Doctors in Australia got the shock of their lives when they discovered that a 64-year-old woman’s troubling symptoms had a seriously unusual cause: an 8-centimeter (3-inch) worm. The worm was pulled out of the woman’s brain, alive and kicking, during a surgical procedure, in what is the first reported case of this particular parasitic infection in a human.

The roundworm Ophidascaris robertsi is an Australian native, and a very common parasite in its usual host, the carpet python. 

“Normally the larvae from the roundworm are found in small mammals and marsupials, which are eaten by the python, allowing the life cycle to complete itself in the snake,” explained Sanjaya Senanayake, an infectious disease expert and co-author of the study, in a statement emailed to IFLScience.

As well as being the first ever human O. robertsi infection reported in the literature, Senanayake said, “To our knowledge, this is also the first case to involve the brain of any mammalian species, human or otherwise.”

The woman, from southeastern New South Wales, was first admitted to hospital in January 2021 with a three-week history of abdominal pain, diarrhea, night sweats, and a dry cough. Scans revealed lesions on the woman’s lungs, liver, and spleen, but further tests showed no evidence of cancer, infection, or autoimmune disease.

The doctors concluded that the patient was suffering from eosinophilic pneumonia of unclear etiology, and treated her with steroids. However, three weeks later she was back in hospital, and her problems only worsened from there. 

Over the next 18 months, the woman was given various treatments, but nothing seemed to fully relieve her symptoms. By June 2022, she was experiencing forgetfulness and depression, so the medical team performed an MRI scan on her brain. Co-author Karina Kennedy, Director of Clinical Microbiology at Canberra Hospital, explained that the scan showed “an atypical lesion within the right frontal lobe of the brain.”

Atypical is an understatement. As Senanayake told the Guardian, the neurosurgeon tasked with investigating the strange lesion made a “once-in-a-career finding,” reportedly shouting, “Oh my god, you wouldn’t believe what I just found in this lady’s brain – and it’s alive and wriggling.”

In the league table of sentences you don’t want to hear in an operating theater, that one comes pretty far up the list.

Now they knew about the unwelcome visitor in the woman’s brain, some of her other symptoms began to make more sense to the medical team. They suspected that worm larvae were also present in other organs, including her lungs and liver. Since this parasite has never been known to infect humans, none of the tests were able to pick it up.

So how did a worm that normally makes its home inside a large snake find its way into a human brain? The patient often foraged by a lake near her home for a native grass called warrigal greens, which she used in cooking. The most likely explanation is that an infected carpet python shed parasite eggs in its feces in the lake, and the woman inadvertently became infected herself from preparing or eating the greens.

While O. robertsi has never been seen in a human before now, there are other Ophidascaris species that infect snakes in other parts of the globe, so it’s not impossible that similar cases will be found in the future. It highlights the continuing threat of zoonotic infections that jump from animals to humans.

The patient in this case is doing better after treatment, though she will continue to be monitored by specialists. In the statement, Senanayake paid tribute to her, saying, “It is never easy or desirable to be the first patient in the world for anything. I can’t state enough our admiration for this woman who has shown patience and courage through this process.”

The study is published in Emerging Infectious Diseases.