Newcastle Disease is caused by a paramyxovirus. Only one serotype of ND is known. ND virus has mild strains (lentogenic), medium strains (mesogenic) and virulent strains (velogenic). The strains used for live vaccines are mainly lentogenic.
Newcastle Disease virus is highly contagious through infected droppings and respiratory discharges between birds. Spread between farms is by infected equipment, trucks, personnel, wild birds or air. The incubation period is variable but usually about 3 to 6 days. Chickens and turkeys are the species affected.
ND causes high mortality with depression and death in 3 to 5 days as major signs. Affected chickens do not always exhibit respiratory or nervous signs.
Mesogenic strains cause typical signs of respiratory distress. Laboured breathing with wheezing and gurgling, accompanied by nervous signs, such as paralysis or twisted necks (torticollis) are the main signs. Egg production will decrease 30% to 50% or more, returning to normal levels in about 2 weeks. Eggs may have thin shells and without shells may also be found. In well vaccinated chicken flocks, clinical signs may be difficult to find.
Inflamed tracheas, pneumonia, and/or froth in the airsacs are the main lesions. Haemorrhagic lesions are observed in the proventriculus and the intestines.
Diagnosis Is made by virus isolation from tracheal or cloacal swabs together with blood testing to demonstrate high antibody levels. Infectious bronchitis or infectious laryngotracheitis can give similar clinical signs, but lesions, blood tests, and virus isolation are decisive.
Treatment and control
There is no treatment for Newcastle disease. Vaccination against ND with live and/or inactivated (killed) adjuvant vaccines is the only reliable control method.