Poultry coccidiosis vaccine on horizon.

Poultry farmers and chicken lovers take heart. Scientists are one step closer to developing a vaccine against coccidiosis, a parasitic disease that costs the U.S. poultry industry $300 million a year. The disease also causes chickens to have a skin color paler than they yellow color desired by consumers.

With monoclonal antibodies produced by the ARS, Russell McCandliss and his colleagues at Genex Corp. of Rockville, Md., used genetic engineering to produce a characteristic protein of one major species of coccidia. When injected into chickens, this experimental antigen stimulates production of antibodies, McCandliss says.

Coccidial protozoans attack birds' intestinal tracts, killing them or weakening them by interfering with efficient feed conversion.

Antigens of some coccidial species induce an immune response that keeps the parasites from penetrating intestinal cells, while others cause the immune system to block the parasites' development once they are inside cells. The ARS and Genex researchers do not yet know how the bioengineered antigen they are using works.

ARS microbiologists Harry Danforth and Patricia C. Augustine used standard hybridoma (monoclonal antibody) technology to develop antibodies that were then used by Genex to isolate coccidial antigens. The ARS researchers took spleen cells from mice that had been injected with coccidia and were producing antibodies against the parasites. They then fused the spleen cells with mouse cancer cells growing in cultures. The cancer cells reproduce rapidly, producing large amounts of the antibodies.

Danforth cautions that the genetically engineered antigen as it exists now provides only partial protection. He hopes further research can alter it to provide more complete protection.

Other possibilities for introducing the coccidial antigen into birds, Danforth says, include isolating the gene coding for the antigen and inserting it into vaccinia viruses or putting the antigen into birds' feed or water. Direct insertion of the antigen gene coding for coccidial resistance in some chicken species is possible, but a long way off, he says. "We haven't considered cloning the gene and putting it into the chicken line yet, but that would be a very interesting prospect."