Since COVID-19 is a respiratory virus it infects the respiratory tract (the nose and lungs) by latching its spiky surface proteins to receptors on healthy cells. The virus then makes copies of itself and multiplies throughout the body causing coughing, shortness of breath, difficulty breathing due to diminished oxygen intake, fatigue, and a fever to rise. The lungs can become inflamed and this can lead to pneumonia, an infection of the small air sacs (alveoli) inside the lungs where blood exchanges oxygen and carbon dioxide. However, this is not the only part of the body that is affected in many patients. In very sick patients conjunctivitis, (more commonly known as pink eye) an inflammation of the membrane that lines the front of the eye and inner eyelid, has shown as a symptom of the virus. Even chills, body aches, sore throat, congestion or runny nose, and nausea or vomiting can be symptoms.
In addition to these symptoms, patients also have shown others that you wouldn’t necessarily link to a respiratory infection. This is due to a certain human cell receptor that the virus uses, called angiotensin converting enzyme 2 or ACE2, that enters into the cell. The lower airways contain more ACE2 receptors than the rest of the respiratory tract, therefore COVID-19 is more likely to go deeper than viruses like the common cold. The ACE2 receptor is expressed on cells throughout the body, including the lung, nose, blood vessels, heart, intestines and even some parts of the brain. This could explain some of the symptoms such as diarrhea, headache, blood clots, heart inflammation, heart attacks, strokes, seizures, mental confusion, and brain inflammation. The virus also infects ACE2-expression cells that help the neurons process smells and taste. This disrupts the cells needed for sensing and prevents the person from smelling or tasting temporarily. However, the loss of taste and smell is not permanent, senses return when new support cells are regenerated within a few weeks. Other symptoms you may not link to a respiratory virus include symptoms of the liver and kidneys. Up to half of hospitalized patients have enzyme levels signaling a struggling liver. Kidney damage is also common in severe cases and makes death more likely. The virus may attack the kidney directly or kidney failure may be part of whole-body events like plummeting blood pressure.
Symptoms also tend to appear in certain combinations. Often reported symptom clusters are flu-like with no fever, flu-like with fever, mainly gastrointestinal, severe respiratory symptoms with fatigue, severe respiratory symptoms with confusion, and severe respiratory and gastrointestinal symptoms.
For most people, symptoms end with a cough and a fever. More than 8 in 10 cases are mild, but unfortunately for some people the infection becomes more severe. Shortness of breath (dyspnea) may begin 5 to 8 days after symptoms appear, then acute respiratory distress syndrome (ARDS) begins a few days later. ARDS can cause a fast heart rate, rapid breathing, sweating and dizziness. It can also damage tissues and blood vessels, making it harder or even impossible to breathe. Those with ARDS often need help breathing from a ventilator. As fluid collects in the lungs, they bring less oxygen to the blood and in turn the blood may not provide the organs with enough oxygen. Not everyone has these symptoms, and not everyone will need medical care, but if symptoms include trouble breathing seek help right away.
Generally, children do not get as sick with this virus as adults do, but they can be infected and it can also be deadly for them. Some children have been admitted to the hospital with multisystem inflammatory syndrome in children or MIS-C, which causes inflammation in the blood vessels and symptoms include fever, rash, belly pain, vomiting, diarrhea and heart problems.
We are still unclear on the long term effects of COVID-19 on the body, however some patients have suffered symptoms for weeks or even months.