D.A. Stagg

Bio: D.A. Stagg is an academic researcher from United Nations Development Programme. The author has contributed to research in topics: Theileria parva & Theileria. The author has an hindex of 8, co-authored 13 publications receiving 351 citations. Previous affiliations of D.A. Stagg include Japanese Ministry of Agriculture, Forestry and Fisheries.

Infection and Transformation of Bovine Lymphoid Cells in vitro by Infective Particles of Theileria parva

Abstract: Infection and Transformation of Bovine Lymphoid Cells in vitro by Infective Particles of Theileria parva

Comparative growth of bovine lymphosarcoma cells and lymphoid cells infected with Theileria parva in athymic (nude) mice.

Abstract: TUMOUR-LIKE growth of bovine lymphoid cells infected with Theileria parva has been observed in whole-body irradiated athymic (nude) mice using cells isolated direct from fatal cases of East Coast fever1, and also using lymphoid cells infected with T. parva, maintained as lines in culture2. Here we compare the growth, in irradiated athymic mice, of this latter cell type with that of similar bovine transformed lymphoid cells of known neoplastic origin. The results contrast with those recorded in the natural conditions in cattle, since cells infected with T. parva grew malignantly in mice whereas bovine lymphosarcoma cells formed localised non-invasive tumours.

Heterotransplantation of Theileria parva-infected cells to athymic mice

Abstract: CONGENITALLY athymic (nude) mice have been used for the heterotransplantation and maintenance of human tumours1–6. In many cases aplasia of the thymus is sufficient to allow tumour growth and other immunosuppressive treatments are apparently unnecessary. Here we describe how infected cells taken from a fatal case of East Coast fever (ECF), regularly produced tumour-like masses only in irradiated athymic mice.

Theileria: Intracellular protozoan parasites of wild and domestic ruminants transmitted by ixodid ticks

Abstract: 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.

Games parasites play: how parasites evade immune surveillance

Abstract: Parasites have evolved an extraordinary variety of mechanisms for surviving in the face of the natural and acquired immune responses of their hosts. A selection of the mechanisms serves to illustrate the challenge involved in developing strategies for immunising against parasites.

Transformation of Leukocytes by Theileria parva and T. annulata

Abstract: Theileria parva and T. annulata provide intriguing models for the study of parasite-host interactions. Both parasites possess the unique property of being able to transform the cells they infect; T. parva transforms T and B cells, whereas T. annulata affects B cells and monocytes/macrophages. Parasitized cells do not require antigenic stimulation or exogenous growth factors and acquire the ability to proliferate continuously. In vivo, parasitized cells undergo clonal expansion and infiltrate both lymphoid and non-lymphoid tissues of the infected host. Theileria-induced transformation is entirely reversible and is accompanied by the expression of a wide range of different lymphokines and cytokines, some of which may contribute to proliferation or may enhance spread and survival of the parasitized cell in the host. The presence of the parasite in the host-cell cytoplasm modulates the state of activation of a number of signal transduction pathways. This, in turn, leads to the activation of transcription factors, including nuclear factor-kappa B, which appear to be essential for the survival of Theileria-transformed T cells.

Integrated control of ticks and tick-borne diseases of cattle in Africa.

Abstract: The problems caused by tick and tick-borne diseases for livestock particularly cattle on the African continent are described and discussed. The control of ticks and tick-borne diseases must receive high priority in Africa with regard to both research and control application because of their widespread distribution in areas of high livestock potential and productivity. The conventional methods of tick and tick-borne disease control are discussed and are found to be inadequate in the conditions prevailing in Africa. Methods of integrated control are suggested and discussed in light of recent development in control methods and those still under development. Any one of these methods may not be adequate to control the problem on its own but when several of the methods are combined an economic and robust integrated control is likely to result. Encouragement is given to attempt this approach in Africa to solve what must be the largest animal health problem of livestock remaining in the world.

Adoptive transfer of immunity to Theileria parva in the CD8+ fraction of responding efferent lymph.

Abstract: Evidence that class I major histocompatibility complex-restricted cytotoxic T lymphocytes (CTL) are involved in immunity to malaria has highlighted the potential importance of these cells in protection against intracellular parasites. Parasite-specific CTL are a prominent feature of the immune response of cattle to Theileria parva, a related apicomplexan parasite. The relationship between the appearance of these cells in the blood of immune cattle under challenge and the clearance of infection suggests that they are involved in the control of infection, but direct evidence is lacking that CTL can mediate protection. We have made a quantitative kinetic study of CTL responses in lymph originating from infected lymph nodes in a number of immune cattle under challenge with T. parva. Direct killing activity and the frequency of CTL precursors (CTLp) within responding cell populations were evaluated. A substantial increase in the proportion of CD8+ CTL was observed between days 8 and 11 after challenge. Frequencies of CTLp as high as 1:32 were observed and activity was essentially confined to the large blasting cell fraction. The analogous response in peripheral blood was of lower magnitude and delayed by 1-2 days. The high frequency of CTLp in efferent lymph permitted the adoptive transfer of this activity between immune and naive monozygotic twin calves. In separate experiments, naive calves lethally infected with T. parva were protected by inoculation of up to 10(10) responding CD8+ T cells derived from their immune twins. Elimination of CD8+ T cells within the inoculum abrogated this effect. These findings provide direct evidence that CD8+ T cells can control T. parva infections in immune cattle.