Sneaky worms

Taenia solium can infect people in two ways: by eating cysts in undercooked meat or ingesting eggs through fecal contamination. The parasite infects pigs, and when they ingest eggs from feces, the worms hatch in the pigs’ guts, bore through the intestines, get into the bloodstream, and migrate into a variety of tissues and muscles. There, they form into encapsulated larvae called cysticerci. If a person eats undercooked meat containing cysticerci, the larvae will develop into adult tapeworms in the person’s intestinal tract and live there, possibly for years. Meanwhile, those infected people will be shedding eggs in their feces.

If those eggs get spread around from poor hygiene and sanitation—into water, food, etc.—and make it into a person’s mouth, they do what they do in pigs. The eggs hatch, burrow into the bloodstream, and then go wandering around, embedding in various tissues, muscles, and organs, including the brain.

When cysticerci enter a person’s central nervous system, it’s a disease called neurocysticercosis (NCC), which is the diagnosis the doctors in Spain gave the man. Testing after his MRI revealed his immune system had made antibodies against Taenia solium, confirming the infection.

NCC can be serious, causing seizures, significant neurological deficits, cognitive decline, stroke, and other problems. But it can also be asymptomatic. The severity depends on where in the brain the worms settle. Luckily for the man, the effects were relatively mild. Doctors prescribed him two anti-parasitic drugs, and he recovered.

“Our case emphasizes that the absence of travel history should not preclude NCC from the differential diagnosis of multiple ring-enhancing brain lesions, even in regions where metastatic cancer is statistically much more likely,” they concluded. If they had caught onto the worms sooner, it would have prevented “unnecessary invasive oncologic procedures and lead to prompt, targeted antiparasitic therapy.”

https://arstechnica.com/health/2026/06/doctors-suspected-man-had-brain-cancer-he-actually-had-worms/