Beware of Blood Flukes: Schistosomiasis and Travelers' Health
Schistosomiasis can be a dangerous, chronic parasitic infection, but prevention and treatment are easy; awareness is key, so read on, adventure travelers...
Trouble in paradise
Traveling to tropical countries can be a wonderful experience; hiking through rainforests, snorkeling in coral reefs, and swimming in natural streams and lakes can all be experiences to remember for a lifetime. Exploring "off-the-beaten-path" locations can be especially rewarding for adventurous travelers. However, below the surface of many seemingly clean and natural bodies of water lurks an unseen danger; the tropical parasite known as Schistosoma, or the parasitic blood fluke.
Parasitic blood flukes, also called schistosomes, are tiny worms that alternately parasitize water snails and humans. They multiply as parasites inside snails, then emerge from their snail hosts as tiny, forked-tailed worms a few millimeters long and about the width of a human hair, known as cercariae. Practically invisible, the cercariae bore into the skin of humans swimming or walking through water, enter the blood stream through surface blood vessels and swim to larger, roomier blood vessels where they mature into male and female adult worms. There, they mate and lay eggs. To reach the outside world, the eggs use sharp spines and proteolytic enzymes to penetrate the blood vessel walls and work their way through the flesh into the intestine (in the case of the common species Schistosoma mansoni and Schistosoma japonicum), or the bladder (in the case of Schistosoma haematobium), where they are released in feces or urine into fresh water (where they can hatch into swimming forms capable of infecting a snail host).
Schistosomiasis prevention and treatment
The main health problems from schistosomes stem from the eggs. This is because, though the reproductive goal of the parasite is for the eggs to exit from the body, they often become embedded in flesh wherever they are laid, and this can be anywhere in the body, including the liver, bladder, lungs, or even the brain, giving rise to inflammation, pain, and serious disease conditions such as cancer, hemorrhage (blood loss), and even epileptic seizures, in the case of eggs lodged in the brain. To ensure the continuation of the parasitic life cycle, the worms lay hundreds of eggs every day, many of which never make it to the outside world, remaining lodged in organs of the human host.
Schistosomiasis is endemic in tropical countries in South America, the Caribbean, Africa, and Asia. There is no vaccine, but treatment is fairly straightforward with praziquantel, an anthelmintic (worm-killing) drug. Often, in the United States and other developed countries, doctors are baffled by the symptoms of schistosomiasis, since there is little training for diagnosis of this disease in common medical school curricula. The diffuse, broad range of symptoms caused by schistosome eggs also makes it a particularly difficult disease to diagnose. Once suspected, however, schistosomiasis infection is easy to detect using simple, widely available immunoassay kits. So, if you are experiencing strange pains and other symptoms after swimming in countries that may be endemic for schistosomiasis, ask to consult with a travel health specialist or parasitologist who can test for the infection. Schistosomiasis left untreated can lead to serious chronic health problems, but treatment is straightforward and easy; travelers treated promptly generally experience no major problems if the infection is quickly cleared.