Special Veterinary Pathology

JOHNE'S DISEASE

Synonym : Paratuberculosis

Definition

• Chronic wasting illness of ruminants with prolonged course, recurrent diarrhoea, dehydration, emaciation and death caused by Mycobaterium paratuberculosis

Aetiology

• Mycobaterium paratuberculosis - Three strains:
• Bovine strain
• Ovine strain
• Scottish strain

Incidence

• The disease is of worldwide distribution and constitutes an important economic problem in cattle

Susceptibility

• Ruminants are usually affected. Horses and pigs may be affected very rarely
• It is less frequently encountered sheep and goats

Transmission

• Infection is ingestion. Faeces containing the organisms serve as the primary source of infection

Pathogenesis

• Incubation period : Long and protracted even upto 2 years
• Organisms enters the body through intestinal mucosa, sets up bacteremia and settles in the mucosa of intestine, mesenteric lymph nodes and tonsil produce a chronic granulomatous inflammation
• Cell mediated immune response and followed by humoral immune response initiated by the release of bacteria by dying macrophages as the disease progresses. Type III (immune complex) reaction may contribute to the development of intestinal lesions. Type I or type III reactions in the intestinal mucosa may result in an increased outflow of fluid and diarrhoea.

Clinical signs

• Emaciation, hide and bound with dry coat
• Normal appetite with increased thirst and diarrrhoea
• Sheep and goat – Diarrhoea is not common, emaciation observed

Gross lesions

• Carcass – Emaciation with gelatinous fat
• Terminal part of ileum – Wall thickened and oedematous
• The mucosa is folded and showed Transverse corrugation or rugae (like cerebral convolution)

JD - corrugation of intestine

• Intestinal wall stretched – Corrugations does not disappear
• Sheep and goats – corrugation – Not marked
• Uterine infection may l ead to uterus may lead tocongenital infection and abortion

Microscopic lesions

• Mucosa, submucosa and mesenteric lymph nodes infiltrated with epithelioid cells with foamy cytoplasm
• In the submucosa, epithelioid cells may fuse to form syncytial mass
• Thickeneing of submucosa, edema, infiltration with neutrophils and eosinophils
• Giant cells may also be seen
• Nodule formation with necrosis and calcification described in sheep and goat and corrugation is not marked in sheep and goat
• Mesenteric lymph node- swollen and juicy

Diagnosis

• Symptoms
• Examination of bowel washings
• Examination of rectal-pinch
• Double intradermal test by Johnin in the neck (Johnin test)
• Complement Fixation Test (CFT)
• Agar Gel Immuo diffusion test (AGID)
• Enzyme Linked Immuno Sorbent Assay (ELISA)