Tyzzer's Disease in a Young Brown-throated Conure (Aratinga pertinax)
Pauline M. Rakich and Kenneth S. Latimer
College of Veterinary Medicine, University of Georgia, Athens, GA 3002
Abstract. Formalin-fixed tissues were submitted from a 7-week-old Brown-throated Conure that was unexpectedly found dead. Histologic abnormalities were confined to the liver, which contained numerous coalescing foci of necrosis and inflammation with myriads of long, slender gram negative rods. The histologic changes and bacterial morphology were compatible with a diagnosis of Tyzzer's disease.
Key Words: Avian, Brown-throated conure, Aratinga pertinax, Tyzzer's disease, hepatitis
Introduction
Tyzzer's disease is a systemic bacterial infection first described in mice in 1917 by Tyzzer, who named the causative agent Bacillus piliformis. Histologic lesions are most common in the liver and intestine. 1 The disease usually affects young animals and presents as an acute, rapidly fatal disorder. 1 Tyzzer's disease has been reported in a wide range of wild, domestic, and laboratory mammalian species2-7 but it appears to be rare in birds. 8
Case Report
A 7-week-old, male, Brown-throated Conure (Aratinga pertinax) was treated for crop stasis and it appeared to recover uneventfully. However, 5 days later the bird was found dead. No clinical abnormalities were apparent in the other 29 birds in the collection. Necropsy examination revealed only a very enlarged, mottled liver. Sections of liver, lung, kidney, pancreas, heart, and spleen were fixed in formalin and submitted for histologic examination.
Microscopic changes were confined to the liver which contained coalescing foci of necrosis involving approximately 50 percent of the hepatic parenchyma. The foci were composed of eosinophilic necrotic debris admixed with degenerate inflammatory cells. Viable hepatocytes at the margin of the necrotic material contained numerous long rods within their cytoplasm (Fig. 1). The bacteria were gram negative and were more clearly delineated with Giemsa and Warthin-Starry stains (Fig. 2) as long, slender, slightly beaded rods in clumps or bundles within the cytoplasm of viable hepatocytes and loose among the necrotic debris. No inflammation or organisms were apparent in the other submitted tissues.
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| Fig. 1. Brown-throated Conure, liver, Tyzzer's disease, H&E stain. Necrotic and viable hepatocytes are present. Bacilli are faintly stained. |
Fig. 2. Brown-throated Conure, liver, Tyzzer's disease, Warthin-Starry stain. Bacilli stain intensely and appear as bundles of organisms within hepatocytes. |
Discussion
Tyzzer's disease has been reported in a wide variety of animals including mice, rats, gerbils, guinea pigs, hamsters, muskrats, rabbits, raccoons, gray foxes, coyotes, lesser pandas, snow leopards, dogs, cats, horses, cattle, and monkeys. 2-7 Although there are no reports of Tyzzer's disease in humans, serum antibody titers to the causative organism have been documented. 2 To the authors' knowledge, however, Tyzzer's disease has been reported in birds only once previously. Saunders and coworkers described a case of Tyzzer's disease in a 4-day-old Cockatiel (Nymphicus hollandicus) that died acutely. The apparent rare occurrence of Tyzzer's disease in birds is surprising since the organism must be isolated in epithelial cells of chick embryos or in tissue culture because it cannot be propagated on artificial media. 2, 9
Clinical disease occurs most commonly in young animals but stressed or immunocompromised adult animals may also be affected. 1, 3, 5 The bird of this report was young and had recently been treated for crop stasis, the stress of which could have contributed to the development of clinical disease. Clinical signs are usually nonspecific and death ensues rapidly. Gross lesions are usually limited to the liver and consist of swelling and mottling; but in some cases, myocardial and intestinal abnormalities are also evident. 3, 7 Microscopically, lesions are most prominent in the liver. Multifocal necrosis is randomly distributed and associated with neutrophilic inflammation. Viable hepatocytes bordering the necrotic foci contain numerous bacteria arranged in bundles within their cytoplasm. 2, 3 Organisms can also usually be demonstrated within cytoplasm of epithelial cells of the distal intestine. 2 In cases with myocarditis, bacteria are also present within myocardial cells. 3, 6, 7 The bird of this report had typical gross and microscopic lesions of the liver; no histologic abnormalities were evident in the heart; and no intestinal tissue was submitted for examination.
The Tyzzer's bacillus is a rod-shaped, gram-negative, spore-forming, motile, obligate intracellular bacterium which was originally named Bacillus piliformis. 1 However, more recently it has been identified as a Clostridium sp. based on its 16 rRNA analysis. 2 Since the vegetative phase of the bacterium is labile, survival of the organism outside the host is thought to be in a sporulated form. 4, 6 Infection may result from ingestion of infective spores from the environment. It has been suggested that the spores are shed in the feces of diseased or adult carrier animals and contaminate pastures, hay, grain, and bedding to thus serve as a source of infection. 3, 6 The route of infection is most likely by oral ingestion of spores and subsequent distribution from the intestine to the liver. A cytotoxin has been demonstrated in some strains of the bacillus and it may be involved in invasion or cause cell lysis. 1 The sporadic nature of disease suggests that it is probably not highly contagious. Of a total of 30 birds in the collection of the owner of the bird of this report, only this single young bird was clinically affected.
References
1. Riley LK, Caffrey CJ, Musille VS, Meyer JK: Cytotoxicity of Bacillus piliformis. J Medical Microbiol 37:77-80, 1992.
2. Duncan AJ, Carman RJ, Olsen GJ, Wilson KH: Assignment of the agent of Tyzzer's disease to Clostridium piliforme comb. nov. on the basis of 16S rRNA sequence analysis. Intl J of Systemic Bacteriol 43:314-318, 1993.
3. Ganaway JR, McReynolds RS, Allen AM: Tyzzer's disease in free-living cottontail rabbits (Sylvilagus floridanus) in Maryland. J Wildlife Diseases 12:545-549, 1976.
4. Webb DM, Harrington DD, Boehm PN: Bacillus piliformis infection (Tyzzer's disease) in a calf. J American Veterinary Medical Assoc 191:431-434, 1987.
5. Boschert KR, Allison N, Allen TLC, Griffin RB: Bacillus piliformis infection in an adult dog. J American Veterinary Medical Assoc 192:791-792, 1988.
6. Humber KA, Sweeney RW, Saik JE, Hansen TO, Morris CF: Clinical and clinicopathologic findings in two foals infected with Bacillus piliformis. J American Veterinary Medical Assoc 193:1425-1428.
7. Young JK, Baker DC, Burney DP: Naturally occurring Tyzzer's disease in a puppy. Vet Pathol 32:63-65, 1995.
8. Saunders GK, Sponenberg DP, Marx KL: Tyzzer's disease in a neonatal cockatiel. Avian Dis 37:891-84, 1993.
9. Timoney JF, Gillespie JH, Scott FW, Barlough JE (eds): Hagan and Bruner's Microbiology and Infectious Diseases of Domestic Animals, 8th ed. Comstock Publishing Associates, Ithaca, NY, 1988, pp. 212-213.
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