A Review on Equine Piroplasmosis: Epidemiology, Vector Ecology, Risk Factors, Host Immunity, Diagnosis and Control

Abstract

Equine Piroplasmosis (EP) is a tick-borne disease caused by apicomplexan protozoan parasites, Babesia caballi and Theileria equi. The disease is responsible for serious economic losses to the equine industry. It principally affects donkeys, horses, mules, and zebra but DNA of the parasites has also been detected in dogs and camels raising doubt about their host specificity. The disease is endemic in tropical and temperate regions of the world where the competent tick vectors are prevalent. Infected equids remain carrier for life with T. equi infection, whilst, infection with B. caballi is cleared within a few years. This review focuses on all aspects of the disease from the historical overview, biology of the parasite, epidemiology of the disease (specifically highlighting other non-equine hosts, such as dogs and camels), vector, clinical manifestations, risk factors, immunology, genetic diversity, diagnosis, treatment, and prevention.

Keywords: Babesia caballi; Equine Piroplasmosis; Theileria equi; epidemiology; equines; tick-borne disease; ticks.

Figure 1

Worldwide distribution of regions where equine piroplasms have been detected or reported across different hosts in the last ten years (2008–2018).

Figure 2

Photomicrograph of Giemsa stained blood smear in Equine Piroplasmosis (EP) parasites prepared from in vitro cultures. (A) Babesia caballi and (B) Theileria equi. The arrow on (A)indicates the two pear-shaped bodies of B. caballi joined at the posterior end; on (B) indicates the four shaped merozoites of T. equi referred to as the “maltese cross”.

Figure 3

Schematic illustration of the life cycle of Theileria equi (A) and Babesia caballi (B) in the vertebrate host and invertebrate vector. Adopted from [23] with few modifications.

Figure 4

Possible transmission routes of equine piroplasmosis.

Figure 5

Schematic presentation of pathophysiology of anemia in equine piroplasmosis. The flowchart illustrates the sequence of events that culminates in anemia and other pathological sequellae.