Fowl cholera (FC) is a highly contagious bacterial disease of domestic and wild birds worldwide. It is caused by
Pasteurella multocida, a gram-negative, non-spore-forming, rod shaped bacteria. There are 16 somatic serotypes of
P. multocida, each with varying pathogenicity. The disease manifests as an acute septicemia or a chronic localized infection. Birds that survive the acute infection, or who are exposed to a low virulence strain, generally exhibit localized infections.
Clinical Signs of Fowl Cholera
Signs vary depending on the form of the disease.
- Acute Form: Infected birds may develop fever, ruffled feathers, lethargy, anorexia, mucoid discharge from the mouth, increased respiratory rate, and cyanosis. Diarrhea might also develop, beginning as a watery, whitish discharge which progresses to a greenish color with mucus present.
- Chronic Form: Presents as a localized infection (swelling, inflammation, and abscess) of the wattles, sinuses, foot pad, sternal bursa, joints (leg or wing), or ears. If the ears are involved, infected birds may exhibit wry neck (torticollis) from involvement of the middle ear. Sometimes tracheal rales and dyspnea may occur secondary to respiratory tract infections. This form of FC may last 3 to 4 weeks and may sometimes persist for years, even after receiving treatment.
Transmission
FC is spread via horizontal transmission through direct or indirect contact with infected birds. It is introduced to flocks through wild birds, rodents, predator attacks (especially involving domestic dogs or cats), newly introduced carrier birds, or fomites (contaminated equipment, etc).
P. multocida can enter through mucous membranes, including oral, nasal, and conjunctival, as well as through cutaneous wounds. Detailed routes in which FC is spread include:
- Direct contact with infected birds: Secretions made from infected birds, requiring close contact with one another.
- Ingestion: Most common route, involving contamination of the environment, feed, or water with feces from infected hosts.
- Predator attacks: Non-fatal predator attacks from wild or domestic animals (dogs, cats, and raccoons are known to be carriers of high amounts of the bacterium in their oral cavities and underneath their nails). Any chicken that has been in a predator's mouth or scratched by a predator should be treated immediately with appropriate antibiotics.
- Fomites: Contamination of equipment, clothing, cages, feeders, etc.
- Aerosol form
P. multocida can persist in the environment for weeks after an outbreak. Chronically infected carriers play a major role in the spread of this disease, and infected birds can remain carriers for life.
