In vitro quantitation of Theileria parva sporozoites for use - TropMed ...

26 Chapter 1: Quantitation of Theileria parva sporozoites: Review of literature
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fever. There is significant leucopoenia in lethal cases (Irvin and Mwamachi, 1983). In contrast to
tropical theileriosis, caused by Theileria annulata, anaemia is not a common feature of East Coast
fever (Wilde, 1967; Maxie et al., 1982). However, Mbassa et al. (1994) claim that a Tanzanian
stock of T. parva causes severe anaemia by merozoites invading erythroid precursors. Fandamu et
al. (in press) also reported significant decrease in the PCV of cattle undergoing lethal reactions
after infection with T. parva Katete. Therefore, it is apparent that some T. parva stocks
exceptionally induce anaemia.
The severity of disease is dependent upon T. parva stock (Morrison, 1996), quantum of infection
(Radley et al., 1974; Dolan et al., 1984b) and bovine host factors (Morrison et al., 1996; Fandamu
et al., in press). For instance, the Boleni strain from Zimbabwe is known to be mild enough for
cattle to control the infection without chemotherapy (Kanhai et al., 1997). Exotic breeds (Bos
taurus) are generally more susceptible to developing clinical disease than African indigenous
(Bos indicus) cattle (Ndungu et al., 2005).
1.1.4. Immunity
Cattle surviving infection develop a solid immunity to the homologous strain of the parasite for at
least three years (Burridge et al., 1972). The role of humoral responses is not considered
significant in ECF immunity as evidenced from the failure of protection against lethal challenge
after transfer of immune sera or colostrum to susceptible animals (Muhammed et al., 1975). In
addition, Creemers (1982) has shown that anti-sera from lethally infected cattle were negative in
antibody-dependent cytotoxic assays indicating that they did not initiate antibody mediated
cytotoxicity. The most studied sporozoite antigenic determinants inducing detectable neutralising
antibodies against sporozoites are the Polymorphic Immunodominant Molecule (PIM) (Toye et
al., 1996) and the 67kD circum-sporozoite protein termed p67 (Nene et al., 1992). Specific
antibodies directed against sporozoites do have the capacity to neutralise the parasite and
consequently control infection but high titres are required for a full effect as the time sporozoites
spend in the extra-cellular environment is very short. It could also be envisaged that specific
antibodies directed against merozoites could play a role on the number of infected erythrocytes.
It can be deduced from the foregoing that long lasting protective immunity is not humoral
mediated. Cell-mediated immunity has been shown to be the major protective mechanism by
demonstration of adoptive transfer of immunity between twins (Emery, 1981; McKeever et al.,
1994). Infected cells express mostly MHC class 1 molecules on their surface. The immune
response, mediated by cytotoxic T-lymphocyte (CTL) of the BoT8 + subset, is directed at these