Beavers get more than their share of blame for spreading Giardia. (Courtesy Photo / Frank Zmuda, Alaska Department of Fish and Game)

Beavers get more than their share of blame for spreading Giardia. (Courtesy Photo / Frank Zmuda, Alaska Department of Fish and Game)

Alaska Science Forum: Beavers not always to blame for fever

If river spray hits you in the face, keep your mouth shut.

By Ned Rozell

Years ago, I worked for a hunting guide on a river in the middle of Alaska. One of my duties was to drive a motorized canoe full of moose meat upstream to a gravel bar where he could fly it out.

When I returned home from that trip, something funny happened: the noises from my abdomen were so loud that my dog barked at them. Though I’m always careful about treating my drinking water, I came back to town with an intestinal parasite known commonly as Giardia.

Here are some facts from the book Giardia and Giardiasis, edited by Stanley Erlandsen of the University of Minnesota and Ernest Meyer of Oregon Health Sciences University:

Giardia is the name commonly used to describe several species of one-celled animals that thrive in an airless environment. One of their favorite anaerobic places is a human’s small intestine, near where it connects to the large intestine.

[Beaver invasion on the Baldwin Peninsula]

Giardia lamblia is the creature that most often knocks humans out for a week or two. It lives in two conditions. One, the trophozoite, looks like a microscopic teardrop. The trophozoite divides by binary fission and makes thousands of copies of itself that attach to the lining of the small intestine.

Trophozoites — so small that dozens of them could line up on the edge of a knife — move with the aid of flagella, described in 1681 as “sundry little paws” by Anton van Leeuwenhoek, a Giardia sufferer who owned a microscope.

Humans pick up the disease by swallowing the resting stage of Giardia, the cyst. Cysts are little tablets that exit an infected animal’s body along with feces. The coating on cysts dissolves within us; the suffering begins.

Animals known to carry Giardia include humans, dogs, cats, beavers, muskrats and bears — and possibly sheep and moose.

Beavers usually get the rap for spreading Giardia (beaver fever), but William Bemrick, a University of Minnesota researcher, said we blame beavers too often. He cited studies on muskrats that showed them to carry even more cysts than beavers that lived nearby.

Bemrick also pointed out that we are pretty efficient at spreading Giardia. Three-hundred million cysts may be present in one milligram of human feces, Bemrick wrote, and these cysts can survive for a month in cool water.

Here’s a way someone might pick up Giardia: A muskrat with Giardia defecates in an Alaska river, releasing millions of cysts that are invisible to the naked eye. You motor a canoe, loaded heavy with bags of moose, upstream. River spray comes over the side of the canoe and wets your face. You lick your lips and swallow a few of the cysts.

A single cyst makes it to your small intestine, morphs to a trophozoite, and divides explosively. In two weeks, enough Giardia have taken up residence to cause a fever, fatigue and diarrhea.

Once you have Giardia, treatment is usually quick with antibiotics, but in some cases it hangs on for months or years. The best plan is to avoid the parasite, especially in rivers and lakes with beavers and muskrats. Boiling water kills the cysts, and filtering water will also remove them.

But if river spray hits you in the face, take these words of advice, sometimes handy in other life situations — keep your mouth shut.

• Since the late 1970s, the University of Alaska Fairbanks’ Geophysical Institute has provided this column free in cooperation with the UAF research community. This year is the institute’s 75th anniversary. Ned Rozell is a science writer for the Geophysical Institute. A version of this column appeared way back in 1998.

Alaska waterways like the Chena River carry Giardia parasites expelled from a variety of animals, including humans. (Courtesy Photo / Ned Rozell.)

Alaska waterways like the Chena River carry Giardia parasites expelled from a variety of animals, including humans. (Courtesy Photo / Ned Rozell.)

More in News

Jasmine Chavez, a crew member aboard the Quantum of the Seas cruise ship, waves to her family during a cell phone conversation after disembarking from the ship at Marine Park on May 10. (Mark Sabbatini / Juneau Empire file photo)
Ships in port for the week of July 13

Here’s what to expect this week.

(Michael Penn / Juneau Empire file photo)
Police calls for Tuesday, July 16, 2024

This report contains public information from law enforcement and public safety agencies.

(Michael Penn / Juneau Empire file photo)
Police calls for Monday, July 15, 2024

This report contains public information from law enforcement and public safety agencies.

(Getty Images)
Peltola leads Republican challengers in latest fundraising report for Alaska U.S. House race

The initial version of this article failed to include donations to candidates… Continue reading

Trees float down Mendenhall River on July 17, 2024. (Jasz Garrett / Juneau Empire)
Suicide Basin fills from heavy rain, but expert says release of water does not appear imminent

Rate of rise increases to about 50 feet per week, but rain expected to slow

People pass by a memorial Tuesday evening for Steven Kissack at the site he was fatally shot by police on Monday. (Mark Sabbatini / Juneau Empire)
Fatal shooting of Steven Kissack by police and community’s response shows Juneau’s failures and heart, mourners say

“If we as a society did fail him then we should make sure we don’t fail others.”

Spawning chum salmon swim in 1990 in Kitoi Bay near Kodiak. A newly released task force report says research should be conducted in a holistic way that considers the complete life cycles and geographic ranges of salmon runs. (David Csepp/NOAA Alaska Fisheries Science Center)
Task force report identifies research needs to better understand Alaska salmon problems

Fishery managers overseeing Alaska’s faltering salmon runs should be able to rely… Continue reading

The U.S. Coast Guard Cutter Kimball, right, and a Japanese naval training vessel travel near the island of Unalaska in 2021. The Kimball intercepted a group of Chinese military vessels operating near the Aleutian Islands on July 6 and 7. (U.S. Coast Guard photo)
Inside the U.S. Coast Guard’s Aleutian encounter with China’s military — and what it means

The Chinese warships weren’t showing up on civilian radar. But the American… Continue reading

Most Read