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The Paracox vaccines

Research at the Institute for Animal Health (IAH, an institute of BBSRC) led to the development of the 2 ‘Paracox’ vaccines now sold worldwide by Intervet/Schering-Plough Animal Health Ltd. These vaccines protect chickens against the economically important disease, coccidiosis. Around 1Bn doses of the vaccine are sold annually worldwide.

Larger version

Three Eimeria maxima oocysts (click for enlarged version)

Coccidiosis is a disease of the intestine of poultry/chickens caused by protozoan coccidial parasites belonging to the genus Eimeria. Seven species infect different parts of the intestine and typically cause bleeding and swelling of the gut and, with some species of Eimeria, a high mortality rate. Toxoplasmosis, a disease that can affect humans, is caused by another type of coccidial parasite.

For several decades, the poultry industry worldwide relied almost exclusively on drugs given in feed to control coccidial infections. Initially the use of drugs was very effective but managing drug-resistance became a problem and control of coccidiosis in breeding and laying birds was hard to achieve.

Around 25 years ago, scientists led by Martin Shirley at IAH initiated work to develop an alternative control strategy based on a safe vaccine. Their approach built on work in the USA by Dr Thomas Jeffers, who found that parasite eggs repeatedly produced early after infection produced lower numbers of progeny, did not cause disease but did induce protective immunity.

By 1989, IAH scientists had developed the first live attenuated vaccine, Paracox-8, which was effective against all 7 Eimeria species and major variants that affect chickens.

Around 50Bn meat birds are produced each year

Manufactured in the UK, the vaccine is now regularly exported to more than 30 countries and in the EU protects virtually all the highly valuable chickens kept for breeding purposes. In 2000, Paracox-5 was launched to control coccidiosis in birds kept for their meat.

The huge scale of poultry production demands that drugs are still used to control coccidial infections in most meat birds but effective control of the parasites using drugs is now a challenge and the global costs of coccidiosis are estimated to be hundreds of millions of pounds. The EU is to consider a ban on drug use in EU poultry feed in the future.

An effective vaccination strategy is vital to the long term future of the poultry industry and in 2002 an IAH-led consortium generated a genome sequence for Eimeria tenella to help provide the leads for the next generation of vaccines.

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