Newcastle disease
Newcastle disease infection by virulent strains of avian paramyxovirus type-1 (APMV-1) cause the highly contagious and notifiable Newcastle disease (ND). This page outlines a current perspective on ND and the viruses responsible.
Clinical signs
Clinical signs of Newcastle disease typically present 2 to 12 days post-exposure to avian paramyxovirus-1 virus (APMV-1). Depending on the severity of infection, the disease is categorized into the following three pathotypes:
Lentogenic: sub-clinical causing mild respiratory/enteric disease
Mesogenic: causes moderate respiratory symptoms, reduced egg production/quality and low-level mortality
Velogenic: causes lethal haemorrhagic lesions on the viscera with significant neurological impairment, respiratory distress and enteric disease
Laboratory confirmation
Virus characteristics
APMV-1s are enveloped, single-stranded, negative-sense, non-segmented RNA viruses. The genome is 15192 base pairs in length, encoding six structural genes, namely NP, P, M, F, HN, and L, as well as 2 accessory genes (W and V).
Diagnostic testing
Confirmatory diagnosis of ND requires the isolation and characterisation of the virus involved.
The diagnosis of APMV-1 can only be performed by national reference laboratories. Molecular testing is conducted on the L gene which is highly conserved among different strains of APMV. oropharyngeal and cloacal swabs or tissues.
The front-line detection method for APMV-1 is rRT-PCR, detecting Haemagglutination inhibition assays can be used on blood serum samples to analyse prior exposure or vaccination status by detecting the presence of anti-HN antibodies.
Notifiable disease criteria
Notifiable APMV-1 is specifically where virulent genetic signatures defined within the F gene cleavage site are detected, and/or a WOAH confirmatory intracerebral pathogenicity index (ICPI) score greater than 0.7 is determined (range 0–2.0).
Epidemiology
Discovery of Newcastle disease
The disease was first identified in 1927 in samples from Newcastle upon Tyne, England, from which it derived its name. Infected birds displayed respiratory and neurological symptoms, leading to reduced quality of life and diminished egg production with some isolates causing extensive mortality.
Global distribution and economic impact
After its initial discovery, NDV was subsequently found to have a global distribution. It continues to have substantial impacts, resulting in significant economic losses within the global poultry industry.
Reporting requirements
Today, the disease remains endemic in many third-world countries whilst outbreaks in first-world, resource rich countries can be difficult to control and have substantial economic impacts. ND is a notifiable disease therefore suspected cases must be immediately reported to the DEFRA Rural Services Helpline, on 03000200301.
Transmission
Susceptible species
Newcastle disease causes highly contagious respiratory and enteric disease in a wide range of birds including chickens, turkey and pigeons. Waterfowl, such as ducks, geese and other wild birds can be carriers of Newcastle disease, often displaying no signs of being sick. Mammalian cases have been reported in the past, including in humans.
Routes of transmission
Transmission occurs primarily through direct contact with bodily fluids of infected birds, especially their faeces. Although it has also been known to spread via fomites (contaminated objects) such as vehicles, equipment, clothing and feed.
Background (needs work)
Wild birds and disease spread
More information on Newcastle disease
Wild birds, particularly pigeons, play a key role in the transmission of APMV-1 viruses at a national level and the movement of wild birds is considered the primary risk factor for disease introduction.
Anseriformes (waterfowl) can also be infected but are generally asymptomatic and may therefore enable cross-continental spread. Galliformes (terrestrial fowl) vary significantly in their clinical response to APMV-1.
Farm-level risk factors
The intensive nature of poultry farming, the transportation of infected flocks between farms, inadequately vaccinated flocks, and inadequate decontamination of facilities before restocking are all additional factors that can increase the risk of disease spread and maintain viruses within farmed flocks.
Classification of paramyxoviruses
Classification system
The classification system has changed numerous times and is based on sequence data from the F-gene. Currently, APMV-1 isolates are divided into two classes (Class I and Class II).
Other avian paramyxovirus serotypes
ND is caused by APMV-1, there are 20 other serotypes known to infect and cause clinical disease in avian species.
APMV-2,3,6, and 7 are associated most with outbreaks of disease in commercial poultry operations.
Discovery of APMV-10
Recently, APMV-10 was isolated from rockhopper penguins (Eudyptes chrysocome) on the Falkland Islands. It was found that the viral hemagglutination activity from this isolate was not inhibited by antisera against any of the nine defined APMV serotypes.
Pigeon Paramyxovirus-1 (PPMV-1)
This was the first incidence of the APMV APMV-1 is endemic in Columbiformes (pigeons and doves) and is known as Pigeon Paramyxovirus-1 (PPMV-1). 10 serotype to be recorded.
Paramyxovirus structure
Morphology and taxonomy
APMV-1s are enveloped, single-stranded, negative sense, non-segmented RNA viruses. They are approximately 150nm in diameter. The viruses belong to the Orthoavulavirus genus, which falls under the subfamily Avulavirinae and family of Paramyxoviridae. The lipid membrane is host-derived and is impregnated with surface glycoprotein spikes.
Structural components
A matrix protein layer encapsulates and a single stranded, negative-sense RNA genome, which itself Image credit: Paramyxoviridae ~ ViralZone
Vaccination and control strategies
Biosecurity measures
These strategies are packaged into a helical ribonucleoprotein (RNP) core. Stringent biosecurity measures should be implemented in all large-scale poultry farming operations, to prevent the introduction and spread of disease.
This generally includes strict access controls, use of a validated disinfection protocol, good housekeeping practices, boot dips prior to entry to facilities and the donning of protective clothing.
The Department for Environment Food and Rural Affairs (Defra) provides detailed information for poultry farmers in the United Kingdom, for both small-scale farming (less than 50 poultry or other captive bird) and larger-scale operations (less than 50 poultry or other captive bird).
Vaccination
While there is no cure for Newcastle Disease, several vaccines are available for prophylaxis. In the 1950s, several vaccines were developed utilizing live or inactivated viruses derived from avirulent class II strains of genotype I or II, such as LaSota and Queensland V4. More recently, the I-2 Newcastle Disease vaccine was developed, offering a thermostable option, that is particularly useful for vaccination efforts in rural poultry farming across the world.
Vaccine effectiveness
Current vaccines primarily concentrate on mitigating the clinical symptoms associated with the disease. It is noteworthy that most commercially available vaccines aim to prevent approximately 90% of morbidity and mortality.
Ongoing challenges
By combining vaccination with robust biosecurity measures, the burden of the disease has been significantly reduced, contributing to the overall control and prevention of the disease. However, despite vaccination efforts and improved control measures, APMV-1 continues to pose challenges to the poultry industry. Outbreaks or occasionally occur, especially in regions with low vaccination coverage where new virulent strains emerge