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Porcine Reproductive and Respiratory Syndrome Virus
Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) is currently the viral disease in swine industry with the greatest economic impact. The virus is endemic in all major swine producing areas worldwide. PRRSV-free countries have comparatively small swine industry with less live animal and by-product trades. To date, countries included in the list are Argentina, Australia, Brazil, Chile, Cuba, Ecuador, Finland, New Caledonia, New Zealand, Norway, Paraguay, Sweden, Switzerland and Uruguay.5
(Photo courtesy of https://www.prrscontrol.com/portal/prrscontrol/news-on prrs/news detail/The+huge+economic+impact+of+PRRS)
China, Philippines, Thailand, and Vietnam had been hit by the atypical highly virulent strains of PRRSV since 2006 and in 2010, spreading among the countries in East and other countries of Southeast Asia.2 In the Philippines, pig production is a major livestock industry amounting to 102.79 billion pesos last 2012 according to Bureau of Agricultural Statistics (BAS). Among the swine infectious diseases, PRRS had the most devastating impact on pig industry from 2007-2012, with approximated economic losses around 6 billion pesos per year.1 The emergence of virulent PRRSV strains poses a threat to countries with high pig densities in the East and Southeast Asia.2
PRRS can cause reproductive or respiratory signs depending on the age and physiologic condition of the animal. In sows and gilts, reproductive problems are commonly seen while respiratory tract illness in younger pigs.3, 5
WHAT IS PRRS AND HOW DOES IT AFFECT SWINE?
PRRSV is an enveloped virus in the group Arteriviridae. It can be inactivated via treatment with ether or chloroform. The virus favors cold temperatures and very stable up to -70°C, however, as temperature increases the virus’ activity is also reduced (at 56°C). Mode of transmission of the virus is via direct or indirect contact with the infected pig. The virus can be shed from the infected animal via nasal secretions/discharges, feces, urine, milk/colostrum and semen (OIE, 2008). The likelihood of semen viral transmission depends on the quantity of virus. As compared to intranasal transmission, this transmission will also require as high as 100 to 1000 times higher viral dose required to infect gilts and sows.
Figure 2. Routes of PRRSV transmission
(Photo courtesy of http://www.prrsresource.com/about-prrs)
PRRS have two distinct forms: reproductive failure and post-weaning respiratory diseases. Gilts and sows infected with the PRRSV may exhibit reproductive failure: abortions, stillborn piglets, mummified foetuses, premature farrowing, irregular return to estrus and lower conception rate. Central nervous system (CNS) signs including incoordination and circling may follow abortions. In general, fewer clinical signs are observed in PRRSV infected boars and these include fever, lethargy, decreased appetite and libido and infrequently, respiratory signs. Studies show a decline in semen quality: decreased motility and presence of proximal and cytoplasmic droplets. PRRSV highly virulent variants cause abortion rates ranging from 10-50%, mortality rate of gilts and sows for up to 10% and mortalities in boars.3, 4, 5
Figure 3. PRRS infection in the sow resulting to stillborn and weak
piglets upon farrowing
(Photo courtesy of http://www.respig.com/pages/disease/prrs.aspx)
Infected piglets in utero or immediately after birth manifest signs that include difficulty in breathing, lethargy decrease in appetite, fever, and swelling of eyelids. Pre-weaning mortality may reach up to 100%. Persistent of the virus in the infected piglets last for about 112 days and post-weaning mortality is also observed. For post-weaning and grower to finisher pigs, clinical signs that can be seen are similar to pre-weaned piglets. Secondary bacterial and viral infections contribute to the severity of the disease in porcine respiratory disease complex (PRDC) (Zimmerman).
Figure 4. Ear edema in PRRS infected older pigs
(Photo courtesy of http://www.thepigsite.com/pighealth/article/142/porcine-reproductive-and...)
Serologic assays such as ELISA and fluorescent antibody test can be used to screen the presence of PRRSV infection in the herd. For more accurate diagnosis, nucleic acid sequencing such as PCR, viral isolation, and immunohistochemistry are methods to demonstrate evidence of the viral DNA3.5
TREATMENT, MANAGEMENT CONTROL, AND PREVENTION
Currently, no treatment is available against PRRSV infections. It is essential to prevent secondary bacterial infection to aggravate the disease condition in the herd. Antibiotic treatment should be administered to diagnosed or suspected pigs for three to four weeks.4 It is important to purchase breeding stock from PRRSV-free herds, quarantine newly acquired pigs for about eight weeks, serology screening can be done to determine PRRSV exposure of the herd and for the newly acquired pigs, provide strict biosecurity: proper disinfection of transport vehicles, methods of insect control, application of air filtration systems.3,4,5
Vaccination of the herd should be considered and depopulation of the infected group of pigs to eliminate the virus.4
1. Abao, L. N. B., Kono, H., Kubota, S., Borejon, J. V., Gaerlan, M. Z., & Promentilla, R. R. (2014). PRRS Outbreaks and Farm Hygiene Management in the Philippines. Japanese Journal of Farm Management, 52(1-2), 131-136.
2. Dietze, K. (2011). Porcine reproductive and respiratory syndrome (PRRS): virulence jumps and persistent circulation in Southeast Asia. Focus on…, 5: 8.
3. OIE. (2008). PRRS: the disease, its diagnosis, preventionand control. Appendices IV and V of the REPORT OF THE OIE AD HOC GROUP ON PORCINE REPRODUCTIVE RESPIRATORY SYNDROME, 1-7.
4. The Pig Site. (n.d.). Porcine Reproductive and Respiratory Syndrome. Retrieved 11 November 2017 from http://www.thepigsite.com/pighealth/article/142/porcine-reproductive-and...
5. Zimmerman, J., Benfield, D., & Christopher-Hennings, J. Porcine Reproductive and Respiratory Syndrome (PRRS). Retrieved 11 November 2017 from https://pdfs.semanticscholar.org/e234/be5584340b4b93a803cd71af16dd1bce89....