Being infected by parasites sounds like something that happens to other people in faraway places. However, parasites that infect humans are far more common than you might think. A lot of them have no symptoms, either, so people can go years without knowing they are infected.
Possibly up to 60 percent of the world’s population has at least one parasite in them right now. That’s right, there’s better than a 50/50 chance that you have one right now. Here is a list of ten of the most common asymptomatic parasites that could be nearer than you might think.
Do you like your steak rare? Well, tapeworms (Taenia solium or Taenia saginata) get into human hosts from raw or undercooked meat. These tape measure–shaped parasites can grow up to 15 meters (50 ft) long. They like to live in people’s intestines and are transferred from animals, mostly cows and pigs. This happens either through the consumption of infected meat or unwashed vegetables.
If a tapeworm larva is eaten, it can grow into a full-blown adult that feeds off of the intestinal wall. This little guy can live in a human gut for nearly 30 years. People can grow old with their parasite. How cute. The tapeworm’s eggs, which can develop into cysts on organs, can be much more dangerous. If the infection is just the tapeworm (or worms), symptoms can be rare or do not appear at all. It will happily live unnoticed for years.
4. Liver Flukes
Liver flukes are parasites that infect the bile ducts and liver. They are one of a number of flatworms that breed in freshwater snails. One way they can infect humans is through the consumption of freshwater fish that share the same environment.
These flat-looking parasites can cause few symptoms in humans. Therefore, someone can be infected without ever knowing it. Mature flukes will eventually cause chronic inflammation of the bile ducts, which often leads to gallstones. While the majority of cases are found in developing countries, there have been cases in Hawaii, California, and Florida.
Two kinds of hookworms that can infect human hosts are Ancylostoma duodenale and Necator americanus. Hookworms make an interesting journey through the human body. They enter through the feet and can sometimes leave itchy rashes at their entry point. They will travel along the bloodstream until they can enter the lungs. Once in the lungs, they irritate lung tissue enough that the infected host coughs them up into their mouth. If even a little bit of that bloody, wormy phlegm gets swallowed, the hookworm is happily in its desired home: the small intestine.
This is a parasite that has been particularly prominent in some communities because it can be transferred from person to person through poop. If infected stool isn’t managed properly or is spread in soil, it can infect others easily. Therefore, now that we have better sanitation practices, hookworm infection has diminished, but it hasn’t disappeared.
It has been argued that the American South was left in an economic lethargy because of hookworms. For about 300 years, nearly 40 percent of the population was infected. If someone is heavily infected with hookworms, it can cause lethargy and mental incapacity. Therefore, with so much of the population infected, the South didn’t have the ability to keep up with its wormless neighbors. Otherwise, there are very few symptoms.
Pinworms are a parasite that can spread very easily. They are generally the most common parasitic infection in North America. They live on the human anus, so it takes just one scratch, and then anything that person touches can be covered with pinworm eggs. If someone swallows an egg, they become infected.
There are generally very few symptoms; sometimes it’s just a mild irritation, which encourages the infected host to scratch their butt and keep spreading the eggs. Mostly, pinworm infections are found in children, but they can easily infect anyone who has been exposed to them.
Ascariasis is a roundworm infestation that attacks the small intestine. It usually spreads from exposure to human feces or uncooked meat, however it can also spread via human-to-human contact. Usually, it has few symptoms, unless the host has a large infestation of these roundworms.
Children are the most likely to display symptoms, and they’re often at a higher risk of getting infected with ascariasis because of their tendency to put their hands in their mouths. They can suffer bloated stomachs and pain as a result. Mostly though, the little roundworms just live in your stomach until they are ready to be pooped out.