Porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome virus (PRRSV) is a virus that causes a disease of pigs, called porcine reproductive and respiratory syndrome (PRRS), also known as blue-ear pig disease (in Chinese, zhū láněr bìng 豬藍耳病). This economically important, panzootic disease causes reproductive failure in breeding stock and respiratory tract illness in young pigs. Initially referred to as 'mystery swine disease' and 'mystery reproductive syndrome', it was first reported in 1987 in North America (2) and Central Europe (3). The disease costs the United States swine industry around $644 million annually, and recent estimates in Europe found that it costs almost 1.5b€ every year. PRRSV is a small, enveloped RNA virus. It contains a single-stranded, positive-sense, RNA genome with a size of approximately 15 kilobases. The genome contains nine open reading frames. PRRSV is a member of the genus Arterivirus, family Arteriviridae, order Nidovirales. Other members of the genus Arterivirus include: equine arteritis virus, simian hemorrhagic fever virus, wobbly possum disease virus, and lactate dehydrogenase elevating virus. The two prototype strains of PRRSV are the North American strain, VR-2332, and the European strain, the Lelystad virus (LV). The European and North American PRRSV strains cause similar clinical symptoms, but represent two distinct viral genotypes whose genomes diverge by approximately 40% (6), thus creating a veil of mystery about the origin of this virus. The genetic variation among the viruses isolated from different places (7-8) increases the difficulty of developing vaccines against it. Similarly, maintaining diagnostic PCR detection assays is difficult due to the high mutation rate of this virus, see Risk of Missed PRRS PCR Detection. In the early 2000s a highly pathogenic strain of the North American genotype emerged in China. This strain, HP-PRRSV, is more virulent than all other strains, and causes great losses in Asian countries worldwide. Later a study showed that accelerated evolution of a group of strains in China.