A retrospective study of a porcine reproductive and respiratory syndrome outbreak in South Africa in 2004

Abstract

Porcine Reproductive and Respiratory Syndrome (PRRS) is a controlled disease in South Africa. This disease is caused by an Arterivirus and occurs commonly in Europe (European serotype) and in the United States of America (American serotype); therefore PRRS is not a trade sensitive disease. However, the disease has severe economic implications for the producer and the local pork industry and the decision was made by the Department of Agriculture, Fisheries and Forestry in association with the South African Pork Producers’ Organization (SAPPO) to eradicate the disease when the first outbreak occurred in 2004 in the Western Cape. Severe disease leading to acute mortalities and almost 100% mortality and morbidity rate in a few pig units in the Jacobsdal area (Kuilsrivier district) in the Cape Town peninsula, alarmed local veterinary consultants during the autumn of 2004. A first diagnosis of Salmonella choleraesuis was confirmed at the Provincial Veterinary Laboratory in Stellenbosch. Antibiotic treatment did not resolve the clinical picture. Sows still aborted and died and young pigs still died from acute respiratory distress. The syndrome was similar to “blue ear disease” because of severe cyanosis visible on the extremities of affected pigs. The first suspected diagnosis of Porcine Reproductive and Respiratory Syndrome virus (PRRSV) was made on post mortem examination on 10 June 2004 and was confirmed on 17 June 2004 with positive ELISA (Idexx Herdchek PRRSV Ab test kit 2XR) results. A stamping out procedure immediately followed through slaughtering of all affected pigs showing clinical signs of PRRSV infection. Pigs in close proximity with possible contact and infection risk were also slaughtered. The movement of pigs was only allowed under Red Cross permit and all pig auctions were stopped. A local and countrywide serological survey was implemented immediately. The results of this survey luckily showed that the outbreak was limited to a few districts in the Western Cape. The probable source of infection is suspected to be uncooked swill originating from the Cape Town Harbour or the Cape Town International Airport, which was fed to pigs. The PRRSV responsible for the outbreak was confirmed on 5 July 2004 as the American serotype by RT-PCR test done at Lelystad, Netherlands. The National Department of Agriculture (NDA)* agreed to compensate pig owners for slaughtered pigs. This decision was further made possible by funding from SAPPO to protect the rest of the commercial pig herd in South Africa to ensure food safety and security. A total of 32 pig units were affected by PRRS of which only one was a commercial unit. All affected pigs were slaughtered by the end of August 2004. Units were cleaned and disinfected by the staffs of the Boland and Swartland State veterinary departments with approved disinfectants which is effective against PRRSV. Cleaned units had to stay empty of pigs for at least 8 weeks after disinfection was completed. Restocking was only allowed from known PRRS-free pig suppliers and regular monitoring was implemented of all previously infected sites and units in high risk areas. On-going serological monitoring revealed no more positive cases since May 2005. It seems that the stamping out procedure and a temporary ban on movement and auctions of live pigs played a primary role in eradication of the PRRSV outbreak in South Africa in 2004. * The name of the NDA has been changed to the National Department of Agriculture, Forestry and Fisheries (DAFF) in 2009, but because the NDA was the applicable name when the PRRS outbreak occurred, NDA will be used in this document.