Ranikhet Disease

 Ranikhet disease is an acute rapidly transmitting viral disease of domestic poultry and other avian groups. It is characterized by respiratory signs (distress, coughing, sneezing), nervous signs leading to wing paralysis, incoordination, torticollis, swelling of head and chalky white diarrhoea. It causes considerable loss to poultry industry by way of morbidity, mortality and drop in egg production.

Distribution

The disease has been recorded from almost all the countries of the world. In India, the disease is widely prevalent in all the states. The disease was first recorded in New Castle, UK, by Doyle in 1926. That is why the disease is known as New Castle disease or Doyle’s disease. The disease was also recorded in Indonesia in the same year. In India, it was recorded in 1927 by Edward from Ranikhet, a hilly station of Uttaranchal. It is most striking disease in India due to heavy mortality ranging from 50-100%.

Sigh (1977) reported several outbreaks of the disease in vaccinated flocks. Concurrent outbreak of the disease along with infectious laryngotracheitis has been observed in Punjab. Kalra (1978) recorded 76 outbreaks in Haryana within the period of 8 years. The Asiatic form of the disease resulting in very high mortality ascribed as Very Virulent New Castle disease (VVND) is very much prevalent in India. Ajinkya (1980) recorded heavy losses in broilers due to the disease in spite of vaccination in several broiler farms. Lowered immunity due to IBD attributed to RD outbreak observed very frequently.

Aetiology

The disease is caused by paramixogroup-1 virus. This is a RNA virus. The virus has got the property of haemagglutination; lysis of mammalian RBC and development of interferon. Based on the production of interferon virus is considered as avirulent or virulent. The virus may affect different vital systems. Virus which has affinity for respiratory tract is known as Asiatic form of virus whereas virus affecting gastro intestinal tract, liver and nervous system is known as viscerotropic and neurotropic virus respectively.

Virus strains are classified as highly virulent (velogenic), moderately virulent (mesogenic) and least virulent (lentogenic).

Susceptible Hosts

The disease is most frequently observed in domestic poultry. More than 230 species from more than half of the 50 orders of birds have been found to get infected with avian paramyxoviruses through natural or experimental ways. Susceptible birds include guinea fowl, pheasants, pigeons, ducks, geese, patridges, parrots, mynahs, pittas, cocktiels, cockatoos, etc. Sparrows, kites and vultures are also affected. Duck and quails are comparatively resistant to this disease.

Mode of Transmission

Virus is excreted during incubation period, during clinical manifestations and for a varying period during convalescence. Chickens are infected with droplet method. Infection may spread through faeces, eggs and infected carcasses.

Air borne transmission is the most important way of transmission. The coughing and sneezing may shed huge quantity of virus and thus contaminate the chicken house, equipment, clothing of personnel, etc. In the faecal materials virus may remain viable for about six months. This may contaminate the food and water and thus act as disseminating agents. Virus may be transmitted through contaminated bedding, incubator and infected eggs.

The disease may be noticed following vaccination. This is not a carrier disease. Following 30 days of infection, birds do not shed virus.

Wild birds may transmit the virus to the domestic flocks. They include pigeons, doves, sparrows, jungle fowl, peacock, kites and vulture.

Mammals like dog, cat, man may occasionally carry the virus from one farm to the other.

Pathogenesis

Depending on the capabilities of producing clinical manifestations, three strains have been categorized. e.g. Lentogenic, Mesogenic and Velogenic. Mild form of the disease is caused by lentogenic strain where principal manifestation is mild respiratory disturbance along with drop in egg production, Less virulent type of disease is caused by mesogenic strain where mortality rate may range from 5-15% manifested with greenish diarrhoea and nervous manifestation. The virulent strain is known as velogenic strain where there is gasping respiration, haemorrhagic diarrhoea. The gross clinical signs and mortality varies based on factors like (a) Immune status of the flock, (b) Severity of exposure, (c) Evidence of concurrent infection. Outbreak have been recorded due to concurrent infections with IBD and Mycotoxin.

Persistence of antigen and antibody in day old chicks has been reported. Intestinal content revealed higher HA titre than other materials such as spleen, brain, thymus, bursa and bone marrow showing tropism of the isolates towards the intestinal contents. Some RD strains grow only in the digestive tract and the virus can be isolated from there when circulating antibodies are present. It indicates that natural spread through faecal oral route is possible.

Vertical transmission of velogenic strain of RD from embryonated eggs have also been suggested. This may be attributed to (a) immunologic tolerance to the virus to which chicks were exposed during embryonic stage (b) total absence of phagocytic activity in embryo which prevented the destruction of virus and formation of immune complexes during the prolonged persistence of the virus in the presence of antibodies.

