Thermotolerant Newcastle disease vaccines for use in flocks of family chickens.

Family chickens provide nutrition and income for poor families in rural areas in developing countries. Newcastle disease is a major constraint limiting the productivity of these flocks. Imported commercial Newcastle disease vaccines, requiring foreign exchange and coming in large dose containers, have been little used in small village flocks. The major problem with these vaccines has been their heat lability. Appropriate vaccines for village use would be locally produced, cheap and to some extent heat tolerant, allowing some independence from the cold chain. Two vaccines derived from naturally thermotolerant Australian strains of Newcastle disease virus have been artificially selected for enhanced heat resistance. One vaccine, V4, is now produced by commercial companies and is used mainly in commercial chickens. Master seed for the other vaccine, 1-2, is held at the University of Queensland, Brisbane, Australia and is made available without cost to laboratories in developing countries. Vaccines based on variants of strain V4 have been available for more than 30 years. Challenge experiments in many countries have indicated that V4 vaccine is protective against a variety of challenge strains. Many of the early studies were part of the search for a village vaccine. The commercialization of V4 vaccine meant that countries wishing to use it in family flocks needed to purchase vaccine or produce and verify their own master seed. Of special interest is the efficacy of V4 vaccine when administered to chickens on suitable feeds. The V4 virus will spread from vaccinated chickens to contact chickens. 1-2 is a Newcastle disease virus similar to V4. Being in the public domain, 1-2 master seed is available for local production of thermotolerant vaccines for use in the national flocks of family chickens. Many countries have undertaken laboratory trials and demonstrated effective protection on vaccination by various means including vaccination with carrier feeds. Some countries progressed to field trials and to campaigns to control Newcastle disease in the village setting. Local production and distribution of an appropriate vaccine has been only part of the process. Innovative extension materials have been developed, contributors to all phases of the project have been trained (vaccinators, laboratory workers and administrators) and lines of communication between all parties have been established.