NEWCASTLE DISEASE (NDV)

Newcastle disease is a highly contagious viral infection that affects many species of domestic and wild birds to varying degrees. Domestic fowl, turkeys, pigeons and parrots are most susceptible while a mild form of the disease affects ducks, geese, pheasants, quail and guinea fowl. The disease can result in digestive, respiratory and/or nervous clinical signs, which range from a mild, almost inapparent respiratory disease to very severe depression, drop in egg production, increased respiration, profuse diarrhoea followed by collapse, or long-term nervous signs (such as twisted necks), if the birds survive. Severe forms of the disease are highly fatal.

What causes Newcastle disease?

Newcastle disease is caused by a paramyxovirus that can vary in pathogenicity from mild to highly pathogenic. Spread is usually by direct physical contact with infected or diseased birds. The virus is present in manure and is breathed out into the air. Other sources of infection are contaminated equipment, carcasses, water, food and clothing. People can easily carry the virus from one shed or farm to another. Newcastle disease virus does not affect humans in the same way that it does birds but it can cause conjunctivitis in humans.

Signs of infection with NDV vary greatly depending on factors such as the strain of virus and the health, age and species of the host.

The incubation period for the disease ranges from two to 15 days. An infected bird may exhibit several signs, including respiratory signs (gasping, coughing), nervous signs (depression, inappetence, muscular tremors, drooping wings, twisting of head and neck, circling, complete paralysis), swelling of the tissues around the eyes and neck, greenish, watery diarrhea, misshapen, rough- or thin-shelled eggs and reduced egg production.

In acute cases, the death is very sudden, and, in the beginning of the outbreak, the remaining birds do not seem to be sick. In flocks with good immunity, however, the signs (respiratory and digestive) are mild and progressive, and are followed after seven days by nervous symptoms, especially twisted heads.

Prevention and treatment of Newcastle disease

There is no treatment for Newcastle disease, although treatment with antibiotics to control secondary infections may assist. The virus can remain alive in manure for up to 2 months and in dead carcasses for up to 12 months, however it is easily killed by disinfectants, fumigants and direct sunlight. Prevention relies on good quarantine and biosecurity procedures and vaccination.