How measles erases immune system’s memory, by researchers

*Beyond rash, infection makes it harder for body to remember, attack other invaders
The most iconic thing about measles is the rash — red, livid splotches that make infection painfully visible.But that rash, and even the fever, coughing and watery, sore eyes are all distractions from the virus’s real harm — an all-out attack on the immune system.

Measles silently wipes clean the immune system’s memory of past infections. In this way, the virus can cast a long and dangerous shadow for months, or even years, scientists are finding. The resulting “immune amnesia” leaves people vulnerable to other viruses and bacteria that cause pneumonia, ear infections and diarrhoea. Those aftereffects make measles “the furthest thing from benign,” says infectious disease epidemiologist and pathologist Michael Mina of Harvard University. “It really puts you at increased susceptibility for everything else.” And that has big consequences, recent studies show.

Details about which immune cells are most at risk and how long the immune system seems to suffer — gleaned from studies of lab animals, human tissue and children before and after they had measles — have created a more complete picture of how the virus mounts its sneak attack. This new view may help explain a larger-than-expected umbrella of safety created by measles vaccination. “Wherever you introduce measles vaccination, you always reduce childhood mortality. Always,” says virologist Rik de Swart of Erasmus. University Medical Center in the Netherlands. The shot prevents deaths, and more than just those caused by measles.

By shielding the immune system against one virus’s attack, the vaccine may create a kind of protective halo that keeps other pathogens at bay, some researchers suspect. After an infected person coughs or sneezes, the measles virus can linger in the air and on surfaces for up to two hours, waiting to make its way into the airways of its next victims. Once inside, the virus is thought to target immune cells found in the mucus of the nose and throat, the tiny air sacs in the lungs or between the eyelids and cornea. These immune cells are decorated with a protein called CD150 that allows the virus to invade, experiments on animals suggest. The virus quickly replicates inside the cells, and then spreads to places packed with other immune cells — bone marrow, thymus, spleen, tonsils and lymph nodes.

“The virus has an enormously strong predilection to infect cells of the immune system,” says Bert Rima, an infectious disease researcher at Queen’s University Belfast in Northern Ireland. Rima and colleagues traced the immune system invasion in preserved human tissue, reporting results in 2018 in mSphere. Eventually, newly made viral particles move into the respiratory tract, where they can be coughed out to sicken more people.

An acute measles infection, which usually lasts several weeks, can sometimes bring ear infections, pneumonia and, rarely, a deadly brain swelling. On their own, those are worri­some outcomes, says Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md. But the loss of immune cells can also leave people vulnerable to infections that the immune system would normally be able to handle.