Newcastle Disease

Newcastle Disease (ND)

Cause
Newcastle disease is caused by a paramyxovirus. Only one
serotype of ND is known. ND virus has mild strains (lentogenic),
medium strength strains (mesogenic), and virulent
strains (velogenic).
The strains used for live vaccines are mainly lentogenic.

Transmission
Newcastle disease virus is highly contagious through infected
droppings and respiratory discharge 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.

Species affected
Chickens and turkeys.

Clinical signs
Newcastle disease 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.
Labored 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 eggs 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 tests 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.