in vitro culture and isoenzyme analysis of giardia lamblia

4.5 DISCUSSION
In the current work, two mice strains have been successfully infected with Giardia
cysts of human origin. These results strongly suggest that the parasite displays
host-preference rather than strict host-specificity and this confirms the findings of
earlier workers (Filice, 1952; Hill et al., 1983; Mayrhofer et al., 1992, Mayrhofer &
Andrews, 1994) who reported cross-species infections with Giardia organisms.
Furthermore, in the current study, mice were infected with Giardia of human origin;
this may have some implications in terms of mice acting as reservoir hosts.
However, in the current study the infections were of short term duration in
neonatal mice therefore further research is still required to clarify the role played
by adult mice in transmission of Giardia to humans and vice versa. As Mastomys
is an indigenous species there could be serious health implications in the South
African context if these were indeed acting as reservoir animals.
Animal infectivity was compared with excystation in vitro with the same sets of
cysts. Of the 53 excystation trials by both animal inoculation and in vitro methods,
varying results were obtained. Although some could be excysted by both methods,
a proportion of the isolated cysts could not excyst in vitro but produced infections
in mice while some failed to produce animal infections whilst they excysted in
vitro. The fact that some cysts could excyst in one model but not the other
suggests that the two methods provide different environments for factors that
initiate the excystation process. Alternately, it is possible that some stimulatory
factors within the cysts are favoured by one of the two excystment conditions but
not the other. These excystment methods therefore provide a marker that implies
strain differences in these morphologically identical Giardia of human origin.
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