The most iconic thing about measles is its rash. Red, angry splotches make this infection painfully visible. But that rash — and even the fever, cough and sore eyes — distracts from the infection’s real harm: an all-out attack on the immune system.
The immune system retains memories of the infections it fights. That helps it know what to do when it encounters familiar germs in the future. But measles wipes clean those memories. The resulting “immune amnesia” from measles can leave people at risk of developing infections from other harmful viruses and bacteria for years, scientists are finding. Pneumonia, ear infections and diarrhea are common side-effects.
That makes measles “the furthest thing from benign,” says Michael Mina. As a pathologist, he studies infectious diseases at Harvard University in Cambridge, Mass. Measles increases people’s susceptibility to everything else, he says. And that has big costs.
Scientists now have a better picture of how the measles virus mounts its sneak attack. They know which cells are most at risk and how long the immune system seems to suffer. Studies helped fill in the details. They came from tests in lab animals and in human tissues and from comparing children before and after they had measles.
This new view may help explain why the measles vaccine seems to have far-reaching effects. The shot prevents deaths — and from more diseases than just measles, says Rik de Swart. He’s a virologist at Erasmus University Medical Center in the Netherlands. By shielding the immune system from one virus, the vaccine may help keep other disease-causing germs at bay.
Locking onto a target
After someone with measles coughs or sneezes, their virus can linger in the air and on surfaces for up to two hours. Once inside its next victim, that virus attacks immune cells. It targets those in the nose, throat, lungs and eyes. These immune cells have a protein called CD150 on their surface. This protein allows the virus to invade, experiments on lab animals show.
Inside the cells, the virus quickly makes copies of itself. Then it spreads to places packed with other immune cells, such as the bone marrow, the spleen, tonsils and lymph nodes. The measles virus has an “enormously strong” preference for infecting immune cells, says Bert Rima. He is an infectious-disease researcher at Queen’s University Belfast in Northern Ireland.
By looking at preserved human tissue, Rima and his colleagues traced how measles invades the immune system. Eventually, newly made viral particles move to the respiratory tract. From there they can be coughed out to sicken more people. The researchers described their findings in the May/June 2018 issue of mSphere.
A severe measles infection usually lasts several weeks. It can sometimes bring ear infections and pneumonia. In rare cases, a deadly brain swelling may also occur. On their own, those are worrisome side-effects, says Anthony Fauci. He is the director of the National Institute of Allergy and Infectious Diseases in Bethesda, Md. But the loss of immune cells also can leave people prone to infections that the immune system would normally fend off.
In 2013, de Swart and colleagues had a chance to study the immune effects of the measles virus in children. These kids were part of a closed-off community of Orthodox Protestants in the Netherlands. Parents in this community refuse to let their kids become vaccinated. As a result, bouts of measles have been common. The community’s last measles outbreak had ended in 2000. So it was just a matter of time before the virus took hold again.
The researchers got permission from parents to take blood samples from healthy children who never had measles. They wanted to study their immune cells. Then, the researchers waited for an outbreak. They would test the kids again after an infection.
And they didn’t have to wait long. An outbreak ripped through the community just as the researchers began collecting blood. Classrooms emptied as sick siblings packed into dark living rooms to protect their sensitive eyes. De Swart’s team had blood samples from before and after 77 of those children came down with measles.
The measles virus targets immune cells called memory B and T cells, de Swart says. These cells remember threats the body has already fought off. They also help the immune system spring into action quickly if those threats return. After the measles outbreak, the numbers of some types of the memory cells dropped in children who had caught the disease. That created an immune amnesia.
De Swart’s team reported its findings November 23, 2018 in Nature Communications.
Long road to recovery
The immune system might take months, or even years, to bounce back from this memory loss. Researchers, including de Swart and Mina, compared health records of children in the United Kingdom from 1990 to 2014. For up to five years after a bout of measles, children experienced more infections than did those who never had the disease. And children who’d had measles were 15 to 24 percent more likely to receive a prescription for medicine to treat an infection. The findings were reported last November 8 in BMJ Open.
Mina and his colleagues found similar results for deaths from nonmeasles infections among children in England, Wales, the United States and Denmark. When measles was rampant, children were more likely to die from other infections, the researchers found. And this added danger from measles stuck around for a long time. Even several years out, measles survivors were more likely to die from other infections than did children who had not gotten measles.
At some point, the immune system can recover its memories. But it’s not clear how. With new methods that can measure these memories, Mina and others hope to figure that out.
Most children get over measles without a problem. “The immune system is incredibly resilient,” de Swart says. Still, measles is not an innocent childhood disease. For some people, the outcome can be severe.
