unparalleled large-scale outbreaks of an originally unknown,
but so-called "high fever" disease in China
Infected pigs were highly contagious, usually affecting
the whole pig population within 3–5 days.
|
"Initially, the "high fever" was suspected to be hog cholera
or African swine fever (ASF). The representative sick pigs had the following
common clinical symptoms: rubefaction, blood spots, petechiae, erythematous
blanching rashes, and pimples, frequently observed in ears, mouth, noses,
back, and the inner thigh.
Other common symptoms included high fever (40-42 deg C
/ 104-107.6 deg F), depression, anorexia, cough, asthma, lameness, shivering,
disorder in the respiratory tract, and diarrhea. Infected pigs could
be divided into 2 groups: group one, which appeared fat and healthy;
and group 2 with thin and debilitated features, ultimately leading to
death. To our surprise, many grown pigs also died during this epidemic
period, which is unlike the case for typical PRRSV infection. |
Since
its first appearance in the United States and Canada, PRRS has been
known to be a serious swine disease associated with major economic
losses worldwide [5], [6].
Moreover, typical PRRS is also called “blue ear” disease
due to a representative symptom of the infected piglets (i.e., “blue
ear”) [42].
Prior to this outbreak of PRRS, we were aware that Northern American
(VR2332)-like PRRSVs, which include the HB-1, HB-2, and BJ-4 strains,
exist in China [12], [43].
However, there is no evidence to suggest they have ever caused a large
scale epidemic of PRRS with fatal cases among grown sows [12], [25], [43].
Here, we describe for the first time an unprecedented outbreak of highly
pathogenic PRRS in China in 2006, which spread to more than 10 provinces
(autonomous cities or regions) and infected over 2,000,000 pigs, resulting
in about 400,000 fatal cases. This epidemic persisted for nearly 3
months and caused considerable economic losses among local pig farmers.
Fortunately, thanks to a collaborative effort, the outbreak was finally
effectively controlled through the combined means of efficient containment,
slaughtering, and vaccine inoculation.
Here our investigation of the
unparalleled large-scale outbreaks of an originally unknown, but so-called "high fever" disease in China in 2006, with the essence of PRRS, which spread to more than 10 provinces (autonomous cities or regions) and affected over 2 million pigs with about 400 000 fatal cases.
Different from the typical PRRS, numerous adult sows were also infected by the "high fever" disease. This atypical PRRS pandemic was initially identified as a hog cholera-like disease manifesting neurological symptoms (such as shivering), high fever (40-42 deg C / 104-107.6 deg F), erythematous blanching rash, etc. Autopsies combined with immunological analyses clearly showed that multiple organs were infected by highly pathogenic PRRSVs with severe pathological changes observed. Whole-genome analysis of the isolated viruses revealed that these PRRSV isolates are grouped into Type II and are highly homologous to HB-1, a Chinese strain of PRRSV (96.5 percent nucleotide identity). More importantly, we observed a unique molecular hallmark in these viral isolates, namely a discontinuous deletion of 30 amino acids in nonstructural protein 2 (NSP2). Taken together, this is the 1st comprehensive report documenting the 2006 epidemic of atypical PRRS outbreak in China and identifying the 30 amino-acid deletion in NSP2, a novel determining factor for virulence, which may be implicated in the high pathogenicity of PRRSV, and will stimulate further study by using the infectious cDNA clone technique.
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1885284
[The paper, freely available online, has been published in the June 2007 issue of PLoS (Public Library of Science) ONE Tian K, Yu X, Zhao T, Feng Y, Cao Z, et al (2007): Emergence of Fatal PRRSV Variants: Unparalleled Outbreaks of Atypical PRRS in China and Molecular Dissection of the Unique Hallmark. PLoS ONE 2(6): e526. DOI: 10.1371/journal.pone.0000526]
Summary
Porcine reproductive and respiratory syndrome (PRRS) is a severe viral disease in pigs, causing great economic losses worldwide each year. The causative agent of the disease, PRRS virus (PRRSV), is a member of the family _Arteriviridae_.
Since
its first appearance in the United States and Canada, PRRS has been
known to be a serious swine disease associated with major economic
losses worldwide [5], [6].
Moreover, typical PRRS is also called “blue ear” disease
due to a representative symptom of the infected piglets (i.e., “blue
ear”) [42].
Prior to this outbreak of PRRS, we were aware that Northern American
(VR2332)-like PRRSVs, which include the HB-1, HB-2, and BJ-4 strains,
exist in China [12], [43].
However, there is no evidence to suggest they have ever caused a large
scale epidemic of PRRS with fatal cases among grown sows [12], [25], [43].
Here, we describe for the first time an unprecedented outbreak of highly
pathogenic PRRS in China in 2006, which spread to more than 10 provinces
(autonomous cities or regions) and infected over 2,000,000 pigs, resulting
in about 400,000 fatal cases. This epidemic persisted for nearly 3
months and caused considerable economic losses among local pig farmers.
Fortunately, thanks to a collaborative effort, the outbreak was finally
effectively controlled through the combined means of efficient containment,
slaughtering, and vaccine inoculation.