Synonyms
Ranikhet disease, Avian pneumoencephalitis, fowl pest, Avian pest distemper.
Aetiology
The disease is caused by a Newcastle disease virus called paramyxovirus. There are several strains of Newcastle disease virus but all these strains are immunologically and serologically similar but differ in pathogenicity. Due to its varying pathogenicity, Newcastle disease virus are grouped into 3: Lentogenic strain, mesogenic strain and velogenic strain.
Lentogenic strains are mild and at times, avirulent while mesogenic strains are intermediate and velogenic strains are very virulent. Examples of lentogenic strains include Hitchner B1, lasota, V4 and F stains etc. Examples of mesogenic strain include komarov, Roakin and H strain etc. Examples of velogenic strains are GB texas, Milano, hertz and kudu strain etc.
Newcastle disease virus agglutinate amphibians, reptiles and avians red blood cells.
Host
It is reported virtually in all diseases of poultry. All ages are susceptible but younger birds are more severely. It may cause conjunctivitis in man.
Transmission
It is transmitted by inhalation of droplets from respiratory tract containing the virus and inhalation of dry faecal substance from digestive tract.
It is also transmitted by ingestion of faeces and faecal substance
Feral birds, other animals, humans, poultry products, fowl equipment and contaminated poultry feed also result in spread of disease.
Clinical signs
The symptoms of Newcastle diseases depend on ages and species of the affected birds, the immune status, presence of concurrent disease and the strain of the infecting virus. The highly virulent and pathogenic virus called the velogenic strain may produce peracute infections where the first indication of the disease is death.
Typically the disease signs such as depression, prostration, greenish diarrhea and edema of the head are observed. Mortality is 100% and nervous signs may occur. There may be total cessation of egg production following thin shell.
The moderately virulent or mesogenic strain usually cause severe respiratory disease followed by nervous signs. Mortality is 50% or more. The respiratory signs include severe dyspnea, coughing, gasping, nasal discharge and presence of stringy saliva from the beak. Nervous signs include paralysis of leg and wing, opisthotonus, ataxia and trembling. In laying birds, there is reduced hatchability and laying of soft shelled eggs. The virus of low virulence or lentogenic strain may cause no disease or mild respiratory distress and mild reduction in egg production in chicken and turkey. However, presence of other disease may result in more severe cases.
Post-mortem lesions
There is no pathognomonic lesion associated with Newcastle disease. Some lesions observed include haemorrhage and necrosis of proventriculus, caeca and small intestine.
There may be also haemorrhage and congestion of the trachea.
Airsacculitis is present.
Diagnosis
Newcastle disease should be suspected when there is respiratory sign, greenish diarrhea, paralysis or heavy mortality is seen in unvaccinated flock. For diagnosis of Newcastle disease to be made at present, the only certain method of diagnosis which also allow characterization of the infecting strain is virus isolation and recognition.
Isolation and recognition of Newcastle disease virus
Sample from live animal include tracheal and cloacal swabs and in dead bird tissue include intestine and trachea.
Samples are placed in phosphate buffer saline containing antibiotic then inoculated into 8-10 days embryonated hen’s egg and held at 37°c until death or dying for 5-7 days. Haemagglutination activity in bacteria free allantoic fluid may be due to any of the avain paramyxovirus or othormyxovirus. Newcastle disease virus is confirmed by haemagglutination inhibition test using specific Newcastle disease antiserum.
Characterization
There are 3 main pathogenicity tests used to characterize Newcastle disease virus:
Mean death time in egg
Intracerebral pathogenicity index in chicks
Intravenous pathogenicity index in chicks.
Control
There are two main control methods of Newcastle disease:
Hygiene and sanitary precaution and good management practice.
Vaccination, both live and inactivated vaccine are recommended.
3 vaccines available for control are produced in Nigerian veterinary research institute(NVRI) vom and are administered as follows:
Age of chicken Type of vaccine Route of Administration
0-1 week NDV- I/O(B1 STRAIN) Intraocular
3-4 weeks NDV- Lasota(lasota strain) drinking water/intraocular
6-8 weeks NDV-Komarov(komarov strain) Intramuscular
Every 6 months thereafter NDV-Komarov Intramuscular