Summery of chicken diseases

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Marek’s Disease

(MD) is caused by a herpes virus that may result in death or severe production loss in both layer and meat chickens. Vaccination will reduce the losses. However, in recent years there has been an increase in Marek’s disease, due to new strains of virus and faster growing, more susceptible birds.

Marek’s disease is a problem in many household flocks, especially those which are not vaccinated at day old. It causes changes in many of the nerves and may cause tumours in the major internal organs (ovary, liver, kidney, heart and spleen).

Methods of spread - The virus remains alive in the environment for as long as eight months. It is shed from the feather follicles and spread in fluff. The virus gains entry when the bird breathes infected dust particles. Marek’s disease is not spread through eggs. The virus is highly infectious and, once it is present in a flock, it spreads rapidly to unvaccinated poultry. Healthy birds can be carriers and infect others.

Newcastle Disease

Newcastle disease is a contagious viral infection causing a respiratory nervous disorder in several species of fowl including chickens and turkeys. Different types or strains of the virus (varying in their ability to cause nervous disorder, visceral lesions and death) have been recognized.
Newcastle disease is highly contagious. All birds in a flock usually become infected within three to four days. The virus can be transmitted by contaminated equipment, shoes, clothing and free-flying birds. During the active respiratory stage, it can be transmitted through the air. The virus is not thought to travel any great distance by this method. Recovered birds are not considered carriers and the virus usually does not live longer than thirty days on the premises.

Signs of Newcastle disease are not greatly different from those of other respiratory diseases. The signs most frequently observed are nasal discharge, excessive mucous in the trachea, cloudy air sacs, casts or plugs in the air passages of the lungs and cloudiness in the cornea of the eye.

The disease in young chickens begins with difficult breathing, gasping and sneezing. This phase continues for ten to fourteen days and may be followed by nervous symptoms. If nervous disorders develop, they may consist of paralysis of one or both wings and legs or a twisting of the head and neck. The head often is drawn over the back or down between the legs. Mortality may vary from none to total loss of the flock.

In adult chickens, respiratory symptoms predominate. Only rarely do nervous disorders develop. If the flock is laying, egg production usually drops rapidly. When this occurs, it takes four weeks or longer for the flock to return to the former production rate. During the outbreak, small, soft-shelled, off-colored and irregular-shaped eggs are produced. Mortality in adult birds is usually low but may be fairly high from some virus strains.

Infectious Bronchitis

Infectious bronchitis is an extremely contagious respiratory disease of chickens characterized by coughing, sneezing and rales (rattling). It is caused by a virus that affects chickens only.
Infectious bronchitis is considered the most contagious of poultry diseases. When it occurs, all susceptible birds on the premises become infected, regardless of sanitary or quarantine precautions. The disease can spread through the air and can "jump" considerable distances during an active outbreak. It can also be spread by mechanical means such as on clothing, poultry crates and equipment. The disease is not egg transmitted and the virus will survive for probably no more than one week in the house when poultry are not present. It is easily destroyed by heat and ordinary disinfectants.

The infection is confined to the respiratory system. Symptoms are difficult breathing, gasping, sneezing and rales. Some birds may have a slight watery nasal discharge. The disease never causes nervous symptoms. It prevails for ten to fourteen days in a flock and symptoms lasting longer than this are from some other cause.

In chickens under three weeks of age, mortality may be as high as thirty or forty percent. The disease does not cause a significant mortality in birds over five weeks of age. Feed consumption decreases sharply and growth is retarded.

When infectious bronchitis occurs in a laying flock, production usually drops to near zero with a few days. Four weeks or more may be required before the flock returns to production. Some flocks never regain an economical rate of lay. During an outbreak, small, soft-shelled, irregular-shaped eggs are produced. Infectious bronchitis is difficult to differentiate from many of the other respiratory diseases. For this reason, a definite diagnosis usually requires a laboratory analysis. Infectious bronchitis is highly contagious and does not always respect sanitary barriers.

There is no treatment for this disease. In young chickens it is helpful to increase the brooder temperature and provide as nearly ideal environmental conditions as possible.

Avian Rhino-tracheitis (ART)

Synonyms: ART, rhino tracheitis
Species affected: Chickens are susceptible to the virus. Experimentally, guinea fowl and pheasants are susceptible, but waterfowl and pigeons are resistant.

Clinical signs - Respiratory signs in poults include snicking, rales, sneezing, nasal exudates (often frothy), foamy conjunctivitis, and sinusitis. Drops in egg production can be as much as 70 percent

Transmission - Spread is primarily by contact with contaminated environments, feed and water, recovered birds, equipment, and personnel.

Egg Drop Syndrome