Regions of an Eimeria tenella antigen contain sequences which are conserved in circumsporozoite proteins from Plasmodium spp. and which are related to the thrombospondin gene family.

Coccidiosis, caused by Eimeria spp., is a major disease of economic importance to the poultry industry. The cloning and characterisation of genes coding for antigens of those species infecting chickens is an initial step in the identification of protective antigens suitable for the development of a genetically engineered vaccine. This report describes the molecular characterisation of an antigen of E. tenella produced by the recombinant lambda amp3 bacteriophage EtHL6. Three native polypeptides corresponding to the EtHL6 antigen, with sizes between 110 and 94 kDa, have been identified on both sporozoites and second generation merozoites of E. tenella by mouse antisera raised against the EtHL6 fusion protein. The DNA insert is a 722-bp EcoRI fragment encoding a polypeptide comprising three tandem blocks of amino acids which are highly homologous to each other. Each region, A, B and C, contains a strongly hydrophilic domain and two pairs of cysteine residues. Computer analysis has identified similarities with a group of proteins which include the circumsporozoite antigen and thrombospondin-related anonymous protein (TRAP) of malaria parasites, human thrombospondin, mouse properdin and the terminal components of the complement pathway.