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

Infection models were developed for adult cows and for young calves using t he same strain of bovine coronavirus (BCV), which for the first time allows experimental reproduction of winter dysentery (WD) in seronegative lactati ng cows. The cattle were infected through direct contact with an experiment ally inoculated calf. All experimental cattle shed faecal BCV with developm ent 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 differen ces were a shorter incubation period in the two youngest calves, but with m ilder 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 ou tbreaks of calf diarrhoea and WD, (2) seronegative cows are more severely a ffected by the infection than seronegative conventionally reared calves, an d (3) unaffected general condition in diarrhoeic calves may lead to underes timation of the occurrence of calf diarrhoea in WD outbreaks. In response to infection, all cattle produced early interferon type 1 in se rum and, except for one calf, in nasal secretions. A finding not previously reported is the detection of interferon type 1 responses in bovine milk. A ll cattle developed high IgM antibody responses and long-lasting IgA antibo dy responses both systemically and locally. The serum IgM antibody response s came earlier in most of the calves than in the cows. Prolonged IgM antibo dy responses were detected in serum and milk, while those in nasal secretio ns 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 adul t 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 mont hs. In conclusion, WD was reproduced in seronegative lactating cows. The cows s howed severe general diseases than seronegative calves infected concurrentl y. Very long-lasting IgA antibody responses were detected both systemically and locally. (C) 2001 Elsevier Science B.V. All rights reserved.