Direct Attack

Many with mild or no symptoms are able to fend off the virus before it gets worse. These people may have symptoms only in the upper airway, at the site where they were first infected. But when someone’s body can’t destroy the virus at its entry point, viral particles march deeper into the body. The virus seems to take a few paths from there, either setting up camp in the lungs, fighting its way into the digestive tract, or doing some combination of both.

“There’s clearly a respiratory syndrome, and that’s why people end up in the hospital. Some people get a gastrointestinal illness with diarrhea, maybe some abdominal pain, which may or may not be associated with a respiratory illness,” says Vinetz.

Once the virus is deeply embedded in the body, it begins to cause more severe disease. This is where direct attack on other organs that have ACE2 receptors can occur, including heart muscle, kidneys, blood vessels, the liver, and potentially the central nervous system. This may be one reason for the vast array of symptoms COVID-19 can cause.

“It's highly unlikely that any other organs can be affected through direct invasion without severe disease,” Vinetz adds.

The brain and nerves may also fall prey to direct attack. Kenneth Tyler, MD, chair of the Department of Neurology at the University of Colorado School of Medicine, cautions that direct central nervous system (CNS) attack is still being worked out at this time. There are many routes a virus could take to invade the CNS. One somewhat disputed view is that the loss of smell could indicate that the nerve responsible for smell is infected and can carry the virus into the CNS, including the brain. “This can be shown to occur in experimental models with non-human coronaviruses and is a potential route of invasion for some other viruses. However, there is no evidence to date establishing that this actually occurs with SARS-CoV-2,” the official name of the virus that causes COVID-19.

Early findings, including those from autopsy and biopsy reports, show that viral particles can be found not only in the nasal passages and throat, but also in tears, stool, the kidneys, liver, pancreas, and heart. One case report found evidence of viral particles in the fluid around the brain in a patient with meningitis.