Key Messages

• Prior PRRSV infection exacerbates the later infection with swine influenza virus (SIV) or porcine respiratory corona virus (PRCV)
• Co-infection of pigs with PRRSV and SIV created a very severe and lasting respiratory disease
• The co-infection with PRRS causes also a severe growth retardation.

Article Brief

The present study was realized to determine the clinical effects of dual infections with PRRSV followed by PRCV or SIV.

Another objective was to determine if PRRSV interferes with the replication of the PRCV or SIV.

A total of 36 pigs of 10 weeks of age (seronegative for PRRS, SIV and PRCV) were assigned to eight groups: control group, PRRSV-only, PRCV-only, SIV-only, PRRSV+PRCV and PRRSV+SIV (three groups). The secondary infections (PRCV and SIV) were performed three days after PRRSV infection.

Pigs were daily monitored for fever, tachypnoea, dyspnoea and coughing. They were also weighed daily and nasal swabs and blood samples were taken.

Fever was only detected in PRRS-infected pigs (one day).

SIV-infected pigs had fever only day while sporadic respiratory signs were seen (when forced to move) and a transient increase in breathing rate (65 per minute). However, when co-infected with PRRSV, the first group of pigs of PRRSV-SIV showed high fever for 10 days peaking at 41.4°C. They were severely affected and depressed and had also a marked anorexia. These pigs showed remarkable respiratory disease between four and 10 days after co-infection. The other two groups of PRRSV-SIV were moderately affected compared with the first group. However, in all of the three groups, average daily gain (ADG) was affected compared with the control, PRRSV-only and SIV-only groups

PRCV did not produce any response. However, when pigs were already infected by PRRS, an inoculation with PRCV produced fever for nine days and pigs developed fever and respiratory disease.

Virus excretion for PRCV was similar regardless of PRRS status and the excretion of SIV in the PRRSV-SIV group was delayed by two days.

This study confirms the hypothesis that the clinical effects of a PRRSV infection may be exacerbated when a concurrent infection with common respiratory viruses occurs.

Reference

VanReeth K., Nauwynck H. and Pensaert M. 1996. Dual infections of feeder pigs with porcine reproductive and respiratory syndrome virus followed by porcine respiratory coronavirus or swine influenza virus: a clinical and virological study. Veterinary Microbiology. 48:325-335.

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