Wednesday, April 15, 2015

That Dreaded Giardia

As a ridgerunner, I've dealt with several cases of hikers unknowingly infected with giardia while on their long distance hike of the Appalachian Trail. You can bet it did not add to their experience to be waylaid by constant "runs". Below is an interesting scientific summary of this illness and its cause and treatment, written by SOLO Wilderness Medicine. SOLO is a terrific resource for all manner of health issues that can affect outdoor enthusiasts. I encourage you to receive their monthly e-mail newsletter and even consider taking a course sponsored by them. Check out also my previous blog on water purification methods when in the wilderness.

Even pristine water sources can still contain harmful microbes that cause illness


Double-trouble for the gut
Giardia lamblia (Giardia lamblia) is a flagellated protozoan parasite that infects the small intestine causing diarrhea, bloating, and bad gas. People contract giardia when they consume contaminated food or water.

Giardia has a very simple life cycle. The dormant giardia cyst, ingested along with contaminated food or water, makes its home in the small intestine where the cyst hatches and changes into a trophozoite. (The trophozoites cause the illness-the un-hatched cysts do not.) The trophozoites then reproduce by binary fission (cell division) and the population grows. 

Utilizing a suction disk, the trophozoites anchor themselves onto the wall of the small intestine. They absorb nutrients from within the lumen of the small intestine. Interestingly, they do not feed on, or harm, the cells lining the small intestine. However, as the population increases, the trophozoites spread out across the surface of the small intestine and effectively block the absorption of nutrients out of the intestine. When this occurs, the body tries to rid itself of the parasite by rinsing it out, thus causing the primary symptom of giardiasis-diarrhea.

Giardia is the most common protozoal infection of the human intestine
         It is the most common cause of epidemic and endemic diarrheal illness in the world.
         It is estimated that one out of six people have giardiasis worldwide.
         It is estimated that 50 percent of individuals with giardiasis are asymptomatic.
         The most common symptom of giardiasis is acute, watery diarrhea.
         It is usually a self-limiting disease.
         Death is extremely rare, usually occurring only in malnourished children.
         Consumption of contaminated food or water is the main way that giardiasis is spread.

Etiology (cause) of giardiasis
Giardiasis is caused by consuming food or water that has been contaminated with the giardia cyst. Once the cyst is ingested, it changes into the infectious trophozoite form that begins to reproduce and populate the lumen of the small intestine. This process of reproduction delays the onset of symptoms by 14 - 21 days.

The symptoms of giardiasis are caused by the proliferation and colonization of the lumen of the small intestine by trophozoites. As their population increases, the body's primary protective mechanism to rid itself of the parasite is a mechanical attempt to flush the parasite out via diarrhea. Symptoms include (in order of frequency):

                          Excessive gas (often a foul-tasting and smelly sulfuric flatulence, or belching)
                          Steatorrhea (pale, foul-smelling, greasy stools)
                          Epigastric pain
                          Anorexia (loss of appetite)
                          Vomiting (rare)

Diagnosis of giardiasis
Diagnosis can by made by taking a patient history, determining potential exposure, and observing the clinical symptoms of acute, watery diarrhea and smelly gas.
Diagnosis is confirmed when microscopic examination of the patient's stool reveals cysts or trophozoites.
Diagnosis is also confirmed when an antigen test of the stool detects giardiasis. 

Treatment of giardiasis
metronidazole (Flagyl) 250mg po tid for 5 days, or
tinidazole (Tindamax) 2g po once with food, or
furazolidone (Furoxone) 100mg po qid for 7 days. (This is typically used for treating children, as it is available in a liquid suspension.) The pediatric dose is 25 - 50mg po qid for 7 days, or
nitazoxanide (Alinia) 500mg po bid for 3 days

This Medical Tidbits article was first published as part of a larger article from the Wilderness Medicine Newsletter Volume 21 Number 5, September/October 2008

1 comment:

Buck said...

Good post! The incubation period of giardia(time from ingestion to symptoms) can can vary from 1-45 days or even more. To quote the CDC:

"Acute giardiasis develops after an incubation period of 1 to 14 days (average of 7 days.)"

For hikers, treating water and washing hands before handling food will prevent most cases of giardia.

Tinidazole, a one-treatment drug is the way to go for most people, but not as good as prevention!