By James M. Harris, BS, DVM, FRSH
Mayfair Veterinary Clinic, Hobart
Newcastle disease is a viral disease of domestic poultry and wild birds that is manifested by gastrointestinal, respiratory and neurological signs with a very high mortality. The virus has a number of strains. The most serious is called velogenic. The mildest is called lentogenic. This classification is based on how quickly they kill chickens or embryonated eggs.
The virus is readily inactivated by heat, fat solvents and high and low pH. Direct sunlight inactivates the virus in 30 minutes but in cool weather virus can remain active in faeces for weeks. The natural hosts are domestic fowl, turkeys, pheasants, pigeons, quail, ducks, geese, ostriches, and many species of wild birds including parrots. Humans can develop conjunctivitis (inflammation of the membranes of the eye.
Newcastle disease is found worldwide. Pathogenic strains are not found in Australia, New Zealand and Papua New Guinea. Irian Jaya, the Indonesian Western side of New Guinea is the closest country to Australia that has the disease. The severe form of the disease has occurred twice in Australia. Both outbreaks occurred in the early 1930's in Victoria. There is a mild strain of the virus in Australia in poultry and some wild birds.
Newcastle disease is highly contagious and can cause very severe outbreaks. Transmission is by direct contact with diseased or carrier birds. The virus is excreted in faeces and expired air and can be spread in bird crates, feed, vehicles, dust, feathers and clothing. Inhaling the virus or eating contaminated material can infect birds. The wind can spread the virus up to 64 meters. Wild birds play an important role in the spread of this virus. Psittacine species and other wild birds from SouthEast Asia and South America are reservoirs.
The incubation period is 5-6 days but can be shorter (2 days) or longer (up to 15 days). The severe strain spreads rapidly. There is marked depression, loss of appetite, rapid breathing, collapse, bright green droppings, and dehydration, swelling of the head, neurological signs and death.
Pathological findings include: haemorrhages and death of tissue in the digestive tract as well as pin point haemorrhages of other internal organs, congestion of the airways, plugs of exudate in the trachea, and thickening of the air sacs. There is a very high mortality of up to 90%. A number of other diseases can resemble Newcastle virus. Samples of tissues and swabs collected from sick and dead birds are needed to confirm the diagnosis.
Newcastle disease is a serious danger to the Australian poultry industry and is considered an Emergency Animal Disease. There is no treatment. If confirmed a wide area will be quarantined. The infected premises will be shut down. No movement of people, vehicles or goods will be allowed to leave or enter and all birds on the premises will be killed. There is no exception to this plan.
To prevent the tragic loss of ones birds it is important to remember never to obtain birds from unknown or questionable sources. It is not worth taking the risk. Smuggled birds present the greatest risk of introducing Newcastle disease into Australia.
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