In a world first, scientists say that an 8cm (3in) worm has been found alive in the brain of an Australian woman.
The "string-like structure" was pulled from the patient's damaged frontal lobe during surgery in Canberra last year.
The woman suffered from what doctors called an "unusual constellation of symptoms" - stomach pain, a cough and night sweats, evolving into increasing forgetfulness and depression.
The red parasite could have been there for up to two months.
Researchers are warning that the case highlights the increased danger of diseases and infections being passed from animals to people.
"Everyone [in] that operating theatre got the shock of their life when [the surgeon] took some forceps to pick up an abnormality and the abnormality turned out to be a wriggling, live 8cm light red worm," said Sanjaya Senanayake, an infectious diseases doctor at Canberra Hospital.
"Even if you take away the yuck factor, this is a new infection never documented before in a human being."
The Ophidascaris robertsi roundworm is common in car
pet pythons - non-venomous snakes found across much of Australia.