“Theileria is a genus of parasitic protozoan that belongs to the phylum Apicomplexa and is closely related to Plasmodium. Two Theileria species, T. annulata and T. parva, are important cattle parasites.T. annulata causes tropical theileriosis and T. parva causes East Coast fever. Theileria are transmitted by ticks. The genomes of T. annulata and T. parva have been sequenced and published.” Wikipedia
Theileria parasites infect a wide range of both domestic and wild animals and are transmitted by ixodid ticks of the genera Amblyomma,Haemaphysalis, Hyalomma and Rhipicephalus.
Theileria are obligate intracellular protozoan parasites that infect both wild and domestic ruminants, and are transmitted by ixodid ticks of the genera Amblyomma,Haemaphysalis, Hyalomma and Rhipicephalus.
There are six identified Theileria parasites which infect these animals; the two most pathogenic and economically important are T. parva and T. annulata.
• T. parva occurs in Eastern and Southern Africa and causes East Coast fever (ECF or Corridor Disease).
• T. annulata causes tropical theileriosis (TT), also known as Mediterranean theileriosis and occurs in North Africa, southern Europe and Asia.
For purposes of this blogs relevance to Game Breeders and industry stakeholders within the Southern African region, we will be focusing on Theileria T. parva.
Theileria parva is the most prevalent Theileria species in sub-Saharan Africa. These parasites renowned for the large economic losses they cause to the agricultural/game breeding industry due to disease outbreaks, mortalities, damage to hides and poor production in animals. Wild Ruminants which can be infected include:
Transmission of Theileria T. Parva
There are three subtypes of T. parva, all of which are transmitted by the brown ear tick, Rhipicephalus appendiculatus. Theileria parva parva, Theileria parva bovis and T. p. parva which produces an acute, usually fatal disease called East Coast fever (ECF). The buffalo acts as a carrier of the parasite and does not normally suffer from clinical disease, which is severe and usually fatal in ruminants.
These parasites have a complex life cycle of development in the vector and host. Rhipicephalus appendiculatus is a three-host tick, feeding on an animal during each of the three stages of its life cycle—larva, nymph and adult. The larvae and nymphs that ingest parasites on one host are in turn infective as nymphs and adults, respectively, when they feed on another host during the next stage of their development. The parasites are transmitted most commonly when ticks feed on infected animals as nymphs and then on susceptible animals as adults.
Theileria parva ingested by ticks first develops in the tick gut. The parasite then migrates to the salivary glands, where it develops further, forming infective sporozoites, which are injected into animals, in tick saliva, when the tick feeds. Inside the host, the sporozoites attach to and enter the white blood cells of the bovine immune system. Within two to three days of invading the lymphocytes, the sporozoites begin to develop into multinucleate bodies called schizonts. The infected lymphocytes are transformed into enlarged lymphoblasts, which begin to multiply. As each lymphoblast divides, the parasite inside the cell also divides, so that both daughter cells produced by a dividing lymphocyte are infected. This process causes the population of parasitized cells to increase rapidly and the infected cells spread throughout the lymphoid system of the animal. Virulent forms of the parasite eventually cause Theileriosis and widespread destruction of the host's cells, which usually kills the animal within three to four weeks of its becoming infected.
Part 2 of this post will be published on 28 January 2016