The porcine haemophili - a laboratory view

Abstract

The porcine haemophili constitute a group of bacteria that include two important pathogens of pigs - Actinobacillus pleuropneumoniae and Haemophilus parasuis. Other members of the group are widely regarded as part of the normal flora of the pig. These organisms, with their demanding growth requirements, have traditionally presented considerable difficulties to veterinary diagnostic laboratories. This review critically examines recent developments in the tools available to diagnostic laboratories. Conventional methods for the isolation and identification of these organisms are reviewed. Several Polymerase Chain Reaction (PCR) tests have been reported - mainly for A. pleuropneumoniae. The specificity of these tests varies - with the recently described PCR for the apxIV toxin gene offering the best specificity to date. A second test, a PCR-RFLP test, has the advantage of giving almost serovar-specific patterns for A. pleuropneumoniae as well as species-specific patterns for H. parasuis. A range of different serological assays has been described for the diagnosis of A. pleuropheumoniae. Of the described assays, the ELISAs based on polysaccharide and long-chain lipopolysaccharide antigens have proven the most valuable. Serological assays based on ELISAs for antibodies to the toxins of A. pleuropneumoniae have found applications in research but have generally lacked the specificity to be of use for broad scale disgnostic application. No robust serological assays exist for H. parasuis.