Completed Research Projects - Sheep
Pathogenisis of OJD: strategic research for diagnosis and prevention
Changes in prevalence of Mycobacterium Paratuberculosis shedding following vaccination with Gudair
Exposure factors: OJD infection & clinical disease
Effects of whole-flock vaccination for OJD
A study of the biological and economic impacts of OJD in affected sheep flocks
Epidemiology of OJD - pasture contamination, age susceptibility & diagnostic tests
Pathogenisis of OJD Strategic Research for Diagnosis and Prevention OJD.031
Farm Animal & Veterinary Public Health Staff
Professor Richard Whittington
Dr David Emery
Dr Kate Bosward
Dr Kumi de Silva
Dr Lyrissa Di Fiore
Dr Deborah Taylor
Dr Doug Begg
Ms Nicole Carter
Dr Reena Mehta
Mrs Anna Waldron
Mrs Rebecca Maurer
PhD Students
Ms Sally Browne
Ms Kate Goldsmith
Mr Sanjeev Gumber
Ms Ling Zhong
Ms Satoko Kawaji
Mr Ian Marsh
National Collaborators
NSW Department of Primary Industries
Elizabet Macarthur Agricultural Institute
Summary
Ovine Johne’s disease is a chronic and intractable problem. Spread of the disease has continued despite stringent regulatory measures, and in the absence of compensation for affected producers has led to severe division within the industry. Vaccination and risk-based trading have been accepted as an interim approach to limit further spread of the disease.
There is clearly an urgent need for better diagnostic tests. The main requirement is for a test that can detect infection in young sheep before the onset of faecal shedding. The test needs to be sensitive, specific, accurate, cost effective and able to distinguish an active infection from one that has died out. New automated technology platforms will be needed if tests are to have wide application in the sheep industries.
None of the work on OJD to date has included basic research. However, the need for this has been recognised and there are opportunities to take advantage of new technologies. Consequently the aims of this program were to research fundamental aspects of OJD including host-pathogen interactions at the cellular level. Protemics, genomics and advanced immunology techniques were applied to in vivo and in vitro models to study the early stages of infection and contrast these with events later in the disease process. The aim was to discover new pathways for disease development and expression that can be exploited later for development of diagnostics, vaccines and chemotherapeutics. Significant progress was made, with three patents pending, a new direct faecal test developed, a panel of antigens for immunodiagnosis awaiting evaluation and many host genes discovered that are involved in early pathogenesis. This project will extend into two new projects to validate technology and extend the findings to cattle.
Source of Funding
Meat & Livestock Australia
Project Timeframe
September 2002 - January 2008
Changes in within-flock prevalence of Mycobacterium paratuberculosis shedding following vaccination with Gudair in high and low prevalence flocks OJD.033
Farm Animal & Veterinary Public Health Staff
Professor Peter Windsor
Professor Richard Whittington
National Collaborators
Dr Jeff Eppleston,
Central Tablelands Rural Lands Protection Board
Dr Evan Sergeant,
AusVet Animal Health Services
Summary
The purpose of the project is to validate the widespread use of Gudair® vaccine for the reduction of bacterial shedding in medium/high prevalence flocks and the prevention of increased shedding in low prevalence flocks. The major outcome from the project will be to allow producers to predict the infectivity of flocks over time following the commencement of a vaccination program.
There is much producer interest, both at an individual and industry level, in the use of Gudair® vaccine to control the impact of OJD in flocks varying in disease prevalence from very low to very high. This project will observe changes over time in the prevalence of mycobacterial shedding following the commencement of a Gudair® vaccination program in flocks varying in initial OJD prevalence. Up to four flocks, each with high, medium or low OJD prevalence at the commencement of a vaccination program will be sampled over a six-year period to estimate changes in the prevalence of shedding as the proportion of vaccinates in the flock increases.
The relevant industry questions being addressed in this project are as follows:
- how long will it take for a vaccination program to reduce mycobacterial shedding to a level where safe trade in low risk sheep can occur?
- can the disease be eradicated by long-term vaccination?
how effective will vaccination be in low prevalence flocks in the control zone? - will vaccination prevent the increase in losses commonly seen in long-term infected flocks?
