Paratuberculosis

• Paratuberculosis is caused by Mycobacterium avium paratuberculosis
• It is characterized by progressive weight loss, debilitation, and eventually death in cattle and other ruminants
• Diagnosis is primarily made by PCR
• There is no satisfactory treatment
• Control requires good sanitation and management practices to avoid exposure among young animals
• Infected animals shed the bacterium in manure, colostrum, and milk
• Infection is most commonly acquired in young animals through contamination of the environment or ingestion of contaminated milk from an infected cow
• Fecal shedding of the bacteria begins before clinical signs are noticeable
• Mycobacterium avium subspecies paratuberculosis (MAP) is excreted in large numbers in feces of infected animals and in lower numbers in their colostrum and milk
• Infection is acquired early in life, often soon after birth
• Clinical signs rarely develop until after animals are sexually mature
• Resistance to infection increases with age but is never complete
• Infection is acquired by ingestion of the organism when nursing on contaminated teats, consumption of contaminated milk, solid feed, or water, or licking and grooming behavior in a contaminated environment
• After ingestion, the pathogen infects macrophages in the GI tract and associated lymph nodes
• Chronic granulomatous enteritis interferes with nutrient uptake, leading to cachexia typical of advanced infections
• Clinical findings include weight loss, diarrhea, coat color fading, and edema due to protein-losing enteropathy
• Clinical signs usually first appear in young adulthood, but the disease can occur at any age over 1 to 2 years
• The organism causes chronic enteritis characterized by diarrhea, unthrifty animals, and progressive weight loss
• Intestinal wall lesions lead to muscle wasting and low milk yield
• Lesions range from a lack of gross lesions to thickened intestines with enlarged lymph nodes
• PCR is the primary method for diagnosis
• Necropsy with culture and histopathology is the gold standard for definitive diagnosis
• Serologic tests are rapid, low-cost methods for confirmation of a clinical diagnosis
• Control measures include good sanitation practices and limiting exposure of young animals to the organism
• Routine testing programs and culling of positive animals are recommended
• Vaccination of calves can reduce disease incidence but does not prevent shedding or new cases of infection
• There are conflicting data on the involvement of the causative organism in Crohn disease in people
• MAP is consistently detected by PCR in people with Crohn disease