Research Projects - Cattle

Ms Jenny Mohler

Specific aims include:

• to determine if Salmonella dam mutant vaccines can confer cross-protective immunity against multiple Salmonella isolates in calves. A principal concern with all modified live vaccines is safety.
• to introduce additional attenuating mutations (e.g., aroA) to reduce the virulence capacity of the Salmonella dam vaccine without compromising efficacy in calves.
• to determine if Salmonella dam vaccines can be used as a platform for delivering passenger antigens to elicit protection against the cognate pathogen. We have chosen the Enterotoxogenic E. coli (ETEC) K99 fimbriae as a model passenger antigen since ETEC strains that express K99 fimbriae account for nearly all cases of ETEC infection in newborn calves and K99 fimbriae are a known immunogen that confers protective immunity against clinically relevant ETEC infections in calves and other species. The K99 fimbriae antigen from ETEC clinical isolates will be expressed in dam Salmonella. Vaccine efficacy will be assessed by elicitation of protective immunity against ETEC diarrheal disease in calves via passive colostral transfer of protective antibodies from vaccinated cows.
• to develop safe and effective vaccines against Salmonella infection of cattle, and to demonstrate that this vaccine platform may be used to express cognate antigens from other pathogens thereby promoting the health and productivity of livestock, reducing Salmonella contamination of livestock, livestock-derived food products, and enhancing food safety.

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. M. bovis virulence factors include the production of leukotoxin, protease, and β-hemolysin along with the presence of fimbriae on the bacterial cell surface that play a role in adherence. M. bovis fimbrial proteins act as immunogens and vaccination with isolated fimbriae stimulates bovine anti-fimbrial antibodies. However, strains of M. bovis are known to differ in their fimbrial antigens, with two types of fimbriae identified along with at least seven distinct serogroups of fimbriated M. bovis. Efficacious application of fimbrial based IBK vaccines requires production of a polyvalent vaccine targeting specific regional isolates.

The aims of this project are:

• to conduct a survey of Moraxella bovis strains in Australia to determine the prevalence of different serotypes across the country
• to determine which virulence attributes are common to most isolates
• to design a pink eye vaccine applicable to prevention of bovine infectious keratoconjunctivitis in Australia.

Associate Professor John House

The prevalence of contagious mastitis in dairy cattle has dropped over the last 20 years. Environmental mastitis subsequently accounts for the largest proportion of intramammary infections and the associated losses in production. Surveys of mastitis conducted in Australia have reported that Streptococcus uberis is the most frequent environmental mastitis pathogen and suggest that coliform mastitis is relatively infrequent in Australian dairy cattle. These prevalence surveys have been conducted in Victoria and reflect the prevalence of disease in pasture fed dairy cattle.

Over the last 10 years there has been a steady and continuing trend toward intensification of the dairy industry with more farms providing supplementary feeding and some farms feeding total mixed rations similar to dairy production systems in Europe and the United States. Working with intensive dairy production systems in NSW we have observed a higher incidence of coliform mastitis than reported in Victorian surveys.

The objective of this study is to determine the prevalence of different mastitis pathogens on intensive dairies in NSW and to investigate the interaction between diet and environment on the major groups (coliforms and streptococci) of environmental pathogens.