- can healthy sheep be vaccinated on arrival at an infected property so that infection and shedding is prevented?
Source of funding
Meat & Livestock Australia
Project Timeframe
January 2003 - March 2009
Exposure Factors – OJD Infection & Clinical Disease OJD.002
Farm Animal & Veterinary Public Health Staff
- Professor Richard Whittington
Dr Om Dhungyel
Mrs Anna Waldron
PhD Students
- Ms Helen McGregor
Mr Sanjeev Gumber
National Collaborators
- Professor Kym Abbott, Charles Sturt University
Novatis Australia Ltd
Merial Australia Pty Ltd
Summary
The aim of this project was to demonstrate whether pastures of low infectivity can be prepared and effectively used to reduce the level of OJD infection, potential production losses and mortalities from OJD in adult sheep in endemically infected flocks.
Sheep were exposed to different levels of M ptb, from birth to weaning and/or from weaning onwards. The different levels of exposure were high (H), medium (M) and low (L) with the level of exposure in the H groups about 10 times higher than in the M groups. The L groups were not deliberately exposed to M ptb but accidental contamination at very low levels did occur. The experiment was replicated.
The study demonstrated that careful management of young sheep can reduce the level of OJD in the flock and reduce the death rate. Steps taken to limit the degree of exposure of pre-weaned lambs to infection from pastures will lead to reduced rates of severe infection in those sheep in later years. Continuous exposure to OJD bacteria throughout early life results in higher infection rates than exposure which is limited to either the pre-weaning or the post-weaning period alone. A critical factor in management is to provide 'low risk' pastures to young sheep at weaning to give them a break from exposure to infection which occurs in the lambing paddocks.
Producers who successfully limit the infection will find themselves in an improved position. Additionally, by using the library of samples collected during the experiment, many more insights will be gained into the epidemiology of OJD, including the relationship between age at first exposure and the time before excretion of the organism, seroconversion, sub-clinical disease effects, clinical disease and death. These insights may allow the development of additional management options and systems which restrict the impact of OJD in flocks and will also improve the overall understanding of the pathogenesis of the disease, interpretation of existing and new diagnostic tests and the value of emerging research tools.
Source of Funding
Meat & Livestock Australia
Project Timeframe
September 1999 - December 2004
Effects of whole-flock vaccination for OJD OJD.015
Farm Animal & Veterinary Public Health Staff
- Professor Peter Windsor
Professor Richard Whittington
Dr Om Dhungyel
PhD Student
Ms Helen McGregor
Summary
Vaccination with Gudair® vaccine in OJD infected flocks has commenced in Australia. To date, use of vaccine has been recommended to be limited to lambs in an attempt to protect sheep before OJD pathology becomes advanced. As vaccination is considered by many graziers to be their best option for reducing losses and managing the disease, careful documentation of the effects of vaccination in a high prevalence infected flock and in older sheep will enhance knowledge and understanding of the benefits of the whole-flock vaccination strategy.
The proprietors of a farm reported a very high mortality believed to be due to OJD. Early estimates suggested that 25% of the flock had died in 1999. A preliminary investigation by The University of Sydney supported the owner's initial suspicion, with post mortem findings suggesting an annual mortality rate of 18.1% (+/- 12%). Vaccination of all sheep was favoured as the quickest way to reduce the OJD-contamination of pastures, the incidence of OJD and the death rate due to OJD.
The study concluded that vaccination combined with management changes led to a significant decline in the risk of OJD mortality and effective control of OJD in a heavily infected flock. Findings also suggested that vaccination may be beneficial in sheep as old as 8 months, even when exposed to a heavily contaminated environment since lambing.
This information will have immediate application to a large number of affected producers in NSW who have chosen or are considering vaccination as their major or initial method of OJD control.
This study provided the first estimate of flock mortality due to OJD based on objective data and was central to explaining the economic impact of OJD in high prevalence flocks. This information assisted development of rational control programmes.
