Re: Vietnam: General News
PORCINE REPRODUCTIVE & RESPIRATORY SYNDROME - VIET NAM (05): REQUEST FOR INFORMATION
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Date: Fri 1 Aug 2008 - Source: VietNamNet Bridge [edited]
http://english.vietnamnet.vn/social/2008/08/796686/
A total of 12 provinces and cities in Viet Nam have blue ear disease in pigs. This disease is spreading its wings in the central province of Quang Nam. Local authorities have decided to buy 20 000 doses of blue ear vaccine. Another central province, Thua Thien-Hue, has said it will allocate VND 270 million (USD 15 900) to prevent this disease. So far, the province has culled more than 1800 pigs.
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Communicated by:
ProMED-mail rapporteur Mary Marshall
[PRRS (Porcine reproductive and respiratory syndrome, also named blue ear disease) is caused by a virus which is currently classified as a member of the newly established order of _Nidovirales_, family _Arteriviridae_, genus _Arterivirus_.
It is now ubiquitous throughout most of the pig-rearing areas of the world and is believed to exist in 2 main forms -- the type 1 genotype, which predominates in Europe and the type 2, which predominates in the USA.
A complicating factor in PRRS epidemiology has been the use of live vaccines, some of which have caused clinical disease and become established in the local pig population.
Such vaccines have allegedly been applied throughout the world, including Asia.
Increasing data indicate that PRRSV is antigenically, genetically, and pathologically very heterogenic.
PRRS was initially reported from Viet Nam in April 2007, allegedly introduced from neighboring China where it had started its massive epizootic in 2006, initially known there as "Swine High Fever Disease."
The disease, declared endemic in Viet Nam since 23 Feb 2008, has spread throughout the country. OIE's summary, including a map, is available at
http://www.oie.int/wahid-prod/public.php?page=event_summary&reportid=5199.
The Chinese PRRS epizootic has been reviewed recently (May 2008) in the paper "Highly Virulent Porcine Reproductive and Respiratory Syndrome Virus Emerged in China" by Y.-J. Zhou, X.-F. Hao et al., in Transboundary and Emerging Diseases, Volume 55, Issue 3-4 (p 152-164). Their abstract says:
"A highly pathogenic pig disease emerged in China in 2006, which was characterized by prolonged high fever, red discoloration of the body, and blue ears associated with high mortality. Porcine reproductive and respiratory syndrome virus (PRRSV) was isolated as the single most prominent virus in the samples collected from affected pigs. The full-length genomic sequence of the virus revealed 2 distinct deletions in the non-structural protein 2 (NSP2) in comparison to all previously reported North American genotype PRRSV. Through extensive surveys in 14 different provinces, 56 additional PRRSV isolates were obtained from affected farms. All of the isolates were found to contain identical deletions in NSP2. To confirm the etiology, 8 60-day-old PRRSV-free pigs were divided into 2 groups and the test group was intranasally infected at a titer of 2 x 10(5.0) tissue culture infectious dose 50 per pig. The inoculated pigs all died at 7, 8, 12, 16, or 21 days post-inoculation with their clinical and pathological findings similar to those in the field. The viruses recovered from dead pigs were identical to the inoculated virus in NSP2 and GP5 genes. Our study shows that the recently emerged PRRSV in China is characterized by 2 discontiguous deletions in NSP2 and is the cause for the current epizootics in China."
In the paper's discussion chapter, the authors concluded:
"Previous studies on the genetic diversity of PRRSV circulating in China showed a clear distinction between the 2 diverse subgroups 1 and 2 within the North American genotype. There are 2 vaccines currently being used in China; the modified live vaccine RespPRRS/Repro and a killed vaccine of CH-1a virus. These vaccines appear to be less effective for the current epizootics.The viruses for both vaccines fall in subgroup 2, whereas isolates associated with the current epizootics belong to subgroup 1. Mutations are found in the prime neutralizing epitope (PNE) on GP5 in the current epizootics when compared to RespPRRS/Repro and other subgroup 2 Chinese PRRSV isolates. Additionally, the highly virulent PRRSV has one or 2 more sites for N-linked glycosylation in GP5 in comparison to the viruses found before 2006. In particular, novel glycosylation sites of N33N34N35 are found to be located closer to PNE, which may have resulted in non-recognition by the immune system.
"The sequence changes in PNE and the newly formed glycosylation near PNE may be important for resistance of the new type PRRSV to current vaccines. Alternatively, the new type may have gained an ability to escape from the immunologic network in the infected hosts. During the surveillance, 8 isolates recovered from affected farms showed almost identical sequences to that of the RespPRRS/Repro vaccine, and these isolates did not contain any deletion in NSP2. Thus, they were regarded as the vaccine virus and so were likely irrelevant to the current epizootics.
The origin of etiology and other factors for current epizootics in China need to be further investigated.
"Nevertheless, we have shown the evidence for PRRSV association with 'high fever syndrome.' The experimental infection has reproduced the disease of high virulence and high mortality compared to the clinical picture seen in classical PRRS. Bioinformatics and genomic analyses also show the great sequence diversity from the previous isolates
obtained in 1996-2005.
"The role that the new type of PRRSV plays in the current epizootics in China and the genetic factors that made the virus highly virulent are extremely important and need to be determined further."
It will be helpful if similar studies, addressing the Viet Nam PRRS virus, become available. - Mod.AS]
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