Key Messages

• The results confirm that the interactions of different times of infection (not only types of viruses) can cause different effects.
• A pre-existing or co-existing PCV2 could interfere or hinder, at least partially, PRRSV infection.
• If PRRSV already established an infection, this partial inhibition was not seen.
• On the other hand, PRRSV could enhance PCV2 replication.

Article Brief

This in vitro study was designed to determine if different co-infection orders of PCV2 and PRRSV would affect the functions of swine AMs.

12 SPF pigs were used (5 to 6 weeks old) for a bronchoalveolar lavage and collection of AMs. Then six different infection protocols of AMs were done: PCV2, PRRSV, PCV2 and PRRSV (18 hours later), PRRSV and PCV2 (18 hours later), PCV2 and PRRSV (simultaneously) and Mock.

The phagocytosis rate (PR) in the PCV2 group was lower than in the Mock group. The PRs in the groups that received only PRRS or PRRS before PCV2 were more affected than in the groups where PCV2 came alone, before or at the same time as PRRS.

A pre-existing or co-existing PCV2 could interfere or hinder, at least partially, PRRSV infection. PCV2 affected PRRSV replication but also reduced the interference of PRRSV on phagocytosis capability of swine AMs.

However, when PRRSV established an infection prior to PCV2 inoculation, the partial inhibition of the PRRSv infection consequences was not seen. On the other hand, PRRSV could enhance PCV2 replication.

The microbicidal rate (KR) after 108h post infection was affected in all inoculated groups without statistical differences.

The levels of IL-8, TNF-α, IFN-α and FasL in all groups with both viruses inoculated were increased, regardless of the infection order compared to infections by PCV2 or PRRSV alone.

The results confirm that the interactions of different viruses (and times of infection) are complicated and can cause a variety of clinical pictures in the field.

PCV2 could be interfering the infection by PRRSv when it comes before PRRSV has been able to establish an infection. The reduced microbicidal rate of swine AMs in all inoculated groups suggests that PCV2 and/or PRRSV infection can cause a higher multiplication and survival of other opportunistic or secondary agents in pig lungs.

Reference

Tsai Y.C., Chang H.W., Jeng C.R., Lin T.L., Lin C.M., Wan C.H. and Pang V.F. 2012. 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.

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