Infectious Coryza in Chickens and Quail: Avibacterium paragallinarum Etiology, Clinical Signs, Treatment, and Prevention

Introduction

Infectious coryza (IC) is an acute upper respiratory disease of chickens and quail caused by the bacterium Avibacterium paragallinarum. The disease is characterized by serous to mucopurulent nasal discharge, facial edema, conjunctivitis, and decreased egg production in layers [1, 60]. While primarily a disease of gallinaceous birds, A. paragallinarum has been isolated from Japanese quail (Coturnix japonica) with typical clinical signs, confirming its host range extends beyond chickens. The economic impact of IC is substantial, resulting from increased mortality, culling, reduced feed conversion, and significant drops in egg production [2, 36]. This article provides a comprehensive clinical reference on the etiology, pathogenesis, clinical presentation, diagnostic approaches, treatment options, and prevention strategies for infectious coryza in chickens and quail.

Etiology and Taxonomy

Avibacterium paragallinarum is a Gram-negative, pleomorphic, non-motile, encapsulated coccobacillus belonging to the family Pasteurellaceae. The bacterium is fastidious, requiring nicotinamide adenine dinucleotide (NAD, also known as V factor) for in vitro growth, although NAD-independent variants have been described [44, 62, 76, 85]. The organism is catalase-negative, oxidase-positive, and reduces nitrates. Colonies on chocolate agar or blood agar with a nurse colony (e.g., Staphylococcus spp.) are small, dewdrop-like, and non-hemolytic after 24-48 hours of incubation in a 5-10% CO2 atmosphere [3].

Serotyping and Genotyping

Classical serotyping of A. paragallinarum is based on the Page scheme, which uses hemagglutination inhibition (HI) tests to classify isolates into serovars A, B, and C. The Kume scheme further divides these into serogroups and serovars based on hemagglutinin antigens [38, 49]. The hemagglutinin protein HMTp210 is a key immunogen and serotyping target; its hypervariable region determines serovar specificity [38, 39, 77]. Molecular serotyping methods, including multiplex PCR targeting the hmtp210 gene, have been developed as alternatives to traditional HI testing [82, 92]. Genotyping approaches, such as enterobacterial repetitive intergenic consensus (ERIC)-PCR and multilocus sequence typing (MLST), have revealed substantial genetic diversity among field isolates [4, 5, 80]. A standardized genome-guided MLST scheme has been proposed for enhanced epidemiological typing [4].

Pathogenesis and Virulence Factors

The pathogenesis of IC begins with colonization of the upper respiratory tract mucosa. A. paragallinarum adheres to ciliated epithelial cells of the nasal cavity and sinuses, facilitated by fimbriae and other adhesins. The capsule is a critical virulence factor; loss of the capsule increases adherence activity but paradoxically decreases virulence in vivo. The bacterium produces a lipooligosaccharide (LOS) and a capsular polysaccharide (CPS), both of which contribute to host inflammatory responses and immune evasion. The LOS is a major component of the outer membrane and is involved in hemagglutination activity.

Biofilm formation has been identified as a potential virulence mechanism, allowing the bacterium to persist in the environment and on mucosal surfaces. Genes involved in biofilm formation have been identified through random transposon mutagenesis. The LuxS quorum-sensing system, which mediates autoinducer-2 (AI-2) production, is present in A. paragallinarum; however, its absence reduces invasion but is not essential for virulence. Iron acquisition systems, including heme utilization pathways, are upregulated under iron-starvation conditions and are essential for in vivo survival. Outer membrane vesicles (OMVs) released by A. paragallinarum contain multiple virulence-associated proteins and can mediate horizontal transfer of antibiotic resistance genes [43, 56].

The host immune response to infection involves both innate and adaptive components. Transcriptional profiling of chicken immunity-related genes during infection reveals upregulation of pro-inflammatory cytokines, chemokines, and major histocompatibility complex (MHC) molecules [88, 91]. A transient increase in MHC-II(low) monocytes has been observed after experimental infection. Macrophage activation assays have been used to evaluate the immunostimulatory capacity of A. paragallinarum antigens in multivalent vaccine formulations.

Clinical Signs

The incubation period for IC is typically 1-3 days following natural exposure, but can extend to 2 weeks. Clinical signs are most pronounced in adult chickens, particularly layers, and are exacerbated by stress, poor ventilation, and concurrent infections [1, 6, 7].

