Introduction
Definition and Etiology:
Newcastle disease (NCD) is one of the most contagious and devastating viral diseases of poultry. It is caused by a paramyxovirus, classified under the Paramyxoviridae family, along with Morbillivirus and Pneumovirus.
Based on antigenic relatedness in haemagglutination inhibition (HI) tests, Paramyxovirus type 1 (PMV-1) is divided into nine serotypes (PMV-1 to PMV-9). Based on the intracerebral pathogenicity index (ICPI), three pathotypes of NCD virus have been identified: velogenic (highly pathogenic), mesogenic (moderately pathogenic), and lentogenic (low pathogenicity).
Nine serogroups of avian paramyxoviruses have been recognized: APMV-1 to APMV-9. Among these, Avian paramyxovirus-1 (APMV-1), also known as Newcastle Disease Virus (NDV), remains the most significant pathogen for poultry.
The genome of NDV contains six open reading frames (ORFs) which encode the following proteins: Nucleoprotein (NP), Phosphoprotein (P), Matrix protein (M), Fusion protein (F), Hemagglutinin-neuraminidase (HN), and Large polymerase protein (L).
Transmission of NCD
NDV is transmitted through aerosols, fecal matter, and other excretions from infected birds. It can also be spread by:
– Introduction of infected birds
– Sale and transfer of sick birds
– Vertical transmission from egg to chick
– Contaminated feed, water, equipment, and human handlers
The spread is often associated with the movement of birds through markets and by traders. Both direct contact with infected birds and indirect contact with contaminated fomites can result in transmission.
Clinical Signs and Pathogenesis
Neurotropic Velogenic NDV:
– Acute respiratory and neurological symptoms
– Coughing, depression, and reduced egg production
– Nervous signs (tremors, paralysis) within a few days
– Mortality: 10–20% in adults; higher in young birds
3. Mesogenic NDV:
– Mild respiratory signs (coughing, sneezing)
– Depression and weight loss
– Reduced egg production for up to 3 weeks
– Nervous signs may occur later
– Mortality around 10%
4. Lentogenic NDV:
– Often subclinical
– Mild respiratory signs and slight drop in egg production in incompletely vaccinated flocks
– No nervous signs; negligible mortality
Diagnosis
Though clinical signs and lesions may suggest NCD, laboratory confirmation is essential. Diagnostic tests include:
– Haemagglutination (HA) and haemagglutination inhibition (HI) tests
– Agar gel immunodiffusion
– Enzyme-linked immunosorbent assay (ELISA)
– Virus isolation and RT-PCR
Prevention and Control of NCD
2. Supportive Therapy:
– Vitamins and supplements such as Ashivita: 25–50 g for 100 birds via drinking water (solution should be consumed within 24 hours)
– Provide clean water, quality feed, optimal temperature, and good ventilation
3. General Control Measures:
– Hygiene: cleaning, disinfection, biosecurity, limiting access to wild birds, personal hygiene for farm workers
– Vaccination: The most effective method to control NCD
– Live and inactivated (dead) vaccines available
– Live vaccines require a cold chain and are sensitive to maternal antibodies
– Vaccination should be followed up with booster doses and monitoring
Conclusion and Recommendations
Newcastle Disease remains a significant economic burden in both village and commercial poultry systems. Velogenic strains are responsible for the highest losses. Improved poultry production through better breeds must be coupled with effective vaccination and biosecurity measures.
Recommendations:
❖ Routine vaccination of poultry flocks should be implemented.
❖ Investigate the role of other avian species in maintaining NCD through serological surveys.
❖ Strengthen control measures, especially in backyard and village poultry systems.
❖ Improve awareness, training, and access to affordable vaccines for smallholder farmers.
Prepared by
Adane Seifu (DVM, MSc in Veterinary Epidemiology)