Completed Research Projects - Sheep (Part 2)
Identifying risk factors for OJD-infection in sheep
Enabling technologies for internal parasites of sheep
Analysis of critical genes in the sheep
Characterisation of crtitical sheep genes
Identification of risk factors for OJD-infection level in sheep flocks OJD.038
Farm Animal & Veterinary Public Health Staff
- Dr Jenny-Ann Toribio
- Professor Richard Whittington
PhD Students
Mr Navneet Dhand
National Collaborators
- Dr Jeff Eppleston, Central Tablelands Rural Lands Protection Board
- Dr Evan Sergeant, AusVet Animal Health Services
Summary
The level of clinical disease experienced due to ovine Johne's disease (OJD) appears to vary considerably between infected sheep flocks in Australia, even for flocks in the same locality that appear to have similar characteristics. This has led to considerable speculation about the potential importance of flock management, soil type, pH and micro-nutrients. Sound understanding about factors that influence disease expression will lead to management recommendations that improve on-farm disease control.
The aim of this project was to identify risk factors for OJD expression in infected flocks and improve the understanding of the epidemiology of the infection. The project consisted of a cross-sectional study on 92 infected properties located in New South Wales, Victoria, Tasmania and Western Australia. The information obtained from each included the OJD prevalence in specific groups of adult sheep measured using pooled faecal culture, details of farm and flock management and soil analyses from paddocks on which the sheep sampled had grazed.
A total of 31 significant farm/flock/management and soil variables were found. Some were likely to be a consequence of OJD infection, but the remainder appeared to be potential risk factors for the severity of the disease. There was a strong relationship between the PFC results and the duration of flock infection, the level of OJD mortality, dam stocking rates, as well as a relation with parent soil type. There was also a consistent but statistically non-significant trend for lower OJD levels in 4-year olds compared to 3-year olds, which may be due to deaths of affected sheep from 2 to 3 years of age. Wethers had significantly higher OJD levels than ewes, which strongly supports the anecdotal observation of higher losses in wether mobs. Higher OJD prevalence was linked to measures correlated with soil fertility including cation exchange capacity, phosphorus buffer index and organic matter content of soil.
Successful completion of this project enables the development of additional recommendations for on-farm control measures for OJD to support vaccination, and may help clarify the ecological niche of M. paratuberculosis, the potential for disease spread into areas not currently affected and the likely level of disease that would be experienced in these areas.
Source of Funding
Meat & Livestock Australia
Project Timeframe
January 2004 - June 2005
Enabling technologies of RNAi and cell culture for internal parasites of sheep AHW.032
Farm Animal & Veterinary Public Health Staff
- Professor Nick Sangster
- Dr Michelle Power
Technical Officer
Ms Krishanthi Gunarathnam
Summary
Research into the biology of sheep nematode parasites suffers from the lack of molecular techniques to study gene function and cell biology. Techniques such as RNA interference and cell culture have potential to improve our understanding of parasites and to identify novel control targets.
RNAi is a technique of gene silencing where individual genes can be switched off and the effects observed. If the affected worms are affected (for example, are paralysed) the gene product may be a good candidate as a control target. Cell culture allows the study of isolated worm components. Given that it is difficult to cultivate these parasites in vitro, cell culture could open up approaches to studying cell biology that are currently unavailable.
In this project we have developed phenotyping tools that will be used to measure RNAi effects and have commenced the gene knockout experiments. These are currently available in the free-living stages of the parasite, but the ultimate aim is to develop the technique for parasites in sheep. Cells recovered from worms have been grown in culture. These will be used to study defined cell types and as a platform for RNAi. They offer several potential advantages as it may be easier to deliver RNA to these cells and their responses will be simpler to interpret than responses in sheep.
The aim is to develop tools for further research. This project falls into a multi-institutional research program with the aim of discovering targets for improved parasite control.
Source of Funding
Meat & Livestock Australia
Australian Wool Innovation
Project Timeframe
February 2004 - February 2006
Neuromuscular physiology of nematode parasites of sheep
Farm Animal & Veterinary Public Health Staff
Professor Nick Sangster
International Collaborators
- Dr Janina Demeler
- Dr Arbeit Fellow (University of Hannover )
Summary
The neuromuscular physiology of nematodes is a rich source of potential parasite control targets. Nerves and muscle are also the site of the action of a range of current anthelmintic drugs. This project has two parts, one to explore the neuromuscular basis of ivermectin resistance with a view to developing resistance detection assays and the second is to discover novel neuropeptides and their receptors which may be useful targets for parasite control.
Several assays are used in the laboratory to measure: muscle contraction (using a force transducer), development, motility, migration and electrical responses in the pharynx of worms. The laboratory is equipped with electrophysiology gear that can be used to measure a range of electrical responses, including patch clamp and voltage clamp.
The project aimed to understand the pharmacology of avermectin/ivermectin resistance in sheep nematodes. This information will help develop tools for molecular diagnosis in the future.
The work showed that:
- drug action and resistance occurred at two distinct sites, pharynx and body muscle of worms;
- the two major drug classes act in similar ways but their receptor populations are not identical in distribution in the worms or/and the three species of parasites;
- resistance is most likely due to different mechanisms in the different species and even isolates of the same species. A single test for resistance is not likely to be found;
Janina Demeler who carried out this work was awarded her Dr Arbeit at the Tierartzliche Hochschule Hannover and the prize for the best thesis in 2005.
Source of Funding
Australian Research Council
Pfizer Australia
Project Timeframe
August 2003 - August 2005
Analysis of critical genes in the sheep/Haemonchus relationship
Farm Animal & Veterinary Public Health Staff
- Professor Nicholas Sangster
- Associate Professor David Emery
- Dr Tony Rowe
National Collaborators
The SGP includes scientists from:
CSIRO Livestock Industries,
University of Melbourne,
and the University of Sydney
Summary
This project dovetails in with our existing project on the sheep/Haemonchus relationship. The emphasis in this new project is to add value by carrying out DNA microarray experiments to identify sets of sheep genes which are up or down regulated during critical events in establishing immunity to Haemonchus. Further work to validate these genes will be performed using quantitative PCR and immunocytochemistry. The aim is to identify genes which may act as future markers for selection of sheep able to mount effective immune responses to worms.
Source of Funding
Meat and Livestock Australia
Australian Wool Innovation
Project Timeframe
May 2004 - April 2007
Characterisation of crtitical genes in the sheep/Haemonchus relationship
Source of Funding
Meat and Livestock Australia
Australian Wool Innovation
within the Sheep Genomics Project (SGP)
Project Timeframe
November 2005 - July 2007