GIARDIA
AND CRYPTOSPORIDIUM IN DRINKING WATER
What are Giardia and
Cryptosporidium?
Giardia and Cryptosporidium
are microscopic parasites that can be found in water. Giardia
causes an intestinal illness called giardiasis or "beaver
fever." Cryptosporidium is responsible for a similar illness
called cryptosporidiosis.
How do these parasites
cause illness?
Both parasites produce
cysts that are very resistant to harsh environmental conditions.
When ingested, they germinate, reproduce, and cause illness. After
feeding, the parasites form new cysts, which are then passed in
the faeces. Studies with human volunteers have shown that ingestion
of only a few cysts will cause illness.
What are the symptoms?
Diarrhoea, abdominal
cramps, gas, malaise, and weight loss are the most common symptoms
caused by Giardia. Vomiting, chills, headache, and fever may also
occur. These symptoms usually surface six to 16 days after the
initial contact and can continue as long as one month.
The symptoms of cryptosporidiosis
are similar; the most common include watery diarrhoea, abdominal
cramps, nausea, and headaches. These symptoms occur within two
to 25 days of infection and usually last one or two weeks; in
some cases they stick around for up to a month.
How are infections
treated?
Giardia is usually
cleared from healthy people without treatment within a month.
Anti-parasitic drugs are available and are particularly helpful
for immunocompromised people in whom the illness could otherwise
develop into a persistent state.
Cryptosporidium will
also usually disappear from healthy people within a month without
treatment. Anti-diarrhoeal drugs and rehydration therapy may be
used if diarrhoea becomes severe. No drugs to fight the illness
have been approved, though many are now being tested.
What extra precautions
can immunocompromised people take?
Both parasites, but
particularly Cryptosporidium, can pose a more serious threat to
immunocompromised people, such as those living with AIDS or cancer,
or transplant patients receiving immunosuppressive drugs. For
these people, the symptoms are more severe and can be life threatening.
It is presently unknown
whether immunocompromised individuals are at greater risk of contracting
giardiasis or cryptosporidiosis than the general public. Nevertheless,
immunocompromised individuals should discuss these risks with
their physicians. People who wish to take extra precautions can
boil their water for one minute to kill any parasites that may
be present. This practice will also destroy any other microorganisms
that might be of concern to these individuals. As bottled water
is not routinely monitored for Giardia and Cryptosporidium, its
suitability as an alternative to boiled tap water is unknown.
What should you tell
your physician?
If you are suffering
from diarrhoea and suspect that your symptoms may be due to Giardia
or Cryptosporidium, visit your physician and mention any exposure
you may have had to water, food, or faeces that may have been
contaminated by the parasites.
How can drinking water
become contaminated with these parasites?
Giardia are often found
in human, beaver, muskrat, and dog faeces. Cattle faeces appear
to be the primary source of Cryptosporidium, although these parasites
have also been found in humans and other animals. Drinking water
sources become contaminated when faeces containing the parasites
are deposited or flushed into water. If treatment is inadequate,
drinking water may contain sufficient numbers of parasites to
cause illness. Other sources include direct exposure to the faeces
of infected humans and animals, eating contaminated food, and
accidental ingestion of contaminated recreational water. The comparative
importance of these various routes of exposure is unknown.
Have these parasites
been found in Canadian drinking water supplies?
Low levels of both
parasites, especially Giardia, were detected in a national survey
of drinking water conducted by Health Canada. Only a small fraction
of the parasites appeared to be viable and their ability to infect
humans was not determined. Nevertheless, outbreaks of illness
linked to these parasites in drinking water have been reported
in several provinces. Their spread in swimming pools has also
been reported.
How can these waterborne
illnesses be prevented?
Municipal drinking
water treatment providing filtration and disinfection with chlorine
can reduce the risk of contracting giardiasis and cryptosporidiosis.
Chlorine by itself is not effective against Cryptosporidium but
can inactivate Giardia. Recent research indicates that ultraviolet
light will inactivate both organisms. Protection of the raw water
supply is also beneficial.
If Giardia or Cryptosporidium
in municipal drinking water is suspected or known to be the cause
of an outbreak, public health authorities will issue a boil water
advisory to help control the spread of illness.
In the outdoors, water
should be boiled for at least one minute before it is used for
drinking, food preparation or dental hygiene. This treatment will
destroy not only Giardia and Cryptosporidium, but also any other
disease-causing microorganisms that might be present. Certain
types of filters can remove the parasites.
Travellers to countries where the safety of drinking water is
suspect should boil or disinfect and filter water that is to be
used for drinking, food preparation, or dental hygiene.
Are water supplies
tested for Giardia and Cryptosporidium?
Unfortunately, no reliable
methods are currently available to detect these parasites on a
routine basis. This is largely because the methods underestimate
the number of organisms present and do not provide any information
on their capacity to cause illness in humans. The tests that do
exist take a few days to come up with results which means they
aren't very good for day-to-day monitoring. Research is underway
in Canada and internationally to develop appropriate detection
methods and treatment technology to safeguard drinking water against
these parasites.
Is there a Canadian
drinking water guideline for these parasites?
Yes and no. A guideline
has been established for Giardia and Cryptosporidium, but because
the current detection methods are not very reliable the guideline
does not give a maximum acceptable concentration (MAC) value for
these parasites in drinking water. The guideline does, however,
encourage water treatment authorities to implement measures aimed
at reducing the risk of illness as much as possible. The guideline
states: "If the presence of viable, human-infectious cysts
or oocysts is known or suspected in source waters, or if Giardia
or Cryptosporidium has been responsible for past waterborne outbreaks
in a community, a treatment and distribution regime and a watershed
or wellhead protection plan (where feasible) or other measures
known to reduce the risk of illness should be implemented."
What is Health Canada
doing to ensure the safety of our drinking water?
Health Canada works
with the provinces and territories to ensure they have access
to the most current scientific information available about issues
related to drinking water. A consistent approach to improving
drinking water quality is provided by Health Canada's Guidelines
for Canadian Drinking Water Quality which are designed to ensure
that Canadians have access to wholesome and safe drinking water.
Return
to Information Library
|