Johne’s disease in cattle
Jai Bhagwan1 , Mahavir Chaudhari2, Sandeep Sangwan3
1Assistant Professor, Department of veterinary medicine, 2 Extension Specialist, Pashu Vigyan Kendra, Sirsa, Lala Lajpat Rai University of Veterinary and Animal Sciences, Hisar, 3 Assistant professor, Khalsa Veterinary College, Amritsar
Paratuberculosis is chronic, contagious granulomatous enteritis characterized in cattle by persistent diarrhea, progressive weight loss, debilitation, and eventually death. The etiologic agent, Mycobacterium paratuberculosis, also known as Mycobacterium avium subsp paratuberculosis, is believed capable of infecting and causing disease in all other ruminants (eg, sheep, goats, llamasand deer) and in captive and free-ranging wildlife.
Etiology and pathogenesis
M paratuberculosis 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—but clinical signs rarely develop in cattle <2 year old, because progression to clinical disease occurs slowly. Resistance to infection increases with age, and cattle exposed at adults age are much less likely to become infected. Infection is acquired by ingestion of the organism when nursing on contaminated teats, consumption of milk, solid feed, or water contaminated by the organism or licking and grooming behavior in a contaminated environment. In the later, bacteraemic stages of infection, intrauterine infections can be seen. After ingestion and uptake in the Peyer’s patches of the lower small intestine, this intracellular pathogen infects macrophages in the GI tract and associated lymph nodes.
In most cases, the organisms multiply and eventually provoke a chronic granulomatous enteritis that interferes with nutrient uptake and processing, leading to the cachexia typical of advanced infections. Fecal shedding begins before clinical signs are apparent, and animals in this “silent” stage of infection are important sources of transmission.
Clinical findings
Paratuberculosis in cattle is characterized by weight loss and diarrhea in the late phases of infection, but infected animals can appear healthy for months to years. In cattle, diarrhea may be constant or intermittent. It typically does not contain blood, mucus, or epithelial debris and is passed without tenesmus. Throughout weeks or months, the diarrhea becomes more severe, further weight loss occurs, coat color may fade, and ventral and inter-mandibular edema may develop due to a protein-losing enteropathy. Milk yield may drop or fail to reach expected levels. Animals are alert, and temperature and appetite are usually normal, although thirst may be increased. The disease is progressive and ultimately terminates in emaciation and death.
Lesions
Carcasses may be emaciated, with loss of pericardial and perirenal fat in more advanced, cachectic cases. Intestinal lesions can be mild, but typically the distal small-intestinal wall is diffusely thickened with a nonulcerated mucosa thrown into prominent transverse folds. Lesions may extend proximally and distally to the jejunum and colon. Histologically, there is diffuse granulomatous enteritis characterized by the progressive accumulation of epithelioid macrophages and giant cells in the mucosa and submucosa of the gut.
Diagnosis
Necropsy with culture and histopathology on multiple tissues is the gold standard for definitive diagnosis. Ziehl-Neelsen stains of tissue samples for acid-fast bacteria usually reveal abundant mycobacteria in lesions.M paratuberculosis has been isolated from a wide variety of tissue sites, but the mesenteric and ileocecal lymph nodes, ileum, and liver are most frequently recommended for diagnostic sampling. Of the serologic tests, those based on ELISA technology offer the highest sensitivity and specificity and are best used to determine the infection prevalence in a herd. Faecal culture is more sensitive and more specific than serology, but the organism grows very slowly (2–4 month) and the assay is more costly than serology. Commercial PCR kits are as sensitive and specific as fecal culture and much more rapid. Tests of cell-mediated immunity, such as the intradermal Johnin test, lymphocyte transformation test, and interferon-γ, are used more on a research basis and may be negative in advanced clinical cases. The complement fixation (CF) test also reportedly is less accurate than other serologic tests.
Control
Control requires good sanitation and management practices aimed at limiting the exposure of young animals to the organism. Calves, kids, or lambs should be birthed in areas free of manure, removed from the dam immediately after birth in the case of dairy cattle, bottle-fed colostrum that has been pasteurized or obtained from dams that test negative, and then reared segregated as much as possible from adults and their manure until >1 yr old. A routine testing program for adults can help focus efforts in controlling the disease. Animals testing positive, particularly heavy shedders or that have strong-positive ELISA results, should be sent to slaughter as soon as economically feasible. Retesting at least annually should be continued until herd tests indicate a low (<5%) infection prevalence. Because intrauterine infection can occur, more aggressive control programs include culling of calves from dams that have or develop signs of the disease.
More general procedures to minimize fecal contamination on the farm can also help, eg, elevating food and water troughs, providing piped water in preference to ponds, and harrowing frequently to disperse feces on pasture. Vaccination of calves <1 month old can reduce disease incidence but does not prevent shedding or new cases of infection in the herd. Cattle inoculated with an inactivated whole-cell, mineral-oil vaccine develop granulomas, one to several inches in diameter, at the site of inoculation (brisket) and may react positively on subsequent tuberculin tests.
