PROGRESS ON DEVELOPING A RECOMBINANT COCCIDIOSIS VACCINE

The past 10 years of research aimed at developing subunit vaccines aga inst a number of apicomplexans, including Eimeria, Plasmodium and Toxo plasma, have, if anything, revealed the complex nature of parasite-hos t interactions. The knowledge gained from this research has shown why developing a subunit vaccine based on a single recombinant antigen fro m one developmental stage of the parasite was an overly optimistic app roach. Many apicomplexan parasites have acquired unique strategies to evade host immunity. The variable expression of genes encoding erythro cyte membrane protein 1 of Plasmodium falciparum [1] (Berendt et al. P arasitology 1994;108:S19-S28) exemplifies one such strategy. The parti cular mechanism for evading immune destruction depends on a number of interrelated factors, not least of which is the parasite life-cycle an d the availability of susceptible hosts. The goal of any vaccine, be i t an attenuated organism or a recombinant antigen, is to break the cyc le of infection. The development of a recombinant vaccine against apic omplexan parasites will depend on identifying those antigens and intra cellular processes that are vital to the parasite survival and those w hich exist merely as a way of evading immunity. The information that f ollows is a review of both molecular biology/biochemistry of eimerian parasites and factors that influence host immune responses to coccidia . Published by Elsevier Science Ltd.