Though you may not hear of it often, cytomegalovirus is a fairly common virus. It is usually harmless, but once contracted, it remains in the system for the rest of a person's life.
Scientists expected to see that the presence of a beta-herpes virus in the system would weaken immunity. That's not what they found.
According to the BMJ Best Practice resource, "Cytomegalovirus (CMV) is a ubiquitous beta-herpes virus that infects the majority of humans."
Infected individuals typically do not experience any symptoms. The virus can be transmitted by coming into direct contact with the bodily fluids, such as blood, of an already-infected individual.
Once acquired, it remains in a person's body for their entire life.
In a new study that was conducted in mice, Dr. Janko Nikolich-Žugich — of the University of Arizona College of Medicine in Tucson — and team decided to look into how, and under what conditions, aging individuals would mount a stronger immune response against viral infections.
Typically, young bodies have stronger defenses. But as we age, our immunity begins to decrease. "That's why older people are more susceptible to infections than younger people," explains Dr. Nikolich-Žugich.
The scientists involved with the new study were interested in finding out how the immune systems of aging individuals might be fortified and rendered more efficient once more.
Does CMV keep the immune system busy?
In this process, Dr. Nikolich-Žugich and team compared older mice infected with CMV with mice in the same age range but without the virus, expecting to see that the CMV-infected mice had a weaker immune system and thus mounted a poorer defense against other viruses.
"CMV doesn't usually cause outward symptoms," notes first study author Megan Smithey, "but we still have to live with it every day since there's no cure."
"Our immune system always will be busy in the background dealing with this virus," she adds.
"We assumed [therefore that] it would make mice more vulnerable to other infections because it was using up resources and keeping the immune system busy," Smithey goes on to explain.
However, the researchers were in for a surprise.
CMV determines 'more robust' defense
Working with a group of aging mice — some carrying CMV and others not — the team tried to infect them all with Listeria, a type of harmful bacteria that is usually found in contaminated foods. Listeriacan cause a disease known as "listeriosis," characterized by fever, sickness, and diarrhea.
The researchers expected the CMV-infected mice to be more susceptible to the bacteria — in fact, they turned out to be more resilient than their CMV-free counterparts.
"We were completely surprised; we expected these mice to be worse off. But they had a more robust, effective response to the infection."
Although they are not yet sure how or why CMV enhances the immune response, the researchers are happy to have made an important discovery about the functioning of the immune system as it ages — namely, that it is capable of mounting a better defense against foreign agents that specialists had previously believed.