Giardiasis

The most common enteric protozoan pathogen worldwide.

A global diarrheal illness.

Infects nearly 2% of adults and 6% to 8% of children in developed countries worldwide.

Nearly 33% of people in developing countries have had giardiasis.

In the United States infection is the most common intestinal parasitic disease.

Known as Giardia lambia or Giardia duodenalis.

A protozoan flagellate.

Have two nuclei, each with four associated flagella, and lack both mitochondria and a Golgi apparatus.

Both cysts and trophozoites can be found in the feces.

Infection occurs by the ingestion of cysts in contaminated water, food, or by the fecal-oral route.

Excystation in the small intestine releases trophozoites.

Each cyst produces two trophozoites which multiply by longitudinal binary fission, remaining in the lumen of the proximal small bowel.

Trophozoites in the small bowel lumen can be free or attach to the mucosa by a ventral sucking disk.

As the parasites transit toward the colon they encyst.

The cyst is the stage found most commonly in nondiarrheal feces.

The parasite is most often carried in an asymptomatic state but can cause endemic or epidemic diarrheal manifestations.

Trophozoites proliferate in the small bowel and encyst in the jejunum.

Cysts are instantly infectious once they leave the host through feces.

An infected person might shed 1-10 billion cysts daily in their feces and it may last for several months.

Cysts can survive in water up to 3 months and are resistant to chlorine.

Transmission can be person to person or via ingestion of contaminated water or food.

Giardiasis occurs more commonly in the developing world.

Giardia gastroenteritis occurs more commonly in travelers to areas with high prevalence, in children attending day care facilities and in men who have sex with men.

Giardia gastroenteritis occurs at higher rate following disasters.

Transmission may occur from drinking contaminated water or when people share personal objects.

Water quality typically worsens during the rainy season.

Giardiasis outbreaks are more common during the rainy season.

Infection can be transmitted by as few as 10-100 cysts.

Highly contagious.

Symptoms normally begin 1 to 3 weeks after a person has been infected.

Symptoms range from mild intestinal problems that resolved spontaneously to complex symptoms lasting several weeks and associated with fatigue, protein losing enterography, abdominal pain, nausea, chronic diarrhea, and weight loss.

By age 5 the disease is nearly universal in the developing world and recurrent infections can occur.

In the U.S. high risk groups include children, male homosexuals, campers, hikers, patients with achlorhydria and international travelers.

Disease in the U.S. are usually sporadic in nature.

Giardia infection rates have been known to go up in late summer.

Hypogammaglobulinemic immunocompromised patients may have virulent disease.


Giardiasis can be transmitted between gay men, and it can be responsible for weight loss and death for individuals who have compromised immune systems, especially HIV.


Oral-anal contact during sex has been known to cause infection.

Humans are the main reservoir of disease but dogs, cats, beavers, guinea pigs may be infected suggesting the infection is a zoonosis.

While animals are infected their importance as a reservoir is not clear.

Rotavirus may work synergistically to enhance pathogenesis with more successful attachment of the ventral disc of trophozoites to the infected epithelium.

Infection in children may cause growth in cognitive impairment with loss of iron and micronutrients.

Between 40-50% of infected patients develop diarrhea.


Yellowing of feces can be caused by giardiasis, 


Patients experience explosive, foul smelling diarrhea with increased passage of gas.

With chronic illness patients may experience malabsorption.

20-40% of patients develop lactose intolerance.

Acute symptoms include:Diarrhea, flatulence,greasy and floating stools, abdominal cramps, nausea, vomiting, dehydration, weight loss, and malabsorption syndrome.

In children, severe infection may delay physical and mental growth, and cause malnutrition.

Cysts can be excreted intermittently, so multiple stool specimens collected on multiple days increases diagnostic sensitivity.

Fecal immunoassays that are more sensitive and specific for diagnosis than stool staining for cysts.

Polymerase chain reaction can be used to identify the subtypes of Giardia.

Effective treatment includes metronidazole.

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