Epidemiology and Transmission of Theileria orientalis in Australasia

Abstract

Oriental theileriosis, a disease primarily impacting cattle is caused by an apicomplexan hemoprotozoan parasite, Theileria orientalis. It has now become established in the Australasia region. The organism was long considered a benign cause of persistent infections; however, an increase in clinical outbreaks since 2006 in the eastern Australian states and New Zealand was associated with the identification of the pathogenic Ikeda (Type 2) and Chitose (Type 1) genotypes. Unlike the pathogenic T. parva and T. annulate, which target leucocytes, clinical manifestation with T. orientalis is due to its effects on erythrocytes, with the infection sometimes designated as Theileria associated bovine anemia (TABA). In Australia and New Zealand, the tick Haemaphysalis longicornis is the principal vector, though other Haemaphysalis species are also likely vectors. The endemic status of infection with pathogenic genotypes in areas with low or absent tick populations is an apparent paradox that may be attributable to alternative modes of transmission, such as mechanical transmission by hematophagous insects (lice, mosquitoes, and biting flies), vertical transmission, and transmission via iatrogenic means. This review addresses the evidence for the different modes of transmission of T. orientalis with particular focus on the reported and potential vectors in Australasia.

Role of Recognition MicroRNAs in Hemaphysalis longicornis and Theileria orientalis Interactions

“…Theileria orientalis ( T. orientalis ) is widely distributed and causes theileriosis, a condition in which the pathogen invades and destroys red blood cells of the host after entering via a tick bite [ 1 , 2 ], and T. orientalis is mainly transmitted by the Hemaphysalis longicornis ( H. longicornis ) vector [ 3 ]. T. orientalis is transmitted throughout a tick’s lifetime.…”

Ticking off the Tick Vectors: Rhipicephalus microplus Fails to Transmit Theileria orientalis

“…Theileria (T.) orientalis, a tick-borne haemoparasite of cattle, is an important cause of non-transforming theileriosis in Australasia, southeast Asia, and the United States [1][2][3]. Clinically affected cattle often display symptoms such as anaemia, hypoxia, weakness, and increased cardio-pulmonary rates [4,5].…”

“…The taxonomy of T. orientalis has been a subject of debate, with three previously proposed species: T. buffeli (Australia), T. sergenti (Japan), and T. orientalis (Europe and elsewhere) [6]. However, recent evidence from PCRdirected sequencing and phylogenetic analyses of major piroplasm surface protein (MPSP) sequences has confirmed that they all belong to the same T. orientalis species, comprising 11 distinct allelic types, including the Ikeda type typically associated with clinical disease [1][2][3].…”

“…Recent associations of Ikeda type T. orientalis with clinical disease outbreaks in cattle herds in Australia (since 2011), New Zealand (since 2012), and the USA (since 2017) indicate that naïve herds are at increased risk of production losses due to high morbidity and mortality [2,3]. To date, Haemaphysalis (H.) longicornis is the only confirmed tick vector for T. orientalis.…”