Isolation of a Cytopathic Virus from Weak Pigs on Farms with a History of Swine Infertility and Respiratory Syndrome

Abstract

Abstract. Severe clinical signs of swine infertility and respiratory syndrome (SIRS) of unknown cause were observed in several Minnesota swine farms between November 1990 and March 1991. Forty-five lung samples of weak pigs were collected from 13 swine farms, and virus isolation was attempted using swine alveolar macrophage (SAM) cultures. A cytopathic virus was isolated from 19 lung samples collected from 6 different farms. Four pregnant sows were infected intranasally with a tissue suspension from which virus was isolated, and 4 6-week-old pigs and 2 contact pigs were infected intranasally with 1 of the isolates. The 4 sows farrowed 12 stillborn and 32 normal pigs. Virus was recovered from 10 of 19 pigs examined. Infected 6-week-old pigs were clinically normal except for slightly elevated rectal temperatures and mild respiratory signs. No or mild interstitial pneumonic lesions were observed in inoculated pigs, but the lesion was obvious in the 2 contact pigs. Seroconversion was observed in sows and pigs as measured by indirect fluorescent antibody (IFA). Serologic identification of the isolates was carried out by IFA using reference serum prepared from an experimentally infected sow. A cytoplasmic fluorescence was observed on the SAM monolayers infected with each of the 19 different isolates. Fluorescence was also observed when the monolayers were tested with SIRS virus ATCC VR-2332-infected sow sera. Replication of the isolates was not affected in the medium containing 5-iodo-2'-deoxyuridine but was inhibited by treatment with ether. The isolates were relatively stable at 56 C and did not agglutinate with various erythrocytes tested. These results are similar to those of previous reports, and the isolates, designated as SIRS virus, were the cause of SIRS on the farms investigated.

Evolution of Porcine Reproductive and Respiratory Syndrome Virus during Sequential Passages in Pigs

“…Clinically, infection may range from totally inapparent to causing severe disease. Generally, clinical signs involve reproductive disorders in pregnant animals and/or respiratory disease in pigs of all ages (11,20,21,23,47,51,63). Reproductive disease in pregnant animals is manifested as late-term abortions or premature farrowings.…”

“…Reproductive disease in pregnant animals is manifested as late-term abortions or premature farrowings. Affected litters have higher proportions of stillbirths and piglets born weak and increased preweaning mortality (11,23,63).…”

Evaluation of Enzyme-Linked Immunosorbent Assay (ELISA)and Immunofluorescent Antibody (IFA) Test for the Detection of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) Antibody in Pigs from Conventional Farms.

“…Sera were subjected for virus isolation and antibody testing by IFA and ELISA. Virus isolation proceeded using SAM as described by Yoon et al [26].…”

Porcine Reproductive and Respiratory Syndrome

“…19 Subsequently, Yoon et a1. 76 isolated several other strains of PRRS virus from 19 lung samples of weak pigs from 6 different farms and designated them as MN-l, MN-2, MN-3, etc. These isolates and the Lelystad virus cross-reacted with monoclonal antibodies against the nucleoprotein of VR-2332 strain.…”