Changes

===Virus Biotypes===

===Virus Biotypes===

Within both BVDV genotypes, isolates can be classified as one of two biotypes. Noncytopathic (ncp) viruses produce no visible cytopathic effect in cell cultures, and infected cells appear normal (Figure 1.2a). Conversely, cytopathic (cp) viruses cause cell vacuolation and death (Figure 1.2b) within 24-48 hours post-infection. Cytopathogenicity gives no indication of disease-causing potential.Noncytopathic BVDV is responsible for the majority of acute and persistent BVDV infections worldwide. Cytopathic biotypes are usually found in cases of the fatal BVD-associated condition, mucosal disease, and are always isolated alongside noncytopathic strains.

BVDV isolates from either genotype can be of a cytopathic or non-cytopathic biotype. Noncytopathic (ncp) viruses produce no visible effects in cell culture, whereas infection with cytopathic (cp) viruses gives cell vacuolation and death. Although non-cytopathic isolates are responsible for the majority of BVDV infections worldwide, cytopathogenicity gives no indication of disease-causing potential. Cytopathic biotypes of bovine viral diarrhoea virus are always isolated alongside non-cytopathic strains, and are found in cases of mucosal disease, a fatal BVD-associated condition.  

Cytopathic viruses have been shown to originate from noncytopathic strains by several mechanisms of mutation. These include insertions of cellular origin, such as ubiquitin sequences, and viral gene rearrangements, duplications and deletions (Deregt and Loewen, 1995). Accumulation of point mutations in the NS2 region and various RNA recombination events are also important (Tautz et al., 1994).

Cytopathic viruses have been shown to originate from noncytopathic strains by several mechanisms of mutation. These include insertions of cellular origin, such as ubiquitin sequences, and viral gene rearrangements, duplications and deletions (Deregt and Loewen, 1995). Accumulation of point mutations in the NS2 region and various RNA recombination events are also important (Tautz et al., 1994).