Spanish Doctors Diagnosed Brain Tumors. The Lesions Were Tapeworm Larvae.

A 60-year-old man in Spain walked into a clinic with a two-week headache that kept getting worse. He also reported subtle behavioral changes. A neurological exam showed mild slowing of his movements, nothing more. His blood work was largely normal, with one exception: elevated immunoglobulin E (IgE), a marker associated with allergies, autoimmune conditions, and parasitic infections.

Then came the CT scan. It showed multiple lesions scattered throughout his brain, with accompanying swelling. According to a case report published in the CDC's journal Emerging Infectious Diseases, the doctors' leading explanation was metastatic cancer, meaning a primary tumor elsewhere in the body that had spread to the brain.

They treated his headache with a corticosteroid anti-inflammatory and sent him through an extensive cancer hunt: a whole-body contrast CT, a colonoscopy, and a hybrid positron emission tomography/CT scan specifically used to map malignancies. All of it came back clean. No cancer anywhere.

The MRI told a different story

Doctors ordered a higher-resolution MRI of the brain. The more detailed imaging removed any ambiguity. The lesions were not tumors. They were encapsulated tapeworm larvae, and the MRI was clear enough to show the scolexes — the heads of the worms themselves — sitting inside each cyst.

The diagnosis: neurocysticercosis, the condition that results when larvae of Taenia solium, the pork tapeworm, migrate into the brain and form cysts. Testing after the MRI confirmed the infection: his immune system had made antibodies against Taenia solium.

A domestic case with no travel history

What made this case notable enough to publish was the apparent transmission route. Taenia solium is not endemic to Spain. The patient said he had never traveled internationally. Under normal epidemiology, that combination makes infection unusual.

His doctors traced back his occupational history. Until roughly a decade before, when he retired, he had worked in construction, regularly alongside coworkers who had migrated from regions where pork tapeworm infection is common. His doctors speculated in the case report that he may have contracted the infection through what they called "cryptic transmission," meaning shared meals or shared bathroom facilities with a coworker who carried an active tapeworm infection. One such coworker was apparently identified as having had such an infection.

How Taenia solium actually spreads

Understanding the transmission matters here, because the parasite has two distinct pathways into a human host.

The first is eating undercooked pork containing larval cysts. That results in an adult tapeworm living in the intestinal tract, sometimes for years, without necessarily causing severe symptoms.

The second, and more dangerous, pathway is swallowing the tapeworm's eggs through fecal contamination. This means contaminated water, food handled by an infected person with poor hygiene, or direct contact. When a human ingests eggs this way, the larvae hatch, bore through the intestinal wall, enter the bloodstream, and migrate to tissues, including the brain. That is the route that causes neurocysticercosis.

According to the Emerging Infectious Diseases case report, the working theory is that this man's former coworker had an adult tapeworm intestinal infection and shed eggs through his feces. Poor sanitation at a worksite or shared meals may have allowed fecal-oral transmission to the patient, possibly years before symptoms appeared. The long incubation before lesions become symptomatic is consistent with known biology of the disease.

The strongest counterpoint

A fair concern: attributing the source to a coworker from a migrant-origin country, without confirmed testing of that individual, is speculative. The case report itself presents this as the doctors' working hypothesis, not a proven chain of transmission. The patient could theoretically have been exposed through contaminated imported food, contact with travelers he did not disclose, or another source entirely. The doctors acknowledge the transmission is cryptic precisely because it cannot be proven directly. That uncertainty is real and should not be glossed over in the name of a tidy epidemiological narrative.

Treatment and outcome

Luckily for the patient, the effects of his infection were relatively mild. Doctors prescribed him two anti-parasitic drugs, and he recovered.

The patient's IgE elevation was the only blood signal pointing toward infection, and even that is nonspecific. Without the MRI's resolution, those cysts could plausibly have been mischaracterized and mistreated as cancer indefinitely. As the doctors concluded in their report: "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." An earlier diagnosis, they noted, would have prevented "unnecessary invasive oncologic procedures and lead to prompt, targeted antiparasitic therapy."

The CDC's Emerging Infectious Diseases journal published the case specifically because domestic transmission of Taenia solium without international travel history is rare and poorly documented in high-income European settings.