Alaska Science Forum: Beavers aren’t always responsible for fever

[ad_1]

By Ned Rozell

Years ago I worked for a hunting guide on a river in the middle of Alaska. One of my jobs was to drive a motorized canoe filled with moose meat upstream to a gravel bank from which it could fly.

When I got back from this trip, something funny happened: the noises in my abdomen were so loud that my dog ​​barked. Although I am always careful in the treatment of my drinking water, I came back to town with an intestinal parasite commonly known 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 single-celled animals that thrive in an airless environment. One of their favorite anaerobic places is the human small intestine, near where it connects to the large intestine.

[Beaver invasion on the Baldwin Peninsula]

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

The trophozoites – so small that dozens of them could line up with the edge of a knife – move with the help of flagella, described in 1681 as “various little legs” by Anton van Leeuwenhoek, a sick man. of Giardia who owned a microscope.

Humans catch the disease by swallowing the resting stage of Giardia, the cyst. Cysts are small tablets that come out of the body of an infected animal with the feces. The coating on the cysts dissolves in us; the suffering begins.

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

Beavers are commonly accused of spreading Giardia (beaver fever), but William Bemrick, a researcher at the University of Minnesota, said we too often blame beavers. He cited studies of muskrats that showed they carried even more cysts than beavers that lived nearby.

Bemrick also pointed out that we are good enough at spreading Giardia. Three hundred million cysts can be present in a milligram of human feces, Bemrick wrote, and these cysts can survive for a month in cold water.

Here’s one way someone could pick up Giardia: A muskrat with Giardia defecates in an Alaskan river, releasing millions of cysts invisible to the naked eye. You drive a canoe, heavily laden with bags of moose, upstream. The spray from the river runs down the side of the canoe and gets your face wet. You lick your lips and swallow some of the cysts.

A single cyst reaches your small intestine, turns into a trophozoite, and divides explosively. In two weeks, enough Giardia have taken up residence to induce fever, fatigue and diarrhea.

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

But if the river spray hits you in the face, follow these tips, sometimes useful in other life situations – keep your mouth shut.

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

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

[ad_2]