Imunidade passiva contra Escherichia coli enterotoxigênica: avaliação sorológica de uma bacterina contendo as fímbrias K99 e F41 no colostro de fêmeas vacinadas e no soro de bezerros

A bacterin from enterotoxigenic Escherichia coli (ETEC), containing fimbriae K99 and F41, was produced and its capacity to induce anti-K99 and anti-F41 antibodies in colostrum of vaccinated cows and in calf serum, and the persistence of these antibodies in neonates were determined. Three experiments were performed on two commercial farms. In all experiments animals were allotted randomly to the blocks, each block consisting of two pregnant females (a vaccinated one and a control one) and their respective calves. In experiment A (farm 1), comprised of 18 blocks, the animals received a vaccine dose 30 days before delivery. In experiment B (farm 1), consisted of 26 blocks, the animals received two vaccine doses (60 and 30 days before delivery). In experiment C (farm 2), consisted of 22 blocks, the animals received two vaccine doses (60 and 30 days before delivery). In experiments A and B pregnant cows and heifers were used and colostrum and serum from 24- to 36-hour-old calves were collected. In experiment C, pregnant embryo-recipient heifers were used and colostrum and sera from calves at 7, 14, 28 and 42 days of age were collected. Anti-K99 and anti-F41 antibodies were detected by ELISA using purified K99 and F41 fimbrial antigens. In experiment A no difference between treated and control groups was observed for the concentration of anti-K99 and anti-F41 antibodies in colostrum and calf serum. In experiment B a difference (P<0.001) was observed for colostrum of vaccinated females and for serum of their calves. In experiment C, difference between vaccinated and control animals was observed for colostrum and calf serum at 7, 14, 28 (P<0.001 in all cases) and 42 days of age (P= 0.003). The results showed the efficiency of the bacterin to induce detectable humoral immune response.Produziu-se uma bacterina de Escherichia coli enterotoxigênica (ETEC) contendo as fímbrias K99 e F41 e avaliaram-se a capacidade de indução de anticorpos anti-K99 e anti F-41 no colostro de vacas vacinadas e no soro de bezerros e a persistência dos anticorpos nos neonatos. Três experimentos foram realizados em duas fazendas comerciais. Os animais foram aleatoriamente alocados em blocos, de duas fêmeas prenhes (uma vacinada e outra controle) e seus respectivos bezerros. No experimento A (fazenda 1), com 18 blocos, os animais receberam uma dose da vacina, 30 dias antes do parto. No experimento B (fazenda 1), com 26 blocos, os animais receberam duas doses de vacina, aos 60 e 30 dias antes do parto. No experimento C (fazenda 2), com 22 blocos, os animais receberam o mesmo esquema de vacinação do experimento B. Nos experimentos A e B foram coletados colostro das parturientes e soro dos bezerros entre 24 e 36 horas de vida. No experimento C, foram usadas novilhas receptoras de embriões e coletados colostro e soro dos bezerros aos 7, 14, 28 e 42 dias de idade. Anticorpos anti-K99 e anti-F41 foram detectados por ELISA utilizando antígenos K99 e F41 purificados. No experimento A não foi observada diferença entre o grupo vacinado e o controle quanto à detecção de anticorpos. No experimento B foi observada diferença (P<0,001) entre o colostro de fêmeas vacinadas e o soro de seus bezerros. No C houve diferença entre o grupo vacinado e o controle para o colostro e o soro dos bezerros aos 7, 14, 28 (P