disease (ND), caused by avian paramyxovirus serotype 1 (APMV-1) viruses.
Newcastle disease (ND) remains a persistent threat to the poultry industry and
is a limiting disease for poultry producers worldwide. The clinical signs
reported in birds infected with NDV differ widely but mainly depend on
virulence of the virus. Other factors determine the outcome of the disease such
as the breed susceptibility, age, immune status, infection with other organisms
and ecological stress. The variety of clinical presentations and the emergence
and spread of new genetic variants make recognition and diagnosis challenging.
A thorough understanding of NDV pathology is important in order to recognize
the disease in the field and to formulate a list of differential diagnoses.
Laboratory testing is essential to confirm field suspicion, to characterize the
virus, and to comply with international reporting requirements. Control of
Newcastle disease is by prevention of introduction and spread, good biosecurity
practices and vaccination. Newcastle disease viruses may infect humans, usually
causing transient conjunctivitis, but human-to-human spread has never been
reported. A combination of live and inactivated ND vaccine, administered
simultaneously, is shown to provide better protection against virulent NDV and
has been successfully used in control programs in areas of intense poultry
production. Locally replicating vaccine strains offer an attractive approach
for immune interventions by providing an effective and durable immunity.
However, continued improvements of ND control will require a better
understanding of immunological mechanisms that are triggered by an immunization
regimen and its effect on virus transmission. A major function of the humoral
immunity is the protection against clinical signs caused by infection with
virulent NDV strains, whereas expansion in the numbers of various leukocyte
subsets at the site of vaccination could be responsible for uptake, processing
of virus antigen and production of antibodies and antiviral cytokines. Mucosal
vaccination would be more attractive, as it induces in addition to systemic
immunity a local IgM, IgA, and IgG, response as well as a mucosal cellular
immune response. These local responses contribute to protection against NDV
infection of the respiratory tract mucosa, which is the first target tissue of
infection with this virus.