From a study in Tamil Nadu, the distribution of grouping based on monoclonal antibody binding pattern were six C, four D, one B and one F. The monoclonal antibody groupings included A, B, C, D, E, F, G, H, L and P. The velogenic viruses were present in groups A, B, C, and D.

Clinical Findings

Signs in young birds:

• Though there is no age restriction as regard infection but the young birds are more susceptible over old birds. Velogenic strain frequently affect the young birds causing severe clinical reactions. Mesogenic and lentogenic strains affect the adult birds.
• Young birds show respiratoru and nervous signs.
• Respiratory signs are characterized by sneezing, coughing, gasping, hoarse breathing and coarse charping.
• Birds remain dull and depressed. They huddle together and remain in one corner.
• Birds excrete watery white faeces.
• Nervous signs appear within few days of exposure.
• Nervous signs include clonic spasms, incoordination, opisthotonos, tremor, lameness.

Signs in adult birds

• A sizeable number of birds show the signs of illness in a flock almost over night.
• Birds pass watery diarrhoeic faeces; The colour of the faeces may vary from greenish to white chalky. This discoloration may be due to the presence of excess bile and urates.
• Birds show hoarse breathing and gasping.
• There is sharp decline in egg production. Fertility and hatchability may be impaired.
• The eggs will have soft shell with irregular shape. Albumin may turn watery.
• Birds may show haemorrhagic conjunctivitis and oedematous keratitis.
• Nervous signs may not be evident in adult birds.

Signs in caged birds include:

• Asymptomatic showing no apparent clinical signs.
• Symptomatic showing signs like anorexia, depression, weight loss, nasal discharge, conjunctivitis, yellowish green diarrhoea, ataxia, opisthotonos, torticollis or headshaking. Leg and wing paralysis.
• Acute death syndrome-huge death rate within a short span of time.

Diagnosis

Diagnosis can be made based on the following.

(a) Apparent diagnosis can be made based on characteristic clinical signs

• rapid spread of disease
• high mortality rate
• respiratory and nervous manifestation
• digestive and nervous manifestation

(b) Characteristic post mortem changes.

(c) Isolation and identification of the virus. Inoculaion of tissue suspension in week old, embryonated eggs by chorio allantoic route – the embryo will die within 48-72 hours. Identification of the haemagglutinating virus through inhibition with known RD antiserum. Paired serum samples may be used for identification.

(d) Serological tests. Serological tests may not always give correct diagnosis especially it may give clear indication to differentiate between a vaccinated from infected. Aitken (1977) opined that serological diagnosis should preferably be used as an adjunct rather than a primary means of diagnosis.

Commonly used routine tests

• Haemagglutination test (HAT)
• Haemagglutination inhibition test (HIT)
• Complement fixation test (CFT)
• Virus neutralization test (VNT)
• Fluorescent antibody technique (FAT)
• Polymerase chain reaction (PCR)

PCR has been used to detect RD virus by amplifying 643 bp fragment on VP2 gene.

PCR coupled with ELISA detection system has been used for detecting RD virus. This is very specific for all the three different pathotypes of RD (NDV); RT-nested PCR is 100 times more sensitive than non-nested RT-PCR.

Differential Diagnosis

The disease has to be differentiated from he under stated disease conditions.

(a) Infectious bronchitis (IB)

• More marked respiratory symptoms
• Air sacculitis
• Abnormal eggs
• Low production

(b) Infectious laryngotracheitis

• More in adult birds
• Prolonged drop in egg production
• No abnormalities in eggs
• No involvement in air sac
• Haemorrhage in larynx and trachea

(c) Avian encephalitis

• Young birds are affected
• Slow spreading than RD
• Birds may continue to eat
• No involvement of air sac
• No enlargement of spleen
• Nervous signs – ataxia, paralysis, nodding of head, torticollis.

(d) Avian influenza

• Respiratory signs
• Greenish diarrhoea
• Oedema of head and neck
• Slight decrease in egg production
• CNS involvement

(e) Vitamin E deficiency

• Young birds are affected
• Prostration
• Unable to move
• Move in circle
• Body cavity filled with gelatinous exudates
• Cavity formation in the brain

(f) Marek’s disease

• Slow spreading
• Paralysis of wings and legs
• Enlargement and thickening of brachial and sciatic nerves.
• Infiltration of lymphocytes and plasma cells in nerve fibres.

Treatment

There is no effective treatment. But, to control the secondary invaders, broad spectrum antibiotics may be used.

In case of outbreak, vaccine with mild strain of (F1) RD virus may be tried. This may minimize the mortality rate due to interference phenomenons where the mild strain is likely to compete with virulent strain. The used of CDF-66 strain vaccine has been suggested during RD outbreak.

