Evolution and genetic diversity of Theileria

Abstract

Theileria parasites infect a wide range of domestic and wild ruminants worldwide, causing diseases with varying degrees of severity. A broad classification, based on the parasite's ability to transform the leukocytes of host animals, divides Theileria into two groups, consisting of transforming and non-transforming species. The evolution of transforming Theileria has been accompanied by drastic changes in its genetic makeup, such as acquisition or expansion of gene families, which are thought to play critical roles in the transformation of host cells. Genetic variation among Theileria parasites is sometimes linked with host specificity and virulence in the parasites. Immunity against Theileria parasites primarily involves cell-mediated immune responses in the host. Immunodominance and major histocompatibility complex class I phenotype-specificity result in a host immunity that is tightly focused and strain-specific. Immune escape in Theileria is facilitated by genetic diversity in its antigenic determinants, which potentially results in a loss of T cell receptor recognition in its host. In the recent past, several reviews have focused on genetic diversity in the transforming species, Theileriaparva and Theileriaannulata. In contrast, genetic diversity in Theileriaorientalis, a benign non-transforming parasite, which occasionally causes disease outbreaks in cattle, has not been extensively examined. In this review, therefore, we provide an outline of the evolution of Theileria, which includes T. orientalis, and discuss the possible mechanisms generating genetic diversity among parasite populations. Additionally, we discuss the potential implications of a genetically diverse parasite population in the context of Theileria vaccine development.

Lessons in Mind Control: Trends in Research on the Molecular Mechanisms behind Parasite-Host Behavioral Manipulation

“…Conceptually, the behavioral changes induced in the host's offspring would enable an increased probability of transmission for the parasites own progeny (Poulin and Thomas, 2008). Most of this research has focused on intracellular protozoan parasites, specifically, Theileria, Toxoplasma, and Plasmodium (Lüder et al, 2009;Hari Dass and Vyas, 2014;Sivakumar et al, 2014;Cheeseman and Weitzman, 2015). The epigenetic programming by the parasite falls into 3 categories: the epigenator, the epigenetic initiator and the epigenetic maintainer (Berger et al, 2009).…”

“…Recently, extensive studies indicate that several intracellular parasite species meet these criteria, implying that in these cases, infection can have a direct impact on gene expression (Lüder et al, 2009;Hari Dass and Vyas, 2014;Sivakumar et al, 2014;Cheeseman and Weitzman, 2015). This in turn has a variety of adaptive consequences for the parasite.…”

“…Firstly, some parasites manipulate their hosts by altering the communication between the immune and central nervous system (CNS) (Friberg et al, 2010;Hakimi and Cannella, 2011;Boucias and Pendland, 2012). Secondly, some may operate via proteomic (Helluy, 1983;Biron et al, 2005Biron et al, , 2006Ponton et al, 2006;Hakimi and Cannella, 2011;Rahman and McFadden, 2011;McDonough and Rodriguez, 2012) and/or genomic mechanisms (Lüder et al, 2009;Hari Dass and Vyas, 2014;Sivakumar et al, 2014). Finally, parasites may secrete molecules that directly interact with the CNS to alter neuronal activity (Klein, 2003;Adamo, 2012Adamo, , 2013Lafferty and Shaw, 2013).…”

Development and Validation of a Quantitative PCR Assay Using Multiplexed Hydrolysis Probes for Detection and Quantification of Theileria orientalis Isolates and Differentiation of Clinically Relevant Subtypes

“…sergenti/T. buffeli complex; however, the name T. sergenti is now considered invalid (4), and T. orientalis is commonly used to refer to all (5). From a clinical perspective, T. orientalis can cause anemia, lethargy, jaundice, fever, abortion, and mortality in cattle (6).…”

“…Clinical infection can also result in decreased milk production in dairy cattle (7). T. orientalis is a conditional pathogen, and while pathogenic forms are largely limited to Eastern Asia and Australasia (5,6,(8)(9)(10), it is frequently detected in asymptomatic animals; these benign forms are globally spread (5,(11)(12)(13)(14). Analysis of the most common genotyping locus (p32), encoding the variable major piroplasm surface protein (MPSP), currently identifies 11 distinct T. orientalis genotypes (13,15,16).…”