Evaluation of alternative reagents on the performance of the modified Knott's test. Vet Parasitol. 2021 Oct;298:109555. Martini M, Capelli G, Poglayen G, Bertotti F, Turilli C. The validity of some haematological and ELISA methods for the diagnosis of canine heartworm disease. Vet Res Commun. 1996;20(4):331-9