The role of vaccination in the eradication of virulent Newcastle disease in Australia particularly in relation to the egg industry

Australia claimed freedom from Newcastle disease (ND) in 2001 following the successful eradication of virulent ND from infected farms. The virulent virus was shown to have been derived from a series of mutational changes of the F protein cleavage site in endemic lentogenic virus, with a pronounced increase in virulence from the precursor virus. However, the detection of further precursor ND viruses in 2001 and outbreaks of virulent ND in NSW and in Victoria in 2002 again associated with mutated endemic viruses, prompted the formation of a ND National Management Group and a Steering Committee. Those committees developed a ND Management Plan. An integrated risk management approach was taken involving five operational projects. A control project involving biosecurity plans, strategic vaccination together with a national surveillance project to detect the presence of precursor and virulent ND virus (vNDV) were the major components of the Plan. Because of the potential for vNDV re-emergence, a vaccination strategy was developed that aimed to outcompete precursor viruses that have sequences close to that of the sequences of vNDV. The only live vaccine permitted is the lentogenic V4 strain. Vaccination uptake in states where vaccination is compulsory has been high although there has been some resistance amongst smaller layer farmers due to the cost of inactivated vaccine. The extent to which vaccination can prevent the spread of precursor virus seems paramount to the success of the program. Failure to communicate with the fringe sector of the industry on the need to vaccinate and to uphold high levels of biosecurity could allow precursor viruses to persist and prevent total eradication.