Avibacterium paragallinarum

Avibacterium paragallinarum is a species of Gram-negative, facultatively anaerobic, non-motile bacteria in the family Pasteurellaceae. It is the causative agent of infectious coryza, an acute respiratory disease of chickens characterized by nasal discharge, facial swelling, and decreased egg production. The bacterium is of significant economic importance in the global poultry industry.

Avibacterium paragallinarum
Scientific classification
Domain:	Bacteria
Kingdom:	Pseudomonadati
Phylum:	Pseudomonadota
Class:	Gammaproteobacteria
Order:	Pasteurellales
Family:	Pasteurellaceae
Genus:	Avibacterium
Species:	A. paragallinarum
Binomial name
Avibacterium paragallinarum (Beaudette and Hudson 1937) Blackall et al., 2005
Synonyms
Haemophilus paragallinarum

Taxonomy

Originally classified as Haemophilus paragallinarum, the species was reclassified into the genus Avibacterium in 2005 based on 16S rRNA gene sequencing and DNA–DNA hybridization studies.^[1]

Morphology and physiology

Avibacterium paragallinarum is a small, pleomorphic, Gram-negative coccobacillus. It is non-motile and non-spore-forming. The bacterium is fastidious, often requiring nicotinamide adenine dinucleotide (NAD or V-factor) for growth, although NAD-independent strains have also been reported.^[2]

Colonies are small, translucent, and dew-drop-like when cultured on chocolate agar enriched with 5% sheep blood. Optimal growth occurs at 37 °C in a 5% CO₂ atmosphere.

Biochemically, the organism ferments glucose, sucrose, and maltose, producing acid but no gas. It is catalase-, oxidase-, urease-, and indole-negative.^[2]

Genome

The complete genome of the type strain (ATCC® 29545™) is approximately 2.81 Mbp with a GC content of 41.11%. It encodes over 2,900 protein-coding genes and includes complete sets of rRNA and tRNA genes.^[3]

Pathogenicity

Avibacterium paragallinarum causes infectious coryza, a rapidly spreading upper respiratory disease of chickens. Symptoms include conjunctivitis, nasal discharge, facial edema, sneezing, and marked reduction in egg production. The disease causes significant economic losses due to decreased productivity and increased culling.^[2]

Transmission occurs via direct contact, aerosols, and contaminated feed or water. Chronically infected carrier birds serve as reservoirs of infection, particularly under stressful conditions.

Diagnosis

Diagnosis involves clinical observation and laboratory confirmation. Bacterial isolation from nasal swabs or infraorbital sinus exudate on enriched media is standard. Molecular diagnostics, including PCR, provide rapid and specific detection.^[2]

Serotyping

Avibacterium paragallinarum strains are grouped into three primary serovars, A, B, and C, based on hemagglutination inhibition tests. This classification is epidemiologically important, as cross-protection between serovars is limited, affecting vaccine design and efficacy.^[2]

Prevention and control

Prevention includes strict biosecurity, good husbandry, and vaccination. Inactivated vaccines are used widely but often provide limited cross-protection. Research on attenuated live vaccines is ongoing and shows promise for broader serovar coverage.^[4]