Genomic analysis of the causative agents of coccidiosis in domestic chickens

Abstract

Global production of chickens has trebled in the past two decades and they are now the most important source of dietary animal protein worldwide. Chickens are subject to many infectious diseases that reduce their performance and productivity. Coccidiosis, caused by apicomplexan protozoa of the genus Eimeria, is one of the most important poultry diseases. Understanding the biology of Eimeria parasites underpins development of new drugs and vaccines needed to improve global food security. We have produced annotated genome sequences of all seven species of Eimeria that infect domestic chickens, which reveal the full extent of previously described repeat-rich and repeat-poor regions and show that these parasites possess the most repeat-rich proteomes ever described. Furthermore, while no other apicomplexan has been found to possess retrotransposons, Eimeria is home to a family of chromoviruses. Analysis of Eimeria genes involved in basic biology and host-parasite interaction highlights adaptations to a relatively simple developmental life cycle and a complex array of co-expressed surface proteins involved in host cell binding.

Population, genetic, and antigenic diversity of the apicomplexanEimeria tenellaand their relevance to vaccine development

“…Examples of naturally occurring genetic diversity have been reliably overcome by the inclusion of more than one "strain" of a single species in some vaccine formulations (11). Each Eimeria species expresses between 6,000 and 9,000 proteins throughout its lifecycle (13), exposing the host to a complex portfolio of antigens. Genetic mapping studies with Eimeria maxima indicated that at least six loci associate absolutely with susceptibility to strong natural immune responses, and additional loci under partial selection also were detectable (14).…”

“…More cost-effective subunit vaccines composed of a small number of Eimeria antigens are needed for the mass broiler market; however, these vaccines are likely to induce more focused immune selection, which potentially could drive rapid selection of vaccine-resistant populations. Eimeria tenella is considered one of the most important species because it is widespread and highly pathogenic (13,15). It also is the best-studied species and therefore was selected as the exemplar in these studies.…”

Diversity of extracellular proteins during the transition from the ‘proto-apicomplexan’ alveolates to the apicomplexan obligate parasites

“…Self-recognition proteins have also been described for gamete fertilization in Plasmodium; namely, members of an amplified gene family which encodes glycophosphatidyl inositol (GPI)-linked proteins composed of 6-cys domains (Van Dijk et al 2010) and the HAP2 protein which functions in membrane fusion (Liu et al 2008). The 6-cys domain proteins are related to the Toxoplasma and Eimeria GPI-linked surface coat SAG proteins, and have been proposed to have originated via lateral transfer of metazoan ephrin proteins (Gerloff et al 2005;Arredondo et al 2012;Reid et al 2014). Ten members of the family are present in Plasmodium and appear to have roles in multiple stages of the lifecycle, including hepatocyte and intraerythrocytic stages (Ishino et al 2005;Sanders et al 2005;Annoura et al 2014).…”

Wider than Thought Phylogenetic Occurrence of Apicortin, A Characteristic Protein of Apicomplexan Parasites

“…HAARs of this type, encoding strings of at least seven amino acids, were found in 57 % of E. tenella genes. Reid et al (2014) found that glutamine HAARs occurred mainly in regions with medium to high solvent accessibility. Due to the glutamine repeats, the N-terminus of the Eimeria apicortins is predicted to be disordered with the highest, near 100 %, probability, which provides, indeed, high solvent accessibility.…”

“…Eimeria protein-coding sequences are known to be extremely rich in homopolymeric amino acid repeats (HAARs), the extent of which is greater in Eimeria than in any other organism sequenced to date (Reid et al 2014). The most common repeat in Eimeria genus is the trinucleotide CAG, which occurs mostly in coding sequences, and encodes preferentially alanine or glutamine.…”