Fowl Cholera (Pasteurella multocida)
Etiology
Fowl cholera (FC) is a highly contagious disease of domestic and wild birds. The disease is caused by Pasteurella multocida, a gram-negative, non-spore-forming, rod shaped bacteria. There are 16 somatic serotypes of Pasteurella multocida, of which 1, 3, and 3x4 are the most common. The pathogenicity of Pasteurella multocida strains is quite variable and the degree of expression of clinical signs varies by host species as well as variations within the host's immune system.
Host Range
Outbreaks of FC occur most frequently in turkeys, chickens, ducks, and geese. The disease is particularly severe in turkeys. Other bird species raised in captivity, as well as wild avian species, may also develop clinical disease. Some domestic mammals are also susceptible.
Epidemiology
FC is spread via horizontal transmission through contact with infected birds, contaminated equipment, personnel, etc. Pasteurella multocida can enter through mucous membranes, including oral, nasal, and conjunctival, as well as through cutaneous wounds. Chronically infected carriers play a major role in the spread of this disease and infected birds can remain carriers for life. The prevalence of Pasteurella multocida among wild birds, rodents, and other domesticated and non-domesticated species is likely responsible for the introduction of the infection into most domesticated poultry flocks.
FC is widely distributed, with periodic enzootic outbreaks occurring in most countries throughout the world. The disease usually manifests as a septicemia, sometimes with high morbidity and high mortality. However, a more chronic and asymptomatic form of the disease can also occur. Young adults are most susceptible to FC infection and physiologic stresses, such as egg lay cycles and seasonal changes, influence susceptibility. FC is more prevalent in the cooler seasons of the year.
Clinical Signs
Signs vary depending on the course of the disease. In the acute form of FC, infected birds may develop fever, ruffled feathers, anorexia, increased respiratory rate, and cyanosis. Cyanosis is often easiest to appreciate on the non-feathered skin of the comb and wattles. Mucoid discharge from the mouth and diarrhea may also occur. Diarrhea often begins as watery and whitish in color, progressing to a greenish color with mucus. In the acute form, signs may be absent and birds may be found dead in their nests. Birds that survive the acute septicemia may later die of dehydration and emaciation. Some birds may survive but remain chronically infected.
In the chronic form of FC, birds that survive acute infection or birds exposed to a low virulence strain, generally exhibit localized infections. The wattles, sinuses, foot pads, sternal bursa, and leg and wing joints may become swollen. Exudative pharyngeal and conjunctival lesions may be present. Sometimes tracheal rales and dyspnea may occur secondary to respiratory tract infections. Infected birds may also exhibit torticollis from middle ear infections and meningeal involvement. The chronic form of FC may last 3 to 4 weeks and may sometimes persist for years.
Post-mortem Lesions
In the acute form of FC, lesions associated with vascular disturbances are common. The veins of the abdominal viscera, especially the duodenum, may be markedly hyperemic. Petechiael and ecchymotic hemorrhages are frequently found throughout the viscera, most commonly the lungs, intestines, heart, and abdominal fat. Excessive fluid may be found in the pericardium and coelomic cavity. In infections with virulent strains of Pasteurella multocida, there may be liver enlargement and coagulative necrosis. Other findings may include pneumonia, especially in turkeys, and excessive mucous along the digestive tract. Lesions of the ovaries may include flaccid follicles, hyperemia, and egg-yolk peritonitis from ruptured ova.
In the chronic form of FC, localized infections may be found throughout the body including the hock joints, foot pads, oviduct, and coelomic cavity. Suppurative lesions are frequently found in the respiratory tract and pneumatic bones. Pneumonia is especially common in turkeys. Caseous exudate and fibrin may also infiltrate the calvarial bones, middle ear, meninges, and air spaces.
Differential Diagnosis
Fowl cholera must be differentiated from erysipelas, acute colibacillosis, Avibacterium gallinarum and complicated Mycoplasma gallisepticum in turkeys and other birds that may have both diseases. Erysipelas is caused by a gram-positive rod. Cholera can be differentiated from other septicemic diseases by isolation of P. multocida. Related organisms that cause cholera-like diseases in poultry include P. gallinarum, P. haemolytica, and P. anatipestifer.
Diagnosis
Culture samples can be taken from the liver, lungs, spleen, wattles or affected joints at necropsy. Additionally, impression smears of the liver and heart blood can also be obtained. Gram-stained impression smears may reveal bipolar, gram-negative rods suggestive of P. multocida. Use of Wright's stain or methylene blue readily demonstrates the bipolar morphology of P. multocida. Rabbits, hamsters, or mice can be inoculated for pure culture. P. multocida grows readily on blood agar but does not grow on MacConkey agar. Isolates should be tested for antibiotic sensitivity and resistance.
Prevention and Control
The elimination of reservoirs of Pasteurella multocida (such as rats, mice, cats, raccoons, skunks, etc.) in contact with domesticated and commercial poultry is one of the most effective management procedures to control the disease.
Both live and inactivated Pasteurella multocida vaccines are available for use in chickens. Three live products are available in the United States; the Clemson University CU low virulent strain; M-9, a mutant of CU of very low virulence; and PM-1, a mutant of CU intermediate in virulence between CU and M-9. Inactivated bacterins are primarily trivalent whole cell products containing the most common serotypes. Autogenous vaccines are also commonly used. A combination of inactivated and live vaccines can reduce the incidence of fowl cholera in susceptible broiler breeder flocks. Since FC is primarily a disease of older birds, broilers are not commonly vaccinated.
Selected References
- Brogden, K.A., K.R. Rhoades, and K.L. Heddleston. 1978. A new serotype of Pasteurella multocida associated with fowl cholera. Avian Dis 22:185-90.
- Charlton, B. R. (ed). 2006. Avian Disease Manual, 6th ed. American Association of Avian Pathologists (AAAP), 953 College Station Road, Athens, Georgia 30602-4875.
- Glisson. J.R., C.L. Hofacre, and J.P. Christensen. 2008. Pasteurellosis and other respiratory bacterial infections. In Diseases of Poultry, 12th ed. Y.M. Saif. et al. (ed.). Blackwell Publishing, Ames, Iowa.
- Glisson, JR. 1998. Bacterial respiratory disease of poultry. Poult Sci Aug;77(8):1139-42. Review.
- Harper, M., J.D. Boyce and B. Adler. 2006. Pasteurella multocida pathogenesis: 125 years after Pasteur. FEMS Microbiol Lett. Dec;265(1):1-10. Review.
- World Organization for Animal Health (OIE) website. 2008. www.oie.int
Thank you to the following individuals for reviewing these materials:
Charles Hofacre
Jaime Ruiz
Jose Bruzual
