Infectious coryza disease in chickens

Farming issues

THIS week we look at a very important poultry disease called infectious coryza. It is a highly infectious disease of chickens and guinea-fowl. The disease is characterised by catarrhal inflammation of the upper respiratory tract especially nasal and sinus mucosae. It is caused by the bacterium haemophilus paragallinarum and is seen in many countries. Morbidity is high but with relatively low mortality.

The route of infection is conjunctival or nasal with an incubation period of one to three days followed by rapid onset of disease over a two to three day period with the whole flock affected within 10 days.

Carriers are important with transmission via exudates and by direct contact. It is not egg transmitted. The disease occurs most often in adult birds. Infection can spread slowly, with chronic disease affecting only a small number of birds or rapidly, with a higher percentage of birds being affected. The bacterium is spread through contact with infected birds or exudates. Recovered birds remain carriers of the bacteria for long periods and as such, once a flock is infected all birds must be considered as carriers. Birds can be more susceptible if already infected with other respiratory viral or bacterial infections. Chronically ill or healthy carrier birds are the reservoir of infection. Chickens of all ages are susceptible, but susceptibility increases with age. The incubation period of infectious coryza is one to three days, and the disease duration is usually two to three weeks. Under field conditions, the duration may be longer in the presence of concurrent diseases.

Clinical signs include swelling around the face and wattles, watery or pus-like discharge from the eyes and nostrils, difficulty breathing (dyspnoea), sneezing, loss of appetite, weight loss and a drop in egg production of up to 40 percent.

Egg production may be delayed in young pullets and severely reduced in producing hens. The birds lose condition mainly due to loss of appetite (inappetance). In the mildest form of the disease the only signs may be depression, a nasal discharge and occasionally slight facial swelling.

In the more severe form there is severe swelling of one or both infraorbital sinuses with oedema of the surrounding tissue which may close one or both eyes.

In adult birds, especially males the oedema may extend to the intermandibular space and wattles. The swelling usually abates in 10-14 days. However, if secondary infection occurs swelling can persist for months. Birds may have diarrhoea, and feed and water consumption usually is decreased during acute stages of the disease.

Infectious coryza can be treated with a number of antibiotics and vaccines. However, control of the disease requires good husbandry practices. Prevention is best achieved using biosecurity principles based on an all-in/all-out replacement policy and ensuring replacement birds are not infected.

If infection occurs, complete depopulation followed by thorough cleaning or disinfecting is the only means for eliminating the disease. The bacterium survives two to three days outside the bird but is easily killed by heat, drying and disinfectants.

If you are keeping a large flock of birds and you are also buying in some, it is important to know the history of the place or farm from where you are buying.

This disease quickly spreads and in communal areas where chickens from neighbouring homestead tend to have common free ranging places, the disease also easily spreads across the village. Resultantly you find there are high mortality rates, with almost every homestead recording losses. This is even exacerbated by the fact that most communal chickens do not receive any medication, be it preventative or curative.

It is therefore good husbandry practice for farmers to give their poultry some prophylactic medication so as to prevent contracting diseases. Additionally you may need to keep at least some antibiotic drugs so that you can react on time and avoid unnecessary losses. Uyabonga umntakaMaKhumalo

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