Six years ago, a 50-year-old Chinese man sought medical help in the UK because he was experiencing a range of distressing symptoms including headaches, seizures, memory loss and an altered sense of smell. Doctors were puzzled by what he was presenting, so they performed a variety of tests on him to find out what could be going on. He didn’t have syphilis, HIV or Lyme disease, but he did have something abnormal in his brain.
MRI scans revealed that the man had a cluster of lesions on the right side of his brain, which doctors believed could be a tumor. A biopsy was taken, and although the brain was clearly inflamed, no signs of cancerous tissue were identified.
For the next four years, doctors kept a watchful eye on the peculiar region. To their surprise, it appeared to be working its way across his brain, and had migrated at least five centimeters before the team decided to operate. It was then that the cause of his symptoms became immediately apparent; a parasitic gatecrasher had been living in his brain.
Surgeons removed the remains of the ribbon-shaped worm that emerged from his tissue, but the amazement didn’t end there as the team had never before seen anything like it in the UK. That’s why they decided to send off a sample for further investigation, which revealed that the critter was a tapeworm called Spirometra erinaceieuropaei.
This rare species, which can be found in Asian countries such as Thailand and Japan, does not commonly infect humans. Since 1953, only 300 infections have been documented worldwide, but none have been in the UK, making this case particularly interesting.
S. erinaceieuropaei begins its life cycle in bodies of water where it infects crustaceans. These are then gobbled up by larger organisms such as frogs or snakes, which act as intermediate hosts before the parasite enters its final host—hungry carnivores such as dogs and cats that wolf down the middle man. In these natural hosts, the worm makes its way to the gut and takes up residence here, but they end up elsewhere when they infect humans because they’re not adapted to living inside them.
Sometimes they find their way under the skin or in the lungs, but if you’re really unlucky, they can wriggle into your brain. Once there, they cause tissue inflammation, or sparganosis, which can trigger a variety of symptoms depending on where the worm is located in the brain.
It’s unclear as to how the man became infected, but possibilities include eating raw meat from an infected animal, or using raw frog poultice—a Chinese remedy used for sore eyes.
Interestingly, analysis of the worm’s genome revealed that it was 10 times larger than that of any other tapeworm so far sequenced. Further scrutiny divulged that certain gene families had been expanded, including those responsible for facilitating host invasion, which could explain why this parasite was able to successfully infect a species that is not normally part of its host repertoire.