MRI showing a tapeworm moving across a man’s brain (Image: Nagui Antoun)

A tapeworm that usually infects dogs, frogs and cats has made its home inside a man’s brain. Sequencing its genome showed that it contains around 10 times more DNA than any other tapeworm sequenced so far, which could explain its ability to invade many different species.

When a 50-year-old Chinese man was admitted to a UK hospital complaining of headaches, seizures, an altered sense of smell and memory flashbacks, his doctors were stumped. Tests for tuberculosis, syphilis, HIV and Lyme disease were negative, and although an MRI scan showed an abnormal region in the right side of his brain, a biopsy found inflammation, but no tumour.

Over the next four years, further MRIs recorded the abnormal region moving across the man’s brain (see animation), until finally his doctors decided to operate. To their immense surprise, they pulled out a 1 centimetre-long ribbon-shaped worm.


It looked like a tapeworm, but was unlike any seen before in the UK, so a sample of its tissue was sent to Hayley Bennett and her colleagues at the Wellcome Trust Sanger Institute in Cambridge, UK.

Genetic sequencing identified it as Spirometra erinaceieuropaei, a rare species of tapeworm found in China, South Korea, Japan and Thailand. Just 300 human infections have been reported since 1953, and not all of them in the brain.

The parasite starts its life in water where it infects crustaceans. These then get eaten by reptiles and amphibians such as frogs and snakes. The worm is then passed on to larger carnivores that prey on these intermediate hosts. “Humans aren’t the natural host for the worm – they’re usually found in cats, dogs and carnivores – so when it enters a human, it doesn’t migrate to the gut as it usually would,” says Bennett. “In previous cases, they’ve been found under the skin, in the lungs or in breast lumps – where people have suspected cancer and found a worm instead.”

Yum yum, brain fat

When they do find their way into the brain, the worms trigger cerebral sparganosis, or inflammation, which is what causes symptoms such as headaches and seizures. “In this case, the patient reported different symptoms as the worm made its way across his brain,” Bennett adds.

As for what the worm was surviving on, tapeworms absorb nutrients such as fats directly through their skin, and brain tissue is rich in fatty acids. “It was moving around in there, so it must have been getting energy from somewhere,” says Bennett.

Because these worms are so rare, the Sanger team decided to take a closer look at its genome. It was around 10 times larger than any other tapeworm sequenced so far, and around a third of the size of the human genome. Part of this was due to an expansion of certain gene families that help the parasite to invade its host – this might underpin its success in a wide variety of animals.

Genome sequencing also revealed that this type of tapeworm is resistant to a conventional anti-tapeworm drug called enzimidazole, but might be sensitive to another drug, praziquantel – although in this case, surgically removing the worm cured the man of his symptoms.

“We did not expect to see an infection of this kind in the UK, but global travel means that unfamiliar parasites do sometimes appear,” says Effrossyni Gkrania-Klotsas, from the Department of Infectious Disease at Addenbrooke’s Hospital, who was also involved in the study. “Our work shows that, even with only tiny amounts of DNA from clinical samples, we can find out all we need to identify and characterise the parasite.”

Journal reference: Genome Biology, DOI: 10.1186/s13059-014-0510-3