in vitro culture and isoenzyme analysis of giardia lamblia

1.3 Transmission
1.3.1 Human hosts
The cyst is spread through the faecal-oral route. Different mechanisms of
transmission have been documented such as direct person to person hand-mouth
transfer. This is more common in children (Isaac-Renton et al., 1993) owing to lack
of personal hygiene and faecal incontinence. Prevalence is higher in children than
in adults in endemic areas (Adam, 1991; Flanagan, 1992). There is suggestive
evidence that institutionalised persons and day care attendees are at higher risk of
infection, for example Cody and colleagues (1994) isolated cysts from chairs and
tables in day care centres. In such settings, transmission rates are expectedly very
high, and can subsequently enhance the overall transmission of the parasite. To
illustrate this, day care attenders were shown to spread Giardia infection to the
community in a controlled study by Polis and co-workers (1986). In this study, data
suggested that 47% of the children in the centre transmitted giardiasis to at least
one household contact. Although humans of all ages are susceptible to infection
with Giardia, the prevalence is higher in children (Farthing et al., 1986) and
infection frequently occurs in immunocompromised individuals (Webster, 1980).
Inadequate sanitation exacerbates dissemination of cysts to the environment.
Surface water supplies are also known to be contaminated with cysts and infected
humans replenish this reservoir. Furthermore, wild and domestic animals such as
beavers, muskrats, dogs and cats have also been implicated in transmission but
their potential as zoonotic reservoirs of giardiasis is still debatable (Erlandsen,
1994). Prolonged occurrence of viable cysts in fresh cool (4°C) water has resulted
in Giardia being reported as the most common aetiologic agent of epidemic
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