Newcastle Disease

Newcastle disease (ND) is a highly contagious viral disease affecting wild and domestic avian species. It is a worldwide problem that presents primarily as a respiratory disease, but depression, nervous manifestations, or diarrhea may be the predominant clinical form. Mortality is variable. Occurrence of a virulent form of the disease is reportable and may result in trade restrictions. Also known as Exotic Newcastle Disease, Pseudo-Fowl Pest, Pseudo-Poultry Plague, Avian Pest, Avian Distemper, Newcastle Disease, Korean Fowl Plague or Avian Pneumoencephalitis, it has became a major menace to the world's poultry industry. It represents a serious economic challenge to all segments of the poultry. Various other poultry and birds as well as mammals including human, also may contract the disease. RD has been recognized in man as almost entirely a localized eye infection, pulmonary and generalized infections have been reported.

ETIOLOGY ( Family: Paramyxoviridae, Genus: Avulavirus)

There are 9 serotypes APMV-1 to APMV-9.Newcastle disease is caused by APMV-1.The virus is filterable , which belongs to micro group having a molecular weight 450 million .The virus is multi-shaped, tailed, sperm like and filamentous form. The virus consisted of 67 per cent protein, 27 percent lipids and a small amount of nucleic acid mainly deoxypentose. The virus possesses haem agglutination activity (HA) for chicken erythrocytes resembling that of Influenza virus. The virus is inactivated by acidic pH and is also ether sensitive.It is also inactivated by formalin and phenol. The virus survives for long periods at ambient temperature, especially in faeces.

There are further four pathotypes:

1. Asymptomatic enteric – Subclinical.

2. Lentogenic

Subclinical to mild respiratory.
In chickens, lentogenic strains usually cause sub clinical infections or mild respiratory.

3. Mesogenic

Respiratory or neurological.
Strains can cause acute respiratory disease and neurologic signs in some chickens, but the mortality rate is usually low.

4. Velogenic

Very virulent.

i. Neurotropic: Respiratory or neurological.

ii. Vicerotropic: Hemorrhagic intestinal lesions.

Virulent Newcastle Disease (vND) includes:

Mesogenic.
Velogenic neurotropic.
Velogenic viscerotropic.

HISTORY:

The disease was first recognized in the middle 1920's. Doyle named the disease after the locality and demonstrated that it was distinct from the dreaded fowl plague or fowl pest. The disease was diagnosed at first in England during 1926 at New castle, hence known as New castle disease. In 1928, the disease was found in Ranikheth near Mukteshwar in Uttar Pradesh in India by Dr. Edward so commonly known as Ranikheth disease. Four panzootics have occured from 1926 to 1981.

SUSCEPTIBILITY :

Chicks are highly susceptible , adults are comparatively less. Turkeys, pigeons, ducks are also susceptible.Birds of all ages are susceptible. Host ranges from chicken, turkeys, guinea fowls, ducks, doves, geese, pigeons, pheasants, crows, sparrows and other free flying birds.

TRANSMISSION:

New Castle disease virus transmitted by inhalation or Ingestion (fecal/oral route).Transmission is via aerosols, birds, fomites, visitors and imported psittacines (often asymptomatic). Chickens are readily infected by aerosols and by ingesting contaminated water or food.It is not usually vertical (but chicks may become infected in hatcheries from contaminated shells). Virus may also be present in eggs laid during clinical disease and in all parts of the carcass during acute virulent infections. Infected birds shed virus in exhaled air, respiratory discharges, and feces. Virus is shed during incubation, during the clinical stage, and for a varying but limited period during convalescence. Infected chickens are the primary source of virus, but other domestic and wild birds may be sources of NDV. Transfer of virus, especially in infective feces, by the movement of people and contaminated equipment is the main method of spread between poultry flocks.

Transmission Routes enumerated are as follows:

(1) Inhalation (Air Borne).

(2) Ingestion (Contaminated feed and water).

(3) Movement of Live Birds and other Animals.

(4) Movement of People and Equipment.

(5) Contaminated Vaccines.

(6) Movement of Poultry Products.

ZOONOTIC IMPORTANCE:

Newcastle disease viruses, whether virulent field viruses or live vaccine, can produce a transitory conjunctivitis in humans. Virus shed in ocular secretions for 4-7 days. For this period contact should be avoided with avian species. Lab workers and vaccination crews are at most risk. No cases from handling or consuming poultry products reported.No human-to-human spread reported.

