Louis L. Harris

Isolation of swine infertility and respiratory syndrome virus (isolate ATCC VR-2332) in North America and experimental reproduction of the disease in gnotobiotic pigs

A recent epizootic of swine infertility and respiratory syndrome (SIRS) in a Minnesota swine herd was investigated. Examination of a sow, neonatal piglets, and stillborn fetuses obtained during the epizootic from the affected herd revealed interstitial pneumonitis, lymphomononuclear encephalitis, and lymphomononuclear myocarditis in the piglets and focal vasculitis in the brain of the sow. Fetuses did not have microscopic lesions. No cause for the infertility and respiratory syndrome was determined. Therefore, attempts were made to experimentally reproduce the disease. Eleven 3-day-old gnotobiotic piglets exposed intranasally to tissue homogenates of piglets from the epizootic became inappetent and febrile by 2–4 days postexposure and had interstitial pneumonitis and encephalitis similar to that seen in the field outbreak. After 2 blind passages in gnotobiotic piglets, tissue homogenates were cultured on continuous cell line CL2621, and a cytopathic virus (ATCC VR-2332), provisionally named SIRS virus, was isolated. Gnotobiotic piglets exposed intranasally to the SIRS virus developed clinical signs and microscopic lesions that were the same as those in piglets exposed to the tissue homogenates, and the virus was reisolated from their lungs. This is the first isolate of SIRS virus in the United States that fulfills Kochs postulates in producing the respiratory form of the disease in gnotobiotic piglets and the first report of isolation and propagation of the virus on a continuous cell line (CL2621). The virus is designated as American Type Culture Collection VR-2332.

Antigenic Comparison of Lelystad Virus and Swine Infertility and Respiratory Syndrome (SIRS) Virus

This study reports the antigenic relatedness of isolates of Lelystad virus collected in the Netherlands, Germany, and the United States. The binding of antibodies directed against these isolates was tested in a set of field sera collected during outbreaks of porcine epidemic abortion and respiratory syndrome in Europe and outbreaks of swine infertility and respiratory syndrome (SIRS) in North America. Two sets of sera from pigs experimentally infected with Lelystad virus or SIRS virus were also tested. Although all 7 isolates reacted with anti-Lelystad virus sera, antigenic variation was considerable. The 4 European isolates resembled each other closely, but differed from the American isolates, and the 3 American isolates differed antigenically from each other. To reliably diagnose Lelystad virus infection, a common antigen must first be identified.

Serologic evidence incriminating a recently isolated virus (ATCC VR-2332) as the cause of swine infertility and respiratory syndrome (SIRS).

and swine infertility and respiratory syndrome (SIRS). tality ranged from 37% to 83% and was accompanied by late term (>day 100) abortion in all but 1 herd. The absence of anorexia in 2 herds and absence of dyspnea in 1 herd may reflect a failure of detection rather than absence of these clinical signs (Table 2). Each case herd was matched with a herd located within 10 miles, of similar size and type of production, and having no history of undiagnosed reproductive failure or respiratory disease in the last 3 years. Sera were collected from approximately 30 representative sows at each of these 16 herds.