Mycobacterium avium subsp paratuberculosis: pathogen, pathogenesis and diagnosis

Johne's disease, or paratuberculosis, is a chronic intestinal infection cau sed by Mycobacterium avium subsp. paratuberculosis. The usually fatal disea se is characterised by cachexia, and in some species diarrhoea, after a lon g pre-clinical phase. Treatment is ineffective and economically impracticab le. The infection primarily affects domestic and free-ranging ruminants, bu t has also been reported in primates, rabbits, stoats and foxes. Since para tuberculosis is often subclinical, under-reporting is suspected, even thoug h the disease is notifiable in numerous countries. Herd prevalence of bovin e paratuberculosis in Europe ranges from 7% to 55%. In the United States of America, herd prevalence is strongly associated with herd size; 40% of her ds of more than 300 head were found to be infected. In Australia,, reported dairy herd infection rates range between 9% and 22%. Paratuberculosis in d omestic livestock entails significant economic losses due to several factor s (e.g. reduced production, premature culling and increased veterinary cost s). Free-ranging and captive wildlife are also at risk from paratuberculosi s.