Fowl Cholera (Pasteurella multocida) in Poultry: Clinical Presentation, Diagnosis, and Control

Etiology

Fowl cholera is a highly contagious bacterial disease of domestic and wild birds caused by Pasteurella multocida, a Gram-negative, nonmotile, facultatively anaerobic, coccobacillary bacterium belonging to the family Pasteurellaceae [1]. The organism is typically 0.3 to 1.0 micrometers in length and 0.2 to 0.5 micrometers in width, exhibiting bipolar staining when treated with methylene blue or Giemsa stains [1]. P. multocida is classified into five capsular serogroups (A, B, C, D, E, and F) based on capsular polysaccharide antigens, and into 16 somatic serotypes (1 through 16) using heat-stable lipopolysaccharide antigens [2, 3]. In poultry, the most commonly encountered serogroups are A (serotypes 1, 3, 4, and 5) and D (serotypes 1, 3, and 4), with serogroup A being the predominant cause of fowl cholera in chickens and turkeys [2, 3]. The bacterium produces a potent dermonecrotic toxin (DNT) in certain serogroup D strains, which is associated with progressive atrophic rhinitis in swine but is not considered a primary virulence factor in avian infections [4].

Epidemiology

Fowl cholera affects a wide range of avian species, including chickens, turkeys, ducks, geese, pheasants, quail, and numerous wild waterfowl and shorebirds [1, 5]. Turkeys are generally more susceptible than chickens, and mortality rates can exceed 50 percent in untreated flocks [5]. The disease is distributed globally, with higher incidence in regions with intensive poultry production, particularly in tropical and subtropical climates [1]. Transmission occurs primarily through direct contact between infected and susceptible birds via respiratory secretions, feces, and contaminated feed or water [6]. The bacterium can survive for several days in organic material, soil, and water, but is rapidly inactivated by desiccation, sunlight, and common disinfectants [6]. Chronic carrier birds, often those with residual respiratory tract infections, serve as the primary reservoir for inter-flock transmission and introduction into naive populations [7]. Mechanical vectors such as rodents, wild birds, and fomites (contaminated equipment, footwear, and vehicles) also contribute to the spread of infection [7].

Clinical Signs

The clinical presentation of fowl cholera is highly variable and depends on the virulence of the infecting strain, the route of exposure, the immune status of the host, and the species affected [1, 8]. Three distinct disease forms are recognized: peracute, acute, and chronic.

Peracute Form

The peracute form is characterized by sudden death in apparently healthy birds, often without premonitory signs [1, 8]. Mortality in a flock can spike dramatically within 24 to 48 hours of exposure, with affected birds found dead in good body condition and with full crops [8]. This form is most commonly observed in highly susceptible flocks, such as unvaccinated turkeys or naive layer flocks, and is associated with septicemic dissemination of the organism [1].

Acute Form

The acute form is the most common presentation in field outbreaks and is characterized by a rapid onset of clinical signs over 1 to 3 days [1, 8]. Affected birds exhibit fever (elevated body temperature), depression, anorexia, ruffled feathers, and a marked reduction in water and feed intake [8]. Respiratory signs include serous to mucoid nasal discharge, dyspnea, and open-mouth breathing [8]. Ocular signs may include conjunctivitis and periorbital swelling [8]. Diarrhea is common, with feces ranging from watery green to yellow-brown, often containing mucus or blood [8]. Cyanosis of the comb and wattles is frequently observed, and in laying hens, egg production drops precipitously [8]. Mortality rates in the acute form typically range from 20 to 50 percent in untreated flocks [1].

Chronic Form

The chronic form develops in birds that survive the acute phase or in flocks with low-virulence strains [1, 8]. Clinical signs are localized and include swollen wattles (wattle edema), facial cellulitis, purulent conjunctivitis, and mucopurulent nasal discharge [8]. Chronic respiratory disease, characterized by tracheal rales and sinusitis, is common [8]. Joint infections (arthritis and synovitis) manifest as lameness, swollen hocks, and reluctance to move [8]. Chronic infections can persist for weeks to months, and affected birds become emaciated and unthrifty [8].

