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Giardia & Giardiasis
|Giardiasis in humans is caused by the
infection of the small intestine by a single-celled organism called
Giardia lamblia. Giardiasis occurs worldwide with a prevalence of
20–30% in developing countries. Additionally, Giardia has a wide range
of human and other mammalian hosts, thus making it very difficult to
Giardia is a genus of anaerobic flagellated protozoan parasites of the
phylum Metamonada in the supergroup "Excavata" (named for the excavated
groove on one side of the cell body) that colonise and reproduce in the
small intestines of several vertebrates, causing giardiasis. Their life
cycle alternates between an actively swimming trophozoite and an
infective, resistant cyst. The genus was named after French zoologist
Alfred Mathieu Giard.
Giardiasis is caused by the ingestion of infective cysts. There are
multiple modes of transmission including person-to-person, water-borne,
and venereal. Person-to-person transmission accounts for a majority of
Giardia infections and is usually associated with poor hygiene and
sanitation. Water-borne transmission is common in United States Giardia
epidemics, which are often associated with the ingestion of unfiltered
water (contaminated). Venereal transmission happens through fecal-oral
contamination. Additionally, diaper changing and inadequate hand
washing are risk factors for transmission from infected children.
Lastly, food-borne epidemics of Giardia have developed through the
contamination of food by infected food-handlers.
A range of clinical syndromes may occur, with gastrointestinal
syndromes being the most prevalent.
Giardia lives inside the intestines of infected humans or animals.
Individuals become infected through ingesting or coming into contact
with contaminated food, soil, or water. The Giardia parasite spreads
when a person accidently swallows it, which can originate from
contaminated items and surfaces that have been tainted by the feces of
an infected human or animal. Consuming unsanitary water or food is also
another way in which the parasite can transfer from being to being.
The symptoms of Giardia, which may begin to appear 1-2 weeks after
infection, include diarrhea, excess gas, stomach or abdominal cramps,
and upset stomach or nausea. The result of these occurrences is weight
loss and/or dehydration, which can be harmful if not treated
immediately. The typical infection within an individual is around 2-6
weeks, but medication can decrease that time period.
A small number of infected individuals experience an abrupt onset of
abdominal cramps, explosive, watery diarrhea, vomiting, foul flatus,
and fever which may last for 3–4 days before proceeding into a more
sub-acute phase. The majority of infected persons develop gradual
symptoms that become recurrent or resistant.
In both the acute and insidious onsets of symptoms, stools become
greasy and malodorous but do not contain blood or pus because
giardiasis does not involve dysenteric symptoms. Watery diarrhea may
cycle with soft stools and constipation. Upper GI symptoms including
nausea, early satiety, bloating, substernal burning, egg-smelling
halitosis, and acid indigestion may be exacerbated by eating and are
generally present in the absence of soft stools.
Prevalence rates for giardiasis range from 20–30% in most developing
countries and 2–7% in developed countries. The CDC estimates that in
the United States there are more than 2.5 million cases of giardiasis
annually. Giardiasis occurs worldwide with increased prevalence in
areas with poor water treatment facilities and unsanitary conditions.
The area of highest prevalence is the tropics and subtropics. Despite
this, giardiasis does affect a large number of individuals living in
highly developed nations with strong infrastructure and water systems.
In the United States, giardiasis is the most commonly reported
pathogenic protozoan disease.
High infection rates occur in hikers and backpackers in the United
States. Giardiasis is a common infection in active outdoors population
because of their exposure to areas inhabited by infected wild animals
and ingestion of free flowing water which may contain cysts.
Furthermore, giardiasis is common in tourists and business travelers to
developing countries, especially Mexico, Southeast Asia, western South
America and Russia. Also, an increased prevalence of giardiasis among
homosexual men has been reported by a number of studies. Because
infection may be caused by poor hygiene, giardiasis has high
infection rates in daycare centers and nursing homes, though the groups
most at risk for infection are overseas travelers and hikers.
Currently, there is no
vaccine to protect humans from acquiring
giardiasis. Preventing Giardia can be accomplished by practicing good
purifying/filter water that may be contaminated or avoiding it all
together, and avoiding fecal contact.
| Did You Know?
|The Centers for Disease
Control and Prevention reports that in the US Giardia infects over 2.5
million people annually.
usually begin 1 to 2 weeks (average 7 days)
after an individual becomes infected. In otherwise healthy individuals,
symptoms may last 2 to 6 weeks. Though symptoms may last longer,
medications can help decrease the duration of symptoms.
|Giardia has no vector. It affects a
wide range of human and mammalian reservoir hosts. Small aquatic or
semi-aquatic wild mammals, such as beavers, muskrats, and small rodents
harbor water-born cysts of giardia and serve as important reservoir
hosts. Furthermore, a variety of birds may also serve as reservoirs of
water supplies, such as water in rivers and lakes and improperly
treated water in developing countries, are also reservoirs of the
waterborne cysts. Often, contamination of surface water is caused by
rain and wind carrying cysts from fields containing or fertilized by
manures of infected humans, livestock, or wild animals to nearby rivers
and streams. Giardia cysts can remain viable in surface water for
approximately two months. As a result, it is more dangerous for hikers
to consume water from rivers and lakes during and immediately after
raining seasons as contamination tend to be most severe during these
periods. Finally, the organism can often be found in soil, food, and
surfaces contaminated with feces containing infectious cysts.
|First and foremost, avoid
contaminated water. Hikers and overseas
travelers to developing countries should consider all water sources
contaminated and thus boil, filter, or treat all water with halogenated
tablets or solutions. Second, avoid foods washed in contaminated water
or that cannot be cooked or peeled, which is especially important for
travelers to developing countries. Using only bottled water and
avoiding raw fruits and vegetables decreases risk of infection
United States, many of the reported cases of Giardia occur in
the summer months. According to virologists and epidemiologists ,this
is the time when hikers and backpackers are
avid because of the ideal climate during these months. Also, this may
be due to the use of community swimming areas by young diaper-aged
children during the summer.