Abstract
Bovine respiratory syncytial virus (BRSV) is one of the major pathogens affecting the respiratory system of young cattle, causing serious economic losses. Data on its epidemiology and occurrence in animals under one-year of age are still scarce in the literature. This study aimed to determine the occurrence of viral activity in three of BRSV seropositive dairy herds (A, B, and C), by serological monitoring of calves from the first day of life until the age of one year, by virus neutralization test. Results showed that in animals from farms A and B, antibody titers increased in the first month, characterizing passive transfer of immunity through colostrums. Over time, the titers decreased till total absence in the sixth and eighth months respectively and then antibodies titration increased in the final months of the study, probably due to natural infection. On property C, although there was a similar antibodies’ dynamics to the others, a period of total absence did not occurred, suggesting that animals may have been infected in the first months of life, despite the presence of colostral antibodies. This study demonstrated fluent BRSV activity amongst animals in all properties.KEYWORDS: antibody titer; bovine respiratory syncytial virus; screening; viral activity; virus neutralization.
Highlights
Property C, there was a similar antibodies’ infected in the first months of life, despite the presence dynamics to the others, a period of total absence did not of colostral antibodies
This study demonstrated fluent occurred, suggesting that animals may have been Bovine respiratory syncytial virus (BRSV) activity amongst animals in all properties
T. Experimental reproduction of respiratory disease in calves with non-cell-culturepassaged bovine respiratory syncytial virus
Summary
O estudo foi conduzido em três propriedades rurais que criavam bovinos para a produção de leite, em regime de confinamento, com predomínio da raça holandesa. Dessa forma, o material foi transportado para o laboratório, centrifugado por 15 min a 1.800 G, e o soro separado em alíquotas de 1 mL, em tubos tipo Eppendorf®, que permaneceram armazenados em freezer a -20°C até o momento de serem testados. Para a pesquisa e titulação de anticorpos contra o BRSV nos soros dos animais foi utilizada a VN de acordo com protocolo proveniente do Laboratório de Viroses de Bovídeos, do Instituto Biológico de São Paulo, SP, descrito por AFFONSO (2010). Como antígeno foi utilizada uma amostra de BRSV padrão estrangeira (ATCC VR-1485), gentilmente cedida pela Dra Edviges Maristela Pituco, responsável técnica pelo Laboratório de Viroses de Bovídeos do Instituto Biológico de São Paulo, SP. As amostras consideradas positivas foram aquelas que inibiram o efeito citopatogênico do vírus a partir da diluição 1:2, ou seja, títulos maiores ou iguais a 0,30, correspondendo ao logaritmo decimal da primeira diluição (1:2)
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