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A Different Perspective Of Newcastle Disease

by 5m Editor
6 June 2007, at 11:50am

EU - This is an Opinion of the Scientific Panel on Animal Health and Animal Welfare regarding a request from the European Commission to review Newcastle disease focusing on vaccination worldwide in order to determine its optimal use for disease control purposes.

In view of a revision of the Community rules on the control of Newcastle disease (ND), laid down in Council Directive 92/66/EEC, a disease of major importance for poultry and other birds, the Commission requested EFSA to provide a complete and update review on this disease, concerning the definition, the role of pigeons and other avian species in the spread of ND and the vaccines used. A risk assessment approach was not requested however, in order to evaluate the present vaccination control strategies, an evaluation of the available data was required.

The working group agreed that the scope of the report should consider the present scientific knowledge and analyse the available epidemiological data from Animal Disease Notification System ADSN system (DG SANCO), HANDISTATUS II data base (OIE) and data from the EU Reference Laboratory (Veterinary Laboratory Agency, VLA, Weybridge) taking into consideration the above mentioned mandate. The evaluation of vaccines and vacc

ination programmes was carried out in close cooperation with EMEA, who delegated two representatives to the working group. EFSA's scientific Panel on Animal Health and Welfare reviewed ND according to the mandate and drew the following major conclusions and recommendations:

In the current EU Directive (92/66/EEC), Newcastle disease is defined as an infection of poultry caused by a virus of avian paramyxovirus type 1 (APMV-1) which has an intracerebral pathogenicity index (ICPI) in day-old chicks (Gallus gallus) of 0.7 or greater. The Panel has no scientific evidence to recommend a change on the definition of ND to include viruses with an ICPI below 0.7. ND should be defined as an infection of poultry and other captive birds with an APMV-1 meeting the criteria as described by the SCAHAW in 1998, allowing the sequencing of the cleavage site of the F gene as a supplement to the ICPI. The use of ICPI tests, for welfare reasons amongst others, should be restricted to situations where there is failure to demonstrate the presence of multiple basic amino acids at the C-terminus of the F2 protein and F (phenylalanine) at residue 117 of the F1 protein. It is recommended that for the purpose of a revised Directive for the control of ND the same definitions for poultry and captive birds as provided in the Directive 2005/94 for the control of AI is used. In addition the future Directive for ND should give a definition of racing pigeons.

Biosecurity measures constitute the most important barrier in preventing the introduction, transmission and spread of ND. Prevention of secondary cases can be achieved through bio-containment. The major risk of ND spread from the index case is the movement of live poultry and birds and all activities linked to mechanical transfer of the virus by human beings, vehicles, crates and cages and any type of farm equipment.

In addition to biosecurity measures, vaccination can be a valuable tool to control disease, however sub-optimal use may result in the infection becoming endemic. Optimal vaccination programs are expected to prevent or reduce transmission and spread. However, it will require some time before optimal flock immunity is attained after vaccination. Currently both inactivated and live virus vaccines are available and have been fully authorised. There are no authorised vaccines for minor species. The present vaccines do not permit a differentiation between the serological response to vaccine and field virus in the surveillance of ND. Therefore the development of DIVA (Differentiating infected from Vaccinated animals) vaccines and the accompanied DIVA diagnostics kits should be further encouraged. However given the fact that current authorised vaccines are very effective and inexpensive to produce, incentives (EU, national) should be provided to promote research and facilitate authorisation of DIVA vaccines and DIVA diagnostic kits.

Pigeons are considered as a reservoir for a specific APMV-1, termed pigeon type paramyxovirus (PPMV-1), which is a virulent Newcastle disease virus (NDV) but requires different control measures as defined in 92/66/EEC. Racing pigeons and game bird populations have close contact with feral and wild birds and are therefore at a higher risk than birds kept indoors of becoming infected.

Virus shedding without obvious clinical signs after recovery is possible. Particularly prolonged virus shedding without disease has been demonstrated in waterfowl and parrots. The majority of APMV-1 isolates from wild waterfowl are low virulent pathotypes. Studies are being carried out to determine whether low virulent APMV-1 strains of wild birds may eventually, once introduced into commercial poultry, evolve into virulent forms.

Clinical diagnosis must be confirmed by the laboratory. Molecular tests and virus isolation should be performed in parallel whenever possible, even if molecular tests give an indication of the virulence of the virus. For the index case it is essential that positive molecular tests are confirmed by virus isolation, which may be postponed but never abandoned. All methods involved in the genetic characterisation should be standardised or at least harmonised within EU, and laboratories accredited in order to assure comparability and reliability of results.

The Panel concluded from the analysis of the available data that neither OIE nor EU data were sufficient to make scientific conclusions about the effect of vaccination since the aim of the collection of these data is beyond the scope of determining the efficacy of the preventive measures.

Surveillance systems for wild birds and commercial poultry, as well as the early warning systems based on clinical signs in poultry that have been developed for Avian Influenza (AI), could be used to evaluate the status of APMV-1 infection in poultry (according to Council Directive 2005/94/EC) and also to study the incidence of APMV-1 viruses in wild birds and other forms of poultry. A similar serological monitoring system as implemented for AI is of limited value for ND surveillance in vaccinating countries because the current tests cannot discriminate between infected and vaccinated flocks (DIVA). Even when DIVA serology to screen vaccinated flocks for infection is used, the virus has to be isolated and discrimination has to be made between virulent and non-virulent isolates including vaccine viruses.

In order to obtain more insight into the prevalence of APMV-1, long term studies would enable a more detailed analysis of virus evolution. The Panel strongly recommends the development of a centralized data collection and management system for ND, which should be harmonised in the EU and made available for research purposes. These long terms studies would allow predicting: a) an increase of the infection pressure; and b) the emergence of new virulent strains, which may constitute a possible threat to poultry and would help determine when a vaccination strategy could be applied.

To view the full report, click here.

5m Editor