Avian Cholera (Pasteurella multocida) in Poultry: Etiology, Transmission, Clinical Signs, and Control

Introduction

Avian cholera, also termed fowl cholera, is a contagious bacterial disease of domestic and wild birds caused by Pasteurella multocida [1, 2]. The disease is recognized globally as a significant cause of morbidity and mortality in poultry flocks, particularly in chickens, turkeys, ducks, and geese [3, 4, 5]. Acute outbreaks can result in mortality rates approaching 100% in susceptible populations, whereas chronic infections manifest as localized inflammatory lesions [1, 6]. Understanding the etiological agent, transmission dynamics, clinical presentation, and evidence-based control measures is essential for effective flock management and disease prevention. This article provides a detailed, publication-grade review of avian cholera in poultry, integrating recent molecular and immunological findings.

Etiology: Fowl Cholera Is Caused by Which Bacteria

Fowl cholera is caused by the Gram-negative, facultatively anaerobic coccobacillus Pasteurella multocida [7, 8]. The bacterium is classified into five capsular serogroups (A, B, D, E, F) and 16 lipopolysaccharide (LPS) genotypes based on the Heddleston scheme [8, 9]. In poultry, capsular serogroup A and LPS genotypes 1, 3, and 4 are most frequently isolated [2, 5]. The species is further subdivided into three subspecies: P. multocida subsp. multocida, P. multocida subsp. septica, and P. multocida subsp. gallicida, with subsp. multocida predominating in avian hosts [10].

The genome of P. multocida encodes numerous virulence factors, including a polysaccharide capsule, LPS, fimbriae, adhesins such as filamentous hemagglutinin (FhaB), and exotoxins [11, 12]. The capsule confers resistance to phagocytosis, while LPS is a major immunogen and determinant of serovar specificity [13, 14]. The kmt1 gene, encoding a species-specific carboxykinase, is a conserved target for molecular detection [7, 15]. Multidrug-resistant strains have been characterized, harboring resistance genes against tetracyclines, sulfonamides, and beta-lactams [16, 7, 17].

Epidemiology and Transmission

Avian cholera occurs worldwide, with outbreaks reported in commercial poultry, backyard flocks, and wild waterfowl [4, 18]. Transmission occurs horizontally via direct contact, aerosolized respiratory secretions, and contamination of feed and water with nasal exudates or feces [3, 1]. Carrier birds, including recovered individuals and asymptomatic fowl, serve as reservoirs and shed the organism intermittently [9, 18]. The bacterium can survive for weeks in organic matter, water, and soil under cool, moist conditions [19].

Avian Cholera Transmission to Humans

Although Pasteurella multocida is primarily an animal pathogen, zoonotic transmission to humans can occur through bites, scratches, or contact with infected bird secretions [7]. In humans, the bacterium typically causes localized wound infections, cellulitis, or respiratory disease, but human-to-human transmission is not documented [7]. Poultry workers and veterinarians should observe standard hygiene precautions when handling infected birds or contaminated materials.

Host Range and Risk Factors

All domestic poultry species are susceptible, but turkeys and ducks are particularly vulnerable to acute disease [3, 5]. Stressors such as overcrowding, poor ventilation, nutritional deficiencies, and concurrent infections (e.g., Mycoplasma gallisepticum) predispose flocks to outbreaks [3, 20]. In broilers, acute fowl cholera can cause 100% mortality within 48 hours [1]. Layer flocks may experience subacute or chronic forms with reduced egg production [9].

Clinical Signs and Pathology

The clinical presentation of avian cholera varies with the virulence of the strain, host immunity, and route of exposure [21, 6]. Three forms are recognized: peracute, acute, and chronic.

Peracute and Acute Forms

Peracute disease is characterized by sudden death without premonitory signs, often in apparently healthy birds [1, 2]. Acute cases present with fever, depression, anorexia, ruffled feathers, mucoid or bloody diarrhea, and increased respiratory rate [3, 6]. Cyanosis of the comb and wattles is common, and death occurs within 12 to 48 hours [1].

Chronic Form

Chronic fowl cholera manifests as localized infections, including swollen wattles, conjunctivitis, sinusitis, arthritis, and torticollis due to middle ear involvement [6]. In laying hens, a drop in egg production and increased numbers of misshapen eggs are observed [9].

Pathological Findings

Gross lesions in acute cases include petechial hemorrhages on the epicardium, serosal surfaces, and abdominal fat; multifocal hepatic necrosis (small, pale foci); and splenomegaly [1, 22]. The liver may exhibit a characteristic "nutmeg" appearance due to congestion and necrosis [23]. In ducks, P. multocida induces liver injury through inflammatory, apoptotic, and autophagic pathways [22]. In broilers, the MAPK-NLRP3-GSDMD signaling pathway mediates liver pyroptosis [23]. Chronic cases show caseous exudates in wattles, joints, and sinuses [6].

