In this blog post, we’ll debunk common misconceptions about parasites and take a look at the parasites we should actually be wary of, along with ways to prevent them.
Misconceptions About “The Host” Caused by the Movie
A long time ago in South Korea, the release of the movie “The Host,” which centered on parasites, sparked a period of intense public interest in various types of parasites, including the “Yeonggasi.” Parasites became a major topic of conversation, appearing not only in the rankings of popular search terms on major portal sites but also consistently showing up in related search queries. I, too, was intrigued by the film’s novel take on parasites and went to the theater to see *The Host* immediately after its release. I had once attended a lecture by a medical school professor who specialized in parasitology as part of a general education course, and throughout the movie, I couldn’t help but notice how different the depiction of the “host” in the film was from what I had learned in that class. Of course, movies inevitably include fictional elements for dramatic effect, and the film’s opening credits explicitly stated that the story differs from the facts about real-life tapeworms. However, given the nature of film as a medium that exerts a significant influence on the public, it seems difficult to prevent the emergence of aversion and prejudice toward tapeworms based on that alone. In fact, a great deal of negative content was posted online, and there were even people who believed that threadworms could parasitize the human brain and control it. In this article, I aim to use threadworms as a case study to correct vague misunderstandings, fears, and misconceptions about parasites, and to introduce several actually dangerous parasites that one might encounter in daily life, along with methods to prevent infection.
First, let’s take a look at the threadworm, the most famous of the countless parasites. Taxonomically, the threadworm belongs to the phylum Nematomorpha. Adult threadworms range in length from about 10 to 90 cm and have a diameter of about 2 to 3 mm, giving them a very thin, long, thread-like appearance. They primarily inhabit clear waterways but can also be found in damp environments such as puddles, ponds, reservoirs, and caves. The question people are most curious about regarding threadworms is, “Can threadworms parasitize humans?” Fortunately, the answer is “No.” The threadworm uses only insects—such as grasshoppers, crickets, katydids, and mantises—as hosts. Even if a threadworm were accidentally swallowed, it would be digested by stomach acid and could not survive. Furthermore, unlike its natural insect hosts, it cannot survive at human body temperature, making it virtually impossible for it to parasitize the human body. In other words, there is no need to be overly afraid based on the portrayal of threadworms in movies. Another reason sand flies are perceived as objects of fear is their unique life cycle, which became a central theme in the movie. As the breeding season approaches, sand flies alter the behavior of their insect hosts, causing them to move toward bodies of water, and eventually break out of the host’s body. While this is a horrifying experience for the host, such a phenomenon cannot occur in humans, who are not hosts to the threadworm. Therefore, even if you happen to see a threadworm in everyday life, while its wriggling movements may be repulsive, there is no need to worry that it will enter your body and control you.
Now let’s look at the parasites we really need to watch out for. A prime example is Anisakis, commonly known as the whale roundworm. While the final host of Anisakis is marine mammals such as whales, various marine creatures we commonly eat—including pollock, squid, mackerel, saury, flounder, and red sea bream—can serve as intermediate or carrier hosts. Therefore, when eating fish, you must pay special attention to its freshness and how it’s prepared. Today, with many people eating raw fish in dishes like sashimi and sushi, this parasite is considered to pose a relatively high risk of infection in everyday life.
Once Anisakis enters the human body, it cannot mature into an adult and usually dies within a few days. So why is it a problem? It is because, while alive, they burrow into the stomach or intestinal mucosa, causing severe abdominal pain. Within a few hours of infection, needle-like pain may occur, and it can also cause vomiting, bleeding, or, in rare cases, severe allergic reactions. Although it was once believed that they could travel through the bloodstream to the brain, this is not currently recognized as a common route of infection. Because Anisakis is firmly attached to the stomach or intestinal lining, it cannot be eliminated with standard deworming medications; treatment typically involves removal via endoscopy. Fortunately, since Anisakis is mostly found in the internal organs of fish, the risk of infection can be significantly reduced by properly preparing fresh fish. However, caution is needed with fish that have been caught a long time ago and have lost their freshness, as Anisakis from the internal organs may have migrated into the flesh. Furthermore, since Anisakis can be killed by sufficient freezing or heating, it is paramount to cook fish safely. If you enjoy sashimi, it is essential to be aware of Anisakis and develop preventive habits.
How is Sparganum transmitted, and why is it known as a dangerous parasite?
Finally, let’s learn about Sparganum, which is known to migrate through various parts of the human body. Sparganum is the larval form of the Manson’s tapeworm. Manson’s tapeworm parasitizes the intestines of felids, such as cats and wildcats, and is excreted in their feces. Daphnia (water fleas) ingest these eggs, and when snakes or frogs eat the Daphnia, Sparganum becomes parasitic in wild snakes and frogs. Once inside the intestines of a snake or frog, the larvae penetrate the intestinal wall before being digested and migrate into the muscles, where they grow—and this is what we call sparganum.
The problem is that some people, believing in unsubstantiated folk remedies or myths, eat wild frogs or snakes—sometimes even consuming them raw. Once inside the human body, sparganum also penetrates the intestinal wall and migrates throughout the body; migration under the skin is relatively common. If a lump that can be felt near the skin develops or if its location changes over time, sparganum infection should be suspected.
The dangers of sparganum do not end there. Although rare, it can migrate to vital organs such as the brain, eyes, and spine, causing serious neurological symptoms or vision impairment. Sparganum is also difficult to eliminate with standard anti-parasitic drugs and must usually be removed surgically. In particular, when it has migrated deep into the brain, the surgery itself is challenging, making treatment very difficult.
How can parasitic infections be prevented?
In the past, when sanitary conditions were poor, many people were infected with parasites such as roundworms and tapeworms, and there was a time in South Korea when the government even recommended regular administration of anthelmintics. Today, as sanitary conditions have greatly improved, such parasitic infections have decreased significantly.
On the other hand, due to the spread of a culture of eating raw foods—including sashimi—and diverse dietary habits, new forms of foodborne parasitic infections continue to occur.
While there are various other parasites besides those introduced so far, there is no need to worry about every single one. The important thing is to understand the routes of infection and follow basic preventive measures.
When eating raw fish, it is best to choose fresh ingredients and use fish from which the internal organs have been promptly removed. Although Anisakis is relatively large and can sometimes be detected with the naked eye, visual inspection alone is not a sufficient preventive measure. The safest method is to use fresh ingredients and, if necessary, consume the food only after it has undergone sufficient freezing or heating.
Additionally, you must avoid eating the meat or internal organs of wild animals raw. This is because following unsubstantiated folk remedies claimed to improve health or vitality can actually lead to serious parasitic infections.
If you experience severe abdominal pain or unusual symptoms after eating raw or undercooked food, you should seek medical attention without delay to undergo appropriate testing. Furthermore, simply practicing basic personal hygiene—such as washing your hands thoroughly after going out and preparing food hygienically—goes a long way toward preventing various parasitic infections.
There is no need to harbor an unconditional fear or aversion toward parasites. Rather than vaguely fearing organisms that cannot parasitize humans at all, the wisest approach is to accurately understand which parasites are actually dangerous and to practice proper preventive measures. With accurate information about parasites and a little caution in daily life, most infections can be effectively prevented. I hope this article has helped you distinguish between parasites that do not harm humans and those that you should actually be wary of, and that it has encouraged you to adopt healthy eating habits and proper preventive measures.
