I pride myself, if anything, on being able to admit when I'm wrong. But even at my wrongest, there is usually an important lesson to be learned. This particular one should be resoundingly clear. Be careful where you pee.
After a heated debate I had with a guy recently, over whether the rumor is true, whether it is dangerous for men to pee off a boat in the Amazon because parasites will swim up your "member", I was forced to engage in a furious bout of googling producing the following results which I feel it is my hallowed duty to share with the rest of you. If you're squeamish, I forewarn you to stop reading now.
It is a documented fact that there is a parasite native to the Amazon river called the Candiru (Vandellia cirrhosa), affectionately known as the "vampire catfish", which will swim up a stream of pee. According to medical science, firsthand accounts, and urban legend, all of which I weigh equally seriously when determining anything worth repeating, this fish is an agressive urinophilic fish, meaning that it is attracted to the smell of urine. This fish will then locate the source of this smell and swim vigorously up the openings of any human or animal cavity.
If this isn't enough to shiver your timbers, let me add this gruesome detail. After the fish swims up your organ, it spreads its spines, yes that's right spines, and begins to feed off of your tissues and blood.
It was also said that even if one caught the fish by the tail, once in the urethra it could not be pulled out because it would spread itself like an umbrella.
Because the fish spreads its gill covers in trying to get oxygen, the sharp spinous processes on the ends of the opercula engage the urethral wall making extraction from the urethra almost impossible or at least most traumatic.
From“Candiru: Urinophilic Catfish Its Gift to Urology,” John R. Herman, M.D.
When candirus parasitize humans, it is usually only when they are skinny-dipping while urinating in the water. The candiru tastes the urine stream and follows it back to the human. It then swims up the anus and lodges itself somewhere in the urinary tract with its spines. Blood is drawn, and the candiru gorges itself on both the blood and body tissue, its body sometimes expanding due to the amount of blood. This is all said to be very painful for the poor person who has this happen to him or her. Unfortunately, they are almost impossible to remove due to the spines. Amputation of the private areas is the cheapest, and most life-changing, way to remove the fish. Actual surgery is extremely expensive and involves inserting the Xagua plant and the Buitach apple up the urethra. These two plants kill and even dissolve the parasitic fish. If surgery is not done in time, the blockage of the urinary tract will prove fatal. The candiru is the only known vertebrate to parasitize humans. (link)
While the jury still appears to be out regarding whether this fish may actually be able to swim up a stream of piss belonging to a guy on a boat, it should be clear that it is not totally impossible. And when in doubt? Cross your legs or pee in a cup. But all humans appear to be fair game, as the Candiru will swim up male and female genitalia alike, and appears to enjoy the anus as well! Clearly a hearty fish. Too bad it's so small or I fancy it may be good eating in the same way that bottom feeders and certain shellfish are particularly tasty. I wonder what the Prophet Mohammed might have to say about this.
For further reading, feel free to look up E. W. Gudger's "On the alleged penetration of the human urethra by an Amazonian catfish called candiru with a review of the allied habits of other members of the family pygidiidae part I" Americal Journal of Surgery 8(1)
I myself am moving onto another promising article found while browsing: Heinrich L. Wehrbein's "Cytological study of gonorrheal pus" Americal Journal of Surgery 8(1)
Who knew medical journals would be so fascinating.