3 research outputs found
Demonstration of differences in virulence between two Theileria parva isolates
H.S. Tindih and J. Naessens are ILRI authorsIn areas with a low incidence of infection due to unimodal presence of ticks, Theileria parva has been observed to induce a disease with relatively low pathology. This is followed by a carrier state, rather than death and therefore provides a better chance of transmission of the parasite back to the tick vector since in unimodal conditions, the different tick stages occur at different times. One isolate from such an area in Zambia, T. parva Chitongo, was compared for virulence with T. parva Muguga, isolated from an area exhibiting a continuous presence of all vector stages in East Africa. To reduce any variation due to infection dose, an in vitro standardized dose was used to initiate infection of groups of three local zebu cattle with each isolate. Parameters of virulence measured were prepatent period, fever, survival (based on ECF index), parasitosis, piroplasm parasitaemia and hematological parameters. Our results suggest that T. parva Chitongo developed a slightly later onset (1–2 days) and lower levels of parasitosis in the lymph node, causing less and later mortality. Comparison of the in vitro rate of transformation confirmed that the time needed to transform an infected lymphocyte took 4 days longer for T. parva Chitongo than T. parva Muguga. Elucidating the mechanism responsible for the lower virulence of T. parva Chitongo could be useful for designing an attenuated vaccine
Demonstration of differences in virulence between two Theileria parva isolates
In areas with a low incidence of infection due to unimodal presence of ticks, Theileria parva has been observed to induce a disease with relatively low pathology. This is followed by a carrier state, rather than death and therefore provides a better chance of transmission of the parasite back to the tick vector since in unimodal conditions, the different tick stages occur at different times. One isolate from such an area in Zambia, T. parva Chitongo, was compared for virulence with T. parva Muguga, isolated from an area exhibiting a continuous presence of all vector stages in East Africa. To reduce any variation due to infection dose, an in vitro standardized dose was used to initiate infection of groups of three local zebu cattle with each isolate. Parameters of virulence measured were prepatent period, fever, survival (based on ECF index), parasitosis, piroplasm parasitaemia and hematological parameters. Our results suggest that T. parva Chitongo developed a slightly later onset (1-2 days) and lower levels of parasitosis in the lymph node, causing less and later mortality. Comparison of the in vitro rate of transformation confirmed that the time needed to transform an infected lymphocyte took 4 days longer for T. parva Chitongo than T. parva Muguga. Elucidating the mechanism responsible for the lower virulence of T. parva Chitongo could be useful for designing an attenuated vaccine.status: publishe
Lymphocytes and Macrophages Are Infected by Theileria equi, but T Cells and B Cells Are Not Required to Establish Infection In Vivo
Theileria equi
has a biphasic life cycle in horses, with a period of intraleukocyte development followed by patent erythrocytic parasitemia that causes acute and sometimes fatal hemolytic disease. Unlike
Theileria spp
. that infect cattle (
Theileria parva
and
Theileria annulata
), the intraleukocyte stage (schizont) of
Theileria equi
does not cause uncontrolled host cell proliferation or other significant pathology. Nevertheless, schizont-infected leukocytes are of interest because of their potential to alter host cell function and because immune responses directed against this stage could halt infection and prevent disease. Based on cellular morphology,
Theileria equi
has been reported to infect lymphocytes
in vivo
and
in vitro
, but the specific phenotype of schizont-infected cells has yet to be defined. To resolve this knowledge gap in
Theileria equi
pathogenesis, peripheral blood mononuclear cells were infected
in vitro
and the phenotype of infected cells determined using flow cytometry and immunofluorescence microscopy. These experiments demonstrated that the host cell range of
Theileria equi
was broader than initially reported and included B lymphocytes, T lymphocytes and monocyte/macrophages. To determine if B and T lymphocytes were required to establish infection
in vivo
, horses affected with severe combined immunodeficiency (SCID), which lack functional B and T lymphocytes, were inoculated with
Theileria equi
sporozoites. SCID horses developed patent erythrocytic parasitemia, indicating that B and T lymphocytes are not necessary to complete the
Theileria equi
life cycle
in vivo
. These findings suggest that the factors mediating
Theileria equi
leukocyte invasion and intracytoplasmic differentiation are common to several leukocyte subsets and are less restricted than for
Theileria annulata
and
Theileria parva
. These data will greatly facilitate future investigation into the relationships between
Theileria equi
leukocyte tropism and pathogenesis, breed susceptibility, and strain virulence