Diagnostics

Definitive diagnosis of avian cholera relies on bacterial isolation and identification of P. multocida from affected tissues (liver, spleen, bone marrow, or exudates) [2, 21]. The organism grows on blood agar or MacConkey agar (weak growth) as small, gray, mucoid colonies with a characteristic "mousy" odor [7]. Biochemical profiling and capsular typing are performed using standard methods [5].

Molecular Detection

Polymerase chain reaction (PCR) targeting the kmt1 gene is widely used for species confirmation [7, 15]. Loop-mediated isothermal amplification (LAMP) assays offer rapid, field-deployable alternatives with sensitivity comparable to PCR [15]. Whole-genome sequencing provides high-resolution typing for epidemiological investigations [8, 10].

Serological Assays

Indirect enzyme-linked immunosorbent assays (ELISAs) using whole-cell antigens or recombinant lipoproteins (e.g., PlpE) detect antibodies in serum and are useful for flock-level surveillance [24, 25, 26]. Commercial ELISA kits are available, but in-house assays can be optimized for local strains [24].

Differential Diagnosis

Avian cholera must be differentiated from other causes of acute septicemia in poultry, including highly pathogenic avian influenza, Newcastle disease, avian colibacillosis, and salmonellosis [1, 6]. The presence of characteristic liver necrosis and positive P. multocida culture confirms the diagnosis.

Treatment and Control

Antimicrobial Therapy

Treatment of affected flocks relies on prompt administration of antibiotics such as tetracyclines, sulfonamides, fluoroquinolones, or penicillins, ideally guided by antimicrobial susceptibility testing [16, 7]. However, multidrug resistance is increasingly reported, limiting therapeutic options [16, 17]. Phage therapy using lytic bacteriophages (e.g., vB_PmuM_CFP3) has shown promise as an alternative or adjunct to antibiotics [27].

Vaccination

Vaccination is a cornerstone of fowl cholera control. Both inactivated bacterins and live attenuated vaccines are available [28, 29, 30]. Inactivated vaccines are typically administered parenterally and require adjuvants such as aluminum hydroxide or oil emulsions to enhance immunogenicity [29, 25, 31]. Novel approaches include gamma-irradiated vaccines [30, 32], subunit vaccines based on recombinant lipoproteins (PlpE, VacJ, OmpH) [33, 34, 35], and outer membrane vesicle vaccines [33]. Live attenuated strains (e.g., PMZ8) generated by serial passage in ducks have demonstrated safety and efficacy [28]. The LPS outer core structure is a critical determinant of vaccine cross-protection [13, 14].

Biosecurity and Management

Control measures include strict biosecurity, all-in/all-out flock management, rodent and wild bird control, and disinfection of contaminated premises [19, 4]. Carrier birds should be culled to eliminate reservoirs [9]. In endemic areas, vaccination combined with improved hygiene reduces outbreak frequency and severity [18].

Fowl Cholera Meaning in Bengali

In Bengali, fowl cholera is commonly referred to as "মুরগির কলেরা" (murgir kolera) or "পোল্ট্রি কলেরা" (poultry kolera). The term "fowl cholera meaning in bengali" is often searched by poultry farmers in Bangladesh and West Bengal to understand the disease. The causative agent, Pasteurella multocida, is known as "পাস্তুরেলা মাল্টোসিডা" in Bengali. Awareness of the disease in local language facilitates communication of control measures [17]. The phrase "fowl cholera meaning in bengali" is also used in educational materials to describe the clinical signs and prevention strategies for this devastating poultry disease.

Diagnostic and Control Decision Tree

The following Mermaid diagram outlines a recommended diagnostic and control workflow for suspected avian cholera outbreaks in poultry flocks.

flowchart TD
    A[Sudden mortality or respiratory signs in poultry], > B{Clinical suspicion of avian cholera?}
    B, >|Yes| C[Collect samples: liver, spleen, bone marrow]
    B, >|No| D[Consider other diagnoses: AI, ND, colibacillosis]
    C, > E[Gram stain and culture on blood agar]
    E, > F[Isolate P. multocida?]
    F, >|Yes| G[Confirm by PCR (kmt1) or biochemical tests]
    F, >|No| H[Perform molecular detection (PCR/LAMP) on tissue]
    G, > I[Antimicrobial susceptibility testing]
    I, > J[Select appropriate antibiotic therapy]
    H, >|Positive| I
    H, >|Negative| D
    J, > K[Implement biosecurity: quarantine, disinfection, cull carriers]
    K, > L[Vaccinate remaining flock with inactivated or live vaccine]
    L, > M[Monitor for recurrence; adjust vaccination protocol]

Conclusion

Avian cholera remains a major threat to poultry production worldwide. The causative agent, Pasteurella multocida, exhibits considerable genetic and antigenic diversity, complicating vaccine development and antimicrobial therapy [16, 8, 10]. Rapid molecular diagnostics, including PCR and LAMP, enable early detection and typing [15]. Integrated control strategies combining biosecurity, vaccination, and prudent antimicrobial use are essential to reduce disease impact [28, 29, 18]. Continued research into virulence mechanisms, host immune responses, and novel vaccine platforms will further improve management of this economically important disease [23, 25, 22].

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