Infectious coryza (IC) is an acute respiratory disease of chickens caused by two species of bacteria which include Avibacterium paragallinarum
(previous referred to as Haemophilus paragallinarum
) and Av. gallinarum
(previously known as H. gallinarum
). The disease primarily affects the chicken's upper respiratory tract, specifically the nasal passages and sinuses. IC occurs in chickens worldwide, with cases reported in North and South America, Africa, and Europe.
The most common clinical signs of IC are serous to mucoid nasal discharge, facial swelling, and conjunctivitis (which presents often as tearing or bubbles in the corner of the chicken's eyes). Chickens suffering from conjunctivitis may have difficulty opening their eyes, due to the presence of sticky discharge. Affected chickens may also show signs of labored breathing, coughing, sneezing, rales, and loss of appetite. Affected laying hens will show decreased egg production of 10-40%. After 5 days of infection, the nasal discharge and tearing of the eyes often disappears, with the facial swelling still remaining. The duration and severity of the clinical signs vary depending on the age, breed, and health status of the bird. Chickens of all ages can get IC, but the disease is usually less severe in younger birds than in adults. When younger birds are infected they often have a reduced incubation period (therefore they get infected faster than adults) and disease course. The typical disease course is 2-3 weeks, however it may persist longer for chickens with concurrent infections.
There are many diagnostic tests available for detection of IC. Diagnosis is confirmed through isolation of the bacteria, which can be accomplished through necropsy, polymerase chain reaction (PCR) testing, direct isolation, and hemagglutination inhibition (HI) testing.
- Direct isolation: For direct isolation, the pathogen can be isolated from sterile cotton swabs obtained from the infraorbital sinus, trachea, and air sac. To be an effective form of diagnosis, the pathogen must be isolated during the acute stage of infection (1 to 7 days of the incubation period).
- Hemagglutination inhibition (HI) test: There are three main forms of HI tests available, which are widely used for detecting changes in antibody titers, in cases of field infection or vaccination, and for evaluating the prevalence of IC within flocks.
- PCR testing: PCR tests are available which provide rapid (often within 6 hours) results.
Diagnosis of the infectious coryza can be more complicated when it occurs alongside other pathogens, especially bacteria like Pasteurella multocida, Ornithobacterium rhinotracheale, Salmonella spp, Escherichia coli, Pseudomonas, Proteus, Staphylococcus spp, Streptococcus spp,
Introduction of new chickens into an existing established flock is the most common way birds are infected. Signs of IC usually occur within 1 to 6 weeks after new chickens (unknowingly recovered carrier birds) are introduced to a flock. Taking birds to outside agricultural events or poultry shows and bringing them back to the flock is another frequent method of how IC is introduced into flocks. IC is transmitted to chickens by:
- Direct bird-to-bird contact
- Inhalation of infectious aerosols, coughed into the air
- Ingestion of feed/or water contaminated with feces or discharge from infected birds
- Contaminated clothing, shared equipment or fomites
Chickens that recover from IC often still remain as carriers, and may intermittently shed the bacteria in their feces during stressful events.
The incubation period for IC is 1 to 3 days.