How viral infections cause long-term health problems
Every day, Davida Wynn sets herself one task: take a bath. Or do the dishes. Or prepare an extensive meal. By the end of the job she is exhausted and has to sit or lie down, and sometimes she falls asleep wherever she is.
“Anything beyond that is really unbearable,” Ms Wynn, 42, said.
Even during small tasks, her heart beats faster, and she often becomes dizzy. At least once a month, she falls at her home outside Atlanta. Once she seriously bruised her face, and another time she hit her knee.
Ms Wynn was infected with coronavirus in May 2020, when she was a nurse in a hospital Covid ward, and became so ill that she was placed in an induced coma for six weeks. Since then, her blood work has shown that she suffers from extreme inflammation, a hallmark of autoimmune diseases.
Coronavirus infection is known to leave a long legacy of health problems, many of which are characterized as long Covid. But editing proof suggests that the coronavirus, independently of that syndrome, also confuses the immune system focused on the bodycause autoimmune disorders in some people.
This result is more likely among those who, like Ms. Wynn, were seriously ill with Covid, several studies suggest.
Covid does not unique on this aspect. Scientists have long known that infections can set the body on the path to autoimmune diseases. The classic example is the Epstein-Barr virus.
About one in ten people with glandular fever, caused by the virus, subsequently develop myalgic encephalomyelitis/chronic fatigue syndrome. Even a groundbreaking study last year linked to the virus to multiple sclerosis.
Many other pathogens can do that too seed autoimmunity – but only in a few unhappy people.
“We are all infected with a large number of viruses, and in most cases we do not develop any autoimmunity,” says Dr. Alberto Ascherio, an epidemiologist at the Harvard TH Chan School of Public Health who led the study on multiple sclerosis. .
Infections with bacteria such as chlamydia and salmonella can inflame the joints, skin and eyes – a condition called reactive arthritis. Enteroviruses can trick the body into attacking its own pancreatic cells, which can lead to diabetes Type 1 diabetes.
Like it Epstein Barr virus, dengue And HIV They are believed to cause autoimmunity in some people. Still, Covid appears to be triggering a clear long-term response, says Dr. Timothy Henrich, a virologist at the University of California, San Francisco.
“There is something specific about SARS-CoV-2 that seems to set it apart, in terms of severity and duration,” he said, referring to the coronavirus.
Early in the pandemic, scientists discovered that antibodies that target the body rather than the pathogen – so-called autoantibodies – are important in Covid. Those who had autoantibodies interferona key part of the body’s initial response to pathogens before coming into contact with the coronavirus was more likely to fare badly or to dying of Covid.
About 10 percent of patients of severe Covidmost men over age 55 had these antibodies, compared to just 0.3 percent in the general population.
“With any viral infection you get autoantibodies, and this has been known for decades,” says Dr. Shiv Pillai, an immunologist at Harvard Medical School.
Many years from now, scientists might be able to see a higher incidence of autoimmune diseases in people who had severe Covid-19, he said, but that is not a foregone conclusion: “There may be many other factors that need to be met before someone gets sick. the sickness.”
Why only some people develop autoimmune diseases is unclear, but the answer likely involves dozens of genes and an environmental catalyst.
Lupus is preceded by high levels of autoantibodies more than a decade before the onset of the disease, but many relatives of patients with lupus who have a similar genetic background never develop the disease.
“The most likely explanation is that you have all these risk factors, you have all these things ready, and there is a final trigger,” says Dr. Iñaki Sanz, an immunologist at Emory University.
To definitively link a virus to an autoimmune disease, rigorous studies would need to follow large numbers of people over many years. The best example of such a study is the study that linked the Epstein-Barr virus to multiple sclerosis.
EBV, a member of the herpes virus family, infects almost everyone at some point. Once in the body it lasts forever; the virus can be reactivated by conditions such as stress and hormonal changes. (Reactivation by EBV is another of the four risk factors for long Covid.)
To investigate the association with multiple sclerosis, Dr. Ascherio and his colleagues from what they call a ‘nature experiment’ – a long-term study of more than 10 million active-duty soldiers in the US military.
Between 1993 and 2013, the researchers collected 62 million serum samples from this racially diverse group. Those infected with EBV had a 32-fold increase in the risk of multiple sclerosis, compared with those who did not have the virus, the scientists found. They did not observe similar relationships with other viruses.
Less than one million Americans has multiple sclerosis, which suggests that other factors also play a role. Still, researchers are now excited about the idea of one vaccine against EBV to prevent multiple sclerosis. (However, no vaccines against EBV are currently available some are in clinical trials.)
Studies from other teams support the link between EBV and multiple sclerosis. Danish researchers followed more than 25,000 people with glandular fever for decades and found that this was the case doubled their chances of developing multiple sclerosis.
And a study published last year offered a possible explanation: EBV mimics a human protein, potentially misdirecting antibodies made against the virus.
About one in four people with multiple sclerosis have these antibodies, “which provide the basis for how EBV could trigger an autoimmune response that would cause multiple sclerosis,” says Dr. William Robinson, an expert in autoimmune diseases at Stanford University who led the study.
This kind of molecular mimicry is one route to autoimmunity. But in other cases, the body may never completely clear a pathogen after infection, and the persistence of the virus – whether that is live virus or simply leftovers – can keep the body in an immune state big alarmwhich ultimately leads to autoimmunity.
Both options suggest treatments. In a small number of people, antiviral medications and vaccination can do that relieve the symptoms of long Covid, suggesting a live virus may be the source. Dr. Henrich is conducting a study on high-dose monoclonal antibodies that would absorb errant viral fragments left in the body.
“If the viral proteins cause an autoreactive process, getting rid of those viral proteins can actually improve overall health,” said Dr. Henrich.
For Ms. Wynn, there is no relief in sight. She has tried a plethora of medications, including treatments for rheumatoid arthritis, but has so far failed to respond.
“It has been a long and difficult process,” Ms Wynn said. “And I can tell you that from a mental perspective it has been absolutely exhausting.”