Kevin and Neill spent a couple of days camping next to a lake in a national park. While at the campsite, they swam in the lake and noticed several trees near their campsite had been damaged by beavers. A couple of weeks after they returned home, both young men began to lose weight and have abdominal pain and diarrhea. Based on this information, the emergency room doctor who treated Kevin suspected his patient had become infected with ________.

a. Influenza
b. B Toxoplasma
c. Giardia
d. Bacillus cereus