Pathology

Gross Lesions

The gross pathology of fowl cholera reflects the septicemic nature of the infection [1, 9]. In peracute and acute cases, the most consistent findings are petechial and ecchymotic hemorrhages on the serosal surfaces of the heart (epicardium), liver, and abdominal fat [9]. The liver is frequently enlarged, friable, and exhibits a mottled tan-to-bronze appearance with multiple pinpoint necrotic foci (miliary necrosis) [9]. The spleen is often enlarged and congested [9]. The lungs may be congested and edematous, and the trachea contains frothy, blood-tinged exudate [9]. In turkeys, the air sacs are frequently thickened and contain fibrinous exudate [9]. The intestinal tract shows diffuse catarrhal to hemorrhagic enteritis, with the duodenum being most severely affected [9].

Chronic Lesions

Chronic cases present with localized lesions. Wattle edema is characterized by subcutaneous edema, cellulitis, and fibrinous exudate in the intermandibular space [9]. Joint lesions include fibrinosuppurative arthritis and tenosynovitis, with thickened joint capsules and purulent joint fluid [9]. Chronic respiratory lesions include fibrinous airsacculitis, pericarditis, and perihepatitis [9].

Histopathology

Histologically, acute fowl cholera is characterized by a severe, diffuse, heterophilic to fibrinous inflammation in multiple organs, with massive bacterial emboli in capillaries and small blood vessels [1, 9]. The liver shows multifocal coagulative necrosis with a peripheral zone of heterophils and macrophages [9]. The spleen exhibits acute splenitis with lymphoid depletion and fibrin deposition [9]. In chronic cases, the wattle and joint lesions consist of a central core of necrotic debris and fibrin surrounded by a zone of heterophils, macrophages, and granulation tissue [9].

Diagnosis

Presumptive Diagnosis

A presumptive diagnosis of fowl cholera is based on the combination of acute mortality, characteristic clinical signs (cyanosis, nasal discharge, diarrhea), and gross pathological findings (miliary hepatic necrosis, petechial hemorrhages) [1, 10]. The disease must be differentiated from other acute septicemic conditions of poultry, including fowl typhoid (caused by Salmonella Gallinarum), avian influenza, Newcastle disease, and colibacillosis [10].

Confirmatory Diagnosis

Confirmatory diagnosis relies on the isolation and identification of P. multocida from affected tissues [1, 10]. Samples of choice include liver, spleen, heart blood, bone marrow, and swabs of the wattle or joint exudate [10]. The organism is readily cultured on blood agar or tryptic soy agar supplemented with 5 percent sheep blood, incubated at 37 degrees Celsius for 18 to 24 hours under microaerophilic conditions [10]. Colonies are small (1 to 2 mm), smooth, grayish, and nonhemolytic, with a characteristic "sweet" or "mousy" odor [10]. A Gram stain of the colony reveals Gram-negative coccobacilli with bipolar staining [10].

Biochemical Identification

P. multocida is catalase-positive, oxidase-positive, and indole-positive [10]. It ferments glucose, sucrose, and mannitol without gas production, and is negative for urease, gelatinase, and growth on MacConkey agar [10]. Commercial biochemical test strips (e.g., API 20E or API 20NE systems) can be used for species-level identification [10].

Serotyping and Molecular Typing

Capsular serotyping is performed using the passive hemagglutination test with specific antisera against the five capsular serogroups [2]. Somatic serotyping is performed using the agar gel immunodiffusion test with heat-stable antigens [2]. Molecular typing methods, including PCR-based capsular typing and multilocus sequence typing (MLST), are increasingly used for epidemiological investigations and strain characterization [11]. A multiplex PCR assay targeting the capsular biosynthesis genes (hyaD-hyaC, bcbD, dcbF, ecbJ, and fcbD) can differentiate serogroups A, B, C, D, E, and F in a single reaction [11].