Control

• Standard hygeinic and sanitary measures are to be adopted with utmost sincerity.
• Sick birds are not to be treated but seggregated. If treatment is at all resorted it should be done in a separate manner from the viscinity of healthy birds, since sick birds will remain as potential source of infection.
• Elimination of source of infection should be made through strict biosecurity measures.
• Seggragation and disposal of dead birds should be done with proper care with bleaching powder or lime.
• All in and all out methods should be adopted to control the disease.
• The entry of visitors should not be used.
• Entry of free flying birds should be restricted.
• Restriction has to be imposed on humans and their equipments since they provide source of infection by creating mechanical transporation avenues for the virus to new locations and to susceptible population.
• Exotic birds may spread the disease to the domestic one and vice-versa. Therefore this aspect should be viewed properly.
• Disifection of the premises to be made. This may be done with 2% sodium hydroxide or 1 in 1000 lysol.
• Fumigatin of the house, hatchery or incubators is to be done. For every 100 cubic feet area, use 20 gms of potassium permanganate with 40 ml of formalin. Shed should be kept closed with curtains for 24 hours. Then the curtains should be unfolded. To minimize the expenditure bleaching powder can be used instead of potassium permanganate at the same dose rate. Humidity should be present and the temperature should be above 22° C.

Before entry of new flocks in the house the following measures are suggested.

• All the organic matters (manure, litter, dust, feathers, etc) are to be removed following spraying with 5 to 10% formalin. Disposal to be made by putting the materials in closed containers (Gunny bag or plastic bag).
• All waterers, feeders, curtains, basket should be removed. These should be cleaned and washed thoroughly with jet of water and then with washing soda solution. They should be sun dried.
• All organic matters to be disposed far away from the farm mixed with formalin or soda.
• All measures to be taken to prevent the entry of rodents.
• All the floor spaces, cages, side wire mesh should be treated with flame gun to prevent the germs.
• Floor should be soaked with strong solution of caustic soda with pH above 12 for 12-24 hours, dose : (i) NaOH (caustic soda) = 11 to 12 gms per litre of water, (ii) Na2CO3 (washing soda) = 50 to 60 gms per litre of water.

In order to undertake spraying of viricidal disinfectant, it should be done 48-72 hours prior to arrival of chicken. The house should be kept vacant for a period of 15 days following outbreak after spray.

Vaccine

Three types of vaccines are used.

(a) Lasota strain or F-strain vaccine

Tis is produced by growing live virus in SPF eggs and then lypophilized. This vaccine was advocated by Rao and Agarwal (1962) and Bansal and Kumar (1977) to protect day old chicks.

Schedule

• 4-10 days old chicks – Intraocular or nasal drop method.
• 4-5 weeks – Intraocular or drinking water as booster
• 15-16 weeks – Drinking water as 2nd booster

(b) R2B vaccine (Mukteshwar strain)

R2B vaccine is produced by growing virus on SPF eggs and then lypophilized. This is used to prevent RD characterised by neuroparalytic symptoms, diarrhoea, etc.

Schedule

• Breeding flocks, replacement pullets at 8-10 weeks of age. Booster vaccine at 17 weeks for commercial layers.
• At 6 weeks following F1 vaccine in general. Dose: Inject 0.5 ml intramuscularly or subcutaneously by using a needle of 20-22 guage.

(c) Newcastle disease killed vaccine

This vaccine contains Lasota strain virus and/or Mukteshwar (R2B) strain virus in inactivated form. This vaccine is used to prevent:

• RD characterized by neuroparalytic symptoms
• Very virulent strain of virus causing heavy mortality
• In broiler, to control cyclical ND problem.
• Virus spead from vaccinated to susceptible flock.

Schedule

Layers and broiler flock at 16th-20th week. In case of cyclical problem in commercial broiler along with 1st Lasota, this vaccine can be used. Dose is 0.2 ml.

In general dose is 0.5 ml subcutaneously in the lower neck region or intramuscularly in the breast muscle.

Precautions

• Sterilized equipment should be used for vaccination.
• Chemical disinfectant should not be used for sterilization.
• Chilled diluent should be used for dilution.
• Re-constituted vaccine should be kept in ice or ice-cold water during the entire vaccination programme.
• For drinking water method, rinse drinking water container with plain water.
• Healthy birds should be vaccinated. They should be provided with good nutrition, adequate heat, water and ventilation.
• Entire quantity of vaccine to be used or disposed while vial is opened.
• Use reconstituted vaccine within 2 hours from mixing.
• Frequently shake the bottle while using the killed vaccine.
• Burn or destroy all left over vaccine.
• Debilitated or stressed birds should not be vaccinated.

Public Health Aspects

The virus is able to produce a self limiting conjunctivitis. Poultry slaughter house workers, laboratory workers and vaccinators are infected.