Chickens

The classic presentation includes:

• Nasal discharge: Initially serous, progressing to mucopurulent and foul-smelling [1, 60].
• Facial edema: Swelling of the infraorbital sinuses, periorbital tissues, and wattles.
• Conjunctivitis: Ocular discharge, frothy exudate, and occasional eyelid adherence [1].
• Sneezing and rales: Audible respiratory sounds, particularly at night.
• Decreased feed and water intake: Resulting in weight loss and reduced egg production [1, 36].
• Egg production drop: Can range from 10% to 40% in laying flocks [1, 84].
• Mortality: Typically low (1-5%) in uncomplicated cases, but can increase with secondary infections or poor management [1, 69].

In broiler chickens, IC may present with less pronounced facial swelling but more severe respiratory distress [31, 69]. Otitis and meningoencephalitis have been associated with IC in commercial broilers, indicating the potential for systemic spread.

Quail

In Japanese quail, clinical signs are similar to those in chickens and include nasal discharge, sneezing, conjunctivitis, and facial edema [70, 93]. Mortality can be higher in quail than in chickens, particularly in young birds. The disease in quail is often underdiagnosed, but serological and molecular surveys have confirmed the presence of A. paragallinarum in quail flocks with respiratory disease.

Morbidity and Mortality

Morbidity in affected flocks is high, often approaching 100% [1, 60]. Mortality is usually low (1-5%) in uncomplicated cases, but can reach 20% or higher when exacerbated by concurrent infections (e.g., Mycoplasma gallisepticum, Ornithobacterium rhinotracheale, Gallibacterium anatis, fowl adenovirus, or Escherichia coli) or adverse environmental conditions [31, 54, 74, 78, 83]. Coinfection with O. rhinotracheale has been reported in broiler chickens and can complicate clinical signs and lesion presentation [31, 83]. Similarly, coinfection with G. anatis can exacerbate the severity of IC, but vaccination against A. paragallinarum can prevent these exacerbated signs.

Lesions

Gross pathological findings are primarily confined to the upper respiratory tract. Typical lesions include:

• Catarrhal to fibrinous rhinitis: Accumulation of mucopurulent exudate in the nasal passages and infraorbital sinuses [60, 69].
• Sinusitis: Distension of the infraorbital sinuses with serous or purulent material.
• Conjunctivitis: Hyperemia and edema of the conjunctiva [1].
• Tracheitis: Mild to moderate inflammation of the tracheal mucosa.
• Otitis media/interna: In cases with neurological signs, purulent exudate may be found in the middle and inner ear.
• Meningoencephalitis: Rarely, fibrinopurulent exudate on the meninges.

Histopathological examination reveals acute to subacute inflammation of the nasal mucosa, with infiltration of heterophils, macrophages, and lymphocytes. Epithelial desquamation and hyperplasia are common. Immunohistochemistry can demonstrate A. paragallinarum antigen within the nasal epithelium and sinus exudate.

Diagnosis

A definitive diagnosis of IC requires isolation and identification of A. paragallinarum from clinical samples, or detection of its nucleic acid using molecular methods.

Sample Collection

Appropriate samples include:

• Swabs: Nasal or infraorbital sinus swabs from acutely affected birds [3, 35].
• Tissue: Nasal turbinates, sinus mucosa, and trachea collected at necropsy.
• Exudate: Infraorbital sinus exudate collected via aspiration.

Samples should be placed in transport medium (e.g., Amies with charcoal) and kept cool during transport [3].

Culture and Isolation

Avibacterium paragallinarum is fastidious and requires enriched media for primary isolation. Recommended media include:

• Chocolate agar: Supplemented with 1% IsoVitaleX or equivalent [3].
• Blood agar: With a nurse colony of Staphylococcus spp. (satellitism phenomenon) [3].
• Selective media: Recently developed selective culture media improve isolation rates by suppressing contaminating flora [3].

Plates are incubated at 37 degrees Celsius in a 5-10% CO2 atmosphere for 24-48 hours [3]. Colonies are small (0.5-1 mm), dewdrop-like, and non-hemolytic [3]. Identification is confirmed by Gram stain (Gram-negative coccobacilli), oxidase (positive), catalase (negative), and NAD requirement. NAD-independent variants have been reported and can be identified by their ability to grow on media without added NAD [44, 62, 76, 85].

Molecular Detection

PCR-based assays are widely used for rapid and sensitive detection of A. paragallinarum directly from clinical samples [22, 33, 52, 64, 66]. Several PCR formats are available:

• Conventional PCR: Targeting the hmtp210 gene or the 16S rRNA gene [22, 75].
• Real-time PCR (qPCR): Probe-based assays offer high sensitivity and specificity for detection in clinical samples [52, 64, 66].
• Multiplex PCR: Allows simultaneous detection of A. paragallinarum and other respiratory pathogens (e.g., O. rhinotracheale).
• Differentiating PCR: Assays that can distinguish pathogenic from nonpathogenic A. paragallinarum isolates have been developed.

