“Beaver fever” is the common, informal term for Giardiasis, a gastrointestinal illness caused by the microscopic parasite Giardia lamblia. The name arose because the infection is often associated with consuming water from wilderness sources, where animals like beavers can contaminate the supply. Giardiasis is a widespread ailment globally and is one of the most common causes of waterborne disease outbreaks in the United States. The illness develops when a person accidentally ingests the parasite, which then colonizes the small intestine.
The Parasite and How It Spreads
The organism Giardia lamblia exists in two forms: the active trophozoite found in the small intestine and a tough, inactive cyst form. The cyst is shed in the feces of infected humans and animals and is remarkably resilient, surviving for weeks to months in cold water sources. Ingestion of a small number of these cysts is sufficient to cause illness.
The primary method of transmission is the fecal-oral route, spreading through contaminated water, food, or surfaces. Untreated surface water from rivers, streams, and lakes is a major source. While wildlife, including beavers, are reservoirs, human waste and poor sanitation are also significant contributors to water contamination.
Person-to-person spread is common, especially in settings like childcare facilities where hygiene practices may be inconsistent. Infection can occur indirectly by touching a contaminated surface, such as a changing table or toy, and then touching the mouth.
Recognizing the Signs of Infection
Symptoms typically appear one to three weeks after exposure. The onset varies widely; some individuals remain asymptomatic but can still spread the parasite through their stool. For those who become ill, symptoms are concentrated in the gastrointestinal tract.
Common signs include severe, watery diarrhea, abdominal cramps, and bloating. A distinguishing feature is the presence of pale, greasy, and foul-smelling stools, a condition known as steatorrhea. Other symptoms include nausea, loss of appetite, and fatigue. Although the colloquial name includes “fever,” a high temperature is an uncommon symptom.
If the infection persists and causes chronic diarrhea, it can result in substantial weight loss and nutrient malabsorption. The active parasite interferes with the normal function of the small intestine. In children, prolonged infection may negatively impact development.
Treatment and Recovery
Diagnosis is achieved by analyzing the patient’s stool samples in a laboratory. Technicians look for the presence of Giardia cysts or active trophozoites to confirm the infection. Because the parasite sheds cyclically, healthcare providers may request multiple stool samples collected over several days for an accurate diagnosis.
For many healthy individuals, the infection is self-limiting and often clears up within a few weeks without medical intervention. If symptoms are pronounced or persistent, prescription antiparasitic medications are used. Common treatment options include Metronidazole, Tinidazole, and Nitazoxanide.
Metronidazole is frequently prescribed over a five-to-seven-day course. Tinidazole is an alternative often favored because it can be effective in a single, high dose. Throughout recovery, managing fluid loss is important, and patients should drink sufficient water or use an electrolyte solution to avoid dehydration caused by diarrhea.
Avoiding Contamination
Prevention centers on avoiding the ingestion of the parasite through careful attention to food, water, and personal hygiene. Campers and hikers must never drink untreated water from streams, lakes, or ponds, even if it appears clean. Water must be purified to remove the resilient Giardia cysts before consumption.
Boiling water is the most reliable method for killing the parasite; a rolling boil for at least one minute is sufficient. Chemical treatments, such as iodine or chlorine, are alternatives, but they are generally considered less effective against Giardia than boiling or specialized filtration. Microfilters designed to remove particles as small as one micron can also physically remove the cysts.
Maintaining meticulous hand hygiene is a primary defense against person-to-person spread. Hands should be thoroughly washed with soap and running water after using the restroom, changing diapers, and before preparing or eating food. When swimming in pools or lakes, people should avoid swallowing the water, as these areas can be contaminated.