Prolonged symptoms of Covid-19 may be associated with difficulty recognising faces, a little-known condition called face blindness, and navigational problems, according to a study.
Previous studies have shown that Covid-19 can cause a range of neurological problems, including the loss of smell and taste, and impairments in attention, memory, speech, and language, known as "brain fog".
The latest research, published in the journal Cortex, is the first to report prosopagnosia, or face blindness, following symptoms consistent with Covid-19.
The condition that can make people fail to recognise familiar faces, has been estimated to affect between 2 and 2.5 per cent of people in the world.
The researchers assessed the case of Annie, a 28-year-old customer service representative and part-time portrait artist in the US, who was diagnosed with Covid-19 in March 2020 and suffered a symptom relapse two months later.
"When I first met Annie, she told me that she was unable to recognise the faces of her family," said Marie-Luise Kieseler, a graduate student at Dartmouth College in the US, adding Annie now relies on voices to recognise people.
Annie also experienced navigational deficits after having Covid-19. She has had difficulty remembering where particular sections in her grocery store are and relies on Google maps and its pin function to remember where she parks her car.
“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,” said study senior author Brad Duchaine, a professor at Dartmouth.
"That co-occurrence is probably due to the two abilities depending on neighbouring brain regions in the temporal lobe," Duchaine said in a statement.
Dr. Vinit Suri, Senior Consultant, Neurology, Indraprastha Apollo Hospitals, New Delhi noted that the exact mechanisms by which long Covid may cause face blindness are not yet fully understood, but there are several possible explanations.
"Firstly, long Covid can cause a range of neurological symptoms which may affect the brain regions responsible for face recognition, causing difficulty in processing visual information and recognising familiar faces," Suri told PTI.
"Secondly, Covid-19 can cause inflammation and damage to the blood vessels, which can lead to reduced blood flow to the brain. This can cause brain damage and cognitive impairments, including face blindness," he added.
The research team conducted a series of tests with Annie to evaluate her problems with face recognition and determine whether she also has difficulties with other perceptual or cognitive abilities.
In one test, Annie was sequentially presented with 60 images of celebrity faces and was asked to name them. Annie correctly identified 29 per cent of the 48 celebrities whom she was familiar with as compared to most people, who can correctly identify 84 per cent of familiar celebrities.
The second test was a doppelganger test. Annie was shown a celebrity's name and then presented with images of two faces: the face of a celebrity and that of someone similar, and was then asked to identify which face was the famous person.
She identified the celebrity in 69 per cent of the 58 trials, as compared to 87 per cent in the control group.
"Our results from the test with unfamiliar faces show that it wasn't just that Annie couldn’t recall the name or biographical information of a famous person that she was familiar with, but she really has trouble learning new identities," said Kieseler.
The research team also obtained self-reported data from 54 individuals who had long Covid with symptoms for 12 weeks or more, and 32 persons who had reported that they had fully recovered from Covid-19.
Most respondents with long Covid reported that their cognitive and perceptual abilities had decreased since they had Covid.
"It was not just a small concentration of really impaired cases but a broad majority of people in the long Covid group reported noticeable difficulties doing things that they were able to do before contracting Covid-19 without any problems," Kieseler said.
"Our study highlights the sorts of perceptual problems with face recognition and navigation that can be caused by Covid-19 -- it is something that people should be aware of, especially physicians and other health care professionals,” Duchaine added.
Dr. Atul Prasad, Principal Director & HOD Neurology, BLK-Max Super Speciality Hospital, New Delhi said this is the first report of long Covid causing prosopagnosia.
"The more we study the virus, the more we realise how much damage it can cause during acute infection and now after infection has settled," Prasad told PTI.
Suri noted that that not all people with long Covid will develop face blindness, and the severity and duration of symptoms can vary widely.
"Further research is needed to better understand the relationship between long Covid and face blindness and to develop effective treatments and interventions for those affected," he added.