Complex puzzle

According to experts, one of the reasons the long-term effects of COVID-19 are so hard to define is the disease's ability to infect a number of major organs, leading to a range of related symptoms.

The experts suggest that this might be partly due to the virus' ability to enter cells by binding to their ACE2 receptors, which are present in many parts of the body.

However, new research points to other receptors possibly acting as alternative routes into cells, according to a study published last month in the journal Stem Cell Reviews and Reports.

Moreover, COVID-19 infection alone usually isn't enough to kill a patient, said Rikard Holmdahl, a senior immunologist at the Karolinska Institute in Stockholm, Sweden. "The leading cause of death is the immune overreaction in the lungs," he said.

Holmdahl added that in some patients, especially severe cases, the body's immune system may go into overdrive and indiscriminately attack the virus and healthy cells in a potentially fatal condition known as a cytokine storm.

If such an attack occurs in the lungs, it will lead to a type of failure called acute respiratory distress syndrome, or ARDS, resulting in low blood oxygen levels in the body and a high chance of death, he said.

Zhang Jinsan, a medical and biology professor at Wenzhou Medical University in Zhejiang province, said once a cytokine storm occurs, it can create a "positive feedback loop" where the more cells the body's immune system destroys, the stronger the immune reaction becomes, damaging more cells in the process.

"At this point, the harm done to the body has less to do with the virus and more to do with the immune system going haywire," he said. "If the immune system turns against the body, it can severely damage various organs at an alarming rate, causing multiple organ dysfunction syndrome."

Due to the compound effects of a viral infection, overactive immune system and organ complications, Zhang said it is difficult to distinguish between the damage caused directly by the virus and that resulting from other complications. "Without knowing the cause of the symptoms, we can't say what issues will emerge, or the best way to tackle them," he added.

Shen Yong, a neurology professor at the University of Science and Technology of China in Hefei, Anhui province, said the coronavirus can attack cells lining the inside walls of blood vessels, which may lead to inflammation, blood clots and high blood pressure.

"I would not be surprised if the virus can cause neurodegenerative diseases by damaging blood vessels in the brain, but this hypothesis requires further research," he said.

This month, a study of 43 cases in the United Kingdom published in the journal Brain found that some COVID-19 patients may experience neurological damage such as strokes, inflammation of the brain and cognitive decline, raising the possibility of the virus having chronic neurological consequences.

Zhang said scientists still know surprisingly little about how the virus affects the body. "My advice for my children is to avoid becoming infected in the first place. There are simply too many unknowns surrounding this pathogen and its long-term effects. It is better to be safe than sorry," he added.