| In late 2006,. there was an outbreak of large-scale swine disease in pig herds in south China. The general symptom is high fever, so it was called“Mystery Fever Disease Syndrome”or‘‘high fever''disease. It was happened at Jiangxi, Hunan Province at the beginning and then spread to almost the whole country covered with more than 20 provinces, and made tremendous loss to the pig industry of China. The characters of the disease is spreading fast and widely, high incidence of a disease, high death rate and low cure rate and so on. Many experts work hard to study the disease, and identified the primary pathogen—PRRSV. The aim of this study was to investigate the role of the PRRSV in this epidemic, including, the nucleic acid variation and the virulence analysis, and eventually uncover the“mystery”of the disease or syndrome. The paper has four parts:From the herds of Xi'an, Baoji, Weinan, Yulin, Hanzhong, Shangluo in Shaanxi Province during this disease outbreaks, totally 146 samples including the serum, lung and spleen/lymph node, were detecteded to Porcine reproductive and respiratory syndrome virus(PRRSV), porcine circovirus type2 (PCV- 2), classic swine fever virus (CSFV) and pseudorabies virus (PRV), four viruses were detected by PCR or RT- PCR..The results showed, the prevalence of PRRSV were 46.6%(68/146);the co-infection rates of CSFV and PRRSV , PCV2 and PRRSV, PRV and PRRSV were 25% (17/68), 19.1% (13/68) and 4.4% (3/68), respectively; the co-infection rates of CSFV ,PCV2 and PRRSV was 14.7%(10/68); the co-infection rates of CSFV, PCV2 , PRV and PRRSV was 2.9% (2/68). All the results suggested that the co-infection of PRRSV and other pathogens is very prevalent in these detected pigs.The samples that were collected in Shaanxi province were inoculated Marc-145 cell which were ready before. The obvious cytopathogenic effects were observed after 72 hours postinfection,and the virus propagation in Marc-145 cell were determined by RT-PCR and IFA.The results suggested that the two isolates were obtained,which was designated as Shannxi-1,Shannxi-2.Two PRRSV isolates were isolated from nosopoietic pigs in Xi'an wildlife park and Huaxian, respectively. The sequence analysis of NSP2, ORF2,ORF3 ORF4, ORF5,ORF6 and ORF7 showed that the nucleotide sequence of these isolates shared 86.0%?96.6% identity with American type isolates ,but only 55.2%with European prototype LV,which suggested the two isolates belongs to American type in genotype.NSP2 gene of these isolates has no 30aa identity with the other American strains,ATCC VR2332,HB-1 etc.In order to well understand the genetic relations of American type isolates ,a phylogenetic tree was generated based on NSP2 and ORF5.Results from the evolutionary analysis indicates that American type isolates can be divided into twe subgroups based on NSP2 and ORF5 genes.PRRSV isolates of China mainland seem belong to different subgroup. Shannxi-1,Shannxi-2 belongs to one subgroup with JXA1,HB-1,and CH-1a,and BJ-4 belongs to the other subgroup with VR2332.The pathogenicity of PRRSV variation (Shannxi-1,Shannxi-2, JXA-1)were researched, which were isolated from pigs of the so called“high fever”in pig herds in Shannxi province. TCID50 of the three PRRSV were detected by Reed-Muench method, The 12 healthy pigs of 40 ages in days which were negative of antibody and antigen of PRRSV were separated into 4 groups. Every group was challenged by 3 isolations respectively. The pigs were isolated artificial feeding. The TCID50 of the isolations were 10-4.8 TCID50/0.1mL,10-4.8TCID50/0.1mL, 10-5.2 TCID50/0.1mL,respectively. Body temperature was measured and clinic symptom was noted everyday. The challenged pigs appeared classical symptom, such as the high body temperatures, secretion with the nose especially with the eyes. PRRSV RNA had been detected from serum and swabs of eye,nasal,throat and fece, and the pathogenicity of Shannxi-2 is stronger than the other.But there is no pig died. |
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