Confirmation of Johne's disease (C-strain) in WA
Johne's disease cattle strain (JD C-strain) was confirmed in southern Western Australia in September 2021. Following a comprehensive investigation and liaison with the WA cattle industry, the Department of Primary Industries and Regional Development (DPIRD) determined eradication was not technically feasible, which was supported by WA cattle industry representatives. Attempting eradication would result in significant economic cost to industry and a large number of WA cattle properties being placed under regulatory control for years while surveillance was undertaken to determine if the disease was present on individual properties, outweighing the impact of the disease itself.
DPIRD has begun transitioning to reduced regulation for JD:
- All strains of JD will remain a reportable disease in WA to support certification for international livestock markets.
- There will be reduced regulatory controls applied in response to detection of JD, which aligns with the national decision to deregulate JD in cattle in 2016.
- Interstate import conditions for JD will be amended at the completion of the transition period and WA producers are encouraged to carefully consider the source of all livestock introduced onto property.
To allow producers to protect the status of their individual properties, and to minimise production impacts on properties where JD is diagnosed, DPIRD will support the WA industry with information on the disease, developing effective on-farm biosecurity programs and the national industry Johne’s Beef Assurance Score (JBAS) program.
More information about the transition to reduced regulation of JD will be provided on this webpage and to industry shortly.
What is Johne’s disease (JD)?
JD is a chronic incurable infectious disease that affects cattle, buffalo, sheep, goats, alpaca and deer. It is caused by the bacteria Mycobacterium avium subsp paratuberculosis and results in progressive diarrhoea, weight loss, reduced production levels and eventually death. The signs of JD in infected animals are often triggered by stress factors such as calving.
There are three strains of Johne’s disease: sheep (S-strain), cattle (C-strain) and bison (B-strain). These strains can affect more than one species, not just the strain they are named for.
How are cattle infected with JD?
The most common way JD arrives on a property is by introducing infected cattle that are not showing any signs of infection.
JD can be spread between livestock through:
- colostrum, milk and faeces of infected animals, or
- soil, feed or water contaminated by the bacteria. The bacteria can survive in the environment for long periods, including in soil for up to 12 months.
Young animals, particularly calves, are most likely to be infected, usually through suckling udders contaminated with infected faeces. They can also be infected by drinking infected colostrum or milk and grazing contaminated pasture or feed. In cattle with visible disease, calves may also be infected in-utero.
Cattle can also be infected through contact with infected sheep, goats, alpaca, deer or buffalo or by grazing land grazed by other infected livestock.
Testing for JD
Although cattle are infected when they are very young (usually as calves), they do not show any signs of disease until they are much older, usually after 3–5 years of age.
Several tests are available for JD, but these should be applied with recognition of their limitations and are best used to detect infection and/or to demonstrate that infection is absent within a herd or property.
Producers should consult their veterinarian to determine the most appropriate testing for their property.
Available tests for detecting JD are listed below:
- Faecal tests – Faecal testing is best used for herd-level testing. The tests look for bacteria in the faeces (by culture) or bacterial DNA (by using polymerase chain reaction (PCR) tests). Faecal tests are not very sensitive when used for individual animals as they will only detect infection in animals shedding bacteria, which can occur intermittently. Faecal testing will not detect young infected animals that are not shedding yet.
- Blood tests – These look for an immune response to infection but can result in a positive result for other Mycobacterium bacteria. Blood tests are not used for definitive diagnosis.
- Post-mortem and laboratory testing – These involve examining dead animals to look for gross and microscopic changes indicative of JD infection and detecting bacteria in the gastrointestinal tract and lymph nodes.