Evaluation of immunoperoxidase test for the detection of antibodies against the bovine leukosis virus (BLV)

A leucose enzo??tica dos bovinos (EBL) ?? uma enfermidade causada pelo v??rus da leucose bovina (BLV), que ocasiona uma infec????o persistente em bovinos, e ?? respons??vel por perdas econ??micas significativas ?? pecu??ria, principalmente a leiteira. Amplamente disseminada no rebanho brasileiro, pode ser manifestada de tr??s formas: aleuc??mica, linfocitose persistente e linfossarcoma. Os animais com anticorpos contra o BLV dever??o ser eliminados ou separados do restante do rebanho, pois significa que s??o portadores e disseminadores do v??rus por toda a vida. O diagn??stico desta doen??a ?? essencial para estrat??gias de controle e erradica????o baseadas na segrega????o de animais infectados no intuito de evitar ou amenizar a transmiss??o do v??rus e, consequentemente, minimizar as perdas econ??micas causadas pela doen??a. Durante a infec????o pelo BLV s??o produzidos anticorpos contra as principais prote??nas virais, gp51, gp30 (glicoprote??nas do envelope) e p24 (prote??na do caps??deo). O teste de imunodifus??o em gel de ??gar (agar gel immunodiffusion AGID) e o ensaio imunoenzim??tico (enzyme-linked immunosorbent assay ELISA) s??o os mais utilizados para diagn??stico. No presente trabalho foi avaliada a t??cnica de imunoperoxidase (peroxidase linked assay PLA) na detec????o de anticorpos contra o BLV. Os resultados obtidos na PLA foram comparados com o teste de AGID e a especificidade dos positivos confirmada pela t??cnica de Western blotting (WB). Foram testadas 201 amostras de soro de bovinos provenientes de propriedades localizadas no munic??pio de Pelotas: 59% (119) foram positivos por PLA e 26% (53) positivos por AGID. Todas as amostras positivas na AGID foram tamb??m positivas na PLA. Dos 32,8% (66) dos soros com resultados conflitantes apenas oito foram confirmados como positivos no WB, indicando serem falso-positivos os demais resultados e constatando que a AGID falhou em identificar 4% de animais positivos para EBL. A t??cnica de PLA para diagn??stico de infec????o pelo BLV se mostrou muito ??til para uso em programas de controle devido ?? maior sensibilidade da t??cnica quando comparada com o teste de AGID. Contudo, a ocorr??ncia de resultados falso-positivos pela PLA inviabiliza o seu uso em programas de erradica????o que envolva o sacrif??cio do animal soropositivo.The enzootic bovine leukosis is an illness caused by the bovine leukosis virus (BLV) which provokes a persistent infection in cattle and is responsible for significant economical losses to the bovines, mainly dairy cattle. It is widely spread in Brazilian cattle and it can come up in three forms: asymptomatic infection, persistent lymphocytosis and lymphosarcoma. The animals that have antibodies against the BLV must be eliminated or separated from the rest of the cattle, because they are carriers and disseminators of the virus during all their lifetimes. The diagnosis of this disease is essential for control and eradication strategies based on the segregation of infected animals in order to avoid or attenuate the transmission of the virus, and consequently, minimize the economical losses caused by the disease. During the BLV infection antibodies are produced against the main viral proteins, gp 51, gp 30 (envelope glicoproteins) and p24 (capsid protein). The agar gel immunodiffusion (AGID) and the enzyme-linked immunosorbent assay (ELISA) tests are the most used for diagnosis. In this report the immunoperoxidase technique (peroxidase linked assay - PLA) was evaluated in order to detect antibodies against the BLV. The results obtained in the PLA were compared with the AGID test and the specificity of the positive ones was confirmed by the Western blotting (WB) technique. Two hundred and one bovine serum samples of cattle coming from the city of Pelotas were tested: 59% (119) were positive in PLA and 26% (53) were positive in AGID. All the AGID positive samples were also PLA positive. From the 32,8% (66) of the conflicting serum results just eight were confirmed as positive in WB, indicating that the rest of the results were false-positive and showing that AGID failed in identifying 4% of the BLV positive animals. The PLA technique for the diagnosis of the BLV infection demonstrated to be very useful to use in control programs because it was more sensitive when compared to the AGID technique. However, the occurrence of false-positive results by the PLA makes its use unviable in eradication programs that involve the sacrifice of seropositive animals