The transmission and impact of paratuberculosis infection in domestic and wild ruminants

Mycobacterium avium subsp. paratuberculosis (M paratuberculosis) infects domestic cattle, sheep, goats, deer, camelids and wild ruminants leading to chronic enteritis known as paratuberculosis (Johne's disease). The infection is chronic, progressive and unresponsive to treatment. Most infected animals do not develop clinical disease but may excrete the bacteria. Clinically sick animals suffer emaciation and in some species diarrhoea, followed by eventual death. During the course of the disease, excretion of M. paratuberculosis in faeces and milk occurs, and the organism spreads through the blood and lymph vessels of infected animals to multiple internal organs. The infection disseminates to both the female and male reproductive organs. Though M paratuberculosis is not classified as a human pathogen, current opinions on the possible role of this mycobacteria in public health is discussed. This article attempts to review the ways and circumstances by which M. paratuberculosis is transmitted within an animal population and the importance of the disease on animal production, Published reports concerning the transmission and epidemiology of the disease are reviewed herein, and preventive and control measures are summarised.