Persistent BVD virus infections in a cattle breeding facility--a case report]

Comprehensive serological and virological monitoring for bovine viral diarrhoea (BVD) virus was applied in a dairy herd. Out of 83 calves 26 persistently infected animals were identified. Four viremic calves showed clinical signs of disease, the others displayed no symptoms. Viral isolates from persistently infected animals were homogenous with respect to their antigenicity. The results of virological and serological investigations allowed an almost complete reconstruction of events following the introduction of BVD virus into the herd. This case illustrates the potentially dangerous and damaging effects of unidentified virus carriers in cattle herds. Strategies for the identification of virus-shedding animals and the limitation of economical losses are discussed.     

Bovine virus diarrhea (BVD)--diagnostic determination of cattle with persistent BVD virus infection

Buffy coats of 1074 cattle were examined for regard to BVD virus using the usual long-termed-cultivation (LTC) in bovine kidney monolayer cell cultures (7 days) whereby 268 carriers could be detected. Serum samples collected simultaneously from the same cattle were examined by means of a short-termed-cultivation (STC) of only two days in stationary macroplate cell cultures. Using this method only 172 carriers were found. Amongst 96 serum samples from animals positive in LTC of buffy coat leucocytes and negative in the STC further 19 cattle were found to be viraemic when the sera were tested by LTC, too. Thus 77 of a total of 268 serum samples (28.7%) taken from viraemic cattle turned out to be negative in the STC as well as the LTC. These results are discussed with regard to the antibody level and the age of the animals. The reduced sensitivity is considered in relation to the favourable time and cost factor. STC of serum samples in connection with the serological results proved to be valuable for the examination of cattle of more than 6 months of age but not for calves below 6 months.     

Genetic diversity and BVD virus.

The various measures of genetic variation of BVD virus was reviewed with emphasis on the implications for future control of virus-induced disease and diagnosis. While experimental data does not support unique serotypes for BVDV, there is substantial antigenic variation among the isolates examined. This variation may permit fetal infections even in animals assumed to be well vaccinated. The genetic differences between cytopathic and noncytopathic strains of BVDV are expressed in infected cells by the production of a p80 protein by cytopathic strains. In addition, cellular gene inserts have been detected in cytopathic strains. Monoclonal antibodies have demonstrated a high degree of diversity with the pestivirus population. Grouping of BVDV isolates by monoclonal antibody analysis is suggestive at best. The use of nucleic acid probes as diagnostic reagents has been compromised by the nucleic acid sequence variation found in the BVDV isolates tested.     

BVD virus infection: prospects for control

Losses resulting from pestivirus infections in cattle are of considerable importance to the livestock industry yet, until relatively recently, they have been poorly understood. The escalation of research effort in this field has started to clarify the pathogenesis and epidemiology of the associated diseases but the evolution of understanding is far from complete. Sufficient information exists to indicate the means by which pestivirus infection is introduced to and maintained in populations of cattle. A brief review of current knowledge is given placing particular emphasis on the role played by persistent infections which have resulted from intrauterine infection. The crux of the problem of control is seen to be the avoidance of fetal infection in early gestation. Ways of achieving this which include the immunisation of female cattle with live or inactivated virus vaccines are discussed and areas requiring further work are indicated.     

Persistent infections after natural transmission of bovine viral diarrhoea virus from cattle to goats and among goats

Bovine viral diarrhoea virus (BVDV) is an economically important pathogen of cattle worldwide. Infection of a pregnant animal may lead to persistent infection of the foetus and birth of a persistently infected (PI) calf that sheds the virus throughout its life. However, BVD viruses are not strictly species specific. BVDV has been isolated from many domesticated and wild ruminants. This is of practical importance as virus reservoirs in non-bovine hosts may hamper BVDV control in cattle. A goat given as a social companion to a BVDV PI calf gave birth to a PI goat kid. In order to test if goat to goat infections were possible, seronegative pregnant goats were exposed to the PI goat. In parallel, seronegative pregnant goats were kept together with the PI calf. Only the goat to goat transmission resulted in the birth of a next generation of BVDV PI kids whereas all goats kept together with the PI calf aborted. To our knowledge, this is the first report which shows that a PI goat cannot only transmit BVD virus to other goats but that such transmission may indeed lead to the birth of a second generation of PI goats. Genetic analyses indicated that establishment in the new host species may be associated with step-wise adaptations in the viral genome. Thus, goats have the potential to be a reservoir for BVDV. However, the PI goats showed growth retardation and anaemia and their survival under natural conditions remains questionable.