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

Dual infections of pigs with porcine reproductive and respiratory synd rome virus (PRRSV) followed by a second common respiratory virus, eith er porcine respiratory coronavirus (PRCV) or swine influenza virus (SI V), were studied. The aim was to determine if dual infections, as comp ared to single virus infections, result in enhanced clinical manifesta tions. It was also examined if PRRSV replication affects replication o f PRCV or SIV in the respiratory tract. Groups of conventional 10 week old pigs were inoculated with PRRSV-only (3 pigs), PRCV-only (4 pigs) or SIV-only (4 pigs). Dual inoculations with PRRSV-PRCV (4 pigs) and PRRSV-SIV (3 groups of 3, 4 and 5 pigs) were performed at a 3 day inte rval. A group of uninoculated control pigs (8 pigs) was included. The infection with PRRSV-only induced a transient fever (40.2 degrees C) a t 2 DPI, but no respiratory signs. The PRCV-only infection remained su bclinical. The SIV-only infection resulted in a one day fever (40.1 de grees C) with moderate tachypnoea and dyspnoea. Mean weight gain in th e virus-inoculated groups was retarded compared with the control group . The PRRSV-PRCV infection induced a 9 day lasting fever (peak 40.9 de grees C) with tachypnoea, dyspnoea and productive coughing. The PRRSV- SIV infection resulted in fever and respiratory signs in all 3 groups. Clinical signs, however, were more pronounced in group 1 than in grou ps 2 and 3. Pigs of group 1 showed fever during 10 days (peak 41.4 deg rees C), tachypnoea, marked dyspnoea with abdominal breathing, and a p roductive cough. Pigs of groups 2 and 3 had fever for 5 and 3 days (pe aks 40.6 and 40.3 degrees C) respectively and mild respiratory disorde rs. Mean weight gain during 14 DPI of the 2nd virus was 5.9 kg in the PRRSV-PRCV group and 4.0, 6.8 and 6.7 ki: in PRRSV-SIV groups 1, 2 and 3 respectively. Mean weight gain during the corresponding period in t he PRRSV-only group was 8.6 kg. It was concluded that dual infections with viruses causes more severe disease and growth retardation than si ngle PRRSV infection. PRCV excretion curves were similar in single and dual virus inoculated groups. Excretion of SIV was delayed by 2 days in the dual inoculated pigs. Thus, replication of the second virus is not (PRCV) or only slightly (SIV) affected by a prior infection with P RRSV.