A Comparison of the Different Vaccines Available for the Control of Newcastle Disease in Village Chickens

This paper briefly reviews the advantages and limitations of the different vaccines available for use against Newcastle disease in village chickens. Inactivated vaccines give very good immunity without vaccinal reactions and have been widely used, but are relatively expensive and require training to apply. Live vaccines are easy to apply and relatively inexpensive, and give moderately good immunity. Vaccinal reactions to them vary according to the vaccine strain. Among the live vaccines, the heat resistant vaccines have the significant advantage for village use of easy transportation, and they have also been widely used in villages. Recombinant vaccines have the advantage that they can be serologically detected independently of the wild virus. FIFTY years or more have passed since vaccine was first used to protect village poultry against Newcastle disease (ND) (Placidi and Santucci, 1952). During this time, a wide variety of types of vaccine has been developed. Many, but not all, have been tested on village poultry. It is the purpose of this paper to present a brief review of the different kinds of vaccine available. It is not the intention to recommend a particular vaccine, but rather to try to outline the relative advantages and limitations of each kind with particular reference to its use in the village situation. Examples will be given of the use of the different vaccines, but this does not pretend to be a comprehensive review of all the work in the field. The principle of vaccination against a viral disease is well known: to elicit an immunological response against the virus in such a way as not to cause the disease itself. The simplest way to do this is to take the virus, kill it, and then inject into the bird. This is an inactivated vaccine. Another approach is to select a naturally occurring virus that is not virulent enough to cause serious disease, and infect the birds with this virus. This is a live vaccine. This approach can be taken further by taking a non-virulent natural virus and selecting a clone from the virus population with desirable properties, such as lack of vaccinal reactions, or heat resistance. This is a cloned live vaccine. Finally, it is possible to specially genetically engineer a vaccine by, for example, taking part of the genetic material of the virus that codes for a surface antigen, and inserting this in another, different, virus to produce a recombinant vaccine. We will now look in more detail at how these different approaches to vaccination have been applied to ND. Inactivated Vaccines Inactivated vaccines are produced by growing a virulent virus in eggs, and then treating it with an inactivating agent, such as beta propiolactone. An adjuvant, such as an oil, is then usually added to make the virus more immunogenic. After inactivation, the vaccine is no longer capable of replication or spread. This means that it has to be individually injected into every bird to be vaccinated. It is normally injected into the back of the thigh muscle, using 0.3 or 0.5 mL per bird. This requires some training, and cannot be done by every keeper of chickens without prior demonstration. Inactivated vaccine produces very high levels of antibodies against ND virus (NDV), and provides a good level of protection against the virulent virus. In intensive poultry production, it is applied after an initial priming vaccination with a live vaccine. In village poultry, we have found that it gives good results in 1 Virologist and Consultant, B.P. 6268, Rabat-Instituts,