Newcastle Disease (Ranikhet Disease)

Newcastle Disease (Ranikhet Disease) is also known as Avian Pneumoencephalitis, Avian distemper and Doyle’s disease.

Newcastle Disease (Ranikhet Disease) is a highly contagious acute viral disease of domestic poultry and other birds, clinically characterized by acute respiratory disease (distress, coughing, sneezing), nervous signs (wing paralysis, inco-ordination, torticollis), bile stained greenish diarrhoea and death.

The name Newcastle disease was coined by Doyle. In India in July 1927, the virus was recognized in Ranikhet by Edwards. Hence it named as Newcastle disease or Ranikhet disease. Nine serotypes of avian paramyxoviruses recognized but only avian paramyxovirus 1 is associated with clearly defined disease.

Etiology

Newcastle Disease (Ranikhet Disease) is caused by avian paramyxovirus serotype 1 (APMV-1), genus: Avula virus, family Paramyxo viridae is an RNA virus. There are 11 serotypes are recognized, but serotype 1 only causes disease.
The NDV encodes six protein (Nucleocapsid protein, phosphoprotein, Matrix protein, RNA dependent RNA polymerase and Fusion protein (contain Haemagglutinin and Neurominidase)
APMV-2&3 causes respiratory disease in turkey.
Based on virulence and tissue tropism Newcastle disease virus classified as velogenic (virulent), Mesogenic (moderately virulent), lentogenic (low virulent).
Velogenic and mesogenic strain mostly causes disease, the low virulent lentogenic strain is widely used as live vaccine.
The virus is comparatively stable in an environment and survives for long periods at ambient temperature, especially in faeces and can persist in houses (in faeces, dust etc) for up to 12 months.
The virus is inactivated at temperatures 56⁰C for 3 hours or 60⁰C for 30 min, acid pH, formalin and phenol.

Epidemiology

Virulent NDV strains are endemic in poultry in most parts of Asia, Africa, and some countries of North and South America, USA and Canada.
The disease was first observed in 1926, in Java, Indonesia and in Newcastle-upon-Tyne, England.
The name Newcastle disease was coined by Doyle. In India in July 1927, the virus was recognized in Ranikhet by Edwards. Hence it named as Newcastle disease or Ranikhet disease.

Host Affected

Domestic chicken is the principal host. In addition to chickens, turkeys, pheasants, guinea fowl, ducks, geese, and pigeons, psittacine birds and wide range of captive and free ranging semi domestic and free-living birds including migratory waterfowl.
NDV has been reported in 241 species of birds.
Mortality is highly variable upto 100%.

Source of infection

Infected chickens, other domestic and wild birds may be sources of NDV.
The virus is shed in all secretions and excretions (faeces, nasal discharge and dust particle) for at least 4 weeks.
Infected birds shed virus in exhaled air, respiratory discharges, and faeces.
Some psittacine species may become persistently infected with velogenic virus and excrete it intermittently for more than 1 year without showing clinical signs.

Transmission

Chickens are readily infected by inhalation of aerosols.
Ingestion of contaminated water or food with faeces of infected birds.
Infection can also spread through inanimate objects, contaminated equipments or by movement of people, by non-avian species like flying insects.
Virus may also be disseminated by frozen chickens, uncooked kitchen waste, foodstuffs, bedding, manure and transport containers.

Pathogenesis

Following inhalation or ingestion of virus, the initial replication occurs in epithelium of respiratory and intestinal tract is followed by haematogenous spread to the spleen and bone marrow.
Secondary viremia results in infection of other organs including lungs, intestine and CNS.
The extent of viral spread within the body related to virulence of strain, which is determined by the amino acid sequence of fusion protein.

Clinical manifestation

*Clinical Signs of Newcastle Disease (Ranikhet Disease)*

Incubation period is usually 5 days.
Severity of infection depends on the virulence of the infecting virus, age and immune status of host. Based on tissue tropism and virulence of virus, the clinical signs are classified into following forms.

Viscerotropic velogenic (Doyle’s form or Asiatic form)

Very acute form with hemorrhagic lesions of the digestive tract.
Respiratory signs includes gasping, coughing, sneezing, and rales predominate in infections, swelling of head and neck, cyanosis of comb and wattle and greenish watery diarrhoea.
Birds survive the acute phase may develop neurological signs.

Neurotropic velogenic (Beach’s form)

Infection with neurotropic strain results in respiratory disease followed by nervous signs such as paralysis of wing, leg, torticollis and muscle spasm with high mortality.
Nervous signs with diarrhoea are typical in pigeons, and nervous signs are frequently seen in cormorants and exotic bird species also.
Poorly vaccinated birds may develop torticollis, ataxia, or body and head tremors 10–14 days after infection and may recover with supportive care.