PCR assays are particularly useful for detecting A. paragallinarum in samples where culture is negative due to prior antimicrobial therapy or poor sample handling [22, 66].

Serotyping

Serotyping is important for epidemiological studies and vaccine selection. The traditional method is the HI test using serovar-specific antisera. Molecular serotyping using PCR targeting the hmtp210 gene is increasingly used as a faster and more accessible alternative [82, 92]. The hypervariable region of hmtp210 can be sequenced to determine serovar [39, 49, 77].

Serology

Serological tests, such as the HI test and enzyme-linked immunosorbent assay (ELISA), can detect antibodies against A. paragallinarum in serum. However, serology is less commonly used for individual diagnosis and is more applicable for flock-level surveillance. The HI test is serovar-specific, while ELISA can detect antibodies against multiple serovars.

Differential Diagnosis

The clinical signs of IC must be differentiated from other respiratory diseases of poultry, including:

• Avian influenza: More severe systemic signs, higher mortality, and potential for neurological involvement.
• Newcastle disease: Respiratory and neurological signs, with higher mortality.
• Infectious bronchitis: Respiratory signs with renal involvement in some strains.
• Mycoplasmosis: Chronic respiratory disease with airsacculitis.
• Fowl cholera: Acute septicemia with high mortality and characteristic liver lesions.
• Ornithobacteriosis: Respiratory disease with airsacculitis, often in turkeys [31, 83].
• Gallibacteriosis: Salpingitis and respiratory signs in layers [74, 78].

A diagnostic decision tree for infectious coryza is presented in Figure 1.

flowchart TD
 A["Clinical Signs: Nasal discharge, facial edema, conjunctivitis"] --> B{Collect Samples}
 B --> C[Nasal/sinus swabs or tissue]
 C --> D{Diagnostic Method}
 D --> E[Culture on chocolate agar + CO2]
 D --> F["PCR: hmtp210 or 16S rRNA"]
 E --> G["Colonies: small, dewdrop-like, NAD-dependent"]
 G --> H["Gram stain: Gram-negative coccobacilli"]
 H --> I["Biochemical tests: Oxidase +, Catalase -"]
 I --> J[Confirm as A. paragallinarum]
 F --> K[Positive PCR result]
 K --> J
 J --> L{Serotyping}
 L --> M[HI test with specific antisera]
 L --> N["'PCR-based serotyping (hmtp210')"]
 M --> O[Serovar A, B, or C]
 N --> O
 O --> P[Report diagnosis and serovar]

Treatment

Treatment of IC is aimed at reducing clinical signs, minimizing mortality, and preventing spread within the flock. Antimicrobial therapy is the mainstay of treatment, but antimicrobial resistance (AMR) is an increasing concern [8, 30, 32, 46, 72, 81].

Antimicrobial Therapy

Avibacterium paragallinarum is susceptible to a range of antimicrobials in vitro, but resistance profiles vary geographically and over time [8, 30, 32, 46, 51, 72, 81]. Commonly used antimicrobials include:

• Tetracyclines: Oxytetracycline and doxycycline are frequently used, but resistance has been reported [8, 72].
• Sulfonamides: Sulfadimethoxine and sulfamethazine, often in combination with trimethoprim.
• Macrolides: Tylosin, tilmicosin, and erythromycin.
• Beta-lactams: Amoxicillin and ampicillin.
• Fluoroquinolones: Enrofloxacin, but resistance is emerging [8, 30].
• Pleuromutilins: Tiamulin.

A standardized broth microdilution method for antimicrobial susceptibility testing of A. paragallinarum has been recommended to facilitate resistance monitoring. Genomic characterization of AMR genes in A. paragallinarum isolates has revealed the presence of resistance determinants for tetracyclines, sulfonamides, and beta-lactams [8, 30, 43]. Horizontal transfer of AMR genes via OMVs has been demonstrated. Commensal bacteria in the chicken gut can contribute to the growth of multidrug-resistant A. paragallinarum.

Alternative Therapies

Alternative approaches to antimicrobial therapy are being explored due to the rise of AMR:

• Probiotics: Implication of probiotics with berry phenolic extracts has shown inhibitory effects against A. paragallinarum in vitro [9].
• Herbal extracts: Chinese herbal medicine extracts have demonstrated bacteriostatic activity against A. paragallinarum [10].
• Probiotic-enhanced vaccines: Enterococcus faecium has been shown to improve vaccine immunity against IC [11].

