Evaluation of Seroprevalence and Risk Factors of Heartworm Infection for Dogs in Rio de Janeiro with Access to Veterinary Care

Acta Parasitologica https://doi.org/10.1007/s11686-024-00859-2 ORIGINAL PAPER Evaluation of Seroprevalence and Risk Factors of Heartworm Infection for Dogs in Rio de Janeiro with Access to Veterinary Care Mariana Guedes1 · Tamiris Gomes1 · Bruno Alberigi2 · Emilene Prudente1 · Alexandre Bendas2 · Thalita Souza1 · Flavya Mendes-de-Almeida3 · Fabiana Batalha Knackfuss4 · Alexandre Merlo1 · Norma Labarthe4 Received: 15 August 2023 / Accepted: 3 June 2024 © The Author(s) 2024 Abstract Heartworm infection is a chronic disease with clinical signs and effects ranging from an asymptomatic condition to severe disease and death. The prevalence of heartworm disease in the state of Rio de Janeiro has been reported to be high (21.3%). The present study was conducted to evaluate the seroprevalence and risk factors of heartworm infection for the canine population with access to veterinary services in different areas of the state of Rio de Janeiro, Brazil. A total of 1787 canine blood samples were obtained from 135 practices across 8 different areas of Rio de Janeiro state (Rio de Janeiro municipality, São Gonçalo municipality, Niterói municipality, Baixada Fluminense, and the northern, southern, eastern, and mountainous areas) and tested for the presence of Dirofilaria immitis antigens and antibodies against several tick-borne disease pathogens using a commercial immunochromatography technique (Vetscan® Flex 4 Rapid Test; Zoetis; NJ USA). Pet owners reported living conditions, physical characteristics, demographics, and clinical signs for evaluation of risk factors for heartworm infection. Only two evaluated risk factors were shown to enhance the risk for D. immitis infection, including having a short hair coat vs. having a medium or long hair coat (OR 2.62) or positive for antibodies to tick-borne disease parasites (OR 3.83). Clinical signs reported for dogs with heartworm disease were typical for that condition. The overall prevalence of heartworm disease in the state was 8.2%, ranging from 2.4% in the mountainous region to 29.4% in the eastern area. It could not be determined if veterinarians were not diligent about dispensing heartworm preventatives or if poor levels of compliance by dog owners were responsible for higher infection rates in some areas of the state. Keywords Epidemiology · Canine health · Prevalence · Parasitology · Preventive measures · Clinical signs · Vectorborne diseases · Mosquito vectors · Dirofilaria immitis Introduction Mariana Guedes 1 Zoetis Indústria de Produtos Veterinários Ltda, Rua Dr. Chucri Zaidan, 1240, 4º andar, São Paulo, SP, BrazilCEP: 04711-130 2 Universidade Federal Rural do Rio de Janeiro, Rodovia BR 465, Km 07, Zona Rural, Seropédica, RJ, BrazilCEP: 23890000 3 Universidade Federal Fluminense, Avenida Ary Parreiras, 507, Icaraí, Niterói, RJ, BrazilCEP: 24220-000 4 Fundação Oswaldo Cruz., Rua Leopoldo Bulhões, 1480 Manguinhos, Rio de Janeiro, RJ, BrazilCEP: 21041-210 Heartworm disease is a cardiopulmonary vector-borne disease caused by Dirofilaria immitis and its endosymbiont Wolbachia. This nematode infects domestic and wild canids, which are the best-adapted hosts and the main source of microfilariae for mosquito vectors [1]. Although canids are the most infected mammals, many other groups may be infected, including humans [2]. Heartworm disease is a chronic disease that causes vascular damage in pulmonary arteries. Clinical signs are variable and range from an asymptomatic condition to weight loss, decreased exercise tolerance, cough, dyspnea, syncope, ascites, cachexia, caudal vena cava syndrome, and death, which is typically due to pulmonary hypertension and right heart failure [3, 4]. 13 Acta Parasitologica D. immitis is a cosmopolitan parasite. The prevalence of canine infections tends to be higher in coastal tropical areas due to conditions that provide abundant, flourishing populations of the vector [5]. In Brazil, canine heartworm disease has been reported in all 5 regions of the country [6, 7]. Besides the vector density, which tends to follow naturally conserved areas, the unprotected canine population, especially stray, feral, or sylvatic animals, increases the risk for new infections [8]. In the state of Rio de Janeiro, the prevalence has been reported to be high (21.3%) [9]. The coastal areas have always been recognized as having the highest number of heartworm cases in the state [10]. After chemoprophylaxis became available in Brazil in the 1990s, infections became rare in Rio de Janeiro, reaching a low level of 3.8%, even when antigen testing was used in former endemic areas [11]. Twenty-four years after the first launch of a macrocyclic lactone, the prevalence started to rebound at previous foci sites, reaching 23.1% in 2014, especially in the coastal area of Rio de Janeiro [12]. For instance, in the eastern region of the state, positive antigen frequencies were reported to be 44.8% [12]. Therefore, since many different factors may influence the environment and mosquito and canine populations, constant surveillance is needed. The present study was conducted to evaluate the seroprevalence and risk factors of heartworm infection for the canine population with access to veterinary services in the state of Rio de Janeiro, Brazil. Materials and Methods Sampling Criteria The state was divided into 8 geographical areas (Rio de Janeiro municipality, São Gonçalo municipality, Niterói municipality, Baixada Fluminense, and the northern, southern, eastern, and mountainous areas of the state) based on population size and environmental characteristics. The number of dogs to be included in each area was calculated with the aid of EPI INFO™ 2000, considering the canine population to be 10% of the human population in each area [13]. The expected canine D. immitis infection frequency ranged from 3% in the mountainous region to 30% in the eastern area [12, 14], with a confidence interval (CI) of at least 95%. Therefore, the estimated number of dogs to be enrolled across the state to provide a statistically relevant sample was 1665. The study was carried out from June to December 2021, despite the strict control of human activities in most Brazilian cities due to the COVID-19 pandemic. The veterinary clinics and practices invited to participate in the study were part of the Zoetis customer base and 13 its partner distributors. Each clinic/veterinary hospital was classified as a practice that recommended heartworm chemoprophylaxis as determined by examination of purchase records that indicated acquisition of products for this purpose in the past 12 months. Practices that met this criterion were accepted to participate in the study and were provided with a copy of the study protocol. One veterinarian in each practice was assigned to be responsible for collecting whole blood samples from clients’ dogs at that location. The number of samples to be collected at each clinic was established based on the number of cases that could (...truncated)