Concurrent infection with PCV2 and PRRSV is known as one of the major causes of PRDC, report Yi-Chieh Tsai of the School of Veterinary Medicine at the National Taiwan University in Taipei and co-authors there and at the University of Purdue in the US.

In a paper published in BMC Veterinary Research, the researchers continue that dual infection with PCV2 and PRRSV consistently leads to more severe clinical presentations and pulmonary lesions than infection with PCV2 alone or PRRSV alone. However, it is not known if dual infections with PCV2 and PRRSV in different infection order may lead to different clinical symptoms in the host.

To mimic the possible field conditions, swine alveolar macrophages (AMs) were inoculated with PCV2 and PRRSV in vitro simultaneously or with one virus 18 hours earlier than the other. The cell viability, cytopathic effects, antigen-containing rates, phagocytotic and microbial killing capabilities, cytokine profiles (IL-8, TNF-alpha, and IFN-alpha) and FasL transcripts were determined, analysed and compared to prove the hypothesis.

A marked reduction in PRRSV antigen-containing rate, cytopathic effect and TNF-alpha expression level was revealed in AMs inoculated with PCV2 and PRRSV simultaneously and in AMs inoculated with PCV2 first then PRRSV 18 hours later but not in AMs inoculated with PRRSV first then PCV2 18 hours later.

A transient decrease in phagocytosis but constant reduction in microbicidal capability in AMs in the group inoculated with PCV2 alone and constant decrease in phagocytosis and microbicidal capability in AMs in all PRRSV-inoculated groups were noted.

The levels of IL-8, TNF-alpha, IFN-alpha and FasL transcripts in AMs in all groups with dual inoculation of PCV2 and PRRSV were significantly increased, regardless of the infection orders as compared with infection by PCV2 alone or PRRSV alone.

Tsai and co-authors concluded that swine AMs infected with PCV2 first then PRRSV later or infected with PCV2 and PRRSV simultaneously displayed marked reduction in PRRSV antigen-containing rate, cytopathic effect and TNF-alpha expression level.

They added that the different inoculation orders of PCV2 and PRRSV in AMs leading to different results in viral antigen positivity, cytopathology and cytokine profile may explain, at least partially, the underlying mechanism of the enhanced pulmonary lesions in PRDC exerted by dual infection with PCV2 and PRRSV and the variable clinical manifestations of PRDC-affected pigs in the field.

Reference

Tsai Y-C., H-W. Chang, C-R. Jeng, T-L. Lin, C-M Lin, C-H. Wan and V. Fei Pang. 2012. The effect of infection order of porcine circovirus type 2 and porcine reproductive and respiratory syndrome virus on dually infected swine alveolar macrophages. BMC Veterinary Research, 8:174. doi:10.1186/1746-6148-8-174

Further Reading You can view the full report (fee payable) by clicking here. Find out more information on porcine reproductive and respiratory syndrome (PRRS) by clicking here. Find out more information on PMWS by clicking here.