Avibacterium volantium Infection in Chickens and Turkeys: Upper Respiratory Disease

Introduction

Avibacterium volantium is a Gram-negative, nonmotile, pleomorphic rod that colonizes the upper respiratory tract of chickens and turkeys [1]. The bacterium was originally classified as Pasteurella volantium before being reclassified into the genus Avibacterium along with Avibacterium gallinarum, Avibacterium paragallinarum, and Avibacterium avium [1]. This reclassification was based on 16S rRNA gene sequencing and DNA-DNA hybridization studies that placed these avian pathogens within a distinct monophyletic cluster separate from the genus Pasteurella [1]. A. volantium is considered a commensal or opportunistic pathogen of the upper respiratory mucosa and is frequently isolated from chickens and turkeys showing mild to moderate rhinitis, sinusitis, and conjunctivitis [1]. Unlike A. paragallinarum, the causative agent of infectious coryza, A. volantium does not typically produce the severe, rapidly spreading respiratory syndrome associated with that pathogen [1]. However, it can contribute to multifactorial respiratory disease complexes when present alongside other viral or bacterial agents.

Etiology and Taxonomy

The genus Avibacterium belongs to the family Pasteurellaceae [1]. Members of this family are characterized as facultatively anaerobic, fermentative, and oxidase-positive rods [1]. A. volantium is distinguished from other Avibacterium species by its biochemical profile: it produces acid from D-glucose, D-fructose, D-mannose, and sucrose but not from lactose or trehalose [1]. It also reduces nitrate and does not produce indole [1]. Table 1 provides key differential characteristics among Avibacterium species.

Table 1. Selected biochemical and growth characteristics differentiating Avibacterium species.

Adapted from Blackall et al. 2005 [1]. NAD: nicotinamide adenine dinucleotide.

Avibacterium volantium requires nicotinamide adenine dinucleotide (NAD, also known as V-factor) for growth, a property shared with A. paragallinarum but not with A. gallinarum or A. avium [1]. This requirement necessitates the use of enriched media such as chocolate agar or media supplemented with NAD for primary isolation [1]. Colonies on blood agar appear small, grayish, and nonhemolytic after 24-48 hours of incubation under 5-10% carbon dioxide [1].

Pathogenesis and Host Interaction

The natural reservoir of A. volantium is the upper respiratory tract of clinically normal and diseased chickens and turkeys [1]. Colonization occurs via adherence to ciliated epithelial cells of the nasal cavity, infraorbital sinuses, and conjunctival mucosa. The exact virulence factors of A. volantium have not been fully characterized, but comparative genomic studies within the Pasteurellaceae family suggest the presence of adhesins, iron acquisition systems, and capsular polysaccharides analogous to those described in A. paragallinarum and Pasteurella multocida [1]. These factors facilitate evasion of mucociliary clearance and establish a localized inflammatory response.

Under field conditions, overt clinical disease is often triggered by concurrent infections, environmental stressors (e.g., poor ventilation, high stocking density, ammonia exposure), or immunosuppression. Viral infections such as avian metapneumovirus (aMPV) [2, 3, 4, 5, 6] and infectious laryngotracheitis virus (ILTV) [7, 6] can disrupt respiratory epithelial integrity and create a permissive environment for opportunistic bacterial colonization. Studies have shown that aMPV subtypes A and B cause ciliostasis and epithelial desquamation in the trachea, predisposing birds to secondary bacterial infections [8, 5]. Similarly, ILTV induces necrotic lesions in the trachea and larynx, facilitating invasion by bacteria like A. volantium [7, 6].

The host immune response involves recruitment of heterophils and macrophages to the site of infection, leading to exudative inflammation. The accumulation of serous or mucoid exudate in the nasal passages and sinuses results in the clinical signs described below.

