Tyzzer's Disease

Description

Tyzzer's disease is an acute, highly fatal bacterial infection that is seen in a wide range of animals. It most commonly affects foals and laboratory animals and occasionally dogs, cats and calves. Tyzzer's disease in foals usually occurs in individual animals, whereas outbreaks of disease occur in rodents and rabbits. The disease most commonly affects young, stressed animals.

The bacteria that causes the disease is Clostridium piliforme (Bacillus piliformis), a gram negative spore-forming intracellular bacterium found in soil and faeces. The aetiology of the disease is poorly understood. Infection most likely results from oral exposure to spores; possible mechanisms include ingestion of spore-forming faeces or contact with carrier animals. Following ingestion, the spores colonise the intestine and liver via the portal circulation. Dissemination to the hepatocytes, enterocytes and myocytes then occurs.

Clinical signs

The disease in rabbits and rodents is usually characterised by an unkempt coat, depression and fatal diarrhoea. Foals are usually aged between one and six weeks of age and are often clinically normal at birth. Rapidly progressive clinical signs relating to an acute hepatitis then develop. Clinical signs include acute lethargy, loss of suckle reflex, severe icterus, neurological signs (such as head pressing or circling), pyrexia and diarrhoea. Animals may be found dead without known pre-existing clinical signs. The course of the disease from the onset of clinical signs to death is usually around 48 hours.

Diagnosis

Tyzzer's disease should be considered in foals in the above age group with clinical signs indicating hepatic disease and laboratory evidence of hepatic involvement. Clinicopathological abnormalities often include metabolic acidosis, hypoglycaemia, haemoconcentration (elevated PCV), increased hepatic enzymes (SDH, GGT and ALP) and serum bilirubin concentration. Coagulation profiles may be abnormal with a prolonged PT, PTT and increased fibrin degredation products.

Ultrasound of affected animals may show a grossly enlarged liver with rounded edges.

Definitive diagnosis relies either on observation of intracellular bacteria at the periphery of liver lesions or on bacterial culture. Giemsa stain is used to visualise the bacteria which are seen as intrahepatocellular filamentous rods.

Laboratory diagnostic tests are of little value in small mammals as death is usually rapid. Recently, a PCR test has been described for use in these animals but this is not currently commercially available.

Pathology

Grossly, hepatomegaly is present with multifocal white-grey areas of necrosis and hyperplasia of the hepatic lymph nodes. On cut section the liver displays loss of normal architecture with haemorrhagic centres in each hepatic lobule. Whitish streaks may be present on the myocardium.

Treatment

Clostridium piliforme has been reported to be susceptible to penicillin, tetracycline, erythromycin, and streptomycin in studies using infected embryonated eggs. High dose sodium penicillin and trimethoprim sulpadiazine have been used successfully to treat foals with Tyzzer's disease. Parenteral nutrition is particularly important in affected animals due to a reduction in hepatic metabolism. Other supportive treatment may include aggressive fluid therapy with dextrose and control of seizure activity using a sedative such as xylazine.

Prognosis

The prognosis for foals with Tyzzer's disease is poor with a mortality rate approaching 100%.

Prevention

No vaccines are available for the prevention of Tyzzer's disease. Good hygiene and adequate colostrum intake are therefore essential for decreasing the risk of disease. Stress factors such as transport and overcrowding have been linked to Tyzzer's disease, therefore these should be minimised.

Also see Tyzzer's Disease - Rabbit.

References

• Borchers, A., Magdesian, G.K., Halland, S., Pusterla, N. and Wilson, W.D. (2006) Successful Treatment and Polymerase Chain Reaction (PCR) Confirmation of Tyzzer’s Disease in a Foal and Clinical and Pathologic Characteristics of 6 Additional Foals (1986–2005) Journal of Veterinary Internal Medicine 20:1212–1218

• Knottenbelt, D.C. A Handbook of Equine Medicine for Final Year Students University of Liverpool

• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial

• Lavoie, J. P., Hinchcliff, K. W. (2009) Blackwell's Five-Minute Veterinary Consult: Equine Wiley-Blackwell

• Sellon, D. C. and Long, M. T. (2007) Equine Infectious Diseases Elsevier Health Sciences