PREVENTION AND CONTROL OF RANIKHET DISEASE IN POULTRY
Ranikhet disease, also known as Newcastle disease is one of the most important viral diseases of poultry that affect a wide range of birds including chicken. Chickens are the most susceptible where it can cause heavy mortality at a very fast rate, if care is not taken to vaccinate the birds. To control this disease, it is important that the farmer should learn how to vaccinate chickens against the disease and how to raise chickens in a way that is more likely to keep them healthy.
Newcastle disease is caused by avian paramyxovirus serotype type 1 (APMV-1), also called Newcastle disease viruses (NDV), of the genus Avulavirus belonging to the family Paramyxoviridae. APMV-1 strains are classified into five pathotypes based on their virulence in chickens, designated: a) viscerotropic velogenic, b) neurotropic velogenic, c) mesogenic, d) lentogenic or respiratory and e) asymptomatic. Lentogenic strains are the least virulent, mesogenic strains are moderately virulent and velogenic strains are the most virulent. Newcastle Disease also known as pseudo-fowl plague, refers to all infections of poultry caused by avian paramyxovirus serotype 1 (APMV-1).
According to the World Bank, ND is ranked as the third most costly poultry disease, after Avian Influenza (AI) and Infectious Bronchitis (IB). At present, a total of 20 Avian paramyxovirus serotypes (APMV-1 to APMV-20) have been identified in different avian species. ND is caused by Avian orthoavulavirus1 (AOAV-1) formerly designated as Avian avulavirus 1 (AAvV-1) or APMV-1 under the genus Orthoavulavirus within subfamily Avulavirinae of the family Paramyxoviridae. NDV strains have been broadly classified into two classes- class I and class II. The class I comprise of a single genotype 1 and are currently divided into 3 sub-genotypes: 1a, 1b and 1c. Class I isolates are of low virulence and have been recovered from both domestic and wild birds. Whereas, the Class II viruses are genetically more diverse and exhibit wider range of virulence, and the complete analyses identified 21 distinct genotypes (I to XXI, excluding genotype XV that contains only recombinant sequences).
Since, its first report in 1926 on the island of Java, now part of Indonesia and subsequently in 1927 in Newcastle-upon-Tyne in England, ND has caused tremendous economic losses to the poultry industry worldwide.
In India, ND was first reported by Edwards in 1928 in Ranikhet region and is popularly called as Ranikhet disease owing to its place of emergence. As for time, it had been a century and the history of ND reflects four major well-established panzootics.
ND virus (NDV) has a wide host range affecting more than 240 species of birds but the disease varies considerably with different species. ND is directly transmitted by either inhalation or ingestion of virus shed in faeces and respiratory secretions of infected or carrier birds. Indirect transmission through transportation of live bird and poultry product, movement of people and equipment, contaminated feed and water, contaminated fomites, vaccines may also occur. Moreover, spillover event from wild avian species into domestic poultry has also been reported. The incubation period for ND ranges from 2 to 15 days with an average of 5-6 days.
The disease vary from asymptomatic or mild infection to acute lethal infection with 100% mortality. NDV has been categorized into five pathotypes based on the clinical and pathologic manifestations in infected chickens, designated as follows:
Velogenic: These are highly pathogenic strains causing mortality upto 100%
Viscerotropic velogenic: It is the severe form of ND which causes haemorrhagic intestinal lesions and characteristic haemorrhages at the proventriculus-gizzard junction and in the caecal tonsils. It is also called as “Asian” or “exotic” form of ND.
Neurotropic velogenic: It causes neurological and some respiratory signs with no gastrointestinal involvement. The typical clinical manifestation includes tremors, ataxia, torticollis, and paralysis of wings and legs. Gross pathologic changes are not observed in the central nervous system.
Mesogenic: It causes mild to moderate respiratory illness and occasional neurologic. Other symptoms include depression, loss of weight and decreased egg production. Mortality is around 10%.
Lentogenic or respiratory: These strains are usually associated with a mild or sub-clinical respiratory infection and a small drop in egg production. There is absence of recognizable gross lesions and mortality is usually negligible.
