Porcine reproductive and respiratory syndrome in China

Abstract

Porcine reproductive and respiratory syndrome (PRRS) is an economically important viral disease for the pig industry worldwide. This disease has brought great losses to the Chinese pig production in recent years, particularly following the emergence of the highly pathogenic PRRS virus (PRRSV), and has become an intractable problem for the development of pig industry in China. This paper will review the history of PRRS, the epidemic of atypical PRRS caused by the highly pathogenic virus, and the molecular characteristics of the Chinese highly pathogenic PRRSV, and the development of vaccines against PRRS in China, as well as current control status and perspective of PRRS in China.

Introduction

Porcine reproductive and respiratory syndrome (PRRS) is characterized by reproductive failure in sows, and respiratory disease in pigs (Albina, 1997, Hopper et al., 1992, Pejsak et al., 1997, Rossow, 1998), and causes economically great losses to the swine industry worldwide (Neumann et al., 2005, Pejsak et al., 1997). The disease was first recognized in 1987 in the United States of America (Keffaber, 1989), and subsequently became a pandemic disease in North America, Europe, and Asia within the succeeding years (Baron et al., 1992, Bilodeau et al., 1991, Benfield et al., 1992, Bøtner et al., 1994, Kuwahara et al., 1994, Wensvoort et al., 1991). By now, PRRS has become an endemic disease in the global swine production, except for several countries, including Sweden, Switzerland, New Zealand, and Australia claimed to be free of this disease (Cannon et al., 1998, Cho and Dee, 2006, Motha et al., 1997).

China not only is the biggest country of pig and pork production but also is the largest consumption market of pork in the world. In China, the number of slaughtered pigs and penned pigs reached 609 millions and 462 millions heads, respectively, and the amount of pork production was 46.2 millions tonnes in 2008, occupying 46% of global pork production (http://www.stats.gov.cn); meanwhile, China imported 2.2 millions tonnes of pork mainly from USA, and exported 4.3 millions tonnes of pork mainly to Russia and other Asian regions in the same year (http://www.chinafeed.org.cn). The Chinese pig-producing regions are mainly located along the Yangtze River, in North China, and some major grain-producing provinces. The breeding pigs include Large White, Landrace, Duroc, Hampshire and Pietrain, and domestic breeding pigs, as well as cross-breeding pigs. Breeding pigs are imported from Europe or North America in China each year. 12,000 heads of breeding pigs were imported in 2008 (http://www.caaa.org.cn). China has large numbers of pig farms with diversity of size, different level of management and bio-security, this leads to the difficulty to completely prevent and control the infectious diseases.

Since PRRS outbreaks were recognized in an intensive pig farms in North China at the end of 1995 (Guo et al., 1996a), the disease has been accompanying the Chinese pig production, and brought considerable cost to the swine industry in China each year although no exact amount was estimated. In particular, the epidemic of atypical PRRS caused by the emerging highly pathogenic PRRS virus (PRRSV) has resulted in huge economic losses to the Chinese pig industry since 2006 (Tian et al., 2007, Yang, 2007).