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Cattle of all ages are susceptible to infection with bovine viral diarrhoea viruses (BVDV).
Distribution is world-wide although some countries have recently eradicated the virus. BVDV
infection results in a wide variety of clinical manifestations, including enteric and respiratory disease
in any class of cattle or reproductive and fetal disease following infection of a susceptible breeding
female. Infection may be subclinical or extend to severe fatal disease. Animals that survive in-utero
infection in the first trimester of gestation are almost always persistently infected (PI). PI animals
provide the main reservoir of the virus in a population and excrete large amounts of virus in urine,
faeces, discharges, milk and semen. Identification of such PI cattle is a key element in controlling
the infection. It is important to avoid the trade of such animals. They may appear clinically healthy,
or weak and unthrifty. Many PI animals die before reaching maturity. They may infrequently develop
mucosal disease with anorexia, gastrointestinal erosions, and profuse diarrhoea, invariably leading
to death. Mucosal disease can arise only in PI animals. Latent infections generally do not occur
following recovery from acute infection. However bulls may rarely have a persistent testicular
infection and excrete virus in semen for prolonged periods.
Identification of the agent: BVDV is a pestivirus in the family Flaviviridae and is closely related to
classical swine fever and ovine border disease viruses. The two genotypes (types 1 and 2) are
classified as separate species in the genus Pestivirus. A third putative genotype, BVDV type 3, has
also recently been proposed. Although both cytopathic and non-cytopathic biotypes of BVDV type 1
and type 2 exist, non-cytopathic strains are usually encountered in field infections and are the main
focus of diagnostic v
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