It is commonly seen in newly born farm animals and occurs in septicaemic and enteric collibacillosis forms.
Etiology: The disease is caused by pathogenic E. coli. Some bacterial strains produce septicaemia while others produce diarrhoea. It occurs in animals of 2-10 days of age but can also occur in 3-week-old animals. The mortality is usually 50% while morbidity may vary from 40 to 70%. Factors like feeding of colostrum, environmental stress, feeding practices, hygienic measures and virulence of organism affect prevalence of disease. It is primarily transmitted by ingestion of contaminated feed or water, or through milk, if mother is suffering from coliform mastitis.
Pathogenesis: Septicaemic collibacillosis is common in foals and lambs but rare in calves. When colostrum is not received by animals, permeability of mucus membrane is increased and organisms gain entry producing endotoxin, septicaemia and shock. Enteric collibacillosis is common in calves. The enterotoxigenic strains of E. coli adhere to upper part of small intestine and multiply and produce enterotoxin which stimulates cAMP production. Owing to it, fluid and electrolytes are secreted in large amounts in lumen and diarrhoea occurs. Animals die due to metabolic acidosis, electrolyte imbalance and dehydration.
Clinical signs: Septicaemic form occurs in first 4 days of life. Animals are dull, depressed, weak and anorectic. Initially there is fever but later on temperature becomes subnormal. Tachycardia is also observed. If animals survive, organisms are localized in different sites causing arthritis, meningitis and pneumonia. Enteric form occurs in animals of 3-5 days of age. There is profuse watery to pasty, light yellow coloured foul smelling faeces which is often mixed with blood. Animals are sucking normally in initial stage and are alert but later on, they become dull and depressed, have subnormal temperature, pale mucus membrane, slow and irregular heartbeat and dehydration.
Diagnosis: It is diagnosed by clinical symptoms and can be confirmed by isolation of the causal organisms. Blood examination reveals haemoconcentration. neutrophilia, leukocytosis, increased urea nitrogen and low blood pH and bicarbonates. Indirect fluorescent or ELISA tests also detect it.
Treatment: The diet of animal should be changed immediately and milk should be withdrawn for 24 h. Equal amounts of 0.85% sodium chloride, 1.3% sodium bicarbonate and 5% dextrose may be mixed for fluid replacement, and it is given @100 ml/kg body weight intravenously in 4-6 h followed by 100 ml/ kg body weight in next 24 h. Dextrose saline or normal saline can also be used to replace fluid loss. As there is metabolic acidosis, so bicarbonates are used but not lactates. Any of the broad-spectrum antibiotics like neomycin, chloramphenicol, tetracycline, nitrofurazone or ciprofloxacin can be used. But this should not be used for more than 3 days. Neomycin or nitrofurazone can be given @ 0.5 g dose orally twice daily. Benzetimide or chlorpromazine is given @ 0.2-0.5 mg/kg body weight to reduce intestinal motility and secretion. As intestinal protectants, kaolin and pectin mixture may be used.
Control: The passive immunity acquired from the colostrum and absorbed into the circulation from the gut is the main defence mechanism against E. coli diarrhoea. Inadequate amounts of immunoglobulins in the colostrum, inadequate intake of the colostrum and inadequate absorption of immunoglobulins from the gut render very young calves susceptible to infection. An improvement in colostrum feeding in the first 6-9 hours of life and dam immunisation against ETEC E. coli F5 (K99) adhesin (Rotavec Corona, Schering Plough Animal Health) are the main ways of controlling disease in herds that have been infected. The disease can be prevented by the use of dam vaccine 4-6 weeks before calving. Reducing the degree of exposure to newly born calves controls the disease in a herd.