TYPE-1 INTERFERON AND VIRUS-SPECIFIC IGA AND IGM ANTIBODIES AS AN AIDIN THE DIAGNOSIS OF ONGOING INFECTIONS IN CALVES

Nine, 4 to 5-week old calves were examined for clinical signs, serum a ntibody titres to four viruses and serum levels of type I interferon ( IFN) after arrival at a rearing unit. All calves had fever and/or diar rhoea within five days after arrival. Serum IFN was detected in all ca lves within 2 to 6 days after arrival. Commonly, IFN was detected in s erum before, or coinciding with, the development of diarrhoea. None of the calves showed any rise in IgG antibody titres to bovine virus dia rrhoea virus, parainfluenza type 3 virus or bovine respiratory syncyti al virus. All calves were seropositive to bovine corona virus (BCV) at arrival and two calves showed a rise in IgG titre to the virus. Howev er, from one week after arrival and subsequently, all calves showed an IgA, and all but one an IgM, response to BCV. This study shows that I FN can be used as a ''non-specific'' indicator of an early virus infec tion in calves and demonstrates the advantage of measuring virus-speci fic IgA and IgM antibodies over Ige antibodies for the diagnosis of on going virus infections in calves with colostrum-derived immunity.