Supportive Care

Supportive care is essential for recovery. This includes:

• Improving ventilation and reducing ammonia levels in the house [6].
• Providing clean, fresh water and palatable feed [1].
• Reducing stocking density to minimize stress [6].
• Treating concurrent infections (e.g., mycoplasmosis, colibacillosis) [31, 54].

Prevention and Control

Prevention of IC relies on a combination of biosecurity, management practices, and vaccination.

Biosecurity

Avibacterium paragallinarum is transmitted horizontally via direct contact, aerosol, and contaminated fomites. The bacterium can survive in the environment for several days, particularly in organic material. Key biosecurity measures include:

• All-in/all-out management: Complete depopulation and cleaning between flocks [6].
• Quarantine: Isolation of new birds for at least 30 days [6].
• Sanitation: Regular cleaning and disinfection of houses, equipment, and footwear [6].
• Rodent and wild bird control: Preventing access to poultry houses [6].
• Visitor restrictions: Limiting access to essential personnel only [6].

A case-control survey of farm characteristics identified several risk factors for IC, including multi-age flocks, poor biosecurity, and proximity to other poultry operations [6]. A retrospective analysis of IC outbreaks in California from 2016 to 2022 identified epidemiologic patterns that can inform control strategies.

Vaccination

Vaccination is a key component of IC control in endemic areas. Both inactivated (bacterin) and live attenuated vaccines are available.

Inactivated Vaccines

Inactivated vaccines are typically bivalent or trivalent, containing serovars A, B, and/or C [12, 42, 63, 71, 84, 86]. These vaccines are administered parenterally (subcutaneous or intramuscular) to pullets before the onset of lay. Protection is serovar-specific, and vaccine efficacy depends on the antigenic match between the vaccine strains and the circulating field strains [12, 61, 86]. Emergent serovar C-1 strains have been shown to be poorly protected by traditional vaccines, necessitating the inclusion of relevant serovars in vaccine formulations. Similarly, serovar B variant strains from Argentina required specific vaccine strains for optimal protection [12]. Tetravalent vaccines containing serovars A, B, C, and an additional local strain have been evaluated in Indonesia.

Live Attenuated Vaccines

Live attenuated vaccines offer the advantage of mucosal immunity and ease of administration (via drinking water or spray) [13, 59]. An attenuated A. paragallinarum strain has been developed and evaluated as a live vaccine candidate, showing promising efficacy [13]. However, live vaccines carry the risk of reversion to virulence and are not widely used in all regions.

Novel Vaccine Approaches

Several novel vaccine approaches are under investigation:

• Subunit vaccines: Recombinant HMTp210 protein and other immunogenic antigens are being evaluated as subunit vaccine candidates [14].
• Nanocarrier-based adjuvants: Polymeric nanocarriers have been used to enhance the mucosal immune response to inactivated coryza vaccines.
• Probiotic-enhanced vaccines: Enterococcus faecium has been shown to improve the immune response to IC vaccination [11].

Vaccination Strategies

Vaccination programs should be tailored to the local epidemiological situation. In endemic areas, pullets are typically vaccinated twice (at 8-10 weeks and 16-18 weeks of age) with an inactivated vaccine. Booster vaccinations may be necessary in long-lived flocks. The efficacy of different vaccination plans against experimental infection has been evaluated [12].

Nonpathogenic Isolates

Nonpathogenic A. paragallinarum isolates have been identified in naive, healthy layer flocks in the United States [15, 16, 17]. These isolates lack virulence genes and do not cause clinical disease [15]. Their presence may interfere with diagnostic PCR assays that do not differentiate pathogenic from nonpathogenic strains. The protective potential of these nonpathogenic isolates against virulent challenge is being investigated [15].

Public Health Significance

Avibacterium paragallinarum is not considered a zoonotic pathogen. There are no reports of human infection with this bacterium. Therefore, IC is of economic and animal welfare concern but does not pose a direct public health risk.

Conclusion

Infectious coryza remains a significant respiratory disease of chickens and quail worldwide, causing substantial economic losses. The causative agent, A. paragallinarum, is a fastidious Gram-negative bacterium with multiple serovars and increasing antimicrobial resistance. Diagnosis relies on culture, PCR, and serotyping. Treatment with appropriate antimicrobials can reduce clinical signs, but resistance is a growing concern. Prevention through biosecurity and vaccination is essential for control in endemic areas. Ongoing research into novel vaccines, alternative therapies, and the role of nonpathogenic isolates will continue to inform best practices for managing this disease.

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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.