Scientists describe the transcriptomes of parasites that cause avian coccidiosis

Researchers described the transcriptomes of three important species of Eimeria, which causes the most serious illness associated with avian farming in the world.

By Fábio de Castro

Agência FAPESP – A group of researchers from the Universidade de São Paulo (USP) reported the transcriptomes of three important species of Eimeria, a parasite that causes avian coccidiosis—the most serious illness associated with avian production the world over. The transcriptome is the set of genes expressed by a cell, tissue or whole organism at a particular stage of development.

The results of this study, which was led by Alda Madeira and Arthur Gruber, both professors at USP’s Parasitology Department in the Biomedical Sciences Institute (ICB), were published in the International Journal for Parasitology. The study was funded by FAPESP under its Research Support-Regular program. The article includes the results obtained by this group over nearly ten years of research involving many other projects.

Aside from characterizing the transcriptome, the article describes the entire genetic sequencing process, details the development of the bioinformatics applied during the study, offers a biological interpretation of the data and describes the Eimeria Transcript Database – a website that provides open access to all of the sequencing data and comparative analyses that were performed. According to the authors, this platform is the largest portal of genetic information for Eimeria.

in addition to Madeira and Gruber, Jeniffer Novaes, Luiz Thibério Rangel, Milene Ferro, Alessandra Manha and Joana de Mello contributed to the article—all of whom are part of the ICB-USP Parasitology Department—and Ricardo Abe, Leonardo Varuzza and Alan Durham from the Computer Sciences Department at USP’s Institute of Mathematics and Statistics.

According to Gruber, even though drugs and vaccines exist for avian coccidiosis, the illness—which is found on farms in all countries, with no exceptions—causes direct losses to avian husbandry and generates indirect costs associated with its prevention.

According to Gruber, today there are two methods to control coccidiosis: the development of new, safer and more specific drugs, and the development of a new generation of vaccines based on the use of defined antigens.

“The pharmaceutical industry hasn’t released a new anticoccidiosis drug in over 15 years. A greater understanding of the proteins that compose the parasites and their possible functions in the parasite life cycle could aid in the development of a new generation of drugs,” Gruber told Agência FAPESP.

“Alternatively, characterization of genes from the most relevant Eimeria species could allow for the identification of possible candidate molecules for the composition of new vaccines,” he added.

Gruber says that instead of sequencing the Eimeria genome, which contains a large number of non-protein coding sequences, the group decided to focus its studies directly on the messenger RNAs, the molecules transcribed from the genome that encode the proteins of a living being.

About four years ago, the researchers determined, in collaboration with an international consortium, the sequence of chromosome 1 of Eimeria tenella. Next, the Brazilian team started looking at the transcripts of the three most relevant species in chicken farming: Eimeria acervulina, Eimeria maxima and Eimeria tenella.

“We generated over 60,000 readings of transcript sequencing, making up the largest information set on the Eimeria genus in existence. One of the interesting aspects of this work is that we did a comparative study of the three species. Plus, the study showed different stages of the parasites in their life cycles, making it possible to identify important genes in each one of these stages,” he affirmed.

The study found that the parasite expresses a specific set of genes in each stage. However, during each stage, the parasite also expresses a series of genes that foretells the following stage.

The scientists showed that a strong association exists between the gene expression and the stage of development: closer stages have more similar patterns of expression. Based on this variation in genetic expression, it was possible to understand the dynamics of the different stages. 

 “The results showed unequivocally that the patterns of expression during different stages of development are strongly correlated with the order of these stages in the life cycle of the parasites. This means that a type of very well-synchronized molecular clock exists that regulates the expression of a set of genes as their products become necessary along the life cycle,” explained Gruber.

According to Gruber, knowing the identities of these genes and their patterns of expression could lead to a greater understanding of the molecular mechanisms that govern the life of a parasite, and therefore aid in the development of new control strategies.

The characterization of the Eimeria transcriptome is one of the many advances made by this Brazilian group in its studies of this parasite. Another advance made by this group is the development of molecular diagnostic methods for the detection and differentiation of the seven species that infect chickens, and more recently, the 11 species that are parasites of domestic rabbits.

“Another important study was the development of a diagnostic method based on Polymerase Chain Reaction (PCR) to differentiate the strains of three Eimeria species, a project developed together with the Laboratório Biovet that resulted in a patent shared by the company, USP and FAPESP in 2007,” said Gruber.

The article "A comparative transcriptome analysis reveals expression profiles conserved across three Eimeria spp. of domestic fowl and associated with multiple developmental stages" by Arthur Gruber, Alda Madeira and others can be read by International Journal for Parasitology subscribers at http://dx.doi.org/10.1016/j.ijpara.2011.10.008.