But there’s a vaccine for measles. With it, “we know how to prevent this potentially lethal disease,” Mina says. “It’s so simple.”
allergy The inappropriate reaction by the body’s immune system to a normally harmless substance. Untreated, a particularly severe reaction can lead to death.
amnesia Impaired long-term memory caused by brain damage, disease, shock or trauma
bacteria (singular: bacterium) Single-celled organisms. These dwell nearly everywhere on Earth, from the bottom of the sea to inside other living organisms (such as plants and animals). Bacteria are one of the three domains of life on Earth.
benign Not harmful to one’s health. Malignant, in contrast, means harmful and generally refers to cancer.
cell The smallest structural and functional unit of an organism. Typically too small to see with the unaided eye, it consists of a watery fluid surrounded by a membrane or wall. Depending on their size, animals are made of anywhere from thousands to trillions of cells.
colleague Someone who works with another; a co-worker or team member.
diarrhea (adj. diarrheal) Loose, watery stool (feces) that can be a symptom of many types of microbial infections affecting the gut.
immune (adj.) Having to do with the immunity. (v.) Able to ward off a particular infection. Alternatively, this term can be used to mean an organism shows no impacts from exposure to a particular poison or process. More generally, the term may signal that something cannot be hurt by a particular drug, disease or chemical.
immune system The collection of cells and their responses that help the body fight off infections and deal with foreign substances that may provoke allergies.
infection A disease that can spread from one organism to another. It’s usually caused by some type of germ.
lymph A colorless fluid produced by lymph glands. This secretion, which contains white blood cells, bathes the tissues and eventually drains into the bloodstream.
marrow (in physiology and medicine) Spongy tissue that develops inside of bones. Most red blood cells, infection-fighting white blood cells and blood platelets form within the marrow.
measles A highly contagious disease, typically striking children. Symptoms include a characteristic rash across the body, headaches, runny nose, and coughing. Some people also develop pinkeye, a swelling of the brain (which can cause brain damage) and pneumonia. Both of the latter two complications can lead to death. Fortunately, since the middle 1960s there has been a vaccine to dramatically cut the risk of infection.
outbreak The sudden emergence of disease in a population of people or animals. The term may also be applied to the sudden emergence of devastating natural phenomena, such as earthquakes or tornadoes.
particle A minute amount of something.
pathogen An organism that causes disease.
pathologist Someone who studies disease and how it affects people or other infected organisms.
pneumonia A lung disease in which infection by a virus or bacterium causes inflammation and tissue damage. Sometimes the lungs fill with fluid or mucus. Symptoms include fever, chills, cough and trouble breathing.
protein A compound made from one or more long chains of amino acids. Proteins are an essential part of all living organisms. They form the basis of living cells, muscle and tissues; they also do the work inside of cells. Among the better-known, stand-alone proteins are the hemoglobin (in blood) and the antibodies (also in blood) that attempt to fight infections. Medicines frequently work by latching onto proteins.
resilient (n. resilience) To be able to recover fairly quickly from obstacles or difficult conditions.
respiratory tract Parts of the body involved in breathing (also called the respiratory system). It includes the lungs, nose, sinuses, throat and other large airways.
risk The chance or mathematical likelihood that some bad thing might happen. For instance, exposure to radiation poses a risk of cancer. Or the hazard — or peril — itself. (For instance: Among cancer risks that the people faced were radiation and drinking water tainted with arsenic.)
sibling An offspring that shares the same parents (with its brother or sister).
T cells A family of white blood cells, also known as lymphocytes, that are primary actors in the immune system. They fight disease and can help the body deal with harmful substances.
tissue Made of cells, it is any of the distinct types of materials that make up animals, plants or fungi. Cells within a tissue work as a unit to perform a particular function in living organisms. Different organs of the human body, for instance, often are made from many different types of tissues.
tonsils Short for palatine tonsils. This is a pair of soft tissues at the back of the throat. They are part of the immune system, which can help to fight infections. Many people get infected tonsils removed, however, and seem no more vulnerable to infection afterward.
tract A particular, well-defined area. For instance, important parts of an animal’s body will include its respiratory tract (lungs and airways), reproductive tract (gonads and hormone systems important to reproduction) and gastro-intestinal tract (the stomach and intestines — or organs responsible for moving food, digesting it, absorbing it and eliminating wastes).
United Kingdom Land encompassing the four “countries” of England, Scotland, Wales and Northern Ireland. More than 80 percent of the United Kingdom’s inhabitants live in England. Many people — including U.K. residents — argue whether the United Kingdom is a country or instead a confederation of four separate countries. The United Nations and most foreign governments treat the United Kingdom as a single nation.
vaccine (v. vaccinate) A biological mixture that resembles a disease-causing agent. It is given to help the body create immunity to a particular disease. The injections used to administer most vaccines are known as vaccinations.
virologist A researcher who studies viruses and the diseases they cause.
virus Tiny infectious particles consisting of RNA or DNA surrounded by protein. Viruses can reproduce only by injecting their genetic material into the cells of living creatures. Although scientists frequently refer to viruses as live or dead, in fact no virus is truly alive. It doesn’t eat like animals do, or make its own food the way plants do. It must hijack the cellular machinery of a living cell in order to survive.
Journal: B.M. Laksono et al. Studies into the mechanism of measles-associated immune suppression during a measles outbreak in the Netherlands. Nature Communications. Vol. 9, November 23, 2018. doi: 10.1038/s41467-018-07515-0.
Journal: K. Gadroen et al. Impact and longevity of measles-associated immune suppression: a matched cohort study using data from the THIN general practice database in the UK. BMJ Open. Vol. 8, November 8, 2018. doi: 10.1136/ bmjopen-2017-021465.
Journal: I.V. Allen et al. Macrophages and dendritic cells are the predominant cells infected in measles in humans. mSphere. Vol. 3, May/June, 2018. doi: 10.1128/mSphere.00570-17.
Journal: M.J. Mina et al. Long-term measles-induced immunomodulation increases overall childhood infectious disease mortality. Science. Vol. 348, May 8, 2015, p. 694. doi: 10.1126/science.aaa3662.