Immunohistochemical analysis of skin and draining lymph nodes of sheep repeatedly infested with the ixodid tick Hyalomma anatolicum anatolicum were studied for different antigen-presenting cells and lymphocyte subpopulations. Infiltration of neutrophils, macrophages and lymphocytes adjacent to the tick bite site were observed. Skin biopsies showed significant increases in dermal infiltration of CD8+ and γδ+ T cells at 72 h and 8 days after both primary and secondary infestation. Infiltrations of MHC-II DR/DQ decreased at 72 h after tick infestation, whereas significant increases were recorded for 8-day skin biopsies. CD1+ cellular infiltrations were observed during secondary infestations at the dermis. Decreased ratios of CD4[ratio ]CD8 T cells and MHC-II[ratio ]CD1 antigen-presenting cells were observed in both infestations compared to healthy skin biopsies. Ratios of αβ[ratio ]γδ T cells increased gradually during infestation compared to uninfested skin. The regional lymph nodes from tick-infested sheep showed an increased CD8+, γδ+ T and CD1+ cellular infiltration compared to control lymph nodes. CD4+ T cells were decreased. There were no significant changes in CD45R+ cellular infiltration either at skin lesions or regional lymph nodes.

Theileria are economically important, intra-cellular protozoa, transmitted by ixodid ticks, which infect wild and domestic ruminants. In the mammalian host, parasites infect leukocytes and erythrocytes. In the arthropod vector they develop in gut epithelial cells and salivary glands. All four intra-cellular stages of Theileria survive free in the cytoplasm. The schizont stages of certain Theileria species induce a unique, cancer-like, phenotype in infected host leukocytes. Theileria undergoes an obligate sexual cycle, involving fusion of gametes in the tick gut, to produce a transiently diploid zygote. The existence of sexual recombination in T. parva has been confirmed in the laboratory, and is presumed to contribute to the extensive polymorphism observed in field isolates. Key parameters in T. parva population dynamics are the relative importance of asymptomatic carrier cattle and animals undergoing severe disease, in transmission of the parasite to ticks, and the extent of transmission by nymphs as compared to adult ticks. Tick populations differ in vector competence for specific T. parva stocks. Recombinant forms of T. parva and T. annulata sporozoite surface antigens induce protection against parasite challenge in cattle. In future, vaccines might be improved by inclusion of tick peptides in multivalent vaccines.

Tick fever or cattle fever (babesiosis) is economically the most important arthropod-borne disease of cattle worldwide with vast areas of Australia, Africa, South and Central America and the United States continuously under threat. Tick fever was the first disease for which transmission by an arthropod to a mammal was implicated at the turn of the twentieth century and is the first disease to be eradicated from a continent (North America). This review describes the biology of Babesia spp. in the host and the tick, the scale of the problem to the cattle industry, the various components of control programmes, epidemiology, pathogenesis, immunity, vaccination and future research. The emphasis is on Babesia bovis and Babesia bigemina.