Infectious Coryza is an infection of chickens that has recently come to prominence in the UK particularly in Backyard fowl. It is likely that because this is a fastidious bacterium to grow, it has been under diagnosed or mistakenly diagnosed as Mycoplasma gallisepticum for which there is a simple blood test. However, combination infections with both organisms would be expected to cause more severe clinical signs.
Infectious Coryza is also known as fowl coryza, roup, contagious or infectious catarrh and umcomplicated coryza.
Avibacterium paragallinarum formerly known as Haempholius paragallinarum. This is a Gram-negative, non-motile, non -spore forming, rod or coccobacilli shaped bacterium. It is a difficult organism to culture usually requiring two growth factors known as factor X (haemin) and factor V (nicotinamide adenine dinucleotide, NAD). There are strains that do not require NAD. It is a facultative anaerobe and grows best in a low oxygen environment (microaerophilic).
Only chickens but it can cause disease in all ages of bird. It is more severe in older birds. It has not been possible to experimentally infect, ducks, pigeons or turkeys.
This is a highly contagious infection that spreads horizontally from bird to bird, requiring very few organisms to cause disease. It is a disease of the upper respiratory tract. The primary source of infection is respiratory exudates from either clinically affected or carrier birds. Infection from drinking water contaminated with a few bacteria or as an aerosol over short distances is possible. Vertical transmission does not occur. Mechanical spread of infection in respiratory exudates may also occur.
The disease has a short incubation period, 1 – 3 days, and will spread rapidly through a flock of susceptible birds in 7 to 10 days. In uncomplicated infections the course of the disease is about 3 weeks. However, concurrent infection with ART, IBV, ILT, mycoplasmas and virulent E.coliwould be expected to increase the severity of the disease. The initial signs will include watery discharges (seromucoid) from the nostril and eyes with swelling of the face with a marked morbidity in the flock but low mortality. Conjunctivitis, closed eyes, open mouthed breathing, lethargy and drops in feed and water consumption. This can result in egg production drops, failure to grow and in the presence of secondary infections severe mortality.
Subcutaneous oedema of the face and wattles, inflammation of the nasal passage, infraorbital sinus and conjunctiva with excess catarrhal to fibrinopurulent mucus. When secondary complications are present, there may be a tracheitis progressing to airsacculitis and pnuemonia.
The history and clinical signs may suggest a diagnosis. Confirmation should be by isolation of A.paragallinarum from the infraorbital sinus or fresh nasal exudate of affected chickens. Culture can be made on blood agar cross streaked with Staphylococcus epidermidis. The plates should be incubated microaerophillically at 37oC for up to 48 hours. The PCR test can be used to confirm the identity of the bacteria from culture or exudates. Serological tests include agglutination, haemagglutination inhibiton and a blocking ELISA test.
Avian metapneumovirus (ART), Infectious Bronchitis (IBV) with secondary E.coli, Infectious Laryngotracheitis (ILT), Mycoplasma gallisepticum (Mg), virulent E.coli and subcutaneous infections following mechanical damage following fighting or mating.
Antibiotic treatment, e.g. doxycycline and fluroquinolones, can alleviate the worst of the clinical signs but will not eliminate infection from the flock. Return to nornal egg production takes longer than clinical recovery following treatment.
A vaccine is available but this has to be specifically imported into the UK under the Special Import Certification. Alternatively, immunisation against the other common infections that may complicate this disease in Backard flocks such as IBV, ILT and Mg may give apparent control. Care should be taken when purchasing replacement stock, swapping stock or borrowing breeding stock either as a possible source of infection or as being susceptible to infection already in the flock. Good hygiene practices and quarantine practices will help reduce the likelihood of introducing infection and the severity of the disease.
Infectious Coryza is a recent diagnosis in Backyard Fowl made by my local AHVLA labs. Details of species affected, clinical signs and post mortem lesions observed can be found by clicking here.