Avian Coryza (Infectious Coryza): Etiology, Clinical Signs, Diagnosis, and Control in Poultry

Etiology

Avian Coryza, also termed Infectious Coryza, is an acute respiratory disease of chickens and other avian species caused by the bacterium Avibacterium paragallinarum (formerly Haemophilus paragallinarum). The organism is a Gram-negative, non-motile, pleomorphic rod that requires nicotinamide adenine dinucleotide (NAD, V factor) for in vitro growth, placing it in the NAD-dependent group of the family Pasteurellaceae [1, 2]. Strains of A. paragallinarum are classified into three serovars (A, B, and C) based on Page's scheme, with additional subtypes recognized by various international typing systems [1, 3]. The bacterium produces a polysaccharide capsule that contributes to virulence via antiphagocytic properties [2]. A heat-labile cytotoxin and a hemagglutinin are also implicated in epithelial damage and colonization of the upper respiratory tract [1].

The term avian coryn occasionally appears in older literature as an abbreviated form of "avian coryza," but modern nomenclature uniformly utilizes "infectious coryza" or "avian coryza" to describe the clinical syndrome induced by A. paragallinarum [2].

Epidemiology

Infectious coryza occurs worldwide, with higher prevalence in regions practicing intensive poultry production and in flocks with poor biosecurity [1, 3]. Chickens are the primary natural host, but the disease has also been reported in pheasants, quail, and occasionally guinea fowl [2]. The bacterium does not survive long outside the host; transmission occurs mainly by direct contact with respiratory droplets, contaminated feed, water, and fomites [1]. Carrier birds (both clinically recovered and asymptomatic shedders) are the principal reservoir for maintaining infection within a flock [2, 3].

Stress factors such as overcrowding, poor ventilation, concurrent infections (e.g., Mycoplasma gallisepticum, infectious bronchitis virus, or Pasteurella multocida), and nutritional deficiencies exacerbate disease severity and prolong outbreaks [1, 2]. Morbidity can reach 100% in naïve flocks, while mortality is generally low (1–10%) unless complicated by secondary bacterial infections such as Avian Colibacillosis: Etiology, Clinical Signs, Diagnosis, and Control in Poultry or Fowl Cholera: Etiology, Clinical Signs, and Post-Mortem Lesions in Poultry [1, 3].

Clinical Signs

The incubation period ranges from 1 to 3 days under natural conditions [2]. Clinical manifestations are predominantly localized to the upper respiratory tract and facial structures. The hallmark signs include serous to mucopurulent nasal discharge, sneezing, and conjunctivitis with periorbital edema and swelling of the infraorbital sinuses [1, 2]. Affected birds often develop facial edema that may extend to the wattles and comb [3]. Dyspnea, open-mouth breathing, and tracheal rales are common when the lower respiratory tract is involved, particularly in complicated cases [1].

Additional clinical findings:

• Anorexia and decreased feed consumption.
• Diarrhea (occasionally observed, especially in severe outbreaks).
• Lethargy and depression.
• Drop in egg production in laying flocks (10–40% reduction) [2, 3].

Clinical signs are often more severe in pullets and young layers than in broilers [1]. The disease must be differentiated from other respiratory infections such as Avian Influenza A Virus in Wild Birds and Poultry: Etiology, Epidemiology, Clinical Signs, Pathology, Diagnostics, Treatment, and Control, Avian Mycoplasmosis: Mycoplasma gallisepticum and Other Species, Vaccination and Control in Poultry, Bordetella avium Turkey Coryza (Rhinotracheitis) in Poultry, and Avian Cholera (Fowl Cholera) in Poultry and Wild Birds: Etiology, Epidemiology, Clinical Signs, Pathology, Diagnostics, Treatment, and Control [3].

Pathological Findings

Gross lesions are confined primarily to the respiratory tract. The most consistent findings include catarrhal to fibrinous inflammation of the nasal passages, infraorbital sinuses, and conjunctiva [1, 2]. The sinuses may be distended with serous, mucoid, or caseous exudate. In chronic or complicated cases, fibrinopurulent airsacculitis, pericarditis, and perihepatitis are observed, often attributable to secondary opportunists such as Escherichia coli or Ornithobacterium rhinotracheale [1, 3].

Histopathological examination reveals acute rhinitis with epithelial desquamation, submucosal edema, and infiltration of heterophils, macrophages, and lymphocytes [2]. The sinus mucosa is hyperplastic and exhibits goblet cell metaplasia. In advanced stages, fibrosis and granulomatous inflammation may develop [1]. No characteristic inclusion bodies are present, distinguishing the condition from viral respiratory diseases [3].

Diagnosis

A definitive diagnosis requires isolation and identification of A. paragallinarum from clinical specimens. Samples are best collected from the infraorbital sinus, choanal cleft, or nasal exudate of acutely affected birds using sterile swabs [1, 3].

Bacteriological Culture

The organism is fastidious; isolation requires enriched media containing NAD (V factor). Suitable media include chocolate agar, blood agar with a Staphylococcus nurse streak (satellitism), or specifically formulated Haemophilus test medium [1, 2]. Plates are incubated in 5–10% CO₂ at 37°C for 24–48 hours. Colonies are small, smooth, translucent, and non-hemolytic. Gram staining reveals pleomorphic Gram-negative rods [2].

