Objective: To validate a polymerase chain reaction (PCR) based method. Enterobacterial Repetitive Intergenic Consensus-PCR (ERIC-PCR), for the fingerprinting of Haemophilus parasuis strains and to use that method to differentiate isolates from apparently related outbreaks of Glässer's disease on three pig farms.
Design: ERIC-PCR was evaluated by comparing 15 different strains that represented all 15 recognised serovars in the Kielstein-Rapp-Gabrielson (KRG) scheme for serotyping H parasuis. Next, ERIC-PCR was used to examine 14 Australian field isolates of H parasuis; 12 collected from three farms suffering apparently related outbreaks of Glässer's disease and two from two other farms with no known connection.
Results: The 15 serovar reference strains all gave unique, reproducible ERIC-PCR fingerprints. The 12 isolates from the three apparently related outbreaks all gave a single fingerprint, which was distinct from any seen in the 15 serovar reference strains and the two other Australian field isolates in the studied farms. The confirmation that all 12 isolates were the same strain allowed the development of a prevention and control program that has prevented the emergence of any further outbreaks of Glässer's disease on the three farms.
Conclusion: ERIC-PCR is a suitable technique for the differentiation of unrelated strains of H parasuis. The finding that the 12 field isolates of H parasuis all shared the same fingerprint is strong evidence that there was a common source of infection on all three farms. This study has shown, for the first time, that ERIC-PCR is a suitable technique for the sub-typing of H parasuis and useful for studying the epidemiology of outbreaks of Glässer's disease.