Newcastle disease In Poultry

Ranikhet disease (RD) is the most common, the most widely prevalent, and economically the most

important viral disease of poultry in our country. It is a very severe, sudden, and rapidly spreading

disease; and may be seen from 6th to 7th day onward up to 72 weeks. It occurs throughout the year,

but is most common in the summer.

Cause

A virus called paramyxovirus. These viruses are of different types. Some are highly powerful and cause most severe form of the disease, others are moderate, while a certain group is only mildly harmful. In addition, there are some viruses that cause infection without showing any symptoms.

Spread

I . Virus spreads through the air.

2. Infection occurs mainly through inhalation or ingestion.

3. Contaminated feed and water spread infection.

4. Movements of people and equipment also spread infection.

5. Away from the bird, that is, in the shed, virus survives for days to weeks.

However, in the dead bird or faeces, virus survives for several months.

Symptoms

Depending on the disease-producing power of the virus, symptoms vary.

I. With very harmful viruses, first indication is sudden death. Then, symptoms such as depression, weakness, lying down, green diarrhoea, swelling of the face, and nervous signs may appear, ending in exhaustion and death. Other signs include twisting of the neck, paralysis of legs and arched position of the body. Mortality may occur up to 100% in chicks. In layers, early symptom is shell-less or soft-shelled eggs, followed by complete stoppage of laying.

2. Moderately harmful viruses usually cause severe respiratory disease and respiratory symptoms. In

adult birds there is marked drop in egg production for several months. Mortality is low.

3. Mildly harmful viruses may cause no disease, or only a mild respiratory distress.

Postmortem Findings

I. Pinpoint haemorrhages on the tips of glands in the proventriculus (Fig. 2, 3).

2. Enlarged and haemorrhagic caecal tonsils.

3. Haemorrhagic lesions in the intestinal wall (in the lymphoid aggregates) (Fig. 4, 5, 6, 7, 8).

4. Spleen shows necrosis (white spots of dead tissue) on its outer surface, and also on the cut surface.

5. Marked congestion of trachea, often with haemorrhages. The airsacs may be inflamed (airsacculitis) and appear cloudy and congested. Airsacs may even contain cheesy (caseous) material.

Diagnosis

I . From the characteristic postmortem findings.

2. Confirmation depends on various laboratory tests, such as HI and ELISA, and also on isolation of the virus and its characterization.

Treatment

There is no treatment.

Control

I. Timely vaccination with live and/or inactivated (killed) vaccine is the only reliable control method.

2. However, under field conditions vaccination alone is not sufficient to control RD. It must therefore be accompanied by good hygiene, good management, and good biosecurity practices.