“Beaver Fever” – Avoid it like the Plague!

I’ll never forget my first backpacking trip into the Wind River mountain range of Wyoming.  It was a week long trek covering over 100 miles of the most pristine, beautiful, high-mountain trails and seldom seen or fished lakes.

I’ve never caught and released so many large rainbow trout and never lacked for my fill of trout for dinner.  Many of the lakes were tucked away in high-mountain box canyons or very remote areas where the snow never completely melts all year.  These lakes are fed by pure mountain water, mostly from the melting snow.

We didn’t give much thought or concern to purifying our drinking water as most of the time we were above the tree line and we felt comfortable the water running off the snow melt was clean and pure.

As we would hike from one lake to another, we would keep our sierra cups hooked on our belts so we could easily grab it and reach down in a stream we were crossing and get a cold drink of water.

As our backpacking trip neared its end, we began hiking at lower altitudes, down in the trees.  That’s where I was foolish enough to continue scooping water out of the streams for a quick drink.  As a result, I was contaminated with “beaver fever”, also known as Giardia, known to be especially abundant near beaver dams.

Luckily, this happened on the last day of our trip so the full effect of Giardia didn’t hit me until after I returned home.  What a blessing!  Had I experienced the full effect of Giardia in the middle of our trek, they would have had to bury me in a shallow grave along the way.

I was so sick and weak as well.  I had to crawl to the bathroom over and over again.  It was an absolutely terrible 10 days!  I never want to repeat that experience again!  Now days, I make absolutely certain I always take an approved water purifier with me whenever I hike in the mountains.  Experience is a great teacher – unfortunately, the lessons can be very costly.

What is Giardia?

Giardia lamblia is a protistan. That makes it a single-celled organism, similar in size to one of your cells. This protistan lives in the intestines of mammals. Many of the microbes that live in our guts are harmless, but this one provokes diarrhea, gassiness, and other gut malfunctions.

It not only reproduces itself in the gut, but can form cysts.  Cysts are basically the hibernating form, much tougher than the active microbe but not able to do anything until it goes active again. Giardia cysts are shed in feces, and when swallowed by a different mammal they can go active once they reach the lower gut.

Giardia can form cysts, which is an inactive form that can survive a long time in water and re-activate when it’s swallowed.

How does one get Giardia?

Drinking water with Giardia cysts is the usual way to get the infection.  Some people have gotten it by swimming in infected waters; but they were very small people and may not have been careful to not drink the water.

The insidious part of it is that it takes very little fecal contamination of water to make it infective. It can be a clear mountain stream, melting off a glacier just half a mile away, but if an infected marmot or raccoon or person pooped by the streamside last week, drinking the water may earn you a Giardia infection.

Giardia occurs in most states too. Nor is it limited to the United States; Giardia infection is one of the most common parasitic infections worldwide.

In the cyst form, it persists somewhere from months to days, depending on temperature, etc. It lasts better in cool, moist conditions.

How does one “not” get Giardia?

Consistently purifying drinking water is a great protection from Giardia. Yes, there have been cases from more casual contact, but they are far more rare.

The good news is that being a protist, Giardia is pretty big. Any filter of reasonable quality will remove it. All the other standard water purification methods such as boiling and various chemical treatments do it too. That’s no accident: Giardia is so widespread and common that you could hardly call something a general water purification method if it didn’t catch Giardia.

How do you know if someone’s got Giardia?

If a person develops yellow, bad-smelling diarrhea that is frothy (with bubbles) but without blood or mucus probably has Giardia. The diarrhea may be a constant thing or may come and go. The person’s likely to be bloated and gassy too, and the gas will smell and taste like sulfur.  Weight loss and lethargy show up after a while, to no one’s surprise.

The most reliably occurring symptoms are abdominal pain and cramping (usually without fever). Since that’s true of most gut disorders, it’s not terribly helpful for diagnosis.

Sometimes people or other animals will have and spread Giardia without showing any symptoms themselves, as well. Their immune systems are controlling it well enough to keep them functioning, but not to eliminate the parasite. Such cases are relevant because of their ability to spread the disease, and because they can develop symptoms at a later time when something else interferes with their immune systems or their gut function.

Fecal smears looking for cysts are effective and pretty easy. However, most preppers won’t have the means on hand; and due to fluxes in microbe populations and such, any given smear from an infected organism is only about 70% likely to show positive though, so persistence might be required.

What can you do about it if someone’s got Giardia?

Most doctors suggest metronidazole (trade name Flagyl). If it’s a recent infection, it’s given 3 times a day for 5 days. People over 8 yrs old get 250 mg (1 tablet) per dose; children 3-7 half that; younger children 1/4 of a tablet per dose. It’s not suitable for pregnant women, especially in the first trimester, and breastfeeding women on high doses shouldn’t give their babies their milk for 24 hrs after a dose.

Giardia infections that have lasted six months or longer should be treated with doses three times as big for 10 days; and quinacrine as well.

Quinacrine (brand name Atabrine) is another option, but not as good because it can cause headaches and vomiting. It’s given as 3 100 mg doses (1 tablet each) per day for a week. Half the dose size for children under 10. If it’s being used for the long-standing infection with the metronidazole, use the same dose but give it for 2-3 weeks.

If you don’t have these … well, the person’s immune system sometimes wins without chemical help against Giardia. Good nutrition will help.

Pets get Giardia too

Many kinds of mammals get Giardia; both suffering symptoms and spreading the microbes. Dogs and cats are at higher risk than people … ever try to stop a dog from taking a lick at a stray puddle when he’s thirsty? Cattle and other food animals also have problems with it, and it can spread very well in their shared water sources.

Symptoms in dogs are very like those in people. Treatment with metronidazole is used for dogs as well as people, and fenbendazole is used in dogs too.

The Bottom Line

Take my word for it – it’s not worth the risk.  Don’t ever drink from any mountain stream or lake without the use of a good water purifier.  Giardia is not something you ever want to get!


Werner, D. 2011. Where There Is No Doctor: A village health care handbook. Hesperian Health Guides, Berkely, CA. Available for download from https://theboatgalley.com/where-there-is-no-doctor-free-download/

Ventura, L. L. A., Oliveira, D. R., Viana, J. C., Santos, J. F. G., Caliari, M. V., & Gomes, M. A. (2013). Impact of protein malnutrition on histological parameters of experimentally infected animals with giardia lamblia. Experimental Parasitology, 133(4), 391.

Ehsan, M. A., Akter, M., Ahammed, M., Ali, M. A., Ahmed, M. U., Leveck, B., & Claerebout, E. (2017). prevalence and clinical importance of cryptosporidium and giardia in human and animals. Bangladesh Journal of Veterinary Medicine, 14(2), 109.

Ward, E. (n.d.) Giardia in dogs. VCA Animal Hospitals. https://vcahospitals.com/know-your-pet/giardia-in-dogs

CDC. 2015. Giardia & Pets. https://www.cdc.gov/parasites/giardi…trol-pets.html


More than 35 years experience in the Preparedness Industry