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


METHODS
Dogs 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.


RESULTS
The 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.


CONCLUSIONS
These 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.
Programa de Pós-Graduação em Medicina Veterinária, Faculdade de Veterinária, Universidade Federal Fluminense, Rua Vital Brazil Filho 64, Santa Rosa, CEP 24230-340, Niterói, RJ, Brazil. inhalabarthe@gmail.com.|Programa Institucional Biodiversidade e Saúde, Fundação Oswaldo Cruz, Av. Brasil 4036, Manguinhos, CEP 21040-361, Rio de Janeiro, RJ, Brazil. inhalabarthe@gmail.com.
Norma Vollmer
NV
Labarthe
Universidade Federal Rural do Rio de Janeiro, Seropédica, RJ, Brazil. jonimarpaiva@uol.com.br.
Jonimar Pereira
JP
Paiva
Programa de Pós-Graduação em Microbiologia, Parasitologia e Patologia, Departamento de Patologia Básica, Universidade Federal do Paraná, Av. Cel. Francisco H. dos Santos, 100, CEP 81530-900, Curitiba, PR, Brazil. reifurla@ufpr.br.
Larissa
L
Reifur
Programa de Pós-Graduação em Medicina Veterinária, Faculdade de Veterinária, Universidade Federal Fluminense, Rua Vital Brazil Filho 64, Santa Rosa, CEP 24230-340, Niterói, RJ, Brazil. fma@centroin.com.br.
Flavya
F
Mendes-de-Almeida
Zoetis, Rua Alexandre Dumas, 1711, 8th floor, tower B, CEP: 04717-000, São Paulo, SP, Brazil. alexandre.merlo@zoetis.com.
Alexandre
A
Merlo
Departamento MIP/CCB/UFSC, Campus Universitário, Trindade, CEP 88040-900, Florianópolis, SC, Brazil. carlospinto@ccb.ufsc.br.
Carlos Jose
CJ
Carvalho Pinto
Universidade de São Paulo, Via Santos Dumont 405, Jardim Santo Antônio, CEP: 11432-501, Guarujá, SP, Brazil. psjuliani@usp.br.
Paulo Sérgio
PS
Juliani
Escola de Medicina Veterinária e Zootecnia da Universidade Federal da Bahia, Av. Ademar de Barros, 500, Ondina, CEP 40170-110, Salvador, BA, Brazil. ornelasam@gmail.com.
Maria Angela Ornelas
MA
de Almeida
Departamento de Medicina Veterinária da Universidade Federal Rural de Pernambuco, Av. Dom Manoel de Medeiros s/n, Dois Irmãos, CEP 52171-900, Recife, PE, Brazil. leucioalves@gmail.com.
Leucio Câmara
LC
Alves
D000818:Animals; D000947:Antigens, Helminth / Q000097:blood; D001769:Blood / Q000469:parasitology; D001938:Brazil / Q000453:epidemiology; D002846:Chromatography, Affinity; D003430:Cross-Sectional Studies; D004183:Dirofilaria immitis / Q000302:isolation & purification*; D004184:Dirofilariasis / Q000453:epidemiology* / Q000469:parasitology*; D004283:Dog Diseases / Q000453:epidemiology* / Q000469:parasitology*; D004285:Dogs; D005260:Female; D008297:Male; D015995:Prevalence; D019371:Topography, Medical
D000947:Antigens, Helminth