Differential Diagnosis

The following table summarizes the key differential diagnoses for fowl cholera in poultry [1, 10, 12].

| Disease | Key Differentiating Features | |, - |, - | | Fowl Typhoid (Salmonella Gallinarum) | Greenish diarrhea, enlarged liver with bronze discoloration, negative blood culture on MacConkey agar | | Avian Influenza | Respiratory signs more prominent, tracheal hemorrhages, positive RT-PCR for influenza A | | Newcastle Disease | Neurological signs (torticollis, paralysis), tracheal rings with hemorrhages, positive hemagglutination inhibition test | | Colibacillosis | Airsacculitis, pericarditis, perihepatitis (fibrinous), E. coli isolation on MacConkey agar | | Infectious Coryza (Avibacterium paragallinarum) | Facial edema, sinusitis, nasal discharge, negative blood culture, A. paragallinarum isolation on chocolate agar | | Mycoplasmosis (Mycoplasma gallisepticum) | Chronic respiratory disease, airsacculitis, negative blood culture, positive serology (ELISA) |

Treatment

Antimicrobial Therapy

Treatment of fowl cholera is based on the prompt administration of antimicrobial agents to which the isolate is susceptible [1, 13]. The drug of choice for many years has been sulfonamides (sulfadimethoxine, sulfaquinoxaline) administered in the feed or drinking water at 0.05 to 0.1 percent for 3 to 5 days [13]. Tetracyclines (oxytetracycline, chlortetracycline) at 200 to 400 g per ton of feed are also effective [13]. Penicillin G (10,000 to 20,000 IU per bird) administered intramuscularly is highly effective in individual birds [13]. However, antimicrobial resistance is a growing concern, with resistance to sulfonamides, tetracyclines, and streptomycin reported in many regions [14]. In vitro susceptibility testing using the disk diffusion method or broth microdilution (minimum inhibitory concentration determination) is strongly recommended to guide therapy [14]. Treatment should be continued for a minimum of 5 to 7 days, and withdrawal periods must be observed according to local regulations [13].

Supportive Care

Supportive care includes providing clean, fresh water, reducing environmental stress, and ensuring adequate ventilation [13]. Affected birds should be isolated from the main flock, and dead birds should be removed promptly to reduce environmental contamination [13].

Control

Biosecurity

Biosecurity is the cornerstone of fowl cholera control [1, 15]. Key measures include:

• All-in/all-out flock management to break the cycle of infection [15].
• Strict quarantine of new birds for a minimum of 30 days [15].
• Rodent and wild bird control programs to eliminate reservoir hosts [15].
• Disinfection of poultry houses, equipment, and footwear using approved disinfectants (e.g., sodium hypochlorite, quaternary ammonium compounds, or formaldehyde) [15].
• Dedicated footwear and clothing for each poultry house [15].

Vaccination

Vaccination is widely used to reduce the incidence and severity of fowl cholera in commercial flocks [1, 16]. Two main types of vaccines are available: inactivated (bacterin) vaccines and live attenuated vaccines [16].

Inactivated Vaccines

Inactivated vaccines are prepared from whole cultures of P. multocida serotypes 1, 3, and 4, inactivated with formalin or beta-propiolactone and adjuvanted with aluminum hydroxide or oil emulsions [16]. These vaccines are administered subcutaneously or intramuscularly to birds at 8 to 12 weeks of age, with a booster dose 4 to 6 weeks later [16]. Inactivated vaccines provide good protection against homologous serotypes but limited cross-protection against heterologous serotypes [16].

Live Attenuated Vaccines

Live attenuated vaccines are derived from avirulent strains of P. multocida (e.g., the Clemson University (CU) strain) and are administered via the drinking water or by aerosol spray [16]. These vaccines induce a strong cell-mediated and humoral immune response and provide broader cross-protection than inactivated vaccines [16]. However, they can cause mild respiratory signs and are not recommended for use in flocks with concurrent immunosuppressive diseases [16].

Vaccine Efficacy

Vaccine efficacy is influenced by several factors, including the serotype of the challenge strain, the route of administration, the age of the birds, and the presence of maternal antibodies [16]. A booster vaccination is essential for long-term protection, and annual revaccination is recommended in endemic areas [16].

Eradication

Eradication of fowl cholera from an infected flock is difficult but can be achieved through depopulation, thorough cleaning and disinfection, and a rest period of 2 to 4 weeks before restocking [1]. In commercial layer flocks, a test-and-slaughter program combined with vaccination may be used to eliminate chronic carrier birds [1].

Fowl Cholera in Hindi

Fowl cholera is known as "मुर्गी हैजा" (Murghi Haiza) in Hindi, reflecting the historical association of the disease with cholera-like symptoms in humans [1]. The term "fowl cholera bacterial" is used to distinguish the bacterial etiology from viral causes of enteritis in poultry [1].

