Scientists have demonstrated in mice for the first time that cardiac issues linked with the flu are not triggered by rampant inflammation and damage in the airways, as previously anticipated.
Instead, some of the sickest flu patients' electrical abnormalities and heart damage are associated with direct influenza infection of cardiac cells.
Flu causes cardiac complications
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Previous study had found flu virus particles in cardiac cells of sick mice, but the researchers couldn't be certain that their presence in the heart was causing cardiac harm.
When scientists infected mice with a genetically modified flu virus that couldn't reproduce in heart cells, the mice exhibited conventional inflammatory flu symptoms but no cardiac problems.
"We demonstrated that even when you have a severe infection in the lungs, if you use that virus that can't reproduce in the heart, you don't have those cardiac problems," said lead scientist Jacob Yount, an associate professor of microbial infection and immunology at Ohio State.
It has long been known that hospitalized flu patients might develop cardiac issues.
According to a 2020 research, over 12% of persons hospitalized with the flu in the United States during an eight-year period suffered abrupt, significant cardiac problems.
Yount has been researching influenza for many years, and his group created a mouse model lacking IFITM3, the gene that codes for a crucial protein in the adaptive immune system's clearance of viral infections.
In a 2019 study, his team discovered that flu-infected mice lacking the IFITM3 gene were more likely to suffer cardiac problems.
These mice are not only very sensitive to flu, but they also lack the same antiviral protein that some people do.
A genetic variation that causes IFITM3 deficiency affects around 20% of Chinese individuals and 4% of Europeans, as per ScienceDaily.
"We know such folks are more vulnerable to serious flu illnesses, and our mice study suggests they're also more vulnerable to cardiac issues from the flu," said Yount, who is also a program co-director of Ohio State's Infectious Diseases Institute's Viruses and Emerging Pathogens Program.
The researchers tweaked the DNA of an H1N1 flu strain for this investigation such that the virus could not commandeer cardiac cells to replicate itself.
They injected normal mice and mice missing IFITM3 with the altered virus and a control virus.
Cardiovascular disease was one of the most frequent chronic (long-term) illnesses among adults admitted to hospitals with flu throughout previous flu seasons; around half of persons hospitalized with flu have heart disease.
The flu vaccine is especially essential for persons who have heart disease or have had a stroke since they are more vulnerable to flu complications.
Vaccination has been linked to decreased incidence of some cardiac events. Among persons with heart disease, particularly those who experienced a cardiac episode during the previous year.
To keep up with evolving viruses, flu vaccinations are changed each season.
Because flu vaccine immunity diminishes over time, yearly vaccination is required to offer the greatest possible protection against flu.
A flu vaccination defends against with the flu viruses that, according to studies, will be most prevalent throughout the upcoming season.
