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.
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]
References
↑ Blackall, P.J.; Christensen, H.; Beckenham, T.; Blackall, L.L.; Bisgaard, M. (January 2005). "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". International Journal of Systematic and Evolutionary Microbiology. 55 (Pt 1): 353–362. doi:10.1099/ijs.0.63357-0. PMID15653900.
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