Changes

==Transmission and Epidemiology==

==Transmission and Epidemiology==

The virus is spread by contact with infected pigs, and infection also be transmitted by infected semen. It has been thought that aerosol transmissionmay occur, particularly under conditions of high humidity, low temperatures, and low wind speeds; but this has been difficult to reproduce. Once infected, adult animals shed PRRS virus for up to 86 days, and younger, weaned pigs for 157 days. Virus excretion in semen can persist for up to 93 days after infection.

The virus is spread by contact with infected pigs, and infection also be transmitted by infected semen. Fomites, such as contaminated needles, boots, overalls and transport vehicles can also transmit PRRS, as can certain species of insects including house flies. It has been thought that aerosol transmission may occur, particularly under conditions of high humidity, low temperatures, and low wind speeds, but this has been difficult to reproduce in the field and experimentally. Once infected, adult animals shed PRRS virus for up to 86 days, and younger, weaned pigs for 157 days. Virus excretion in semen can persist for up to 93 days after infection.

PRRS virus can also be transmitted by fomites, such as contaminated needles, boots, coveralls, transport vehicles, and shipping containers. Farm personnel are not a risk, unless hands are contaminated with blood from viremic pigs. Finally, transmission via certain species of insects (mosquitos [ Aedes vexans ] and house flies [ Musca domestica ]) has been reported. The role of migratory waterfowl has not been determined. While biologic transmission of PRRS virus has been documented in immature Mallard ducks, results have not been reproducible experimentally using adult Mallards, nor have infected pigs been able to transmit virus to adult Mallards housed under field conditions.

==Pathogenesis==

==Pathogenesis==