Newcastle disease (ND) is one of the most economically and clinically important poultry diseases. According to the World Bank , it is ranked as the 3rd most costly poultry disease, after avian influenza (high and low pathogenic) and after infectious bronchitis.
Despite many years of enforcement of international and national trading regulations, introduction of the biosecurity concept, harmonization and spreading of laboratory diagnostic and monitoring techniques, implementation of vaccination programs, ND is still listed among the most damaging poultry diseases considering both clinical and economical consequences.
Some regions or countries like Western Europe, the USA, Brazil, etc. have successfully reduced and even phased out the incidence of the disease, so that ND is nowadays considered only an epizootic risk. The vaccination programs, if applied, are always of the “light” type (hereafter called “low challenge areas”).
On the contrary, many countries from Latin America, Eastern Europe, Africa, the Middle East and Asia are still cohabiting with the enzootic form of the disease with continuous waves of unavoidable pressure regularly plaguing them. In these countries, vaccination is considered as a routine obligation guided by modest ambitions that are simply restricted to ensuring clinical and economical protection in case of challenge (hereafter called “high challenge areas”).
Wild birds populations of backyard poultry, small scale farming operations and traditional live bird markets ensure the spreading of the ND virus and are important factors explaining from where the disease comes from and how it circulates throughout the world.
But ND is also seen, even today, in poultry producing operations that are much better organized, following stringent biosecurity rules and often applying an intensive vaccination program. In fact, this has been a frustrating paradox that has really drawn the attention of veterinarians and production managers until the concept of flock monitoring and flock profiling have become popular.
As a consequence, NDV antibody testing conducted on samples taken from broilers at the end of the growing period or during the production phase in layers, has revealed the frequent presence of low antibody positive, or even fully antibody negative flocks in spite of (sometimes) very intensive vaccination programs including one or more inactivated and several live attenuated ND vaccines.