East Coast Fever: Theileria Parva Infection of Cattle

Aetiology

The aetiological agent, Theileria parva, and its intralymphocytic stages, the schizonts in lymphoid cells, was first described by Koch (1903).

The taxonomic classification of Theileria parva is as follows: (Irvin, 1987).

• Sub Kingdom - Protozoa

• Phylum - Apicomplexa

• Class - Sporozoea

• Subclass - Piroplasma

• Order - Piroplasmida

• Family - Theileriidae

• Genus - Theileria

• Species - Theileria parva

T. parva is a parasite of the Cape buffalo (Syncerus caffer) that has adapted to infect and undergo transmission in cattle (Uilenberg, 1981, Morrison, et al, 2020) and is highly pathogenic in cattle. Three subspecies of T. parva were recognized, namely Theileria parva parva, Theileria parva lawrencei and Theileria parva bovis. These parasites cause East Coast fever (ECF), Corridor disease and January disease respectively in cattle. They were distinguished on clinical and epidemiological parameters as they are morphologically and serologically indistinguishable (Burridge et al, 1973). The parasite(s) are also transmitted by the same tick vector Rhipicephalus appendiculatus. In classical ECF caused by T. parva parva, macroschizonts and piroplasms are plentiful. The clinical and epidemiological differences between the subspecies are that T. parva lawrencei is a buffalo parasite which produces relatively few, small schizonts and very few, if any piroplasms in cattle thus making inter–cattle transmission by the tick inefficient (Young et al., 1973, Morrison et al, 2020). T. parva bovis differs from T. parva lawrencei in that plentiful piroplasms are produced in cattle and it can therefore, be transmitted between cattle (Norval et al., 1992). T. parva bovis was distinguished from T. parva parva because it produced a carrier state in recovered animals and the number of parasites in T. parva bovis infections are normally lower than in T. parva parva infections.