Transfection with circular donor plasmid pHEA-Bac and the restriction enzyme Asc I resulted in fluorescent parasites in the in vitro cultures at a similar level to the cultures infected with co-transfected (pHEA-Bac + pH 4-IFP2-A + Asc I) parasites (Fig. 2H) but did not result in any EYFP expression in parasites following in vivo infection of chickens. The gene discussed is PYDC1; the disease is infection.