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Cryptosporidium
and Giardia lamblia
You may have heard in the news about Cryptosporidiosis
and Giardiasis outbreaks in a number of regions
within the United Kingdom. Both of the organisms
involved are pathogenic and can be waterborne.
Long recognised as a parasite
of animals, cryptosporidium has only recently
been shown to cause illness in humans. Research
is still continuing; this information sheet
is compiled from present available knowledge.
Infection by Cryptosporidium
and Giardia is fairly rare
in people. It normally originates with infected
farm animals and can be transmitted from one
person to another. The symptoms in human beings
are usually severe stomach cramps, sickness
and diarrhoea, nausea, fatigue and weight
loss. The incubation period is from 7 to 14
days and the illness can last from two weeks
onwards depending on vulnerability. Patients
with certain chronic conditions and children
are at higher risk.
Cryptosporidium
organisms (protozoa) form protective oocysts
between 4 to 7 microns in size. Giardia are
also in the form of oocysts but slightly larger,
between 6 to 10 microns in size. (One micron
is one thousandth of a millimetre). This allows
them to survive outside the body of the host,
in a watercourse, and protects them against
disinfection methods such as chlorination
or ultra-violet radiation.
Cryptosporidium
is not killed by normal chlorination and is
only made harmless by long exposure to concentrated
ultra violet light or specialised chemical
treatment, Giardia is killed
by long contact with chlorine or long exposure
to concentrated UV light. However the most
successful method of removing oocysts from
a water supply is by filtration through microstrainers
or cartridge filters.
These oocysts are found
in surface waters e.g. rivers, streams and
some springs. It is unusual to find them in
borehole or deep well waters unless there
are fissures allowing surface waters into
the source.
Occurrence is usually seasonal,
normally found after heavy rainfall in the
spring and autumn when animal faeces are flushed
into watercourses.
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