Kinetics of single and dual simultaneous infection of pigs with swine influenza A virus and porcine reproductive and respiratory syndrome virus

Abstract

Background: Simultaneous viral infections exhibit the phenomenon of viral interference, but understanding of the effect of one virus on another is limited.

Objective: Evaluate and compare clinical characteristics, immune and acute phase response, viral shedding and viral load in pigs singly and doubly inoculated with swine influenza A virus (swIAV) and porcine reproductive and respiratory syndrome virus (PRRSV).

Animals: Fifty-four 7-week-old piglets.

Methods: Clinical status and gross lung lesions were scored. Titration of swIAV was carried out in Madin-Darby canine kidney cells. The PRRSV RNA was quantified using a commercial qPCR kit. Antibodies were detected by hemagglutination inhibition assay and commercial ELISA. A lymphocyte proliferation assay was used to measure antigen-specific T-cell responses. Acute phase proteins were determined using ELISA.

Results: No differences were found between mean clinical scores, swIAV and PRRSV shedding, and magnitude of the humoral and T-cell response between single-inoculated and dual-inoculated groups. Concentrations of C-reactive protein and haptoglobin increased in PRRSV-inoculated and coinoculated groups, whereas serum amyloid A concentration was increased in groups inoculated or coinoculated with swIAV. Mean swIAV TCID₅₀ titers in the lungs did not differ significantly between coinoculated and swIAV single-inoculated pigs. A significantly higher mean copy number of PRRSV was found in the lungs of PRRSV only-inoculated pigs at 2 day postinoculation (DPI). From 4 DPI, no significant differences in PRRSV load were identified.

Conclusions and clinical importance: Coinfection of pigs with swIAV and PRRSV did not potentiate clinical signs, lung lesions, immune response, and replication of the viruses in the respiratory tract.

Keywords: coinfection; disease; immune and acute phase response; viral load; viral shedding.