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Porcine Reproductive and Respiratory Syndrome (view source)
Revision as of 16:12, 27 August 2010
, 16:12, 27 August 2010→Aetiology
==Aetiology==
==Aetiology==
The etiologic agent is a virus in the group Arteriviridae. The virus is enveloped and ranges in size from 45 to 80 mm. Inactivation is possible after treatment with ether or chloroform; however, the virus is very stable under freezing conditions, retaining its infectivity for 4 mo at -70°C. As the temperature rises, infectivity is reduced (15-20 min at 56°C).
The etiologic agent is a virus in the group Arteriviridae. The virus is enveloped and ranges in size from 45 to 80 mm. Inactivation is possible after treatment with ether or chloroform; however, the virus is very stable under freezing conditions, retaining its infectivity for 4 mo at -70°C. As the temperature rises, infectivity is reduced (15-20 min at 56°C).
This family of enveloped, positive-sense, single-stranded RNA viruses, established in 1996, was classified formerly in the Togaviridae family. It has only one genus, Arterivirus, whose virus species are antigenically distinct from each other.
Viral Characteristics
* These positive sense, single-stranded RNA viruses are medium in size (50 - 70 nm) have a spherical appearance due to the envelope, but the nucleocapsid is icosahedral in shape (see Fig. 25.1).
* They possess a lipoprotein envelope with ring-like structures on the surface, but no gross surface spikes.
* They replicate in the cytoplasm of macrophages and endothelial cells.
* The genome is 13K nucleotides in length, has a 5'-methylguanosine cap and a 3' poly A tail of approximately 50 nucleotides. The genome alone is infectious.
* Individual viruses are antigenically distinct and host specific; they establish persistent infections
==Transmission and Epidemiology==
==Transmission and Epidemiology==