Fowl cholera

is a contagious, bacterial disease of birds caused by Pasteurella multocida. Acutely, it causes elevated mortality. Chronically, it causes lameness, swollen wattles (in chickens), pneumonia (in turkeys), and torticollis, but it can also be asymptomatic.

Etiology and Transmission

Pasteurella multocida, the causal agent of fowl cholera, is a small, gram-negative, nonmotile rod with a capsule that may exhibit pleomorphism after repeated subculture. P multocida is considered a single species although it includes three subspecies: multocida, septica, and gallicida. Subspecies multocida is the most common cause of disease, but septica and gallicida may also cause cholera-like disease.

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 (or serotypes). P multocida can be subgrouped by capsule serogroup antigens into five capsular types (A, B, C, D, and F) and into 16 somatic serotypes. Turkeys and waterfowl are more susceptible than chickens, older chickens are more susceptible than young ones, and some breeds of chickens are more susceptible than others

Clinical findings from fowl cholera vary greatly depending on the course of disease. In acute fowl cholera, finding a large number of dead birds without previous signs is usually the first indication of disease. Mortality often increases rapidly. In more protracted cases, depression, anorexia, mucoid discharge from the mouth, ruffled feathers, diarrhea, and increased respiratory rate are usually seen. Pneumonia is particularly common in turkeys.

Lesions observed

Lesions observed in peracute and acute forms of the disease are primarily vascular disturbances. These include general passive hyperemia and congestion throughout the carcass, accompanied by enlargement of the liver and spleen. Petechial and ecchymotic hemorrhages are common, particularly in subepicardial and subserosal locations. Increased amounts of peritoneal and pericardial fluids are frequently seen.

Confirmed by bacterial culture
Although the history, signs, and lesions may aid field diagnosis, P multocida should be isolated, characterized, and identified for confirmation. Primary isolation can be accomplished using media such as blood agar, dextrose starch agar, or trypticase soy agar. Isolation may be improved by the addition of 5% heat-inactivated serum. P multocida can be readily isolated from viscera of birds dying from peracute/acute fowl cholera, whereas isolation from suppurative lesions of chronic cholera may be more difficult. At necropsy, bipolar microorganisms may be demonstrated by the use of Wright’s or Giemsa stain of impression smears obtained from the liver in the case of acute cholera. In addition, immunofluorescent microscopy and in situ hybridization have been used to identify P multocida in infected tissues and exudate
Good management practices, including a high level of biosecurity, are essential to prevention.
Rodents, wild birds, pets, and other animals that may be carriers of P multocida must be excluded from poultry houses. The organism is susceptible to ordinary disinfectants, sunlight, drying, and heat.
Eradication of infection requires depopulation, followed by thorough cleaning and disinfection
Antibiotics may reduce mortality but won't eliminate P multocida from a flock
A number of drugs will lower mortality from fowl cholera; however, deaths may resume when treatment is discontinued, showing that treatment does not eliminate P multocida from a flock. Eradication of infection requires depopulation and cleaning and disinfection of buildings and equipment. The premise should then be kept free of poultry for a few weeks.

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