Mesogenic (Beaudette’s form)

Acute respiratory and some times lethal nervous infections of young chicks
There is a loss of appetite, listlessness, abnormal thirst, huddling, weakness, and somnolence
G.I symptom includes crop dilatation, presence of foamy mucus and fibrinous exudates in the pharynx, a similar discharge also noticed from the beak, and yellow-green diarrhoea.
In layers, there is a sudden decrease in egg production together with depigmentation and/or loss of shell and reduction in the albumen quality of eggs.

Lentogenic (Hitchner’s form)

Causes mild or inapparent respiratory infections of chicks.

Necropsy Findings

Non-supurative encephalomyelitis in CNS.
Virulent velogenic strains cause predominantly hemorrhagic lesions, particularlly in trachea, oesophagus/proventriculus caecal tonsil, proventriculus-pin point haemorrhage at the tip of papillae and in the posterior half of the duodenum, the jejunum, and ileum.
In addition to this egg peritonitis, edematous, hemorrhagic or degenerated ovary is also seen.

Sample collection

Live birds: Cloacal swabs, droppings, oro-nasal swabs and paired sera sample.
Dead birds: Brain, bile, caecal tonsils, liver, spleen, lung, kidney and heart tissue or pooled organ samples.

Diagnosis

Based on clinical signs and lesions.
Isolation of virus in an allantoic route of inoculation of embryonated egg at 9-11 days of embryonation.
Demonstration of viral antigen on impression smears by IFT and other serological like HA and ELISA.
Demonstration of viral antigen by RT-PCR are highly valuable.
The haemagglutination inhibition test is used most widely used to diagnose antibodies against NDV. It is useful to assess the vaccinal immune status of the birds to be tested and on prevailing disease conditions.
The virulence of virus is confirmed by intracerebral pathogenicity index (ICPI) or intravenous pathogenicity index (IVPI) by intracerebral or intravenous injection of suspected sample in a day old SPF chicks.
The pathogenicity index <60 hrs- Velogenic, 60-90 hrs- Mesogenic and >90 hrs for lentogenic strain.
Nucleotide sequence analysis to detect genetic differences for comparison of isolates from different outbreaks and to identify the source of those infections.

Differential diagnosis

Prevention

Vaccination

Vaccines are available for chickens, turkeys, and pigeons and are used to induce an antibody response.
Unfortunately, ND vaccines do not provide sterile immunity.
There are three types of vaccine used for ND:
1. Live lentogenic- F strain and Lasota.
2. Live mesogenic – Komarov, Roakin, Mukhteswar, R₂B.
3. Inactivated vaccines.
Live lentogenic vaccines are usually derived from field viruses that have been shown to have low pathogenicity for poultry but produce an adequate immune response.
Healthy chicks are vaccinated with live vaccine F strain as early as day 1–4 of life through nares or conjuctival sac.
Live lentogenic vaccines, chiefly B1 and LaSota strains, are widely used and typically administered to poultry by mass application in drinking water or by spray. Mucosal immunity induced in birds by vaccination with live vaccines applied by these routes. These birds shed the low amount of vNDV, when infected with vNDV compared with the immune response induced by an inactivated vaccine. This type immunization is also called as priming.
Mass vaccination methods are less labor intensive but if not applied properly may lead to <85% of the flock being immunized, (For herd immunity greater than 85% of birds in a flock should be immunized).
Mesogenic strains are used only in areas, where ND is epidemic and in village chickens.
These vaccines are suitable only for secondary vaccination because of their high virulence.
Normally mesogenic vaccine, such as Komarov, Roakin, Mukhteswar and R2B are used as secondary vaccines after a primary vaccination with a lentogenic vaccine.
Inactivated vaccines are usually given after an initial priming vaccination with a live vaccine
Vaccine is usually administered through water, aerosol spray, eye or nasal drops, or by injection.
Oil-adjuvanted inactivated vaccines are also used after live vaccine in breeders and layers and may be used alone in situations where use of live virus may be contraindicated (eg, in pigeons).
The frequency of revaccination to protect chickens throughout life largely depends on the risk of exposure and virulence of the field virus challenge.
Fowlpox or turkey herpesvirus–vectored NDV vaccines are commercially available for chickens and have the advantage of being able to be administered in ovo at the hatchery.

Vaccination schedule for layer against Newcastle disease:

Broilers are vaccinated with Ranikhet disease F strain at 7, and 21 days

Control

Implementation of strict biosecurity measures.
National Level- Quarantine, slaughter and vaccination (Ring vaccination).
Farm level- Strict hygienic practices and medical measures.
Import restrictions on chickens and eggs.
Quarantine of psittacine birds in the same air space as non-immune chickens.