Disease

Secondary Infection with <em>Streptococcus suis</em> Serotype 7 Increases Virulence of Highly Pathogenic PRRS

Highly Pathogenic PRRS virus (HP-PRRSV) infection increased susceptibility to S. suis serotype 7 (SS7) infection, and co-infection of HP-PRRSV with SS7 significantly increased the pathogenicity of SS7 to pigs, according to researchers in China.

1 January 2011

3 minute read

By: Jackie Linden

Porcine reproductive and respiratory syndrome (PRRS) virus and Streptococcus suis are common pathogens in pigs. In samples collected during the porcine high fever syndrome (PHFS) outbreak in many parts of China, PRRSV and S. suis serotype 7 (SS7) have always been isolated together.

To determine whether PRRSV-SS7 co-infection was the cause of the PHFS outbreak, Min Xu of Harbin Veterinary Research Institute and co-authors there and at Guangdong Academy of Agricultural Sciences, Jinlin University and Northeast Agricultural University in Harbin evaluated the pathogenicity of PRRSV and/or SS7 in a pig model of single and mixed infection. Their paper was published in Virology Journal.

Respiratory disease, diarrhoea and anorexia were observed in all infected pigs. Signs of central nervous system (CNS) disease were observed in the highly pathogenic PRRSV (HP-PRRSV)-infected pigs (4/12) and the co-infected pigs (8/10). However, the symptoms of the co-infected pigs were clearly more severe than those of the HP-PRRSV-infected pigs. The mortality rate was significantly higher in the co-infected pigs (8/10) than in the HP-PRRSV- (2/12) and SS7-infected pigs (0/10).

The deceased pigs of the co-infected group had symptoms typical of PHFS, such as high fever, anorexia and red colouration of the ears and the body. The isolation rates of HP-PRRSV and SS7 were higher and the lesion severity was greater in the co-infected pigs than in mono-infected pigs.

Xu and co-authors concluded that HP-PRRSV infection increased susceptibility to SS7 infection, and co-infection of HP-PRRSV with SS7 significantly increased the pathogenicity of SS7 to pigs.

Reference

Xu M., Sh. Wang, L. Li, L. Lei, Y. Liu, W. Shi, J. Wu, L. Li, F. Rong, M. Xu, G. Sun, H. Xiang and X. Cai. 2011. Secondary infection with Streptococcus suis serotype 7 increases the virulence of highly pathogenic porcine reproductive and respiratory syndrome virus in pigs. Virology Journal 7:184 doi:10.1186/1743-422X-7-184