Changes

==Aetiology==

==Aetiology==

The virus that causes PRRS is an aterivirus, within the Arteriviridae family. The arteriviruses are the only genus contained within the Arterivirdae family, and other members include the agent responsible for equine viral arteris and lactate dehydrogenase-elevating virus of mice. These viruses are antigenically distinct from each other. Arteriviruses are enveloped viruses of 45 to 80 nm in diameter with a spherical appearance due to the shape of the envelope. However, the positive-sense single-stranded RNA genome is contained within an icosohedral nucleocapsid. The lipoprotein envelope has ring-like structures on its surface, but there are no gross surfae spikes. Arteriviruses have a tropism for macrophages and endothelial cells, where they reproduce in the cytoplasms. The genome is 13Kb in length, and is infectious itself without the capsid or envelope. The viruses are host-specific, and persistent infections are established after invasion. 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 virus that causes PRRS is an aterivirus, within the Arteriviridae family. The arteriviruses are the only genus contained within the Arterivirdae family, and other members include the agent responsible for equine viral arteris and lactate dehydrogenase-elevating virus of mice. The viruses are host-specific and antigenically distinct, and establish persistent infections after invasion.  

 

Arteriviruses are enveloped viruses of 45 to 80 nm in diameter with a spherical appearance due to the shape of the envelope. However, the icoshedral nucelocapsid that contains the positive-sense single-stranded RNA genome is actually icosohedral. The lipoprotein envelope has ring-like structures on its surface, but there are no gross surface spikes. Arteriviruses have a tropism for macrophages and endothelial cells, where they reproduce in the cytoplasm. The genome is 13Kb in length, and is infectious itself without the capsid or envelope.

 

Arteriviruses are inactivated by traetment with chloroform or ether. They are very resistant to freezing, althouth infectivity is in reduces as temperature risees.

==Transmission and Epidemiology==

==Transmission and Epidemiology==