Clinical Signs in Chickens and Turkeys

A. volantium infection typically manifests as mild to moderate upper respiratory disease. In both chickens and turkeys, the most common signs include:

• Serous to mucoid nasal discharge
• Mild infraorbital sinus swelling
• Conjunctivitis with ocular discharge
• Sneezing and rales
• Reduced feed intake and slight depression in affected individuals

These signs are generally less severe than those caused by A. paragallinarum in infectious coryza. Turkeys may develop more pronounced sinusitis, with distention of the infraorbital sinuses that can impair vision. In chickens, the disease is often self-limiting in uncomplicated cases, lasting 5-10 days. However, when coinfection with aMPV [2, 3, 4, 5, 6] or ILTV [7, 6] occurs, the clinical picture becomes more severe, with higher morbidity, prolonged recovery, and increased risk of secondary complications such as airsacculitis or colibacillosis.

Gross and Histopathological Lesions

Gross lesions are confined to the upper respiratory tract. The nasal passages and infraorbital sinuses contain variable amounts of serous, mucoid, or catarrhal exudate. The conjunctivae may be hyperemic and edematous. In chronic or complicated cases, the exudate may become caseous, particularly in turkeys.

Histologically, the nasal and sinus mucosa shows congestion, edema, and a mixed inflammatory infiltrate dominated by heterophils and macrophages. The epithelium may exhibit focal degeneration, loss of cilia, and hyperplasia of goblet cells. In the trachea, mild to moderate lymphocytic infiltration and deciliation can be observed, especially if a concurrent viral infection is present [8, 5].

Diagnosis

A definitive diagnosis of A. volantium infection requires laboratory isolation and identification of the bacterium from clinical specimens. Nasal swabs, sinus aspirates, or conjunctival swabs are the preferred samples. Swabs should be placed in transport medium (e.g., Amies medium with charcoal) and kept cool until processing.

Culture and Biochemical Identification

Specimens are plated onto chocolate agar (or blood agar cross-streaked with a Staphylococcus feeder colony to supply NAD) and incubated at 37°C with 5-10% CO2 for 24-48 hours [1]. Grayish, nonhemolytic colonies 0.5-1 mm in diameter are suggestive of Avibacterium spp. [1]. Presumptive identification is based on Gram stain morphology (Gram-negative rod, often pleomorphic) and requirement for NAD [1]. Definitive species identification is achieved through biochemical testing as outlined in Table 1 [1].

Molecular Detection

PCR assays targeting the 16S rRNA gene with species-specific primers can differentiate A. volantium from other avian Pasteurellaceae. Sequencing of the 16S rRNA gene provides definitive confirmation [1]. Multiplex PCR panels that simultaneously detect A. paragallinarum, A. avium, A. gallinarum, and A. volantium are available in reference laboratories. These molecular methods are particularly useful when samples contain mixed bacterial populations or when the organism is nonviable due to improper transport or antibiotic therapy.

Differential Diagnosis

Upper respiratory disease in chickens and turkeys can be caused by a range of infectious agents. Table 2 outlines primary differentials.

Table 2. Key differential diagnoses for upper respiratory disease in chickens and turkeys.

Cross-reference with the existing articles on Infectious Coryza in Chickens and Quail and Avian Metapneumovirus for further detail.

A diagnostic algorithm for suspect Avibacterium volantium infection is presented in Figure 1.

flowchart TD
 A[Chicken or turkey with nasal discharge, sinusitis, conjunctivitis] --> B{Collect nasal/sinus swab}
 B --> C[Culture on chocolate agar + NAD, 37°C, 5% CO2, 48h]
 C --> D[Grayish nonhemolytic colonies]
 D --> E{Need NAD?}
 E -->|Yes| F[Gram-negative pleomorphic rod]
 E -->|No| G[Consider other Pasteurellaceae]
 F --> H["Biochemical panel: catalase, urease, lactose, trehalose"]
 H --> I[Profile consistent with A. volantium?]
 I -->|Yes| J["Confirmation: 16S rRNA PCR + sequencing"]
 I -->|No| K[Identify other Avibacterium spp.]
 J --> L["Diagnosis: A. volantium upper respiratory disease"]
 L --> M["Assess co-infections: aMPV, ILTV, Mycoplasma"]
 M --> N[Select antimicrobial therapy based on susceptibility testing]

Figure 1. Diagnostic algorithm for Avibacterium volantium upper respiratory infection in chickens and turkeys.

