Epidemiology of BHV 1 virus infections in dairy herds

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Abstract
SUMMARY The epidemiology of bovine herpesvirus 1 (BHV 1) infections was studied in 20 dairy herds. Periodic serological surveillance of these herds during three consecutive years (1980–82) was combined with clinical studies. In 19 herds seropositive cows were found indicating previous exposure to BHV 1. One herd had its first experience with BHV 1 during the study. No indication of virus circulation for at least three years was found in eight herds. In five herds an interval of 2 years without an indication of virus circulation was followed by infections in yearlings, first- and second-calf cows during the third year. One or two cycles of virus circulation in calves and/or yearlings during the 3 year survey were detected in six herds. Most BHV 1 infections passed unnoticed. Signs of respiratory disease inassociation with BHV 1 infection were observed in three herds: young animals were most seriously affected. Clinical manifestations of BHV 1 infections were less pronounced than a few years ago when infections in cows caused frank signs and diagnosis was frequently possible on the basis of a typical clinical picture. BHV 1 was the cause of abortions in the herd that experienced its first infections during thissurvey. A survey of the age-specific BHV 1 neutralizing antibody pattern may be helpful for tracing animals and herds at risk of an outbreak of infectious bovine rhinotracheitis.