The River of Doubt: Theodore Roosevelt's Darkest Journey

by Candice Millard

When it comes to parasitizing people, a very rare occurrence, the candiru’s modus operandi is to enter through an

orifice—from a vagina to an anus. It is most famous, however, for wiggling its way into a urethra. The most widely discussed, if highly controversial, theory is that candirus are attracted to urine streams, mistaking them for the gill streams of fish. Before the unsuspecting bather knows what is happening, the candiru has followed the stream to its source, slipped inside, sunk its spines in the soft tissue, and begun to gorge on its host’s blood. For the candiru, this is a fatal move. While it can easily swim out of a fish’s gills, it cannot find its way out of a human urethra. Even if it could swim backward, its stiff spines prevent it from going in any direction but forward.