Biochemical Identification

Presumptive identification relies on NAD dependence (V factor requirement), catalase and oxidase production, and failure to ferment certain sugars such as lactose and sucrose [1]. Commercial identification systems (e.g., API NH strips) can be used, but results must be interpreted with caution for avian isolates [3].

Molecular Diagnostics

Polymerase chain reaction (PCR) assays targeting the 16S rRNA gene or the hagA gene (encoding hemagglutinin) provide rapid, sensitive, and specific detection directly from swabs or exudates, even in mixed infections [2]. Real-time PCR protocols with high-throughput capability are available for surveillance and outbreak investigations [3]. Molecular characterization of serovars is performed using multiplex PCR schemes that differentiate Page serovars A, B, and C [1].

Serological Testing

Agglutination and hemagglutination inhibition tests can detect antibodies, but they are less commonly used in acute diagnosis due to variability in sensitivity and specificity [1, 3]. Serology is more valuable for flock profiling post-vaccination.

Differential Diagnosis

The clinical similarity between infectious coryza and other respiratory diseases of poultry is high. Table 1 summarizes key differential features.

Table 1. Differential Diagnosis of Avian Coryza versus Common Respiratory Diseases in Poultry

Diagnostic Algorithm

A structured approach to diagnosing suspected outbreaks is provided in the flowchart below.

flowchart TD
    A[Suspected Avian Coryza outbreak], > B{Clinical signs: facial edema, nasal discharge, sinus swelling, sneezing}
    B, > C[Collect swabs from sinuses / choanal cleft of acutely ill birds]
    C, > D[Culture on NAD-enriched media under CO2]
    D, > E{Colony growth and Gram stain}
    E, >|Gram-negative pleomorphic rods + satellitism| F[Biochemical identification: catalase +, oxidase +, V factor dependence]
    E, >|No growth or other organisms| G[Consider alternate diagnoses]
    F, > H[Confirm by PCR or serotyping]
    H, > I[Final diagnosis: Avian Coryza]
    H, > J[If negative, re-evaluate differentials]

Treatment

Antimicrobial therapy reduces clinical severity and mortality but does not consistently eliminate the carrier state [1, 2]. Selection depends on in vitro sensitivity testing, as resistance is reported for several antibiotics [3]. Commonly used agents include:

• Sulfonamides (e.g., sulfadimethoxine, sulfamethazine): administered in feed or drinking water for 3–5 days.
• Tetracyclines (e.g., oxytetracycline, chlortetracycline): 200–400 g/ton of feed or 10–20 mg/kg body weight for 5–7 days.
• Erythromycin and tylosin: 10–30 mg/kg for 3–5 days.
• Florfenicol: increasingly used due to efficacy against multidrug-resistant strains [1, 3].

Treatment response is often rapid (within 48 hours), but relapse can occur following withdrawal if management factors are not corrected [2]. Anti-inflammatory drugs are occasionally used to reduce edema, though corticosteroid use is discouraged due to immunosuppressive effects [3].

Control

Control of infectious coryza involves a multi-faceted strategy combining management, biosecurity, and vaccination.

Biosecurity

Strict all-in/all-out management, cleaning and disinfection of houses between flocks, and preventing introduction of carrier birds are essential [1]. The bacterium is susceptible to common disinfectants such as quaternary ammonium compounds and hypochlorite [2]. Rodent and insect control, as well as restricting personnel movement, reduce transmission risk [3].

Vaccination

Commercial bacterins (killed vaccines) containing serovars A, B, and C are widely used in endemic regions [1]. Vaccination is typically administered to pullets at 8–12 weeks of age, with a booster at 16–18 weeks [2]. Autogenous vaccines may be prepared from locally circulating strains [3]. Vaccination reduces clinical disease and egg production loss but does not prevent infection or carriage completely [1]. It is a critical component of control in multi-age layer complexes.

Eradication

Eradication from a flock is difficult due to the carrier state. Depopulation of infected flocks followed by thorough cleaning and restocking with coryza-free birds is the most reliable method [2]. In breeding stock, isolation and serological monitoring combined with vaccination can be used to maintain negative status [1, 3].

Integrated Approach

Because infectious coryza often occurs concurrently with other respiratory pathogens, integrated control of Avian Mycoplasmosis in Poultry: Clinical Signs and Control and Avian Influenza in Poultry: Clinical Signs, Surveillance, and CDC Guidelines is recommended [2]. Good ventilation, optimal stocking density, and adequate nutrition help prevent stress-induced outbreaks [3].

References

[1] Saif, Y.M. (ed.). Diseases of Poultry, 13th ed. Ames, IA: Wiley-Blackwell, 2013.

[2] Merck & Co. The Merck Veterinary Manual, 11th ed. Kenilworth, NJ: Merck Sharp & Dohme Corp., 2016.

[3] World Organisation for Animal Health (WOAH). Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, Chapter 3.3.11: Infectious Coryza. Paris: WOAH, 2021. *** 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.