Cattle suffering from BJD generally have a good appetite however their ability to absorb nutrients from their food is impaired, leading to progressive weight loss, severe emaciation and eventually death. Diarrhoea and bottle jaw are commonly seen in cattle with BJD.
Unlike most other diseases, BJD has a very long incubation period of 1 to 15 years. Due to this long incubation period signs of BJD are usually only seen in cattle over 3 years of age.
Infected cattle shed the BJD bacteria in their manure, contaminating pastures. The organisms are very hardy and can survive on the pasture for up to 12 months. Cattle may be infected when grazing contaminated pasture and calves may be infected by suckling faeces contaminated udders. Some calves of infected cows are born infected, and some infected cows pass the BJD bacteria in their milk.
Young calves up to 30 days of age are most susceptible to the disease. Susceptibility decreases with age with cattle over 12 months becoming increasingly resistant to the infection.
In Australia BJD is most common in dairy cattle in south-eastern Australia, however the disease can also occur in beef cattle, goats and alpacas. The major implication for beef producers are the trading restrictions that are imposed on infected herds and regions.
Further information on work in progress and management advice for industry can be found at:
Animal Health Australia’s Johnes Disease Information Centre