Experimental reproduction of winter dysentery in lactating cows using BCV — comparison with BCV infection in milk-fed calves

Abstract

Infection models were developed for adult cows and for young calves using the same strain of bovine coronavirus (BCV), which for the first time allows experimental reproduction of winter dysentery (WD) in seronegative lactating cows. The cattle were infected through direct contact with an experimentally inoculated calf. All experimental cattle shed faecal BCV with development of diarrhoea, being profusely watery with small amounts of blood in the most severely affected animals, including both cows and calves. The cows, in contrast to the calves, showed depressed general condition and appetite leading to a marked decrease in milk yield. Further age-associated differences were a shorter incubation period in the two youngest calves, but with milder fever and milder decrease in white blood cell counts. These findings shed light on the apparent epidemiological differences between WD and calf BCV diarrhoea suggesting that, (1) the same strains of BCV cause natural outbreaks of calf diarrhoea and WD, (2) seronegative cows are more severely affected by the infection than seronegative conventionally reared calves, and (3) unaffected general condition in diarrhoeic calves may lead to underestimation of the occurrence of calf diarrhoea in WD outbreaks. In response to infection, all cattle produced early interferon type 1 in serum and, except for one calf, in nasal secretions. A finding not previously reported is the detection of interferon type 1 responses in bovine milk. All cattle developed high IgM antibody responses and long-lasting IgA antibody responses both systemically and locally. The serum IgM antibody responses came earlier in most of the calves than in the cows. Prolonged IgM antibody responses were detected in serum and milk, while those in nasal secretions were much shorter. BCV-specific IgA was present in nasal secretions from all cattle throughout the 6 months follow-up. The IgA antibody response in serum was detected up to 17 months post-infection and the duration showed an age-related variation indicating a more prominent IgA memory in the adult cattle and in the older calves than in the younger ones. BCV-specific IgG was detected in all cattle during the experimental period of up to 22 months. In conclusion, WD was reproduced in seronegative lactating cows. The cows showed a more severe general diseases than seronegative calves infected concurrently. Very long-lasting IgA antibody responses were detected both systemically and locally.

Achados clínico patológicos durante um surto de disenteria de inverno em bovinos no Rio Grande do Sul

“…Entretanto, a pequena variação da temperatura ambiente durante o surto (16-24 o C) (INMET 2007) pode não ter sido decisiva no surgimento da doença, visto que Travén et al (2001) também não constatou a influência da temperatura ambiental como fator predisponente.…”

“…Reforçando o envolvimento do coronavírus bovino nesta doença, Van Kruiningen et al (1987) demonstraram a presença do vírus nas lesões intestinais e Travén et al (2001) reproduziram uma doença clínica compará-vel à disenteria de inverno em vacas e bezerros soronegativos para o vírus com material oriundo de casos naturais da doença.…”

On the etiology of an outbreak of winter dysentery in dairy cows in Brazil

“…In a few days, up to 100% of the herd may be affected with acute and severe dysentery, which might be bloody, with the excretion of large amounts of enteric tissue, depressed body condition, dehydratation and marked decrease in milk production (Tråven et al 2001).…”

Surto de diarreia em vacas de um rebanho leiteiro na região sul de Minas Gerais: detecção de coronavírus bovino nas fezes

“…Desde a década de 70, vários trabalhos vêm apontando o envolvimento do coronavírus bovino nestes surtos (Van Kruiningen et al 1987;Saif et al 1991;Travén et al, 2001). No Brasil, a primeira detecção de coronavírus nas fezes de vacas adultas com diarreia foi relatada por Brandão et al (2002) no Estado de São Paulo.…”

“…Foram consideradas positivas as amostras que apresentaram padrão de migração das bandas de RNA similares aos apresentados pela amostra NCDV (Nebraska Calf Diarrhea Virus) de rotavírus (White et al, 1970) Os aspectos clínicos e epidemiológicos do surto são compatíveis com os descritos na disenteria de inverno (Saif, 1990). Os resultados dos exames laboratoriais, a exemplo do que tem sido descrito por diversos autores (Van Kruiningen et al, 1987;Saif et al, 1991;Travén et al, 2001;Brandão et al, 2002;2007a, b), reforçam o envolvimento do coronavírus bovino no surto descrito. A técnica de reação em cadeia pela polimerase mostrou-se útil para o diagnóstico rápido da presença do coronavírus em amostras fecais de vacas com diarreia.…”