When Annie reunited with her family for the first time a few months after being ill with COVID-19, it was clear the disease was not yet done with her.

"My dad's voice came out of a stranger's face," Annie told the researchers investigating her case.

Annie (a pseudonym to protect her privacy) had normal facial recognition before she was diagnosed with COVID-19 in March 2020. A few days later she started to recover, only to relapse after several months. Now her case study suggests we can add 'face blindness' (prosopagnosia) to a long and growing list of brain problems caused by the disease.

The new study surveyed more than 50 other patients struggling with long COVID and most were finding it harder to identifying familiar faces, since their infections.

"Faces are like water in my head," Annie explained, describing how trying to remember a face is now like being asked to replicate a Chinese character after one viewing when you're unfamiliar with the language.

The 28-year-old part-time artist previously needed to look at her subject maybe once every 15 to 30 minutes while working on a portrait. Now Annie has to refer back constantly.

Dartmouth College neuropsychologists Marie-Luise Kieseler and Brad Duchaine presented Annie with a series of tests and confirmed that her trouble with recognition is due to specific face memory defects and not wider issues.

But Annie has also been experiencing trouble navigating her way through familiar environments, having difficulties with her orientation and having to rely on Google map pins to relocate her car. Navigation difficulties are also common in others with prosopagnosia.

"The combination of prosopagnosia and navigational deficits that Annie had is something that caught our attention because the two deficits often go hand in hand after somebody either has had brain damage or developmental deficits," explains Duchaine.

"That co-occurrence is probably due to the two abilities depending on neighboring brain regions in the temporal lobe."

During the course of her infection Annie had lost her sense of smell and taste, struggled with breathing and had high fever for a few days. Since relapsing, the facial recognition and navigation problems have been accompanied by other long COVID symptoms including fatigue, concentration problems, and brain fog. Later, she developed balance issues and migraines as well.

Due to issues with insurance, Annie has not undertaken an MRI.

"So a stroke cannot be excluded as the cause of her symptoms, especially given the evidence for increased risk of stroke with COVID-19," the team cautioned in their case study.

Regardless of the specific mechanism behind the symptoms this is yet another example of how COVID-19 can cause neurological problems.

"Our study highlights the sorts of perceptual problems with face recognition and navigation that can be caused by COVID-19 – it's something that people should be aware of, especially physicians and other healthcare professionals," Duchaine urges.

The majority of people with long COVID the researchers surveyed reported noticeable neurological difficulties doing things they found easy before, not just a minority of severe cases.

"It's been known that there are broad cognitive problems that can be caused by COVID-19, but here we're seeing severe and highly selective problems in Annie," says Duchaine, "and that suggests there might be a lot of other people who have quite severe and selective deficits following COVID."

The case study was published in Cortex.