Vaccination against Tropical Theileriosis

Abstract

Theileria annulata, the cause of tropical theileriosis is propagated in cattle with stage‐to‐stage transmission by Hyalomma ticks. Three stages in the life cycle of the parasite‐tick‐derived sporozoites, intramononuclear schizonts, and erythrocytic merozoites‐infect cattle. When cattle are inoculated with schizont‐infected cells, the parasite is transferred from the donor cell to the recipient. The main pathological damage in cattle is induced by the schizont stage. Each development stage of T. annulata elicits a specific immune response. Schizont‐infected lymphoid cells can be grown indefinitely in culture and prolonged cultivation results in loss of virulence. Blood‐derived schizonts induce stronger immunity than culture‐derived schizonts, which suggests that restrictions on the parasite population or antigenic variation occur during prolonged cultivation. The duration of immunity following sporozoite or schizont infections has not yet been determined, but does not appear to be lifelong. The attenuated, culture‐derived anti‐theileria vaccine proved to be safe and effective in prevention of field theileriosis in large enzootic areas.

Extensive Polymorphism and Evidence of Immune Selection in a Highly Dominant Antigen Recognized by Bovine CD8 T Cells Specific for Theileria annulata

“…Despite the intimate relationship of the parasite with the host cell, inoculation of animals with a few thousand allogeneic T. annulata-infected cells results in transfer of infection into cells of recipient animals (24), by a mechanism that is poorly understood. This property has allowed parasitized cell lines to be used for vaccination, but such cell lines need to be subjected to prolonged passage in vitro followed by testing in vivo to ensure that they are fully attenuated for virulence (40,41). Although T. annulata-infected cells have been used with success to vaccinate cattle in the field, experimental vaccine trials have indicated that the stimulated immunity is less effective against challenge with heterologous parasite strains compared to the homologous strain (9,41).…”

Attenuated vaccines for tropical theileriosis, babesiosis and heartwater: the continuing necessity

“…The vaccine induces immunity that lasts from 14 months to four years [18,19] but revaccination might be required if cattle are not exposed to natural challenge. Field isolates present a mix of antigenically diverse parasite populations, and accumulated evidence has shown that this has a limited impact on the protective immunity induced by the vaccine [14]. Analysis of parasite-population structures based on the major merozoite and piroplasm surface protein Tams1, has provided additional evidence for the broad protection engendered by attenuated cell-culture vaccines against heterologous field challenge [20].…”

“…Following infection with schizonts, which are responsible for the main pathology, protective immunity is induced against homologous challenge, whereas partial immunity is induced against heterologous challenge or challenge by infected ticks [14].…”

“…Inside the red blood cell, they develop into the piroplasm stage [13] (Figure 1c). Of all stages, only schizonts can be grown in vitro and, after prolonged cultivation, they become attenuated, which is the basis for culture-derived vaccines [14].…”

Decreased serum sialic acid, albumin-globulin ratio and total protein levels in cattle heavily infected with Theileria annulata

“…Tropical theileriosis has been reported earlier in different regions of Turkey (8,10,22). T. annulata is propagated in cattle with stage-to-stage transmission by Hyalomma ticks (2,19). The main pathological damage in cattle is induced by the schizont stage (19).…”