March 9, 2011

Asian veterinarians surprised by behaviour of HP-PRRS in Vietnam

Asian scientists are unable to explain local dissimilarity in occurrence of highly pathogenic PRRS (HP-PRRS) strains in several areas in South East Asia, delegates heard at this week's Asian Pig Veterinary Society (APVS) Congress in Pattaya, Thailand.

Dr Nguyen Tung, attached to the Vietnamese National Center for Veterinary Diagnosis in Hanoi, explained to his audience about the observation and analysis of highly pathogenic Porcine Reproductive and Respiratory Syndrome (HP-PRRS) in Vietnam and its neighbour countries Laos and Cambodia.

Tung explained that since its first happening in March 2007, mainly two strains of HP-PRRS have been observed. Therefore, one was called the 2007 virus and the other, as it hit last year, the 2010 virus. Outbreaks in 2008 and 2009 were less severe and turned out to be mutations of the 2010 virus.

Tung said he and his team of scientists found that in Southern Vietnam and Cambodia, both strains can still be found as shown by the coexistence of the 2007 and 2010 strains. Oddly enough, in Northern Vietnam and neighbouring Laos, the 2007 strain appears to have completely disappeared. Tung indicated he did not know why this difference exists now.

In the APVS Congress' parallel sessions, delegates suggested that perhaps climate could have an effect, since North and South Vietnam are hundreds of kilometres apart. HP-PRRS is identified by being atypical as the virus has a unique 30 amino acid deletion in non-structural protein (NSP) 2 although this does not seem to cause its virulence.

There is ongoing discussion among scientists about whether HP-PRRS alone was the major cause of Swine High Fever Disease, which had badly affected the Chinese pig industry from 2006 onwards, or whether co-infection by other pathogens may be a more logical reason.