Diagnostic Workflow

The following Mermaid diagram illustrates the diagnostic workflow for fowl cholera in poultry [1, 10].

graph TD
    A[Clinical Signs: Acute mortality, cyanosis, diarrhea], > B{Postmortem Examination}
    B, > C[Gross Lesions: Hepatic necrosis, petechiae]
    C, > D[Sample Collection: Liver, spleen, heart blood]
    D, > E[Gram Stain: Bipolar coccobacilli]
    E, > F[Culture on Blood Agar: 37C, 18-24h]
    F, > G[Colony Morphology: Small, gray, nonhemolytic]
    G, > H[Biochemical Tests: Catalase+, Oxidase+, Indole+]
    H, > I[Serotyping: Capsular A or D]
    I, > J[Antimicrobial Susceptibility Testing]
    J, > K[Treatment: Sulfonamides or Tetracyclines]
    K, > L[Control: Biosecurity + Vaccination]

References

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[2] Carter GR. Studies on Pasteurella multocida. I. A hemagglutination test for the identification of serological types. Am J Vet Res. 1955;16(61):481-484.

[3] Heddleston KL, Gallagher JE, Rebers PA. Fowl cholera: gel diffusion precipitin test for serotyping Pasteurella multocida from avian species. Avian Dis. 1972;16(4):925-936.

[4] Foged NT, Nielsen JP, Pedersen KB. Differentiation of Pasteurella multocida toxigenic strains from non-toxigenic strains by a monoclonal antibody against the dermonecrotic toxin. Vet Microbiol. 1988;18(3-4):267-277.

[5] Glisson JR, Hofacre CL, Christensen JP. Fowl cholera. In: Saif YM, editor. Diseases of Poultry. 12th ed. Blackwell Publishing; 2008. p. 739-758.

[6] Snipes KP, Hirsh DC, Kasten RW, et al. Survival of Pasteurella multocida in a simulated poultry environment. Avian Dis. 1989;33(4):681-685.

[7] Carpenter TE, Snipes KP, Wallis D, et al. Epidemiology of fowl cholera in California: a case-control study. Avian Dis. 1988;32(4):701-706.

[8] Christensen JP, Bisgaard M. Fowl cholera. In: Pattison M, McMullin PF, Bradbury JM, Alexander DJ, editors. Poultry Diseases. 6th ed. Saunders Elsevier; 2008. p. 149-159.

[9] Cheville NF, Rimler RB, Heddleston KL. Pathologic changes in fowl cholera. Vet Pathol. 1978;15(5):600-608.

[10] Rimler RB, Glisson JR. Fowl cholera. In: Swayne DE, editor. A Laboratory Manual for the Isolation and Identification of Avian Pathogens. 5th ed. American Association of Avian Pathologists; 2008. p. 56-62.

[11] Townsend KM, Boyce JD, Chung JY, et al. Genetic organization of Pasteurella multocida capsular loci and development of a multiplex capsular PCR typing system. J Clin Microbiol. 2001;39(3):924-929.

[12] Blackall PJ. Infectious coryza: overview of the disease and new diagnostic options. Clin Microbiol Rev. 1999;12(4):627-632.

[13] Hofacre CL, Glisson JR. Fowl cholera. In: Merck Veterinary Manual. 11th ed. Merck & Co.; 2016. p. 2345-2350.

[14] Watts JL, Sweeney MT, Lubbers BV. Antimicrobial susceptibility testing of Pasteurella multocida from poultry. J Vet Diagn Invest. 2009;21(5):678-682.

[15] Carpenter TE, Hird DW, Snipes KP. Biosecurity for fowl cholera. Prev Vet Med. 1991;11(3-4):221-228.

[16] Rimler RB, Davis RB. Fowl cholera: immunity and vaccination. Avian Dis. 1977;21(4):681-688. *** Disclaimer: This article is for educational and informational purposes only. It is not intended to substitute for professional veterinary advice, diagnosis, treatment, or regulatory guidance. Always consult a licensed veterinarian or qualified specialist regarding animal health, disease diagnosis, and therapeutic decisions.