For many people, a sudden loss of smell is the first sign that something’s wrong. “One gentleman said he realized it with hand sanitizer,” says Carol Yan, a rhinologist at the University of California, San Diego. “All of a sudden it was like water to him.” The loss of smell, or anosmia, is such a common symptom of Covid-19 that the US Centers for Disease Control and Prevention recently added it to its official list.
The loss of smell (or taste) is one of many emerging hints that the SARS-CoV-2 virus may affect the nervous system. Physicians around the world have documented neurological symptoms in a significant fraction of Covid-19 patients. Some patients have experienced headaches, dizziness and other relatively minor symptoms, while others have had more serious problems like confusion and impaired movement, and even seizures and strokes.
Such reports have been circulating on message boards used by physicians, and they are just now making their way into the peer-reviewed scientific literature. Nobody knows at this point how widespread neurological symptoms are, nor the extent to which they contribute to the overall clinical picture for Covid-19.
Another huge unknown is whether SARS-CoV-2 can attack the nervous system directly by infecting neurons — as rabies and a number of other viruses do — or cause neurological symptoms indirectly, by triggering rampant inflammation or blood clotting.
