COVID-19 is known as a respiratory infection, causing acute respiratory distress syndrome and debilitating and, in some cases, permanent damage to the body and – to a lesser-known degree – the brain.
The latest figures from the Centers for Disease Control and Prevention report approximately 5 million infections from COVID-19 and more than 160,000 deaths. Globally, the U.S. figures represent 25% of all infections (20 million) and 22% of all deaths (730,000). The infection statistics are likely to be lower than the true incidence, as 90% of people infected with COVID-19 have no symptoms.
The principal flu-like symptoms – fever, cough and shortness of breath – range from very mild to very severe. The viral load is similar. Regardless of symptom severity and respiratory failure, the principal cause of death occurs in less than 10% of cases. Persistent symptoms of headaches, anosmia (loss of smell), ageusia (loss of taste), general exhaustion, achy joints and confusion were initially considered normal in response to severe respiratory infection.
The extreme autoimmune response to COVID creates a “cytokine storm,” leading to hyperinflammation in the entire body. Patients develop permanent damage to multiple organs, including scarring to lung tissue and heart muscle, and renal damage due to blocked ducts. Alarmingly, patients in their 30s and 40s – without pre-existing conditions such as high blood pressure or diabetes – develop life-threatening blood clots and strokes, as the virus makes blood thicker and stickier than normal.
COVID’s brain impact
The persistent loss of smell and taste, headaches, dizziness, vertigo, impaired memory and loss of hearing are indicative of the virus affecting the brain. Scientists believe the virus is entering the brain via the gastrointestinal tract and the vagus nerve, or via the epithelial cells at the back of the nose that communicate with the brain’s olfactory bulb and forebrain.
COVID-19 has been detected in the cerebrospinal fluid of patients, and magnetic resonance imagery shows changes to bilateral gray matter volume in the olfactory cortices and hippocampi, perhaps accounting for the persistent anosmia and ageusia.
The debilitating “brain fog” and memory deficits patients experience may be attributed to viral inflammation and activation of neuroimmune cells, such as microglia and astrocytes. These cells play a central role in normal memory function and, when activated due to inflammation, modify how neurons communicate. Microglia have been shown to change shape and behavior, morphing from the role of caretaker to assassin and destroying healthy brain cells; and astrocytes start to block connections between neurons, preventing memories from forming.
Brain inflammation, even if short-lived, can be permanent. Brain imaging of COVID-19 patients indicates signs of white-matter inflammation, consistent with brain autopsy of patients who died from the virus. Infected patients that developed a stroke show neuronal atrophy, primarily in the medial temporal lobe, an area associated with the auditory cortex, perhaps explaining the commonly reported loss of hearing and persistent tinnitus.
Myalgic encephalomyelitis (chronic fatigue), acute disseminated encephalomyelitis (inflammation of the brain and spinal cord), Guillain-Barre syndrome (muscle weakness due to delays in signals between nerves), febrile seizures and epilepsy all have been diagnosed following COVID infections, indicative of the virus’ impact on the brain and central nervous system.
Patients admitted to the hospital due to COVID are more likely to develop delirium, a short-term neurological complication associated with confusion and disorientation. Delirium typically occurs in older adults but has been reported in patients of all ages.
Depression and anxiety are endemic in patients recovering from COVID, regardless of a prior history of a psychiatric disorder, and independent of severity of infection. Patients with the greatest loss of sense of taste and smell show the highest levels of depression and anxiety.
Time will tell how COVID ultimately impacts the brain. For now, the focus needs to be on infection prevention and the development of a vaccine. Until then, social distancing and regular handwashing remain the most effective preventive strategies.
Rita Hitching is a local researcher and teacher who writes on teen brain development. She aims to help teens understand themselves by using the latest neuroscience data to explain how the teen body and brain develop and publishes those explanations on her website, teenbrain.info.