Genome of man's rare brain worm detailed in online 'WormBase'

Researchers have succeeded in sequencing the genome of a rare tapeworm that resided in the brain of a British man for four years.

There have only been 300 reports of the worm, known as Spirometra erinaceieuropaei, since 1953 and it has never appeared in the UK before. As the parasite is so rare it is not known exactly how it entered the man's body, although it is possible that it could have been caused by the man consuming tiny crustaceans from lakes, eating raw meat from amphibians and reptiles or by using a raw frog poultice, which is a Chinese remedy to cause sore eyes.

Although the man is now systemically well now, the worm causes sparganosis in humans, which is an inflammation of bodily tissues. When the parasite is inside the brain this can cause seizures, memory loss and headaches.

In this case, the worm in the man's brain was found to be only 1cm long, but before it was diagnosed and removed, it had travelled 5cm from the right side of the brain to the left. It took four years of eliminating other diseases, followed by regular MRI scans to discover what was causing the man's headaches and seizures. Comparing the MRI scans, it is possible to see the worm travelling slowly across the brain.

Even when the parasite was spotted, it wasn't possible to identify it as Spirometra erinaceieuropaei. "The key thing in this case was that the pathologist recognised it was a parasite," Matt Berriman tells WIRED.co.uk. It was removed using precision surgery and placed on a histology slide. "They pulled it out essentially with a biopsy needle."

Researchers then had to go about identifying the worm. This took several months -- and not just because we're not used to seeing such parasites in the UK. Even in countries like China and Korea where the parasite originates, it is so rare that there is very little information known about it.

"The clinical histology slide offered us a great opportunity to generate the first genome sequence of this elusive class of tapeworms," says Hayley Bennett from the Wellcome Trust Sanger Institute. Bennett, who was first author of the study detailing the genetic findings from the parasite, points out that because they only had a very tiny piece of DNA to work with -- "just 40 billionths of a gram" -- they had to make some very tough calls about exactly they wanted to find out from the DNA.

In all creatures there is one particular gene known as "the barcode of life" that can be sequenced in order to determine the exact species of the animal. When they did this to the parasite, the researchers discovered that it was a Spirometra erinaceieuropaei worm, and that of the two known sparganosis-causing worm species, the one in the man's brain was the more benign of the pair.

They also managed to generate sufficient DNA sequence data to put together a draft genome, which is now being used to investigate known and potential treatment targets.

"We made a couple of sequencing libraries -- one was very good," says Berriman. This was enough to piece together the draft genome quite nicely. He admits though that "this is not a good example about how to build a genome". Ideally to make a reference genome you wouldn't need to use a histology slide at all, he says.

View original post here:
Genome of man's rare brain worm detailed in online 'WormBase'