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Arquivo Brasileiro de Medicina Veterinária e Zootecnia

Print version ISSN 0102-0935On-line version ISSN 1678-4162

Arq. Bras. Med. Vet. Zootec. vol.52 n.3 Belo Horizonte June 2000 



Dirofilaria immitis infection in dogs from Maceió, Alagoas, Northeast region of Brazil

[Infecção por Dirofilaria immitis em cães de Maceió]


A.C. Brito1, L.S. Viana1, E.M. Duarte, E.M.M. Rocha1, G. Fontes1, N. Regis2

1Centro de Ciências Biológicas da Universidade Federal de Alagoas
Praça Afrânio Jorge, s/n
57010-020 – Maceió, AL
2Instituto Aggeu Magalhães, FIOCruz - Recife, PE


Recebido para publicação em 13 de setembro de 1999.
Apoio Financeiro: Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq
Apoio Logístico: Fundação Nacional de Saúde – Alagoas



Dirofilaria immitis Leidy, 1856 (Nematoda, Onchocercidae) is more often found in the pulmonary arteries and in the right ventricle of the heart of dogs. However, this filaria specie can also occasionally be found in others canines, felines and even in humans (Grieve et al., 1983). The parasite causes canine heartworm disease and Culex, Aedes, Anopheles, Mansonia and Psophora mosquitoes are the intermediate hosts harboring the infective third stage larvae (Loftin et al., 1995). In Brazil, canine dirofilariasis has been reported nationwide. Even though there were found cases in states such as Pará, Amazonas, Piauí, Paraíba, Pernambuco, Bahia, Minas Gerais, São Paulo, Espírito Santo, Rio de Janeiro, Rio Grande do Sul and Paraná (Costa et al., 1986; Rodrigues-Silva et al., 1995) there were no records of occurrence of D. immitis in the state of Alagoas (Northeast region) until now.

The prevalence for this zoonosis is estimated to be in the range of 1 to 3%. The samples used to search for D. immitis microfilariae (mf) were obtained from seven out of 27 districts of Maceió, Alagoas State capital. A total of 2,007 male and female domestic dogs older than nine months of age were sampled for a small amount of capillary blood from March/1995 through March/1997, between 9AM and 5PM. Two thick smears (100µl) were prepared from capillary blood collected from one of the ears of each dog. Blood smears were stained with Giemsa method and examined under a microscope at 100´ magnification. As a measure of quality control, all slides were re-examined by a second technician. Mf were detected in only 62 of the 2,007 animals, with a prevalence rate of microfilaraemic dogs of 3.1% (95%; confidence interval=2.7-3.4).

From 11 positive randomly chosen dogs, 10ml heparinized venous blood were sampled in order to observe motility, size and morphology of the mf. The presence of soluble antigen against adult D. immitis was investigated using a commercial test [Witness Dirofilariae Test - Rhone Merieux – MERIAL (Campinas, Brazil)], based on rapid immuno migration technology, which uses antibodies against specific epitopes of D. immitis soluble antigen. The modified Knott technique (Watson, 1973) was used to measure the size of mf. Due to the fact that the standard deviation of length was rather small and the data did not fit a normal distribution, the number of mf obtained using an ocular micrometer was arbitrarily limited to 15. The mean size of D. immitis mf was 300.38±8.89µm in length and 7.83±0.88µm (SD) in width. In wet blood smears the mf undulated in place without forward motion. Based on the diagnostic criteria methods used, such as motility and morphology, 5 out of 11 microfilaremic dogs were found infected with D. immitis.

Females of Culex quinquefasciatus were allowed to feed on blood withdrawn from one of these dogs using an artificial feeding apparatus (Rutledge et al., 1964). Females alive after 12-15 days of feeding were dissected in phosphate buffered saline on a glass slide. The head, thorax and abdomen of each mosquito were separated, torn apart and examined under 100´magnification. Developmental stages of D. immitis were identified using descriptions of their size, shape and location (Zytoon et al., 1992). L1, L2, and L3 larvae were observed in the Malpighian tubules of C. quinquefasciatus females fed with blood containing 560 D. immitis mf/ml. This supports the notion that the infected dogs indeed carried D. immitis mf, since, among Onchocercidae, only species of Dirofilaria genus are known to develop within the Malpighian tubules cells and lumen (Symes, 1960).

Dirofilariasis is considered a zoonosis with a potential to cause human disease (Labarthe et al., 1997). In humans it produces symptoms that may be misdiagnosed as pulmonary neoplasia, and thereby leading to unnecessary thoracic surgeries in these patients (Rodrigues-Silva et al., 1995). Further studies on the subject are required in order to evaluate the possibility of human dirofilariasis.

Keywords: Dog, Dirofilaria immitis, dirofilariasis, Culex quinquefasciatus




De 2.007 amostras de sangue examinadas de cães da cidade de Maceió-AL, foram detectados 62 (3,1%) animais positivos para a presença de microfilárias (mf). Em 11 cães, escolhidos aleatoriamente, foi colhido sangue venoso para a identificação específica de Dirofilaria immitis. Para tal, foram utilizadas a motilidade, o tamanho, a morfologia das mf e a presença de antígenos solúveis do parasito, sendo encontrados cinco animais portadores de D. immitis. Mosquitos da espécie Culex quinquefasciatus foram alimentados com sangue de um cão portador de D. immitis. O desenvolvimento de formas larvárias foi observado nos túbulos de Malpighi, confirmando a ocorrência da dirofilariose canina causada por D. immitis na cidade de Maceió-AL.

Palavras-chave: Cão, Dirofilaria immitis, dirofilariose, Culex quinquefasciatus




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