Abstract
Eimeria species parasites can cause the disease coccidiosis, most notably in chickens. The occurrence of coccidiosis is currently controlled through a combination of good husbandry, chemoprophylaxis and/or live parasite vaccination; however, scalable, cost-effective subunit or recombinant vaccines are required. Many antigens have been proposed for use in novel anticoccidial vaccines, supported by the capacity to reduce disease severity or parasite replication, increase body weight gain in the face of challenge or improve feed conversion under experimental conditions, but none has reached commercial development. Nonetheless, the protection against challenge induced by some antigens has been within the lower range described for the ionophores against susceptible isolates or current live vaccines prior to oocyst recycling. With such levels of efficacy it may be that combinations of anticoccidial antigens already described are sufficient for development as novel multi-valent vaccines, pending identification of optimal delivery systems. Selection of the best antigens to be included in such vaccines can be informed by knowledge defining the natural occurrence of specific antigenic diversity, with relevance to the risk of immediate vaccine breakthrough, and the rate at which parasite genomes can evolve new diversity. For Eimeria, such data are now becoming available for antigens such as apical membrane antigen 1 (AMA1) and immune mapped protein 1 (IMP1) and more are anticipated as high-capacity, high-throughput sequencing technologies become increasingly accessible.
Highlights
Eimeria have been recognised as important intestinal parasites of poultry for more than 100 years (Chapman, 2014)
A key question is whether new anticoccidial vaccines will suffer the same fate as most anticoccidial drugs, with swift selection for vaccine-resistant parasite populations that undermine vaccine value? Without such understanding, the decades of research into recombinant anticoccidial vaccines may be undone within months of vaccine release. In this targeted review we summarise the existing options for control of Eimeria species parasites which infect chickens, explore the candidates available for inclusion in sub-unit or recombinant anticoccidial vaccines and discuss the current understanding of genetic diversity for these antigens
Several candidate antigens have been identified for use in recombinant anticoccidial vaccines
Summary
Eimeria have been recognised as important intestinal parasites of poultry for more than 100 years (Chapman, 2014). Oocysts defined by genotypes that confer drug resistance, enhanced virulence or even immunological escape from vaccine-induced protection, appear identical to other oocysts, leaving the farmer, veterinarian and scientist in the dark (Peek and Landman, 2003; Williams et al, 2009). The decades of research into recombinant anticoccidial vaccines may be undone within months of vaccine release In this targeted review we summarise the existing options for control of Eimeria species parasites which infect chickens, explore the candidates available for inclusion in sub-unit or recombinant anticoccidial vaccines and discuss the current understanding of genetic diversity for these antigens
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