Porcine reproductive and respiratory syndrome virus

Arterivirus
Virus classification
Group: Group IV ((+)ssRNA)
Order: Nidovirales
Family: Arteriviridae
Genus: Arterivirus
Species: Porcine reproductive and respiratory syndrome virus
For the Marvel Comics Superhero, see Blue Ear (comics).

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.

Classification

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 (Meulenburg et al., 1992, Lee and Yoo, 2005).

PRRSV is a member of the genus Arterivirus, family Arteriviridae, order Nidovirales.[1] The three other members of the genus Arterivirus are: equine arteritis virus, simian hemorrhagic fever virus, and lactate dehydrogenase elevating virus (4-5).

Strains

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.[2]

Clinical signs

Subclinical infections are common, with clinical signs occurring sporadically in a herd. Clinical signs include reproductive failure in sows such as abortions and giving birth to stillborn or mummified fetuses, and cyanosis of the ear and vulva. In neonatal pigs, the disease causes respiratory distress, with increased susceptibility to respiratory infections such as Glasser's disease.


Control

Porcine Reproductive and Respiratory Syndrome (PRRS) is a complex disease. Modified Live Vaccines (MLV) vaccines are the primary immunological tool for its control, but PRRS control goes way beyond than just vaccination, and in order to achieve sustainable results, a systematic approach should be implemented. It requires a full understanding of the disease and a set of tools to achieve a long term success, therefore a standardized 5 step process has been developed to successfully achieve PRRS control. A strong platform to consolidate PRRS control in pig farms, large production systems and even geographical areas has been developed. This platform is a pig population approach having as main goals: - to maximize immunity, - reduce PRRS virus (PRRSv) exposure and - prevent new PRRSv infections. The Complexity of PRRS has allowed implementing successfully this methodology in the Swine Industry around the globe.


See also

References

  1. ↑ Balasuriya and Snijder (2008). "Arteriviruses". Animal Viruses: Molecular Biology. Caister Academic Press. ISBN 978-1-904455-22-6.
  2. ↑ Song J, Shen D, Cui J, Zhao B (Oct 2010). "Accelerated evolution of PRRSV during recent outbreaks in China". Virus Genes 41 (2): 241–5. doi:10.1007/s11262-010-0507-2. PMID 20652733.

External links