COVID-19 can wreak havoc on your body. So will it cause health issues decades down the road?

The illness once dubbed a "pneumonia of unknown cause" in the early days of 2020 has revealed itself to be something far more strange.

Two years into this pandemic, we now know COVID-19 can lead to a dizzying array of symptoms from heart inflammation to brain fog to the loss of sense of smell or taste. Some people's toes turn red; others go on to develop diabetes. SARS-CoV-2 also impacts various organsand sometimes causes long-lasting breathing problems, fatigueor chronic kidney impairment.

Time and research have shownthat the virus has quite a knack for wreaking havoc on the human body under the right conditions. So what will that mean for the long-term health of millions of people who've been infected months, yearsor even decades down the road?

"There are some 'known' unknowns, likewhat will the rate and duration of long COVID be for different individuals," said Matthew Miller, an associate professor with McMaster University's Immunology Research Centre in Hamilton.

"And then there are 'unknown' unknowns, like what might happen 30 or 50 years from now."

Infections linked to diabetes, neurological issues

SARS-CoV-2's ability to spread throughout the body is largely tied to the spike proteins on its surface, which bind to ACE2 a protein on the surface of various types of human cells like a key into a lock.

That means the virus can reach far beyond the respiratory tract, causing inflammation wherever it spreads.

"We've already shown this virus, even in the acute stage, does have impact on the brain and on our central organs like the heart, and pancreasand areas where other viral infections have caused longer-term inflammatory changes that have led to chronic disease," said Dr. Cory Neudorf, the public health, health systems and social policy impacts pillar co-lead forCoVaRR-Net, a team of Canadian researchers who banded together during the pandemic.

"I wouldn't be at all surprised if we see more chronic diseases due to COVID in the years to come."

SARS-CoV-2 infections have been linked to the onset of diabetes during childhood, for instance.

A Januaryreport from the U.S. Centers for Disease Control and Preventionshowed that youth under the age of 18 were more likely to receive a new diabetes diagnosis a month or more post-infection than young people who didn't have COVID-19 and when compared withrespiratory infections before the pandemic.

"These findings are consistent with previous research demonstrating an association between SARS-CoV-2 infection and diabetes in adults," the report continued.

Other research has linked even mild cases of COVID-19 to long-term neurological symptoms.

One recent U.S. study, which has not yet been peer-reviewed, involved autopsy results from nine patients and an analysis of the impacts onlab mice that were purposely infected with SARS-CoV-2.

"What we found was that the relatively mild, acute course of SARS-CoV-2 in this mouse model elicits prominent neuro-inflammation," lead researcher Michelle Monje, a professor of neurology at Stanford University in California, said during an interview with CBC News.

The team suspects that could be what's behind the "brain fog" described by some people following a bout of COVID-19, similar to what some people experience after having chemotherapy treatment.

Lingering symptoms can be 'debilitating'

The feeling of post-infection brain fog, along with other lingering effects, is often referred to as long COVID a phenomenon that's well documentedbut still not fully understood.

Dr. Angela Cheung, a senior scientist-clinician at the University Health Network in Toronto,has spent much of the pandemic working with long COVID sufferers asthe co-lead investigator for the Canadian COVID-19 Prospective Cohort Study.Patients'symptoms, she said, are all over the map from extreme exhaustion to heart palpitations to sleep disruption.

"Some people have only a little bit, and they say, 'Oh, my smell is not quite back,'" she said. "But some people have very debilitating symptoms to the point that they can't do things, they have to lie in bed all day, they can't maintain a job."

Miller, the researcher atMcMaster, said he's most concerned about those kinds of long-term health impacts that arise soon after infectionand seem to persist for prolonged periods, "or perhaps even for life."

"What I would not be particularly worried about is the likelihood that 10, 20 years from now, tons of people are going to experience some major chronic illness that is related to SARS-CoV-2 infections," he said.

But even rare illnesses, in the context of a global pandemic, could become a substantial burden on the health-care system just by virtue of the sheer number of people getting infected all at once.

Lessons from 1918 pandemic impacts

That's a lesson from the 1918 influenza pandemic, which sickened more than 500 million people a third of the world's population at the time and had a dramatic impact on global health in the short term, including tens of millions of deaths.

That global health crisis was also linked to a more modest impact on survivors' health later in life. One Swedish study, for instance, found that having exposure to the 1918 flu strain before birth, in the womb,may have resulted in higher rates of health issues and hospitalizations in adulthood.

Typically, later impacts are linked to genetic mutations thatcan predispose someone to a certain disease, Miller noted.

"An infection compounded on top of that genetic predisposition might be enough to tip the scale, so that person experiences a disease that they might not have experienced otherwise," he said.

WATCH | Doctors strive to solve long COVID as patients struggle to recover:

Doctors search to solve long COVID as patients fight to recover

3 years ago

Duration 6:14

Nearly two years into the COVID-19 pandemic, doctors and health experts are searching to find a cause and treatment for long COVID, while patients are simply fighting for their recovery.

Miller also said one aspect of this virus, compared withmany others, should be somewhat reassuring: Our bodies do seem to clear it out.

Unlike HIV, herpes virusesor varicella-zoster the virus known for causing chickenpox in childrenand shingles later in life SARS-CoV-2 doesn't appear to stick around indefinitely like a ticking time bomb, which reduces the risk of severe health outcomes developing decades later.

Still, given all of the unknowns around this coronavirusand how little time has passed since it began spreading among humans, Miller said major questions remain over how infections will affect people down the line.

"The vast majority of people who get COVID have mild infection and survive," he said. "But it doesn't account for what might happen in the future as a result of those infections."