Giardia intestinalis, also known as Giardia lamblia and Giardia duodenalis just to keep things interesting, is the most common disease-causing parasite in the world. While North America got the short end of the stick when it comes to parasite shares worldwide, Giardia didn't pass us by. There are approximately 15,000 cases reported to the Centers for Disease Control each year; undoubtedly many go unreported, as the protozoa don't cause any symptoms in some people. It is estimated that 20-40% of the world's population has giardiasis.
As the most common protozoal infection in the United States, giardiasis is more common in northern states and afflicts children under the age of 10 years and adults 35-44 years most frequently. [1] Infections are most common in late summer, when people ingest the cysts by drinking contaminated water. Yes, even those crystal clear mountain streams can harbor Giardia. (However, in glacial run-off above the treeline, the risk of giardia is greatly diminished.)
The cysts are ingested and activated by stomach acid. They develop into trophozoites, attach to the intestinal walls, and make more cysts to infect others. These new cysts then are excreted with feces. The cysts can also be passed by infected food handlers or in swimming pools and recreational waters. Even chlorinated swimming pools don't eliminate the risk as it requires about 45 minutes of exposure to chlorine before the cysts are killed.
One to two weeks, sometimes more, after ingesting the cysts, the following symptoms begin:
diarrhea. It's described as quite foul, watery and greasy, yellow, and frothy--full of bubbles, but without any blood or mucus.[2]
burping. There is a great deal of burping, and the burps taste like sulfur.
gas. There is likewise a lot of gas.
bloating. The abdomen is rather swollen.[3] For most individuals, the illness passes in four to six weeks. Standard treatment is with metronidazole, 250 mg, 3 times per day, for 5-7 days, with food.[4]
Alternative treatments not approved by the FDA include albendazole, 400 mg per day for 5 days and mebendazole (no dosing regimen provided). A tincture from Japanese barberry or Oregon grape may also be effective.[5]
References:
[1] Julia E. Painter, et al., "Giardiasis Surveillance--U.S. 2011-2012," Surveillance Summaries, Centers for Disease Control and Prevention, 1 May 2015 https://www.cdc.gov/mmwr/preview/mmwrhtml/ss6403a2.htm (accessed 3 March 2020).
[2] David Werner, Where There Is No Doctor, 145.
[3] Ibid.
[4] Joseph Alton, Alton's Antibiotics, 176; Cynthia Koelker, Armageddon Medicine, 173.
[5] Stephen Buhner, Herbal Antibiotics, 164.
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