Imported ocular loiasis in Northeast China: a case report of a morphologically identified adult Loa loa infection Imported Ocular Filariasis: A Clinical Case Report

The Invisible Traveler and the Eye's Detective Work

Imagine your body is a bustling city, and your immune system is the police force, constantly patrolling the streets to keep things safe. Sometimes, however, tiny, invisible hitchhikers—parasites—can sneak in on a plane or a boat from faraway places. One such hitchhiker is a worm called Loa loa. It lives in the rainforests of Central and West Africa and is carried by day-biting flies, kind of like a mosquito that only comes out when the sun is high. Usually, these worms live under the skin, but sometimes they decide to take a scenic tour across the surface of the eye. This is a rare event for most of the world, especially in places like China where these worms don't naturally live.

The big mystery doctors face with these travelers is that they are often "ghosts" in the blood. Even if a person is infected, a standard blood test might come back empty, showing no sign of the tiny baby worms (microfilariae) that usually give the infection away. This makes diagnosis tricky. If a doctor doesn't know the patient recently visited Africa, they might think the eye problem is just a simple irritation or a different kind of bug. The key to solving this puzzle isn't just looking at the blood; it's asking the right questions about where the patient has been and looking very closely at the eye itself. When a worm is actually seen moving, it's like finding the culprit right at the scene of the crime, but doctors still need to be careful about how they treat the rest of the body to avoid making things worse.

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The Case of the Wandering Worm in Northeast China

This story takes place in Yanbian Prefecture, in the northeast corner of China, a place far from the African rainforests where the Loa loa worm usually hangs out. In August 2025, a 44-year-old man walked into the eye clinic at Yanbian University Affiliated Hospital with a very strange complaint: he felt something moving inside his right eye. It wasn't a scratch or a speck of dust; it was a sensation of a living thing crawling near the inner corner of his eye.

The patient had a history that was the missing piece of the puzzle. He had lived and worked in Gabon, a country in Central Africa, for five years before returning to China just two months prior. While in Gabon, he had been bitten by insects many times. Back in China, he had already had some health scares, including a fever and a surgery on his ankle, both of which showed that his body was fighting hard against something invisible—his blood was packed with eosinophils, a type of white blood cell that acts like a specialized anti-parasite squad. In fact, his eosinophil count was sky-high, reaching 34.7% of his total white blood cells, with an absolute count of 3.73 × 10⁹/L.

When the doctors looked at his eye with a special microscope called a slit lamp, they saw something amazing and terrifying: a transparent, thread-like worm wiggling right under the clear skin of the eye (the bulbar conjunctiva). It was alive, moving, and about 50 mm long (roughly the length of a small finger) and 0.5 mm wide. The worm was so clear it was almost invisible until it moved.

Here is where the detective work got intense. The doctors took blood samples at different times of the day and night, hoping to find the tiny baby worms (microfilariae) that usually float in the blood. But the blood tests came back negative every single time. No baby worms were found. This is a common trap in these cases: the adult worm can be right there in plain sight, but the blood tests can still say "nothing here."

The doctors decided to act fast. They numbed the eye with drops and made a tiny cut to gently pull the worm out. They were careful to get the whole thing out without breaking it. Once the worm was in a jar, the lab team examined it under a microscope. They saw specific features, like little bumps on its skin and baby worms inside its body, which confirmed it was an adult female Loa loa.

The patient felt much better immediately after the worm was removed. However, the story didn't end there. A week later, the patient told the doctors he had taken a medicine called ivermectin that he had brought back from Gabon on his own. The doctors were worried. While ivermectin is a powerful medicine, taking it without a doctor's supervision can be dangerous if a person has a high number of these worms in their body, as it can cause severe reactions. The paper suggests that because the blood tests were negative, it's hard to know exactly how many worms were hiding inside him, but the risk of self-medicating is real.

What This Story Teaches Us

This case is a perfect example of why travel history is the most important tool in a doctor's kit when dealing with strange eye symptoms. The main finding here is that even if blood tests are negative, a moving worm in the eye of someone who recently visited Central Africa is almost certainly Loa loa. The paper argues against the idea that a negative blood test means the patient is safe or uninfected. In fact, the authors suggest that relying only on blood smears can lead to missed diagnoses.

The paper also highlights a crucial safety rule: never take strong anti-parasite medicine on your own. The patient's decision to take ivermectin without medical supervision was risky because doctors couldn't be sure how many worms were still inside him. The safest path is to remove the visible worm, identify it, and then have a specialist plan the rest of the treatment carefully.

In the end, this case shows that in a world where people travel everywhere, a simple feeling of something moving in the eye can be a sign of a complex, imported infection. It reminds us that the answer to a medical mystery often lies not just in the lab, but in the story the patient tells about where they've been.