Newcastle disease is caused by avian paramyxovirus serotype type 1 (APMV-1), also called Newcastle disease viruses (NDV), of the genus Avulavirus belonging to the family Paramyxoviridae. APMV-1 strains are classified into five pathotypes based on their virulence in chickens, designated: a) viscerotropic velogenic, b) neurotropic velogenic, c) mesogenic, d) lentogenic or respiratory and e) asymptomatic. Lentogenic strains are the least virulent, mesogenic strains are moderately virulent and velogenic strains are the most virulent.
Velogenic NDV is endemic in areas of Mexico, Asia, the Middle East, Africa, Central and South America, and in wild birds of North America. Lentogenic isolates are found in poultry throughout the world.
Outbreaks of velogenic ND have a tremendous impact on backyard chickens in developing countries where these birds are a significant source of protein. Morbidity and mortality rates can be up to 100% in unvaccinated chickens. The total yearly cost of the disease is estimated to be US $2 billion.
NDV can be transmitted by inhalation or ingestion (faecal/oral route). Birds shed virus in faeces and respiratory secretions. APMV-1 is readily transmitted on fomites. Virus survival is prolonged by the presence of faeces, for example on eggshells.
The incubation period in poultry varies from two to 15 days. Lentogenic strains usually cause subclinical infections or mild respiratory disease. Mesogenic strains can cause acute respiratory disease and neurologic signs in some chickens but the mortality rate is low. Velogenic strains cause clinical signs, which vary from sudden death to lethargy, conjunctival reddening and swelling of the head, watery greenish diarrhea and respiratory signs. They also cause neurologic signs such as tremors, paralysis and torticollis (twisted neck).
Outbreaks in large flocks are eradicated with quarantine, depopulation of all infected and exposed birds, and thorough cleaning and disinfection of the aviaries. Live, inactivated, and recombinant Newcastle disease vaccines are available commercially; although they do not provide sterile immunity.
For further information, view our Newcastle Disease product development work.