You're Away: Freshwater Swimming
Schistosomiasis. It might not roll off the tip of your tongue, but it is an infection that affects more than 200 million people worldwide in the tropics. It is caused by a tiny worm, whose eggs are passed by humans in their urine or feces, depending upon the species (of worm, that is). Assuming our human has no access to toilets or latrines, then the local freshwater river or lake is the next best spot. These eggs will then inhabit certain types of snails, and after a month there, are released into the water.
Local people with freshwater exposure become infected when these immature worms penetrate the unbroken skin. After a complicated migration in the human body, they develop into adult worms, and go about producing more eggs. The eggs can cause damage to various organs, including our liver, bowel or bladder.
And that is why we suggest to people that they avoid swimming in fresh water, particularly in tropical Africa, The Amazon, and rural areas of Southeast Asia. If you have no choice, i.e. Lake Malawi looked too inviting, then try to swim in the deeper water where there are no snails (assuming you know how to swim). Fast moving streams, which is where whitewater rafters get exposed, are probably less of a risk. If you do think you have been exposed, rubbing your skin down vigourously with a towel will lessen the risk of larval penetration. Some people will choose to get “dewormed” with the drug paraziquantel after they have been exposed. Tests can also be done once you are home to see if you have become infected.