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Listeriosis: Introduction |  |
| Listeriosis is quite rare in birds and usually occurs as a septicemia or sometimes as a localized encephalitis. Encephalitis combined with septicemia has been seen in young geese. Chickens, turkeys, geese, ducks, canaries, and parrots appear to be the most commonly affected avian species. |
| In workers at poultry-processing plants, conjunctivitis due to
Listeria
monocytogenes
has been linked to handling of apparently normal but infected chickens. Human infections have also resulted from consumption of contaminated poultry or poultry products. Abortions and congenitally infected babies have been associated with handling of
L
monocytogenes
-positive birds or those that have died with the disease, but these cases were not confirmed. |
| Etiology and Epidemiology: |
|
L
monocytogenes
is a gram-positive, coccoid to bacillus-shaped, nonsporeforming bacteria that tends to form long filaments, particularly in older cultures. Based on somatic and flagellar antigens, several serotypes have been described.
L
monocytogenes
can be cultured on blood and tryptose agar or brain-heart infusion. It is widely distributed among avian species. The organism is common in feces and soil, with numbers increasing in late winter and early spring. It has been isolated from apparently normal birds and from birds dying of causes other than uncomplicated listeriosis; therefore, it is possible that carrier birds play an important role in the perpetuation of the disease in birds and mammals. It is commonly
associated with concurrent diseases such as coccidiosis, infectious coryza, salmonellosis, and parasitic infections demonstrating the largely opportunistic character of the organism. |
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| Clinical Findings: |
| Young birds appear to be more susceptible than mature ones. Transmission and subsequent infections occur by ingestion of contaminated nasal secretions, feces, and soil. Infection can also occur via inhalation and wound contamination. In most avian species, the incubation period has not been documented; in turkeys, it is 16 hr to 52 days. Frequently,
L
monocytogenes
infections are subclinical. Chickens and turkeys are relatively resistant to natural infection. However, signs of infection are suggestive of a septicemia and include depression, listlessness, and peracute death. In this form, it is common to find only dead birds. In the subacute and chronic forms, signs are related to encephalitis and include torticollis, stupor, paresis, and paralysis. Adult birds may die suddenly with septicemia, while young birds tend to have
chronic infections. Emaciation and diarrhea are seen in some affected birds. |
Lesions:
| In uncomplicated listeriosis, lesions include multiple areas of degeneration and necrosis of the myocardium with congestion, increased pericardial fluid, and pericarditis. Petechial hemorrhages can be seen in the proventriculus and heart. Splenomegaly and hepatomegaly with bile retention and focal areas of necrosis are common. In the encephalitic form, no gross brain lesions are seen; microscopically, however, gliosis in the cerebellum with microabscesses containing
gram-positive bacteria are present in the midbrain and medulla. |
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| Diagnosis: |
| Listeriosis can be suspected based on the history, clinical signs, necropsy lesions, and microscopic observation of the bacteria in the myocardial fibrils, hepatocytes, or both. The diagnosis can be confirmed by isolation from the blood, liver, heart, spleen, or brain of a gram-positive, nonacid-fast, nonsporeforming bacillus that is catalase-positive, motile, aerobic, and that ferments sugars. Isolation by direct culture of the affected tissues may not be successful because of
low concentration of organisms in the tissues; however, recovery increases significantly if a portion of the specimen is refrigerated for 4-8 wk and subcultured weekly. Chick embryos are readily infected and can be used for organism identification. |
| Differential diagnoses include colibacillosis, pasteurellosis, erysipelas, velogenic viscerotropic Newcastle disease, and many other acute and chronic bacterial diseases. |
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| Treatment and Control: |
| The organism is often resistant to many of the commonly used antibiotics. However, the tetracyclines have been efficacious in both the acute and subacute forms when given at 25 mg/kg, PO, sid for 1 wk. Treatment of the chronic form is usually unsuccessful. Widespread use of antimicrobials in the feed for growth promotion may have prophylactic value. Rigid sanitation and disinfection procedures with culling and isolation of affected birds may be helpful.
Prevention should focus on identifying and eliminating the source of infection. |
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