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PATHOGENESIS AND EPIDEMIOLOGY OF INFECTIOUS DISEASE

A fundamental understanding of the genetic basis of virulence and of the host response to infection, as well as of the behaviour of infectious pathogens in animal populations, is essential to rational development of improved control measures. APCAH staff and students have conducted research that has:

  • Discovered the role played by recombination between attenuated vaccines in the genesis of novel virulent strains of infectious laryngotracheitis virus vaccines, and demonstrated the role of recombination in the evolution of other major animal herpesviruses.
  • Discovered the basis for high frequency antigenic variation in pathogenic mycoplasmas, work that has explained the persistence of these important infectious agents and that has explained problems encountered in serological diagnosis.
  • Defined the immunomodulatory effect of glycoprotein G of infectious laryngotracheitis virus and shown that deletion of the gene encoding it reduces the virulence of this important viral pathogen. This work has led to the development of a novel attenuated vaccine to control infectious laryngotracheitis.
  • Demonstrated that high concentrations of Rhodococcus equi are exhaled by young foals and thus that they may represent a contagious risk to each other. This work has led to suggestions for changes in management aimed at reducing the prevalence and severity of this disease on horse studs.
  • Defined the major bacterial pathogens responsible for peracute mastitis in sheep in Australia, indicating the targets for future vaccination strategies.
  • Identified virulence factors required by E. coli to cause disease in the respiratory tract in chickens and in the reproductive tract in dogs.
  • Identified key indicators of susceptibility to endometritis in mares.

Our recent studies have been applying high throughput sequencing and bioinformatics analysis to discovery of novel pathogens and to conducting detailed genetic mapping studies for epidemiological investigations. We have also been integrating genomics and metabolomics to explore the roles of specific genes in virulence.

VACCINE DEVELOPMENT

Bacterial and viral vaccines developed in APCAH include:

  • Mycoplasma gallisepticum ts-11, an attenuated live vaccine strain that is licensed through the world for control of mycoplasmosis in chickens.
  • Mycoplasma synoviae MS-H, an attenuated live vaccine strain that is licensed through the world for control of mycoplasmosis in chickens.
  • Mycoplasma hyopneumoniae ts-19, an attenuated live vaccine strain that is licensed for control of enzootic pneumonia in pigs.
  • An attenuated vaccine against infectious laryngotracheitis virus that is currently being assessed for development by commercial partners.
  • We have also developed candidate vaccines for the control of colibacillosis in poultry and mycoplasmosis in cattle.

DIAGNOSTIC TEST DEVELOPMENT

APCAH staff and students have developed novel recombinant antigens for improved serological diagnosis of Mycoplasma bovis, Mycoplasma gallisepticumMycoplasma synoviae, Mycoplasma hyopneumoniae, Mycoplasma pneumoniae and laryngotracheitis virus infections. The ELISAs based in these antigens have offered infectious improved sensitivity and specificity over previously available assays and a number of these antigens are now the basis of commercially available kits produced by our commercial collaborators.

Real-time polymerase chain reaction assays have been developed for most major bacterial and viral pathogens of poultry and applied to diagnosis and strain differentiation. These assays are offered to the industry and the public through our diagnostic laboratory and offer improved sensitivity and specificity over previously available assays, as well as strain differentiation for some pathogens.

Polymerase chain reaction assays have been developed to detect feline and equine respiratory pathogens and are provided as a diagnostic service to the veterinary profession.

ANTIMICROBIAL STEWARDSHIP

The primary goal of antimicrobial stewardship is to optimise clinical outcomes while minimising unintended consequences of antimicrobial use, including the emergence of resistance. Given the association between antimicrobial use and the selection of resistant pathogens, the frequency of inappropriate antimicrobial use is often used as a surrogate marker for the avoidable impact on antimicrobial resistance. The combination of effective antimicrobial stewardship with a comprehensive infection control program has been shown to limit the emergence and transmission of antimicrobial-resistant bacteria.

Australian Veterinary Prescribing Guidelines

Laura Hardefeldt
laura.hardefeldt@unimelb.edu.au

Glenn Browning
glennfb@unimelb.edu.au

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