Updated canine infection rates for Dirofilaria immitis in areas of Brazil previously identified as having a high incidence of heartworm-infected dogs

Abstract

BackgroundCanine heartworm infections were frequently diagnosed in Brazil before the new millennium. After the year 2000, the frequency of diagnosis showed a sharp decline; however, a few years later, new evidence indicated that the parasite was still present and that canine infection rates seemed to be increasing. Therefore, an updated survey of canine heartworm prevalence was conducted in several locations in south, southeast, and northeast Brazil.MethodsDogs from 15 locations having previously reported a high prevalence of heartworm infection were included in the survey according to defined criteria, including the absence of treatment with a macrocyclic lactone for at least 1 year. Blood samples from 1531 dogs were evaluated by an in-clinic immunochromatography test kit (Witness® Heartworm, Zoetis, USA) for detection of Dirofilaria immitis antigen. At each location, epidemiologic data, including physical characteristics and clinical signs reported by owners or observed by veterinarians, were recorded on prepared forms for tabulation of results by location, clinical signs, and physical characteristics.ResultsThe overall prevalence of canine heartworm infection was 23.1%, with evidence of heartworm-infected dogs detected in all 15 locations studied. There was a tendency for higher prevalence rates in environmentally protected areas, despite some locations having less-than-ideal environmental temperatures for survival of vector mosquitoes. Among physical characteristics, it was noted that dogs with predominantly white hair coats and residing in areas with a high (≥20%) prevalence of heartworm were less likely to have heartworm infection detected by a commercial heartworm antigen test kit than were dogs with other coat colors. In general, dogs older than 2 years were more frequently positive for D. immitis antigen than were younger dogs. Clinical signs of heartworm infections were rare or owners were unable to detect them, and could not be used for reliable prediction of the presence of heartworm.ConclusionsThese results indicate that the prevalence of D. immitis has increased in these areas of Brazil over the past few years. Small animal practitioners in these areas should include routine screening tests for heartworm infections in every dog’s annual evaluation protocol and make sure to have uninfected dogs on prevention.

Atualização sobre a epidemiologia de<i> Dirofilaria immitis </i>na América do Sul e no México: revisão de literatura

“…In the coastal cities of the state of Bahia, the results were as follows: Ilhéus -no infected dogs detected (CARLOS et al, 2007); Lauro de Freitas -20.3%;and Salvador -20% (LABARTHE et al, 2014). In the coastal cities of the State of Pernambuco, the following results were reported: Itamaracá -49.5% and Recife 36.7% (LABARTHE et al, 2014) or 11.54% (RAMOS et al, 2016). In the largest region, the tropical North, which is where the rainforest comprises approximately 75% of the territory, and on the coastal areas of the state of Pará, including Marajó Island, the largest fluvial-maritime island of the world, heartworms infected dogs at different rates, ranging from 32.5% (FURTADO et al, 2009) to 53.5% (GARCEZ et al, 2006).…”

“…The prevalence rates in the state of Rio de Janeiro were as follows: Mangaratiba -16.3%; Niterói -58.6%; Cabo Frio -27.5%; and Armação de Búzios -62.2%. The prevalence rates in the cities of São Paulo State were: Guarujá -2.8% and Bertioga -7.6% (LABARTHE et al, 2014) (Table 3). …”

“…In the State of Santa Catarina the cities Florianópolis and Araquari had canine infection rates of 2.1% and 7.3%, respectively. In the State of Paraná the canine infection rates were as follows: Guaratuba -24.5%, Guaraqueçaba -31.8%, and Pontal do Paraná -26.3% (LABARTHE et al, 2014) (Table 3).…”

“…Years after the sharp decline in the Brazilian prevalence, small animal veterinarians started to observe an upward trend in the number of heartworm-infected patients encountered in their practices. In an effort to confirm or disprove these reports, these endemic areas were revisited in a new survey: A total of 1,531 canine samples was collected in Santa Catarina, Paraná, São Paulo, Rio de Janeiro, Bahia, and Pernambuco states, and 23.1% were found to be antigen positive (LABARTHE et al, 2014) (Table 3).…”

Updated canine infection rates for Dirofilaria immitis in areas of Brazil previously identified as having a high incidence of heartworm-infected dogs

“…With regard to size, smaller dogs were more inclined to have a cough and lose weight more frequently, possibly due to heart or respiratory diseases associated with other etiologies [38,39].…”