8.2.1 Giardia lamblia
Although usually associated with water, or transmission from person to
person by poor hygiene, a number of outbreaks of the diarrhoeal disease
caused byGiardia lamblia, which may also be known asG. intestinalisor
Lamblia intestinalis, have been confirmed as foodborne outbreaks. The
organism survives in food and water as cysts but, although it can be
cultured in the laboratory, it does not normally grow outside its host.
The infective dose may be very low and once ingested the gastric juices
aid the release of the active flagellate protozoa, known as trophozoites,
which are characterized by the possession of eight flagella and two nuclei
(Figure 8.3). The organism is not particularly invasive and it is not clear
how the symptoms of diarrhoea, abdominal cramps and nausea are
caused but it is possible that a protein toxin is involved.
Giardiacysts have been found on salad vegetables such as lettuce and
fruits such as strawberries and could occur on any foods which are
washed with contaminated water or handled by infected persons not
observing good hygienic practice. Confirmed foodborne outbreaks have
implicated home-canned salmon and noodle salad but the difficulty of
demonstrating low numbers of cysts in foods may be one reason why
foods are rarely directly implicated.
Although the cysts are resistant to chlorination processes used in most
water treatment systems, they are killed by the normal cooking proce-
dures used in food preparation.
Figure 8.3 Giardia lambliatrophozoite
Chapter 8 275