EPIDEMIOLOGY:

The epidemiology of virus is incompletely understood; however, wild birds, particularly waterfowl, may' be the reservoir hosts for lentogenic viruses.These viruses could become more virulent after becoming established in poultry. Some recent outbreaks were apparently caused by velogenic viruses that had emerged from local, low pathogenic isolates.Virulent NDV strains are endemic in poultry in most of Asia, Africa, and some countries of North, Central, and South America. Other countries, including the USA and Canada, are free of those strains and maintain that status with import restrictions and eradication by destroying diseased poultry. Vaccination makes the assessment of true geographical distribution difficult. However international monitoring is done by the FAO and OIE.

PATHOGEGESIS & CLINICAL SIGNS:

Onset is rapid, and signs appear throughout the flock within 2-12 days (average 5) after aerosol exposure. Spread is slower if the fecal-oral route is the primary means of transmission, particularly for caged birds. Observed signs depend on whether the infecting virus has a predilection for respiratory, digestive, or nervous systems. Respiratory signs of gasping, coughing, sneezing, and rales predominate in low virulence infections. Nervous signs of tremors, paralyzed wings and legs, twisted necks, circling, clonic spasms, and complete paralysis may accompany, but usually follow, the respiratory signs in neurotropic velogenic disease. Nervous signs with diarrhea are typical in pigeons, and nervous signs are frequently seen in cormorants and exotic bird species. Respiratory signs with depression, watery-greenish diarrhea, and swelling of the tissues of the head and neck are typical of the most virulent form of the disease, viscerotropic velogenic Newcastle disease (VVND, also called exotic Newcastle disease), although nervous signs may also be seen. Varying degrees of depression and inappetence are observed. A partial or complete cessation of egg production may occur. Eggs may be abnormal in color, shape, or surface, and have watery albumen. Mortality is variable but can be as high as 100%.

SIGNS AMONG BABY CHICKS AND GROWlNG CHICKENS:

Gasping, coughing, aphonia, depression, partial or complete inappetance, increased thirst are the common fmdings of respiratory system. Nervous signs including partial or complete paralysis of extremities, muscular tremor and rhythmic, clonic spasms.Peculiar attitudes including "Torticollis", opisthotonus, emprosthotonus and lateral deviation of head, partial or complete paralysis of one or two legs was the only sign observed in several outbreaks of RD.

SIGNS IN LAYING FLOCK:

The disease usually appears suddenly and spreads quickly through susceptible flocks, drop in egg production, laying of soft or imperfectly shelled, profuse fluid diarrhea, rapid dehydration of body, also effects like Absence of air cells, watery albumen and a rough discolored and chalky shells egg quality. A high per cent of hens lay abnormal eggs upto 45 days after infection.

POST-MORTEM CHANGES:

Lesions vary with species and virulence.The main changes seen at post mortem are as follows:

Edema of the head and neck region,
Emaciation and dehydration,
Ulcers in intestine and lymphoid tissues,
Liquification of ovas,
Congestion in trachea,
Spleenomegaly and Presence of Egg Yolk in the abdominal Cavity.
Hemorrhages in proventriculus, caecal tonsils, brain, liver, lungs, kidneys, mesentry, bursa.
Edema of the interstitial or peritracheal tissue of the neck, especially near the thoracic inlet.

DIAGNOSIS:

Diagnosis can be made on the basis history, vaccination, age, sudden death, symptoms and lesions. Diagnosis can be made on

(1) Symptoms and Lesions.

(2) Laboratory Diagnosis.

A presumptive diagnosis may be made on signs, post-mortem lesions, rising titre in serology. Diagnosis may be confirmed by isolation of a hemagglutinating virus identified by inhibition with Newcastle disease antiserum. A rise in hemagglutination-inhibition antibodies in paired serum samples also confirms the disease.

For the Identification of the agent:

Inoculation of 9-11-day-old embryonated chicken eggs followed by:
examination of haemagglutination activity.
inhibition of haemagglutination by ND virus-specific antiserum.

Samples used are tracheal and cloacal swabs (or faeces) from live birds or from pools of organs and faeces from dead birds.

For Pathogenicity assessment:

Plaque test in chicken embryo fibroblast cultures.
Mean death time of embryonated chicken eggs.
Intracerebral pathogenicity index in 1-day-old chickens.
Intravenous pathogenicity index (IVPI) in 6-week-old chickens.

For Serological tests:

Haemagglutination inhibition test.
ELISA.

