Older women with high antibody levels to a common viral infection may be more vulnerable to frailty and die earlier than other women their age, a new study suggests.
The virus in question is cytomegalovirus, or CMV, which infects most people at some point in their lives - up to 80 percent of U.S. adults by the age of 40. In healthy people, the infection usually causes no symptoms, and is considered dangerous only for newborns infected during pregnancy and for people with compromised immune systems, such as those with AIDS virus.
However, once CMV gets into the body, it stays there for life. That leaves the question of whether, as people age, the virus has any health effects.
“Our current understanding of what long-term CMV infection does in people with normal immune function is limited,” said Dr. George C. Wang, an instructor of medicine at Johns Hopkins University in Baltimore and the lead researcher on the current study.
He and his colleagues found that among 635 women in their 70s, those with the highest levels of CMV antibodies were more likely to become frail or die over the next several years than women who were negative for CMV antibodies.
The findings point only to a relationship between CMV and frailty and mortality, and do not prove cause-and-effect. However, two factors bolster the case that CMV may be a direct contributor, Wang told Reuters Health in an email.
One factor is that the researchers looked at the women’s CMV antibody levels and then followed them over time to see which participants became frail or died; so the antibody elevations preceded the outcomes.
The other is that the investigators found a “dose-response” relationship between CMV antibodies and frailty and mortality; that is, women with the highest antibody levels had the highest risks.
Exactly what high antibody levels signify is not certain, but, Wang said, they may indicate that the dormant CMV has been “reactivated” in the body a relatively greater number of times. It could also mean that a person has had the virus for a longer period or has been infected more than once - by different strains of CMV.
In this study, 543 women had antibodies to CMV, while the rest - 92 women - were negative for antibodies. When the researchers broke the former group into four subgroups based on their antibody levels, they found that the group with the highest levels was more than twice as likely to become frail over the next three years as antibody-negative women were.
Among women who were negative for antibodies, nearly 3 percent became frail per year; that figure was 9 percent in the group with the highest CMV antibody levels. When the researchers factored in other variables - including age, race and any diagnoses of heart disease or diabetes - high CMV antibody levels remained linked to an increased risk of frailty.
Similarly, women with the highest antibody levels had a nearly three-fold greater risk of dying over the next five years as women with no CMV antibodies. A total of 91 women died during the study period; the yearly death rate was 1.4 percent in the antibody-negative group, and 5.3 percent in the group with the highest antibody levels.
In theory, a greater number of CMV reactivations, or a longer exposure to infection, could affect a person’s health by creating more inflammation in the body, according to Wang. Inflammation is believed to contribute to a number of disease processes; heart disease, for example, involves inflammation within the blood vessels.
More studies are still needed to understand how persistent CMV infection may affect the health of people with normal immune function, according to Wang and his colleagues.
Even if the virus does contribute to poor health in some older adults, right now there is no practical way to address it.
“At present, there is no effective antiviral therapy against CMV that is sufficiently free from adverse side effects to merit administering to otherwise healthy people,” Wang said.
He added that he hopes the current study will fuel current research efforts to develop anti-CMV vaccines and the “next generation” of antiviral drugs for treating congenital CMV and infections in immune-compromised people.
For healthy people to be screened for CMV antibodies - and possibly treated - there would first have to be safer drugs and effective vaccines available, Wang said.
SOURCE: American Journal of Epidemiology, online April 16, 2010.