Diagnostico molecular da Leishmaniose visceral canina: avaliação do swab conjuntival em cães assintomáticos e em cães vacinados / Molecular diagnosis of canine visceral leishmaniasis: conjunctival swab evaluation in asymptomatic dogs and vaccinated dogs

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

19/02/2010

RESUMO

The epidemiological control of visceral Leishmaniasis (VL) in Brazil involves the elimination of infected dogs. Therefore, reliable diagnostic tests are essential to prevent the transmission of the disease or unnecessary culling of dogs. The VL control in Brazil is based on serological surveys, nevertheless serologic assays present problems related to sensitivity and specificity. Polymerase chain reaction (PCR) proved to be a rapid and sensitive technique for detection of Leishmania. However, non-invasive samples are an essential tool in this context, since they are simpler, painless and more easily accepted by dog owners. A useful method is the conjunctival swab (CS) that uses a sterile swab to sample the dog conjunctiva. The SC was highly sensitive for the VL diagnosis by PCR. The objective of this study was to evaluate by CS the prevalence of infected animals in two groups of dogs: asymptomatic and vaccinated against VL. The first group had 30 asymptomatic dogs with positive serological and parasitological tests. The SC samples were compared with two non-invasive samples: blood (B) and skin biopsy (SB). The samples were analyzed by two different PCR methods: kDNA PCR-hybridization and ITS-1 nPCR. The volume of DNA sample used for kDNA PCR-hybridization was 1.0  L and ITS-1 nPCR volume was 10.0 L. The DNA sample volume used was of 1.0 L and 10.0 L respectively. Using CS samples the kDNA PCR- hybridization was able to detected parasite DNA in 24/30 dogs (80%) using the right conjunctiva (RC) and 23/30 dogs (76.6%) with the left conjunctiva (LC), 17/30 dogs (56.7%) by means of SB and 4/30 dogs (13.3%) with B. The CS positivity obtained combining RC and LC results was of 90% (27/30 dogs). The assay of CS samples by ITS-1 nPCR revealed that 25/30 dogs (83.3%) were positive when using RC and 20/30 dogs (66.6%) were positive when using LC. Via the same method 15/30 dogs (50.0%) were positive by SB and 17/30 dogs (56.7%) with B. The CS positivity obtained by ITS-1 nPCR combining RC and LC was of 83.3%. The CS positivities for RC and LC were significantly higher (p<0.05) than SB and B for kDNA PCR- hybridization method. Statistical difference in relation to SB and B was verified by ITS-1 nPCR only for RC. Methods kDNA PCR-hybridization and ITS-1 nPCR showed similar sensitivities to CS and SB samples. Moreover, the positivity of ITS-1 nPCR 11 for B samples, was significantly higher than that obtained by kDNA PCR-hybridization, indicating that the sensitivity of the PCR may vary with the tissue examined. The best sensitivity in this study (90%) was obtained from CS samples (by combining both conjunctivas) associated with kDNA PCR-hybridization. This level of sensitivity was similar to that obtained in other studies using CS for the VL diagnosis in symptomatic dogs. The second group was of 42 military dogs, all of them vaccinated against VL. In this group CS and compared with the results obtained by serological tests. The serological tests were carried out independently by three laboratories. Laboratories 1 and 2 (Lab1 and Lab2) were private laboratories. Laboratory 3 (Lab3) was the National Reference Laboratory. The first serological screening performed by the Lab 1 showed 15 reactive dogs and 4 dogs were classified as indeterminate. Due to the high positivity found in this test, animals with reactive and indeterminate serology according Lab 1 were subjected to new serological tests by Lab 2 and Lab 3. Lab 2 confirmed only 3 reactive dogs and 2 animals were undetermined. The Lab 3 found 7 reactive dogs and 3 dogs were classified as indeterminate. Dogs that were confirmed as reactive by Lab 3 were euthanized. The molecular diagnosis by PCR, using CS, was performed in all 42 animals and was able to detect Leishmanial DNA in 17 dogs. Comparing the PCR results with those obtained by serological test of Lab 1, PCR was positive for 10 reactive and one indeterminate case, but was negative for 5 reactive and 3 indeterminate cases. In addition, the PCR was positive in 5 non-reactive cases. The reactive and indeterminate cases according to Lab 1 that were PCR negatives, tested negative in the serologic assays of Lab 2 and Lab 3. For the Lab 2, the PCR confirmed the 3 reactive cases and was positive for the 2 indeterminate cases. In relation to Lab 3, the PCR confirmed all 7 reactive cases and test positive for the 3 indeterminate cases. The PCR assay confirmed all cases simultaneously reactive in the serologic tests of two laboratories. Our results showed that the SC is a sensitive and practical method for collecting samples, allowing reliable diagnostic tests by PCR and showed higher sensitivity than other low invasive samples. We conclude that the use of CS for the regular screenings of dogs by PCR should be considered.

ASSUNTO(S)

leishmaniasis dogs diagnosis infection diseases leishmaniose visceral diagnosticos cães parasitologia

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