Wilderness Acquired Diarrhea - Causes

Causes

Infectious diarrhea acquired in the wilderness is caused by various bacteria, viruses, and parasites (protozoa). The most commonly reported are the protozoa Giardia and Cryptosporidium. Other infectious agents may play a larger role than generally believed and include Campylobacter, hepatitis A virus, hepatitis E virus, enterotoxogenic E. coli, E. coli O157:H7, Shigella, and various other viruses. More rarely, Yersinia enterocolitica, Aeromonas hydrophila, and Cyanobacterium may also cause disease.

Giardia lamblia does not tolerate freezing but can remain viable for nearly three months in river water when the temperature is 10°C and about one month at 15–20°C in lake water. Cryptosporidium may survive in cold waters (4°C) for up to 18 months, and can even withstand freezing, although its viability is thereby greatly reduced. Many other varieties of diarrhea-causing organisms, including Shigella and Salmonella typhi, and hepatitis A virus, can survive freezing for weeks to months. Virologists believe all surface water in the United States and Canada has the potential to contain human viruses, which cause a wide range of illnesses including diarrhea, polio and meningitis.

Modes of acquiring infection from these causes are limited to fecal-oral transmission, and contaminated water and food. The major factor governing pathogen content of surface water is human and animal activity in the watershed. The risk of WAD from untreated water may have been over-stated relative to the risk from insufficient hygiene.