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Postgraduate Projects - Masters Research Students

A comparative study of the sensitivity of antigen capture ELISA and PCR to detect epizootic haematopoietic necrosis virus in spiked tissue homogenates of rainbow trout

Mr Tho Nguyen Dang

Mr Tho Nguyen Dang
Research support: University of Sydney International Postgraduate Research Scholarship.
Supervisors: Dr RJ Dixon, Professor RJ Whittington

Epizootic haematopoietic necrosis virus (EHNV) can cause high mortality (100%) in redfin perch and mild morbidity and mortality in rainbow trout. The Fish Diseases Commission of the Office International des Epizooties (OIE) has recommended that an antigen capture ELISA be the standard diagnostic test for EHNV infection. As PCR is routine in many diagnostic laboratories, this study was initiated to determine whether PCR would be more sensitive than the ELISA, subsequently reducing false negative results in virus testing. The results showed that the PCR had increased sensitivity compared to the ELISA in detecting EHNV. The practical implications of these results were addressed. Additional data were obtained through transmission experiments in redfin perch on the host-pathogen relationship. Pre-existing antibody mediated immunity was demonstrated in redfin perch that were refractory to infection with an isolate of EHNV shown previously to be highly virulent for this species.

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A National Survey of Bovine Infectious Bovine Keratoconjunctivitis and characterization of virulence attributes.

Mr Craig McConnell

Mr Craig McConnell
Research Support: Schering Plough Animal Health
Supervisor: Associate Professor JK House

Infectious bovine keratoconjunctivitis (IBK) is considered the most common ocular disease of cattle throughout the world. Despite the susceptibility of the causative bacterium, Moraxella bovis, to a large number of antimicrobial compounds the treatment of affected cattle has many disadvantages and the prevention of IBK is therefore preferable. IBK pathogenesis is linked to two M bovis virulence factors; namely, surface-associated pili and a haemolytic exotoxin (cytolysin) with corneotoxic properties. Pili have been shown to be antigenic and immunogenic and have been recommended as either cellular or acellular vaccine components. Efficacious application of pili based IBK vaccines requires production of a polyvalent vaccine targeting specific regional isolates. Cytotoxicity is mediated by the M bovis calcium-dependent cytolysin which is a β-haemolytic, leukotoxic pore-forming protein (MbxA protein) that belongs to the repeats in the structural toxin (RTX) family of pore-forming toxins and is encoded by the gene mbxA. The objective of this project is to evaluate pili serologic cross-reactivity, assess for the presence of RTX operons, and to measure antimicrobial susceptibility of Moraxella strains isolated from Australian IBK outbreaks.

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Efficacy of DNA Adenine Methylase Salmonella Vaccines Against Heterologous Challenge in Holstein-Friesian Bull Calves

Ms Virginia (Jennie) Mohler

Ms Virginia (Jennie) Mohler
Research Support: United States Department of Agriculture
Supervisors: Associate Professor John House, Dr. Keith Walker, and Dr. Michael Hornitzky

This is a Bachelor of Science (Veterinary)/PhD project. Salmonella are important pathogens of livestock and humans. Increasing antibiotic resistance in food producing species; concerns about antibiotic residues; stock losses; and residual poor growth rates indicate that vaccination would be more economically effective. Traditional salmonella vaccines elicit protection against a single strain of Salmonella. In intensive animal agriculture multiple Salmonella serovars are endemic. A major challenge in the development of a commercial Salmonella vaccine is to find a product that provides sustained cross-protective immunity.

Salmonella Typhimurium containing a deletion of the gene required for DNA adenine methylation (DAM) are avirulent yet confer protective immunity as modified live vaccines in murine, avian and bovine models of salmonellosis. DAM controls several important and diverse biological processes including DNA replication, methyl-directed mismatch repair, transposition, and the expression of pili required for colonization of host tissues. Experiments conducted in mice and poultry have demonstrated the capacity of DAM attenuated S. typhimurium to induce protection against heterologous salmonella challenge. Results from current research in calves indicates that protective efficacy of DAM vaccines against subacute heterologous infection with Salmonella Dublin.

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Dietary and management impacts on the prevalence of environmental mastitis pathogens.

Ms Lucy Shum

Ms Lucy Shum
Research Support: Pfizer Animal Health
Supervisor: Associate Professor JK House

There has been a significant decline in the incidence of contagious mastitis due to improvements in milking management in the dairy industry. Intra-mammary infections are now caused predominantly by environmental pathogens, particularly environmental Streptococci spp., coliforms, and environmental Staphylococci spp.. Australian mastitis surveys conducted on pasture based dairies in Victoria report Streptococcus uberis to be the most common environmental mastitis pathogen with few cases of coliform mastitis. In contrast coliform mastitis is reported to be common in Europe and North America. According to the results of mastitis cultures conducted at the UVCC coliform mastitis is more frequent in this region than reports from Victoria. The dairy industry in NSW reflects a diversity of management systems ranging from pasture based to intensive freestall production systems. The objective of this study is to determine the prevalence of mastitis pathogens in NSW dairy farms and to investigate the interactions between diet and environment on the incidence of environmental mastitis pathogens.

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