Ovine Johne’s disease

About the disease

Ovine Johne’s disease (OJD) is a serious wasting disease of sheep that can result in significant economic losses from deaths, lost production and trading restrictions.  The disease is caused by a bacteria, with infected animals shedding the organism in manure; contaminating pastures and water sources and spreading the infection.

Prevalence of OJD is increasing with current estimations at more than 100 infected flocks across Tasmania.

OJD is currently managed through an the National Johne’s Disease Control Program, coordinated by Animal Health Australia (AHA).

In Tasmania, DPIPWE continues to provide input into the program though reporting of results from abattoir monitoring and maintaining necessary regulations to support OJD prevalence zones.

To understand the potential economic impacts of OJD on the carcase at the point of slaughter, click here to download the factsheet.

Key disease features

Causative organism: Mycobacterium paratuberculosis (M.avium subspecies paratuberculosis) sheep strain.

Transmission and infection: The bacteria lives mainly in the intestines and is passed out of the body through manure, where is can survive on pasture for several months where it can infect other grazing animals. The disease is occasionally transferred in utero in sheep.  Infection can occur pre or post weaning through contaminated udders, pasture, feed or water.  Infection can occur at any age, infection is acquired earlier when pasture is highly contaminated.  Most susceptible are young sheep.  The bacteria moves primarily with stock movements such as introductions, strays, and agistment but property to property transmission is recognised in infected areas through the movement of infected dung along watersheds.

Incubation: Can be many months between exposure to bacteria and shedding of bacteria which may result in clinical (observable) or subclinical (non observable) disease. On a flock basis it may be a number of years before the disease is recognised.

Clinical disease: Weight loss, diarrhoea (occasionally), death. Clinical symptoms more often seen in sheep older than two years of age, but disease is regularly reported in weaners and hoggets on heavily infected farms.

Subclinical disease: Sheep can be infected with and shed bacteria but show no obvious clinical symptoms.  The disease may progress to clinical infection, remain subclinical or sheep may recover from the infection with no shedding.   Survival in environment:  can survive for extended periods in faeces, soil or water.  Survival depends on temperature, sunlight and desiccation.  Bacteria can survive in sheep pellets for over 12 months if in shaded location.

Control in infected flocks: First and foremost, control should include a vaccination program with Gudair® in combination with the careful selection of sheep for introduction to the property, attention to boundary fences to prevent strays, grazing management flock profiling and removal of the high risk cohorts if this is feasible. Vaccine (Gudair) early in life reduces level of faecal shedding and deaths and development of clinical signs of disease by 90%. Grazing management to minimise exposure of young sheep to bacteria helps maximise effectiveness of vaccine.

Eradication of disease: Eradication is difficult except through destocking and decontamination of pasture or possibly after several generations of vaccination. Recent trials have shown that a small but significant number of sheep will continue to shed after five years of vaccination. Extended vaccination is likely to continue to suppress the disease but research is continuing to determine the long-term impact on the disease. Subsequent monitoring through abattoir surveillance and testing using pooled faecal cultures can assist in determining the effectiveness of disease control practices.

Further information

Animal Health Australia’s OJD website – click here.

National OJD Management Plan 2007-2012 – click here.

Animal Health Australia OJD factsheet – click here.

OJD information at DPIPWE’s Biosecurity website – click here.

OJD and safe vaccination technique presentation – click here.

First Aid instructions for needle stick injuries – click here.

Gudair® MSDS – click here.

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