Treatment and Control

Antimicrobial therapy should be guided by culture and susceptibility testing because resistance patterns vary among isolates. Commonly used antimicrobials include tetracyclines, sulfonamides/trimethoprim combinations, and macrolides. Administration via drinking water or feed is practical for flock treatment. The therapeutic response is generally good if initiated early and if predisposing factors are addressed.

Biosecurity measures are critical for control. Because A. volantium is often part of the normal respiratory flora, complete elimination from a flock is rarely attempted. Instead, management should focus on reducing stress, improving ventilation, controlling dust and ammonia levels, and preventing viral co-infections through vaccination programs.

Vaccination against aMPV and ILTV can reduce the incidence of severe respiratory disease and thereby limit opportunistic bacterial infections [5, 9]. There is no commercially available vaccine specifically for A. volantium, as it is not considered a primary pathogen requiring targeted immunization.

Conclusion

Avibacterium volantium is a minor pathogen of the upper respiratory tract in chickens and turkeys, but it can contribute to significant morbidity when acting in concert with other respiratory agents. Accurate diagnosis requires isolation and biochemical or molecular identification. A comprehensive diagnostic approach that includes screening for viral co-infections is essential for effective management. Continued surveillance and genomic characterization of Avibacterium isolates will improve understanding of the virulence potential and host range of this species.

References

[1] Blackall PJ, Christensen H, Beckenham T, et al. Reclassification of Pasteurella gallinarum, [Haemophilus] paragallinarum, Pasteurella avium and Pasteurella volantium as Avibacterium gallinarum gen. nov., comb. nov., Avibacterium paragallinarum comb. nov., Avibacterium avium comb. nov. and Avibacterium volantium comb. nov. Int J Syst Evol Microbiol. 2005;55:353-362. URL: https://pubmed.ncbi.nlm.nih.gov/15653900/

[2] Nguyen V, Ramsubeik S, Jerry C, et al. Avian Metapneumovirus Subtype A Infection in Commercial Chickens (Gallus gallus domesticus) and Turkeys (Meleagris gallopavo) in California. Avian Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41739619/

[3] Clontz DM, Hoerr FJ. Avian Metapneumovirus: A Review of Pathogenesis and Its Effect on Diagnosis. Avian Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41739607/

[4] Selim M, Sharafeldin TA, Mor S. Avian Metapneumovirus 2024 North American Outbreak: Genomics Direct Future Plans. Avian Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41739604/

[5] Marzo E, Guirado E, Taberner E, et al. A new method for testing avian metapneumovirus vaccine efficacy: Evaluation of tracheal ciliary activity after a challenge. Vaccine. 2025. URL: https://pubmed.ncbi.nlm.nih.gov/40876141/

[6] Mo J, Mo J. Infectious Laryngotracheitis Virus and Avian Metapneumovirus: A Comprehensive Review. Pathogens. 2025;14(1):22. URL: https://pubmed.ncbi.nlm.nih.gov/39861016/

[7] Yunita MN, Khairullah AR, Saepulloh M, et al. Infectious laryngotracheitis: A serious threat to poultry health. Open Vet J. 2025. URL: https://pubmed.ncbi.nlm.nih.gov/41200314/

[8] Körner L, Morito HLE, Ludlow M, et al. In vitro Models and Molecular Tools for Investigation of Avian Metapneumovirus-Host Interactions. Avian Dis. 2026. URL: https://pubmed.ncbi.nlm.nih.gov/41739608/

[9] Yang W, Zhang J, Dai J, et al. Multiple pathways to evaluate the immunoprotective effect of Turkeys Herpesvirus recombinant vaccine expressing HA of H9N2. Poult Sci. 2025;104(2):104449. URL: https://pubmed.ncbi.nlm.nih.gov/39577170/ Additional general references on avian respiratory bacteriology and diagnostic methods were consulted from standard veterinary textbooks, including Diseases of Poultry (14th edition) and the Merck Veterinary Manual (12th edition). *** 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.