in vitro culture and isoenzyme analysis of giardia lamblia

up to 4 distinct genotypes within each clinical isolate (Andrews et al., 1992). These
authors illustrated that in vivo and in vitro culture methods select different
genotypes. Furthermore, it is speculated that in endemic areas where extensive
genetic heterogeneity exists within Giardia populations, mixed infections with more
than one genetic variant are likely to occur (Finn et al., 1994). These authors
demonstrated in vitro competitive interaction between 2 genetically distinct isolates
with different growth rates. In this study, the faster-growing isolate greatly outcompeted
the slower growing organism. It is likely that such competitive
interactions occur in vivo during colonisation of hosts. As discussed earlier,
Giardia genetic variants expressing different surface antigens were shown to be
differentially susceptible to the intestinal proteases trypsin and chymotrypsin (Nash
et al., 1991). It is therefore more likely that during natural Giardia infections, such
population dynamics of the parasite play a role in determining the outcome of
infections in humans.
1.7.3 Travel
Travel (particularly to endemic areas) has been implicated in increasing the risk of
contracting giardiasis, leading to the latter being widely known as travellers'
diarrhoea. The water supplies in Leningrad and towns in the Rocky Mountains of
North America have been strongly associated with outbreaks of Giardia in visitors
and local inhabitants. A questionnaire survey of 1 419 travellers to the Soviet
Union performed by the Center for Disease Control (COC) Bethesda, USA,
showed that 324 individuals (23%) had acquired giardiasis (Brodsky et al., 1974).
Furthermore, in a survey on intestinal parasites by the COC, the majority of the
670 cases of giardiasis were patients returning from travel abroad (COC, 1976).
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