TYZZER'S DISEASE
STEPHANIE SPECK
Bundeswehr Institute of Microbiology, Department of Virology and Rickettsiology, Munich, Germany
Tyzzers disease, also named haemorrhagic disease of muskrats and Erringtons disease, was first described as a fatal epizootic diarrhoeal disease in Japanese waltzing mice (Mus musculus).
It is characterized by typical necrotic lesions in the liver with intracellular bacteria adjacent to the necrotic foci, and in epithelial cells of the intestine(48).Clostridium piliforme (previously named Bacillus pili- formis) is an obligate intracellular, pleomorphic, sporeforming bacterium. Its vegetative form (within the host) comprises Gram-negative slender rods, 0.5 μm wide and 8—10 μm long, which do not survive long outside a host. The spores are resistant to freezing and thawing and may remain stable and infective for years in the environment. Six serologic groups are identified among isolates of C. piliforme, and a single host species might be infected with strains of more than one group.
Tyzzer’s disease is most commonly known as an acute disease of laboratory animals (mouse, rat, hamster, gerbil, rhesus monkey) and commercially bred rabbits but also affects horses (foals) and other domestic animals. A few cases have occurred in captive birds (49). In colonies oflabora- tory animals mortality can be very high. Greatest loss occurs in weanlings, but adult individuals are also affected. Clinical disease appears in animals stressed by transport, overcrowding, poor sanitation or corticosteroid administration. Tyzzer’s disease has been described in a variety of free- ranging and captive mammals. A case ofTyzzer’s disease in a free-ranging Eurasian otter (Lutra lutra) occurred in a cub found weak on the Isle of Harris, Scotland(50).
I nfectious spores are shed in the faeces and transmission is believed to be by ingestion of spores.
Tyzzer’s disease is an intestinal infection that spreads to the liver via the portal vein. The location of bacteria only within apparently healthy cells at the border of necrotic areas indicates a cell-to-cell spread by contact. Clostridium pili- forme seems to have an affinity for epithelial and smooth muscle cells of the intestine, hepatic and myocardial cells(48). Gross lesions vary among species, but enteritis is usually present. Most commonly, the caecum, colon, and terminal ileum are affected. Ulcerative haemorrhagic colitis and typhlitis and focal hepatic necrosis are typical findings in muskrats (O ndatra zibethicus). Characteristic lesions in the liver appear as multiple 1—3 mm white foci. Lesions in the myocardium appear as streaks or white foci in some species(49). Excess serous fluids in the pleural, pericardial and peritoneal cavities were striking features in a European otter(3) and also occur in other species. Splenomegaly has been described in some cases. Histologically, necrosis of intestinal epithelial cells, submucosal oedema and polymorphonuclear cell infiltration are seen. Bacilli are demonstrated in epithelial and muscle cells. Hepatic lesions vary from foci of acute coagulation necrosis with only a few granulocytes to fibrotic scars surrounded by macrophages and occasional multinucleated giant cells. Bundles of long, slender bacilli are present in apparently healthy cells at the margins of necrotic foci. In chronic lesions, organisms may be absent(49).In most species, Tyzzers disease is an acute fatal disease. Diarrhoea, depression, anorexia, and a ruffled, uneven hair coat may be observed during the brief clinical course. Dysentery occurs in cottontail rabbits (Sylvilagus floridi- anus) and muskrats(49). Bilateral corneal oedema has been reported in a Eurasian otter(50).
Diagnosis of Tyzzers disease is usually by microscopic demonstration of the characteristic intracellular bacteria associated with compatible lesions in sections with silver staining, such as Warthin-Starry or Levaditi. Liver is routinely chosen for examination and intestinal tissue should also be examined. Serological diagnostic methods are developed for laboratory animals but have not been validated for wild animals. Clostridiumpiliforme does not grow in cell-free media but can be grown in embryonated eggs and several mammalian cell lines.
The acute course of disease and intracellular location of the organism make treatment difficult. Although antibiotic treatment with oxytetracyclins, penicillins, cephalosporins or erythromycin may be attempted to control outbreaks in laboratory animals, there are no suitable measures for the control and treatment of Tyzzer’s disease in wild animals.