Outbreaks of highly pathogenic porcine reproductive and respiratory syndrome in Jiangxi province, China

In 2007, herds of pigs in Jiangxi Province, China experienced outbreaks of a severe form of suspected porcine reproductive and respiratory syndrome (PRRS) characterized by high fever, high morbidity and mortality in animals of different ages. 152 swine sera and 42 tissues (consisting of liver, lung, lymph node and kidney) from five herds of pigs were collected. Pigs were diagnosed as infected with a highly pathogenic form of the PRRS virus (PRRSV) based on ELISA and reverse transcriptase polymerase chain reaction (RT-PCR) results. Serological surveys indicated that 67-100% of the examined pig herds in Jiangxi Province were seropositive. 42 tissue samples were used to detect classical swine fever virus, porcine circovirus type 2 and PRRSV. Results indicated that only PRRSV was detected in 42 samples. 12 PRRSV amplified products of five herds, which consisted of two or three samples randomly selected from each herd, were used for sequencing. Subsequent nucleotide sequencing showed that the NSP2 gene had 99-99.7% nucleotide and 99.2-100% derived amino acid sequence identities among 12 tissues with that of the PRRS-JXA1 strain, deletions of 29 amino acids corresponded to positions 534-562 of the NSP2 gene sequence. These results revealed that the diseased pigs were all caused by fatal PRRSV variant. Compared with the same period in 2006, the number of positive cases from Jiangxi Province remained unchanged. These findings demonstrated that the highly pathogenic Northern American type PRRSV was still spreading in Jiangxi Province, China in 2007.