Protozoa Parasites

The simplest type of animal, consisting of just one cell, protozoa most frequently infect humans through contaminated water. About 30 different types of protozoa are parasites in humans, but the three related to food safety are Giardia, Cryptosporidium, and Cyclospora.

Giardia

Giardia lamblia is responsible for the most common parasitic infection in the world, and is most frequently associated with the consumption of contaminated water. Another common source of infection is child-care centers.

Giardia inhabit the small intestine by attaching themselves to the cells of the intestinal wall, from which they absorb their nourishment. Giardia was once thought to be nonpathogenic, but more recent evidence indicates that it interferes with the absorption of fats.

Infection with this organism causes recurring attacks of diarrhea and the passage of stools containing large amounts of unabsorbed fats and yellow mucus. Giardia is the most frequent cause of diarrhea other than bacteria. The illness usually lasts one to two weeks, but some cases last up to months or even years.

Giardia is primarily transmitted through surface streams and lakes that have been contaminated with the feces of infected livestock and other animals. People get infected with the parasite not only from drinking the surface water but also from eating the infected livestock. The proper heating of meat and fish kills this parasite, and campers can treat stream and lake water with boiling, filters, and purifiers. When a Giardia infection is contracted in spite of these precautions, medications can be taken for the symptoms.

Cryptosporidium

Drinking water contaminated with human or animal feces is the source for this microscopic parasite. The typical symptom is a low-grade fever, which occurs two to three days after ingesting the parasite and lasts about two to three weeks. The identification of C. parvum is difficult because routine stool examinations do not detect the parasite; tests specifically designed for its detection must be used. There is currently no reliable treatment available, so preventative measures are the best defense.

Cyclospora

Relatively new on the scene, Cyclospora cayetanensis is most likely spread through the oral-fecal route, by contaminated water, or by food that has been exposed to contaminated water. Cyclospora infects the small intestine, resulting in symptoms of watery diarrhea, bloating, loss of appetite and weight, stomach cramps, gas, muscle aches, fatigue, and a low-grade fever. Onset usually occurs within a couple of days of exposure, and the duration ranges from one to eleven days, but can continue for up to a month with relapses occurring after that unless the sufferer is treated with antibiotics.