Global perspectives on infectious coryza: Pathology, immunity, and economic impact in chickens

Abstract

Coryza is an acute respiratory infection of chickens (Gallus gallus domesticus) caused by the Gram-negative bacterium Avibacterium paragallinarum of the Pasteurellaceae family. This disease is highly contagious and has spread widely throughout the world, with relatively high incidence rates in Southeast Asia, South America, and Africa. Common clinical manifestations include infraorbital sinus swelling, nasal exudate, conjunctivitis, and decreased production performance, both in broiler chicken growth and egg production in laying hens. Infection can be acute, subclinical, or chronic, depending on the virulence of the bacterial strain, the host's immune system, and environmental factors. Pathologically, the disease begins with bacterial colonization of the upper respiratory tract epithelium, followed by activation of a local inflammatory response that leads to neutrophil and lymphocyte infiltration, mucosal edema, and increased mucus secretion. The immunity developed is serotype-specific, so the use of vaccines appropriate for the serotypes circulating in a region is the primary preventative measure. Transmission occurs through direct contact between individuals, aerosols, or through contaminated objects (fomites), with the rate of spread influenced by population density, cage sanitation, and the movement of chickens between farms. Other predisposing factors include stress, the presence of secondary infections, and suboptimal environmental management. Diagnosis is established through a combination of clinical observation, bacterial isolation and culture, serological testing, and molecular techniques such as PCR to differentiate it from other respiratory diseases with similar symptoms. Effective control requires a comprehensive approach, including serotype-based vaccination, strict biosecurity practices, good cage management, and efforts to minimize stress on chickens. Economically, coryza causes significant losses due to reduced productivity and increased costs of treatment and prevention. This review aims to provide the latest updates on the epidemiology, pathogenic mechanisms, clinical presentation, diagnostic methods, therapy, and control strategies for coryza, while also identifying challenges and prospects for further research.