Source of Funding
Meat & Livestock Australia
Project Timeframe
September 2000 - June 2004
A study of the biological and economic impacts of OJD in affected sheep flocks in NSW OJD.023
Farm Animal & Veterinary Public Health Staff
- Dr Jenny-Ann Toribio
Professor Peter Windsor
PhD Student
Mr Russell Bush
Summary
Anecdotal reports of the extent of mortality due to ovine Johne's disease ranged from less than 1% to over 20% of adult sheep per year, but there were no objective data. The aim of this study was to estimate the annual mortality rate due to OJD on twelve affected sheep flocks in four different regions of NSW using the methods developed in project OJD.015.
OJD mortality estimates were derived from farm records (livestock inventories) and quarterly farm visits (necropsy inspections). A most likely cause of death was determined for 362 sheep on the basis of findings related to the environment, clinical signs, gross pathology and histopathology. OJD was most likely to have contributed to the death of 250 of these sheep. OJD mortality increased from 1 year of age (10.4%) to peak at 4 years of age (35.6%) and was very similar between wethers (49.6%) and breeding ewes (50.4%).
On the 12 farms, the average OJD mortality rate based on inventory records was 6.2% (range 2.1% to 17.5%), more than twice that considered acceptable (from all causes) in sheep flocks in southern Australia. The OJD prevalence in 2-year old sheep based on pooled faecal culture ranged from 0.7% to > 23% on the 12 farms and was found to be associated with OJD mortality rate.
The average decrease in gross margin due to a farm being infected with OJD was 6.4% (range 2.2% to 15.4%) and the average estimated cost of OJD losses on the 12 farms over the 12- month study period was $64,100 ($15,569 to $154,083). The average estimated cost of annual OJD losses/DSE was $7.68 ($0.84 to $20.51) while annual OJD losses/ha were $65.92 ($6.75 to $244.80).
This study provided the first objective data on the true impact of OJD and the findings are generally applicable to sheep flocks in southern Australia. Industry groups claiming that OJD does not present a threat on-farm can now be provided with accurate figures on direct losses attributable to OJD within the endemic area of NSW. There was a wide range of impacts, with some very high mortality rates. The data can be used to justify vaccination programs, other control options and the general concept of disease control and prevention.
The challenge for industry is to use the scientific findings from this study and other recent research to prepare education and extension material to address issues of misinformation about OJD and to develop cost effective strategies for the future control and management of OJD.
Source of Funding
Meat & Livestock Australia
Project Timeframe
September 2001 - October 2005
Epidemiology of Ovine Johne’s Disease – Pasture contamination level, age susceptibility and diagnostic tests (OJD.028)
Farm Animal & Veterinary Public Health Staff
- Professor Richard Whittington
Dr Om Dhungyel
Mrs Anna Waldron
Ms Natalie Schiller
Ms Angela Reeves
PhD Students
- Ms Helen McGregor
Mr Sanjeev Gumber
National Collaborators
Australian Animal Health Laboratory, CSIRO
Summary
The aim of this project was to determine whether pasture contamination rates and the age of sheep when they are first exposed to infection influence the occurrence of ovine Johne's disease. The outcomes were targeted to improve understanding of the development of OJD and will facilitate development of control strategies based on pasture management.
The principle conclusions from this study were that post-weaning lambs were highly susceptible to infection with M. paratuberculosis and if exposed to high levels of contamination a proportion will develop severe infection leading to clinical disease and death. Hoggets and adult ewes are less likely than lambs to develop clinical disease after exposure to M. paratuberculosis. Nevertheless, even adult ewes may become infected and later act as a source for transmission of the disease. Lateral spread of OJD is a serious threat; it is not necessary for infected sheep to be present in a paddock for transmission of infection to occur if infected sheep are present in neighbouring paddocks. Conventional wire strand fences do not prevent spread of infection. For diagnosis on a flock basis, pooled faecal culture is more effective than the agar gel immunodiffusion assay for detection of the infection at relatively early stages in young sheep. Pooled faecal culture detected infection in sheep only 6 months after first exposure to contaminated pasture, when they were 11 months of age.
Samples were stored from sheep in this project for later research, for example in project OJD.031. In addition, blood samples were provided regularly to CSIRO for validation of the gamma-interferon assay for diagnosis of OJD.
The results of this study will have immediate impact on the management and control of OJD as they provide objective data to support and extend current recommendations for livestock grazing management.
Source of Funding
Meat & Livestock Australia Limited
Project Timeframe
November 2001 - June 2005