Giardiasis: The Daily PANCE Blueprint

The answer is D. Giardia lamblia (Giardia duodenalis)

Two weeks of greasy, floating, foul-smelling stools with bloating and belching after drinking untreated stream water is giardiasis — infection with Giardia lamblia, the flagellated protozoan sometimes nicknamed “beaver fever.” The trophozoites carpet the duodenum and jejunum and blunt the brush border, producing a malabsorptive, non-inflammatory diarrhea: fat is not absorbed, so stools are pale, oily, and float, and the illness runs weeks rather than days with weight loss. The absence of fever, blood, mucus, and fecal leukocytes is what tells you this is not an invasive process. Diagnose with a stool antigen test or PCR, which have replaced the old “three stools for ova and parasites”; treat with tinidazole (single dose) or metronidazole — nitazoxanide is a good alternative in children. Working through the distractors: Entamoeba histolytica causes invasive dysentery with bloody stools and can seed a right-upper-quadrant liver abscess; enterotoxigenic E. coli is classic traveler’s diarrhea but is watery, self-limited, and lasts days, not weeks; Cryptosporidium is the closest mimic and shares the waterborne route, but it causes prolonged, high-volume watery diarrhea and matters most in immunocompromised hosts, especially AIDS with a CD4 count under 100; and norovirus is an explosive vomiting-and-diarrhea illness over 24 to 72 hours. Prevention is the practical pearl: boiling or filtering backcountry water — chlorination alone does not reliably kill the cysts.