P.PSH.1307 - Q-Fever: A new approach to combatting an old Australian livestock problem

Summary

Q fever is a debilitating bacterial disease of humans, with close association with cattle the most commonly reported risk factor. This project will investigate the progress of the infection in cattle, in order to better understand the risk posed to humans, and the possibility of vaccinating livestock to mitigate this risk.

Objectives

The project objectives are as follows:

1. Refinement and validation of existing and new assays.
2. Evaluate livestock health and reproductive consequences of C. burnetii.
3. Define C. burnetii shedding and infection risks associated with processing.
4. Quantify the productive or reproductive losses associated with coxiellosis and use this data to develop a model that will begin to evaluate the economic impact of coxiellosis on animal production at the herd level and inform the potential value of livestock vaccination as a risk management strategy.
5. Isolate and characterise C. burnetii strains.
6. Develop evidence-based guidelines for management of coxiellosis in herds.

Key findings

Detailed reproductive data was collected from an intensive dairy herd, showing cattle that were seropositive at calving were less likely to become pregnant than those that were seronegative at calving. C. burnetii exposure was not strongly associated with foetal loss or abortion however calves born from cows with a positive PCR vaginal swab were more likely to die within a few days of birth than calves from cows that tested negative.

Infection with C. burnetii was common in beef cattle presenting at abattoir, with evidence of infection in herds from a wide geographic area and very high seroprevalences in some mobs. Seroprevalence was higher in cows of parity six or above than in younger cows, steers or heifers. A C. burnetii positive sheep flock was not identified despite trialling multiple methodologies across ~25 different flocks.

Another key outcome was the isolation of C. burnetii strains from cattle enrolled in the study that have also been isolated from Australian Q fever patients across multiple clonal complexes, confirming the Q fever public health risk that cattle infected with C. burnetii present. The C. burnetii strains identified in cattle are also found in other species, including wildlife. Within a cattle herd, multiple types of C. burnetii can co-circulate.

Benefits to industry

This discovery research project has advanced the knowledge of the pathogenesis of coxiellosis in Australian cattle herds with the findings suggesting that C. burnetii may be causing important production losses.

MLA action

No further investment is planned in this area of research, MLA will share the final report on the MLA R&D reports page.

Future research

The project has provided evidence-based recommendations for areas where future research should be directed to understand the true impact of this pathogen on the Australian livestock industry. The considerable knowledge around best practice for sampling and diagnosis of this pathogen both in the animal and in farm environments is available to inform future research and diagnostic efforts. Coxiella burnetii isolates are in archival storage providing a unique resource for future projects or vaccine development.

Future research in beef cattle and herds should be directed towards:
- further understanding the pathogenesis of infection with C. burnetii and investigating the role C. burnetii plays in reproductive failure and calf mortality across a larger number of Australian beef herds
- understanding how the high seroprevalence at slaughter translates into risk of exposure of people in abattoirs to the pathogen along the slaughter line
- further assessment of the geographic distribution and prevalence of C. burnetii in Australian cattle herds and potentially in sheep flocks
- detailed review of the economic benefits and costs, feasibility and risks of a program to develop an Australian vaccine for animals 4.3.1 against C. burnetii to control infection in animals and humans.