Newcastle disease / Ranikhet disease (ND/RD)
This disease is caused by Newcastle disease virus (NDV) belonging to the genus Paramyxovirus of the family Paramyxoviridae. Along with HPAIV, NDV is also included in 'List A' diseases of OIE. Newcastle disease is highly contagious. All birds in a flock usually become infected within 3 to 4 days. The virus can be transmitted by contaminated equipment, footwear and clothing and free-flying birds. During the active respiratory stage, it can be transmitted through the aerosol route. In India, Edwards (1928) reported the disease from Ranikhet in Almora district (Uttarakhand) hence it is also called as Ranikhet disease. The virus agglutinates red cells from chickens, turkeys, guinea pig, wild birds and human O cells.
Symptoms and lesions: On the basis of the clinical signs and the virulence of the associated strains 5 distinct forms of RD are described here.
Doyle's form (Asiatic form/velogenic viscerotropic RD): This is the acute and fatal infection of chicken of all ages caused by the most virulent from the virus. The mortality may go up to 100% in fully susceptible chicken. Clinical signs are greenish blood stained diarrhea, dehydration, tremor, torticollis and paralysis of legs and wings. Hemorrhagic lesions are prominent in the digestive tract particularly around the orifices of glands in the proventriculus, caecae and small intestine. Regressive changes are seen in the lymphoid tissue.
Beach's (pneumoencephalitic) form : It shows sudden onset of severe respiratory symptoms such as coughing gasping, lower egg production and mortality ranges between 10 and 50% but can go up to 90% in young chicken. There may be proliferative lesions in the lungs and on purulent encephalomyelitis.
Beaudett's form: This type is caused by mesogenic strains and characterized by acute respiratory and sometimes nervous infections in young chicks. The clinical sings are coughing, anorexia and lowered egg production; mortality is rare except in very young susceptible birds.
Hitchner's form: This is a mild inapparent respiratory infection caused by a lentogenic strain. Serious respiratory distress has been reported with LaSota stain.
Asymptomatic enteric form : Causes only gut infection but with no clinical manifestation and can be detected only by an increase in antibody titre or by virus isolation from the alimentary tract.
In turkeys, the symptoms are usually mild and may be unnoticed unless nervous disorders develop. During an outbreak, turkeys will produce eggs with a chalky white shell. NDV can cause conjunctivitis in human beings.
Diagnosis: The disease can be diagnosed from clinical symptoms and PM lesions. The virus can be isolated in developing chick embryos that shows hemagglutination (HA) and specific identification is made by HA inhibition (HI) test with mono-specific antiserum to NDV. Detection of viral antigens in the above specimens by HA, fluorescent antibody and immunoperoxidease tests and of antibody by HI , Immunofluorescence or ELISA tests.
Prevention and control: Proper hygiene and management are necessary to avoid introduction of the disease and to prevent the dissemination of the virus. In disease free areas, RD is controlled by slaughter policy and immunoprophylaxis using vaccines. In India where the disease is endemic, the most practical method of control of this disease is vaccination. Both live (LaSota, F, R2B etc.) and inactivated vaccines are effectively being used to control this disease.