Samples taken include clotted blood samples or serum.

DIFFERENTIAL DIAGNOSIS:

Highly pathogenic avian influenza: Infectivity of the virus is very high i.e. 1 : 10000, subcutaneous hemorrhages on shank, Buldging of head, Cyanosis of Comb and wattle, 100 per cent mortality.
Fowl cholera: The causative organism is Pasturella avisepticabipolar organism, Infra-orbital/facial swelling-unilateral occurs.
Infectious Laryngotracheitis: Haemagglutination test is negative.
Infectious Coryza
Fowl pox(diphtheritic form)
Psittacosis or Pacheco’s disease
Infectious bronchitis
Spirochetosis - The causative agent is Borrlia ansrina.
Fowl typhoid : Causative organism is salmonella gallinarum. There are digestive disturbances.
Management problems

Water or feed deprivation.
Poor ventilation.

ECONOMIC IMPORTANCE:

Its global economic impact is enormous. It is more costlier than any other animal virus. In developed countries, where the more virulent forms of the virus have been eradicated, trade embargoes and restrictions cause significant economic losses during outbreaks. Continued control measures followed are also very expensive. Also repeated testing for trade purposes is required which makes it much more expensive. Economic Impact on developing countries is more. It effects quality and quantity of dietary protein and also has a significant effect on human health. Outbreaks of virulent Newcastle disease have a tremendous impact on backyard chickens in developing countries, where these birds are a significant source of protein and the disease is endemic.Low pathogenicity isolates, which are common in poultry worldwide, can decrease productivity but have no impact on international trade. Chickens are particularly susceptible, and may experience morbidity and mortality, rates upto 100 per cent.

TREATMENT

At present there is no effective treatment of any value. Proper housing and general good care are indicated in an effort to shorten the duration and severity of the infection.

PREVENTION & CONTROL

For prevention following steps are important

1) Strict Biosecurity Practises.

2) Vaccination.

An early recognition of the disease and application of strict sanitary measures are of great value in the control of the disease.

Sanitary prophylaxis

Strict isolation of outbreaks
Destruction of all infected and exposed birds
Thorough cleaning and disinfection of premises
Proper carcass disposal
Pest control in flocks
Depopulation followed by 21 days before restocking
Avoidance of contact with birds of unknown health status
Control of human traffic.
One age group per farm (‘all in-all out’) breeding is recommended

Medical prophylaxis

Vaccination with live and/or oil emulsion vaccines can markedly reduce the losses in poultry flocks
Live B1 and La Sota strains are administrated in drinking water or as a coarse spray. Sometimes administered intranasally or intraocularly. Healthy chickens may be vaccinated as early as day 1-4 of life, but delaying vaccination until the second or third week increases its efficiency
Some other infections (e.g. Mycoplasma) may aggravate the vaccine reaction. Killed virus vaccine should then be used.

CONTROL

Control of Ranikhet diseases can be effective with judicious application of sanitary and vaccination measures.

Vaccination: Two types of vaccines are available in India, one for the adult birds an another for younger birds or body chicks. The virus strain for Raniketh disease vaccine used for adult birds age over weeks was evolved at the Indian veterinary Research Institute. The vaccine consists of freeze - dried virus grown in chick embryos. Vaccination of birds 6 weeks old and above confers immunity for 1 to 3 years. Care should be taken to vaccinate bird’s not carrying heavy coccidian infection. Birds with heavy worm infection or coccidiosis are not protected even with a good vaccine.

Deworming: Birds should be dewormed starting from one week prior to R2B/RDVK vaccination and repeated at 3-week intervals so as to give a total of 4 deworming shots before housing at 18 weeks of age. Piperazine compounds, albendazole, mebendazole etc. can be used against round worms. Against tape worms, Niclosamide, Praziquintel, Albendazole can be used.While medicating through drinking water, it should be done by mixing the required quantity of medicine in the quantity of water that chicks normally consume in 4 hours time (say approximately 6 litres per one hundred, 6 week-old chicks, per day). Additional water should be given only when all the medicated water is consumed by the chicks.

Ectoparasites: The birds should be dusted or dipped and houses fumigated as soon as there is indication of ectoparasites. The following may be used for dusting and dipping. Dipping should be avoided on rainy days. Head dipping has to be avoided. Tick tox, synthetic pyrithrine compound.(Dose – as per manufacturer’s instructions) or Butox Deltamethrin compound.(Dose – as per manufacturer’s instructions) can be used.