A North Korean defector was shot crossing the country’s border with South Korea and his doctors discovered many, many parasites inside him. But if he hadn’t been shot, it’s possible one particular type of worm—a roundworm—could have continued to live inside of him and grow without any signs that something was wrong.

Based on information in the Korea Biomedical Review, one particular parasite that infected the defector may be Ascaris lumbricoides, a roundworm that is rarely found in the United States.

The worm described is about the right size for Ascaris—ten inches is within the worm’s typical length, which can reach up to 19 inches. The Review reported that the worm was spread through plants fertilized with human feces, which is also typical for Ascaris. The patient seemed to be suffering from malnutrition—also something that can occur as a result of becoming infected with this worm. And Ascaris is more often found in tropical climates, according to information from the Centers for Disease Control and Prevention’s website on the worm, which would explain Korean doctors’ surprise when they found it.

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"I have been doing surgery for more than 20 years, but I have not seen such parasites. I will not be able to find them in [South] Korea," Dr. Lee Guk-jong, the surgeon who operated on the patient, told the Review .

Ascaris worms may be living in up to 1 billion people. This particular infection blocked the intestine of a 3-year-old boy, who survived. South African Medical Research Council via Flickr

The worms live in a person’s intestine, but they don’t stay there. After hatching from an egg, an immature worm can move into a person’s bloodstream and go to the lungs and stomach.

About one billion people in the world may be infected with Ascaris, and roundworm infections as a whole are even more common. Other roundworms includes whipworm and hookworm, as well as one type found in pet poop.

Ascaris infections can be nearly undetectable. According to the CDC’s website, people who are infected may have no symptoms until there are a profuse amount of the worms. Some of the symptoms that can happen are relatively subtle; worms can be found in a person's poop, and an infected person might have stomach pain or a cough.

Roundworms can be resilient; according to Medline Plus, Ascaris eggs can live for 10 to 24 months. Thankfully, there are treatments that will kill them; three drugs are commonly used for this purpose, according to the UK's NHS.

Unfortunately for the North Korean defector, however, the parasites are making his recovery more difficult; Lee told the Review that the doctors are "struggling with treatment" and that the worms are eating the wounded areas.