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Fowl Cholera: Introduction |  |
| Fowl cholera is a contagious, widely distributed disease that affects domestic and wild birds. It usually occurs as a septicemia of sudden onset with high morbidity and mortality, but chronic and asymptomatic infections also occur. |
| Etiology and Transmission: |
|
Pasteurella
multocida
, the causal agent, is a small, gram-negative, nonmotile rod that may exhibit pleomorphism after repeated subculture. In freshly isolated cultures or in tissues, the bacteria have a bipolar appearance when stained with Wright’s stain. Although
P
multocida
may infect a wide variety of animals, strains isolated from nonavian hosts generally do not produce fowl cholera. Strains that cause fowl cholera represent a number of immunotypes, which complicates widespread prevention by using bacterins. The organism is susceptible to ordinary disinfectants, sunlight, drying, and heat. Turkeys are more susceptible than chickens, older chickens are more susceptible than young ones, and some breeds of chickens are more susceptible
than others. |
| Chronically infected birds are considered to be a major source of infection. Dissemination of
P
multocida
within a flock is primarily by excretions from mouth, nose, and conjunctiva of diseased birds that contaminate their environment. |
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| Clinical Findings: |
| These vary greatly depending on the course of disease. In acute fowl cholera, dead birds are usually the first indication of disease. Fever, depression, anorexia, mucoid discharge from the mouth, ruffled feathers, diarrhea, and increased respiratory rate are usually seen. Pneumonia is particularly common in turkeys. |
| In chronic fowl cholera, signs and lesions are generally related to localized infections. Sternal bursae, wattles, joints, tendon sheaths, and footpads are often swollen because of accumulated fibrinosuppurative exudate. There may be exudative conjunctivitis and pharyngitis. Torticollis may result when the meninges, middle ear, or cranial bones are infected.
|
Lesions:
| Many of the lesions are related to vascular disturbances. Hyperemia is especially evident in the vessels of the abdominal viscera. Petechial and ecchymotic hemorrhages are common, particularly in subepicardial and subserosal locations. Increased amounts of peritoneal and pericardial fluids are frequently seen. The liver may be swollen and often develops multiple, small, necrotic foci. |
| |
| Diagnosis: |
| A presumptive diagnosis may be based on the characteristic signs and lesions and demonstration of gram-negative, bipolar organisms in blood and other tissues. A more conclusive diagnosis requires isolation and identification of
P
multocida
. |
| |
| Prevention: |
| Good management practices are essential to prevention. Rodents, which are often carriers of
P
multocida,
must be excluded from poultry houses. Adjuvant bacterins are widely used and generally effective; autogenous bacterins are recommended when polyvalent bacterins are found to be ineffective. Attenuated vaccines are available for administration in drinking water to turkeys and by wing-web inoculation to chickens. These live vaccines can effectively induce immunity against different serotypes of
P
multocida
. They are recommended for use in healthy flocks only. |
| |
| Treatment: |
| Sulfonamides and antibiotics are commonly used; early treatment and adequate dosages are important. Sensitivity testing often aids in drug selection. Sulfaquinoxaline sodium in feed or water usually controls mortality, as do sulfamethazine and sulfadimethoxine. Sulfas should be used with caution in breeders because of potential toxicity. High levels of tetracycline antibiotics in the feed (0.04%), drinking water, or administered parenterally may be useful. Penicillin is often
effective for sulfa-resistant infections. |
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