Mycobacterium paratuberculosis (MAP) is a bacterium of the genus Mycobacterium. It is globally distributed and primarily causes a chronic intestinal disease in various animal species, particularly ruminants. While its impact on animal health is well-documented, MAP is also a subject of ongoing scientific research into its potential broader implications and interactions within different biological systems.
Understanding the Bacterium
MAP is classified as Mycobacterium avium subspecies paratuberculosis, an obligate pathogenic bacterium. It is known for its slow growth rate, making it challenging to culture in laboratory settings. A distinguishing feature of MAP, like other mycobacteria, is its acid-fast nature, meaning it retains certain stains even when exposed to acid-alcohol due to the waxy mycolic acid in its cell wall.
This bacterium exhibits resilience in various environments, capable of surviving on pasture for over a year and even longer in water. MAP primarily affects the intestinal tract of its hosts, where it can sequester itself inside white blood cells, potentially contributing to its persistence. The organism requires mycobactin for growth, a substance most other mycobacteria can produce themselves. This unique requirement aids in its identification.
Johne’s Disease in Animals
In animals, MAP is the causative agent of Johne’s disease, also known as paratuberculosis, a chronic and contagious granulomatous enteritis. This disease primarily affects ruminants such as cattle, sheep, and goats, leading to progressive weight loss, debilitation, and ultimately death. Clinical signs often appear in young adulthood, between 2 to 7 years of age in cattle, though it can occur earlier in other species.
Common symptoms include chronic diarrhea, which can be intermittent then constant in cattle, though it may not be present in sheep and goats. Despite a good appetite, affected animals experience significant weight loss, and in advanced stages, they may develop ventral and submandibular edema, commonly referred to as “bottle jaw,” due to protein loss. Transmission usually occurs through the fecal-oral route, with young animals often acquiring the infection early in life by ingesting the organism from contaminated environments, teats, or colostrum and milk from infected mothers. The disease has a significant economic impact on the agricultural industry due to reduced productivity, culling, and trade restrictions.
Investigating Human Health Links
There is ongoing scientific research and debate regarding a potential association between MAP and certain human conditions, particularly Crohn’s disease, a chronic inflammatory bowel disease. MAP has been found in higher numbers within the intestines of Crohn’s disease patients compared to healthy individuals or those with other conditions like ulcerative colitis. This has led researchers to explore whether MAP could play a role in the development or progression of Crohn’s disease.
MAP can potentially enter the human food chain through contaminated milk or meat products. Studies show that MAP in milk can survive pasteurization, raising human health concerns given its widespread presence in dairy herds. While the link between MAP and Crohn’s disease is not definitively proven and remains actively investigated, it represents a significant area of study due to public health implications. The presence of antibodies against MAP has also been associated with an increased likelihood of Crohn’s disease patients requiring biological therapy.
Management and Prevention
Management and prevention strategies for MAP infections in livestock aim to reduce the spread of the bacterium and minimize its economic impact. Diagnostic methods used in animals include fecal culture, polymerase chain reaction (PCR) tests, and serology tests. While fecal culture is considered a definitive diagnosis, PCR offers faster detection of the organism’s DNA.
Farm-level biosecurity measures are important for control. These include:
Strict hygiene, ensuring clean calving environments.
Preventing young animals from consuming contaminated feces.
Separating calves from infected dams at birth.
Feeding calves pasteurized colostrum or milk replacers.
Control strategies often involve testing and culling infected animals to reduce the bacterial load in the herd. Vaccination is available in some regions but is used under strict regulatory control. It does not completely prevent shedding or new cases and can interfere with tests for bovine tuberculosis. Eradication is challenging due to the bacterium’s resilience, slow growth, and widespread presence in animal populations.