Newcastle Disease

Worldwide, Newcastle disease (NCD) is probably the most common disease of small household and village poultry flocks. Throughout the world, NCD is known to spread from village to village, town to town, island to island totally decimating chicken populations.

Presenting complaints are respiratory disease with mild respiratory signs such as a cough, tracheal rales, or rattling when breathing and other general signs of illness in milder forms. Complaints of CNS manifestations, such as torticollis, paresis, and paralysis, may be seen in addition to the respiratory signs.

In some cases, the owner may find a large amount of their flock dead with no previous clinical signs.


Causative Agent

Newcastle disease, so named because one of the first outbreaks was identified in Newcastle-upon-Tyne in England, is caused by avian paramyxovirus serotype 1 (APMV-1). APMV-1 viruses vary in the effects caused by their infection.

The various types of NCD viruses can be referred to as lentogenic, mesogenic or velogenic.

Lentogenic NCD viruses are typically subclinical or cause mild respiratory signs. Mesogenic NCD viruses typically cause respiratory signs and occasional nervous system signs but with low mortality. Velogenic NCD viruses cause high mortality often without previously noted clinical signs.

Velogenic NCD viruses are further classified as viscerotropic or neurotropic. Viscerotropic velogenic NCD causes hemorrhagic gastrointestinal lesions, and neurotropic velogenic NCD viruses cause high mortality typically after respiratory and nervous signs.


Clinical Signs and Lesions

Onset is rapid, and signs appear throughout the flock within 2–12 days (average 5) after aerosol exposure. Spread is slower if the fecal-oral route is the primary means of transmission, particularly for caged birds. Young birds are the most susceptible.

Birds infected with lentogenic strains show respiratory signs of gasping, coughing, sneezing and rales. Lesions of bacterial septicemia, such as fibrinous polyserositis and vasculitis, may be present in secondary bacterial infections.

Birds infected with the mesogenic strains have moderate respiratory signs such as coughing, rattling when breathing, CNS signs, and general signs of illness such as inactivity, reluctance to move, and a “puffed up” appearance and there may be some mortality in the flock. Lesions with mesogenic strains consist of reddening of the trachea, and lungs may be red and moist.

Respiratory signs with depression, watery greenish diarrhea, and swelling of the tissues of the head and neck are typical of the most virulent form of the disease, viscerotropic velogenic Newcastle disease. Varying degrees of depression and inappetence are seen. Partial or complete cessation of egg production may occur. Eggs may be abnormal in color, shape, or surface and have watery albumen. Birds are often found dead. Lesions of velogenic NCD typically consist of hemorrhages of the gastrointestinal tract including esophagus, proventriculus, small and large intestine, and cecal tonsils. There may be facial edema and hemorrhage of the conjunctiva.


Transmission Route

The virus is typically transmitted by aerosol route from respiratory tract secretions but the virus may also be transmitted by fecal/oral route and, as with other avian pathogens, through fomites.


Diagnosis

- PCR
- ELISA

NCD virus can be isolated from oropharyngeal or cloacal swabs or tissues from infected birds.


Prevention & Control

There are many relatively inexpensive and effective modified live vaccines available for NCD. Lately NCD vaccines typically include infectious bronchitis vaccine virus as well.

Poultry vaccines are typically applied through mass vaccination procedures including spraying of the vaccine or adding it in the drinking water. In backyard situations, water vaccination would be the easiest, most practical method of application.