Obesity is a global health problem whose risks are well known. For example, the United States Institute of Diabetes and Kidney and Digestive Diseases collects comprehensive information on the negative health consequences of excess weight: type 2 diabetes, high blood pressure, heart disease, stroke, sleep apnea, syndrome fatty liver, some types of cancer …
Despite the widely publicized risks of the accumulation of adipose tissue in the body, globally half of humanity suffers from some degree of overweight or obesity.
Now, a new study in mice could provide a clue to how obesity could also increase the severity of infection with the influenza virus, which causes the common or seasonal flu.
The scientific paper has been published in mBio , an open-access journal of the American Society for Microbiology. The study’s conclusions indicate that obesity could affect viral diversity, probably due to an impaired immune response in overweight individuals.
Therefore, obesity would explain why the virulence of influenza varies so much from year to year, and could provide clues for developing an annual influenza vaccine.
The study’s principal investigator, Dr. Stacey Schultz-Cherry – a faculty member at St. Jude Children’s Research Hospital – explains how, due to the way cells respond to flu in an obese body, we may suspect that overweight people do not have good antiviral responses :
“Obesity would allow the virus to replicate faster and the body to make more mistakes. Some of those mistakes are potentially beneficial for the virus.”
Could obesity help the virus to mutate every year?
The problem with the flu is that the virus mutates, and each year a new vaccine is created. Thus, Schultz-Cherry and his colleagues hypothesized that the obese microenvironment may allow the flu virus to change more rapidly.
Method
To find out, the researchers infected ‘fit’ mice and obese mice with the influenza virus for 3 days, allowing the virus to replicate. They then recovered the viruses from the obese and lean mice and gave them back to obese and lean mice, respectively; again, they allowed 3 days for replication and then repeated this process.
“We wanted to imitate what happens during an epidemic, in which the virus passes from one person to another,” they explain.
Flu among thin people vs. flu among obese people
Would it make a difference if the virus is transmitted between thin people or between obese people?
Taking the mouse models, the researchers discovered that, as it went from an obese mouse to an obese mouse, the virus mutated. The variants exhibited increased viral replications, resulting in increased virulence in these overweight mice . “There were different populations, and some of these viruses were more virulent than the lean mouse to lean mouse strains,” explains Schultz-Cherry.
Conclution
When cells interact with the flu, the body generally prepares an immune response to stop the virus from replicating and spreading. As well; the new research showed that this emergency response was ‘muffled’ in obese mice.
This is not the first time a link has been established between obesity and the flu virus. Previous research has shown that people who are obese or overweight have a higher viral load of influenza in their exhaled breath and that they take longer to clear the virus. In addition, animal studies have shown that the influenza virus can spread deeper into the lungs for longer periods of time when there is obesity.
Should we trust a study done in mice?
The use of animal models in biomedicine serves to have a starting point in the study of some pathologies; but also, they are used because the biological similarities between humans and animals are often many. Among mammals, a large part of the genome is shared, which gives these studies clinical relevance; but this does not mean that the animal models that are studied are identical to humans. This means that we must be cautious before applying conclusions to humans.
The researchers have stated that, in the future, they would like to study what is happening at the population level in humans. Studies like this give clues to find out if obesity is one of the reasons why we now see so much viral drift every season , and that it causes vaccines to be continually updated.
