The genome of a rare tapeworm has been sequenced by biologists after the parasite lived inside the brain of a man for four years.

Spirometra erinaceieuropaei is a species of tapeworm which can affect humans and other animals.

Inside intestinal tracks of cats and dogs, these creatures can grow to lengths up to five feet. Eggs laid by the parasite develop into larvae, which then passes to other animals and people through feces.

Since 1953, the giant worm has only been seen 300 times, and this marks the first time the human parasite has been recorded in the United Kingdom. When humans are infected by the tapeworm, surrounding tissues swell, in a condition known as sparganosis.

Doctors are uncertain how the UK resident became infected with the worm, although the parasite may have arrived through small crustaceans, frog poultice, or meat from lizards or amphibians. The patient suffered from severe headaches and seizures, and doctors spent four years testing the man for various diseases and conditions to explain the symptoms. Health care workers examined MRI images taken between July 2008 and June 2012. The series of recordings revealed a worm, just four-tenths of an inch  long, dug two inches through his brain during that period.

"The clinical histology slide offered us a great opportunity to generate the first genome sequence of this elusive class of tapeworms. However, we only had a minute amount of DNA available to work with - just 40 billionths of a gram. So we had to make difficult decisions as to what we wanted to find out from the DNA we had," Hayley Bennett from the Wellcome Trust Sanger Institute, said.

One single sequence, "barcode of life" was analyzed by investigators, eager to determine the species of worm, in an effort to treat the patient. Despite the small quantity of material available to researchers, the team was also able to produce a draft genome.

Examination of the genetic structure of the S. erinaceieuropaei could allow researchers to develop a new generation of treatments to assist those suffering from sparganosis.

The genome of S. erinaceieuropaei contains 1.26 gigabytes of information, roughly ten times greater than other tapeworms, and one-third as many as human beings. Much of this genetic information is duplicate code, but much is likely used to invade animals hosts and digest proteins.

Early analysis of the genetic code reveals the species is immune to albendazole, a medicine currently used to treat other species of tapeworms.

The unnamed patient is now free of the worm, and recovering well.

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