Tissues that express ACE2: lungs, nose, digestive system, heart, nervous system, kidneys, and reproductive system are all susceptible to infection by SARS-COV-2: BioRxiv

coronavirus electron micrograph from NIAID– CC license

A preprint article published in BioRxiv on April 16 (from China, supported by the Natural Science Foundation of China) identifies the tissues which express ACE2 on their cell surfaces and are thus susceptible to invasion by SARS-COV2.  The researchers studied 31 different cell types and found many, previously unknown, that express ACE2.  In order of sensitivity, they found that the lungs, nose, large and small intestines, the esophagus, fallopian tubes (parts of the uterus), and testis were identified as high-risk organs.  The heart, kidneys, brain, and gall bladder were also found to express ACE2.

This study shows that large parts of the body are potentially infected by the virus.  In particular, the nose and throat, the lungs, and the digestive system are exposed and must be readily infected.  Spread of infection to the heart, brain, and gall bladder as well as the kidneys could occur in severe COVID-19.

There is evidence from other studies that an over-active immune system could be responsible for some of the manifestations in severe disease.  Overproduction of cytokines (molecules that mediate inflammation) can cause extreme reactions in many infectious diseases. This appears to be a problem in patients who start to go downhill a week or so after infection.

The development of pneumonia and heart dysfunction (low blood pressure or heart failure) as well as mental or cognitive problems can be seen when the patient is suffering from severe infection.  Even relatively mild infections are associated with confusion and hallucinations, especially at night.

These problems are happening to a small proportion of patients (perhaps 20% of apparent or symptomatic infections) but the most insidious aspect of this disease is the number of patients who have no symptoms at all, yet are secreting virus and thus contagious to others (this may happen in 30% or more of patients; the evaluation of sailors trapped on the Theodore Roosevelt found that 60% of virus-positive people were asymptomatic.)

As the virus spreads like a wildfire through the human population, we are discovering more about how it attacks the body.  We are also learning more about how our bodies work.