Asymptomatic: They cause only the replication of the virus in the intestinal tissue of the infected chicken resulting in subclinical enteric infection.
ND also has a zoonotic dimension since initial exposure to infectious material can induce transitory unilateral conjunctivitis with congestion, lacrimation, pain and swelling of the sub-conjunctival tissues, which is usually self-limiting.
MODE OF TRANSMISSION
z Direct contact with secretions especially droppings and nasal secretion from infected birds
z Contaminated feed, water, utensils, premises, human clothing etc.
SOURCES OF VIRUS:
z Respiratory discharge, faeces.
z All parts of the carcass
z Pig, calves, human and turkey can harbour and spread the virus as healthy carriers.
z Dogs and cats fed on birds which had died due to RD are known to excrete the virus through faeces from 5 days to 5 months. Turkeys are known to excrete the virus for 1 year.
z Rainy season in India has been found to be more favorable for the occurrence and spread of the disease. Neural form of the disease is more common in summer.
SIGNS/ SYMPTOMS
Clinical signs of the disease depend upon the immune status and age of the bird. The airways, gut and nervous system tend to be infected.
z Chickens rapidly become weak and often die without showing any symptoms
z Respiratory and/or nervous signs, mainly – Gasping and coughing Drooping wings, dragging legs, twisting of the head and neck, circling, depression, inappetence, complete paralysis.
z Partial or complete cessation of egg production
z Eggs are misshapen, rough-shelled, thin-shelled and contain watery albumin z Greenish watery diarrhoea
z Swelling of tissues around the eyes and neck.
Post-mortem lesions
Gross lesions are usually seen in birds affected by velogenic strains of the virus. They have been characterized especially in chickens with viscerotropic strain, but they are not pathognomonic of the disease. Sometimes, birds with neurological signs or that died suddenly show few or no gross lesions.
Lesions may include:
- Swelling of the head, periorbital area and/or neck.
- Petechiae or haemorrhages in the serous membranes of the digestive system and the mucosa of the proventriculus and intestine.
- Haemorrhages in the lymphoid tissue of the respiratory tract and digestive system, especially in the cecal tonsils and Peyer’s patches.
- Enlarged spleen, friable and spotted with necrotic/haemorrhagic areas.
- Oedema around the thymus and bursa of fabricious of young birds.
- Oedema, haemorrhages or degeneration of ovaries.
Lesions caused by lentogenic pathotypes are usually limited to congestion and mucous exudates in the respiratory tract, with opacity and thickening of the air sacs.
TREATMENT
There is no specific treatment of RD. The best way to prevent the disease is by good management and vaccination.
PREVENTION AND CONTROL
Sanitary prophylaxis:
z Isolate the infected bird(s) immediately after detecting any clinical symptom.
z Dispose the dead bird properly either by burning or by burying in a deep pit.
z Thoroughly clean and disinfect the poultry shed and its premises (use disinfectant like Lysol, Phenol etc.)
Medical prophylaxis:
z Vaccination is the best way of preventing Ranikhet disease.
z Only healthy birds should be vaccinated.
Vaccination Schedule:
Age Vaccine Dose Route
4-5 days old chick F-1/ Losota 1 drop Eye / Nostril
35 days F-1/ Losota 1 drop Eye / Nostril
8- 10 wks R2B strain 0.5 ml SC / IM
Good Management:
z Good housing can reduce disease transmission. An elevated, well-ventilated chicken house ensures hygiene and minimizes infection.
z Clean the chicken house at least once a week. After cleaning, put ash on the floor and walls to stop problems with fleas and mites.
z Daily provide some extra feed such as maize bran, ground grains, green leaves, worms etc. Good nutrition will give a better immunity.
z Always provide fresh and clean drinking water.
Control measures during an outbreak:
z Do not sale or get away any sick bird.
z Isolate all sick bird from the healthy flock.
z Never vaccinate sick bird
z Do not transport sick / dead bird to other areas which are free from the disease.
z Dispose dead bird properly either by burning or burying in a deep pit.
z Restrict the movement of people, cars, other animals and parts of infected birds (such as eggs, feathers, etc.) from the village to other areas that are free from the disease.
DR DEEPAK PD. SINHA, VENKYS
