Brief Informational Sketches of Some Other Mastitis Pathogens

Kansas State University College of Veterinary Medicine
Mississippi State University College of Veterinary Medicine
Virginia-Maryland Regional College of Veterinary Medicine
Texas A & M University College of Veterinary Medicine.

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Calf Diarrhea Pathogen Information: Escherichia coli

Introduction: Escherichia coli, or E. coli, is a gram-negative rod-shaped bacteria which is commonly found in aerobic environments but can also survive in anaerobic environments, and is therefore called a facultative anaerobe. E. coli is ubiquitous in the environment and the digestive systems and feces of humans and farm animals, but most types of E. coli do not cause disease.

Epidemiology: Pathogenic strains of E. coli can be carried in healthy young and adult animals, and through their feces it can be spread throughout the farm environment to bedding, equipment, the ground, and various parts of the cow, including the teats and udder. Calves with diarrhea due to ETEC are particularly adept at contaminating the environment, as they shed great numbers of infectious organisms in their feces.

Most cases of calfhood diarrhea caused by E. coli are due to a type called Enterotoxigenic E. coli, or ETEC. It is unusual to find diarrhea due to E. coli infection in calves older than 3 or 4 days of age. E. coli frequently acts together with other pathogens, such as rotavirus and coronavirus, in causing calf diarrhea. If pathogenic ETEC is found in a calf older than 3 or 4 days, it is usually part of such a mixed infection. Much less common than ETEC is another strain of E. coli, Attaching and Effacing E. coli or AEEC, which can cause a hemorrhagic colitis in calves 2 to 5 weeks of age.

E. coli bacteria can survive in bovine feces for long periods of time and retain their infectious and enterotoxin-producing abilities.

Zoonotic Risk: The potential for zoonotic transmission of Escherichia coli is high, as it is very common in the environment. As mentioned above, most strains do not cause disease, but some strains can cause diarrhea in humans. In addition, some uncommon strains are very dangerous to humans. E. coli strain 0157:H7, an Enterohemorrhagic E. coli (EHEC) strain, can cause Hemolytic/Uremic Syndrome in humans, which can lead to acute renal failure and death. Studies culturing dairy and beef cattle feces found E. coli 0157:H7 in less than 1% of samples.

Clinical features of E. coli infection/ Specific therapeutic objectives: E. coli diarrhea occurs most commonly in calves less than 4 days old. Diarrhea, dehydration, and metabolic acidosis are key features of enteric E. coli infection, also known as colibacillosis. Diarrhea is profuse, pasty to watery, foul smelling, and occasionally flecked with blood. The calf's temperature may be elevated before clinical signs are observed, but it is generally normal progressing to subnormal once clinical signs are seen. There is also progressive dehydration and metabolic acidosis, which may be profound. These calves generally respond well to treatment of fluid deficits and acidosis (link to ancillary therapy page).

Enterotoxigenic E. coli (ETEC) may also cause enteric toxemia, which can lead to toxic shock and death within 2 to 6 hours. Calves suffering from this condition may exhibit bloating and fluid-filled intestines, which can be heard by balloting the abdomen, instead of diarrhea. They may also exhibit periodic apnea, bradycardia, pallor, convulsive motions, cool extremities and pale mucous membranes. The prognosis for this condition is poor.

Diagnosis/Necropsy findings/Sampling goals: Isolation of E. coli from the feces of an affected animal does not confirm diarrhea due to E. coli infection. Antemortem diagnosis of colibacillosis is achieved by isolating from the affected calf a strain of E. coli that is shown by analysis of its antigens to be pathogenic.

Necropsy findings in affected calves include dehydration and flaccid, fluid-filled intestines, which may have normal or hyperemic mucosal surfaces. Necropsy should be done very shortly after death to ensure minimal autolysis of the tissues and minimal invasion and proliferation by other bacteria. Samples of all segments of the intestinal tract (duodenum, jejunum, ileum, and colon), as well as mesenteric lymph nodes, should be preserved in formalin and submitted for histopathological analysis. Uncontaminated samples of the ileum and colon and their contents should be submitted for bacterial culture.

Specific prevention measures/Vaccination: Standard measures taken to reduce the incidence of calf diarrhea in beef and dairy herds should be observed (link to prevention page) to control E coli diarrhea. In addition, cows may be vaccinated late in gestation with bacterins of E. coli strains linked to calf diarrhea. This will cause increased protection of the calf through enhanced colostral immunity, provided that the calf receives adequate colostrum soon after birth. There is also an oral calf vaccine that must be given before colostrum is ingested to be effective, and several brands of antibodies to E. coli, which can be administered orally to calves in their first few hours of life. None of these approaches is an appropriate substitute for good hygiene and colostrum management in preventing E. coli diarrhea.