Infectious coryza remains one of the respiratory diseases frequently encountered in poultry farms, affecting both broilers and layers. Although it is considered a classic disease, coryza should not be underestimated due to its rapid transmission and significant impact on production performance.

In addition to feed quality and chick genetics, poultry health is one of the key determinants of success in livestock farming. Health problems can affect feed consumption, growth, flock uniformity, and egg production. When a disease develops into a respiratory infection involving multiple pathogens, the resulting economic losses can become even greater.

One disease that is still frequently encountered in the field is infectious coryza, commonly known as snot. The disease is caused by the Gram-negative bacterium Avibacterium paragallinarum, which primarily affects the upper respiratory tract of chickens. The bacterium exhibits antigenic diversity and is classified into serovars A, B, and C. These antigenic differences are important because cross-protection between groups is not always adequate. Therefore, the compatibility between vaccines and strains circulating in the field is an important consideration in disease control.

Coryza is known for its high morbidity, while mortality in uncomplicated cases is generally relatively low. However, these figures do not necessarily reflect the limited economic impact of the disease. Reduced feed and water consumption, impaired growth in broilers, and decreased egg production in layers can be among its major consequences.

Transmission and Clinical Signs

Infectious coryza is primarily transmitted through direct contact with infected chickens. Birds that have recovered from infection but become carriers can also serve as a source of transmission to healthy chickens. Indirect transmission may occur through contaminated drinking water, feed, farm workers, and poultry house equipment.

Due to its transmission characteristics, controlling coryza requires more than simply treating chickens showing clinical signs. If the source of infection remains within the flock or poultry house environment, cases may reappear after treatment has been completed.

Environmental conditions and management practices also influence disease severity. Extreme weather fluctuations, inadequate ventilation, excessive stocking density, poor litter quality, feed changes, and stressful handling can worsen the birds’ condition. Pre-existing immunosuppressive diseases may also increase susceptibility to infection.

The initial clinical signs of infectious coryza generally involve the upper respiratory tract. Chickens may exhibit sneezing, difficulty breathing, and nasal discharge. In the early stages, the discharge may appear watery before becoming thicker and more mucoid.

One easily recognizable sign is nasal discharge accompanied by an unpleasant odor. The infection may subsequently progress to conjunctivitis and facial swelling.

This swelling is associated with inflammation and the accumulation of exudate in the infraorbital sinuses, the sinus cavities located beneath the eyes. As the fluid accumulates and becomes thicker, the chicken’s face appears enlarged, particularly around the eyes. This condition causes discomfort and can lead to reduced feed and water consumption.

In layer chickens, the consequences can be directly reflected in egg production. Previous research in Indonesia reported a 10–40% decline in egg production among chickens affected by infectious coryza. The study also demonstrated that tetravalent vaccination could reduce the severity of clinical signs following challenge with Indonesian A. paragallinarum serovar A and B isolates.

Meanwhile, in broilers, reduced feed intake due to respiratory problems can result in suboptimal growth and poor flock uniformity. In pullets, prolonged health problems can also hinder birds from achieving their target body development.

Pathological examinations may reveal inflammation in the sinuses, larynx, and trachea. In certain cases, caseous material may be found in the sinus cavities. When chickens experience mixed infections, the pathological changes and clinical signs may become more varied.

This article is an excerpt from the Animal Health section of the September 2026 edition of Poultry Indonesia magazine. Read the full article in the September 2026 edition of Poultry Indonesia magazine . For subscriptions or further information, contact us via WhatsApp  or email sirkulasipoultry@gmail.com.

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