According to National Geographic, measles is still responsible for more than a hundred thousand deaths each year. It is highly contagious, being able to spread through the air and before the infection is even obvious. It has always been a dangerous disease but new studies revealing that it also causes ‘immune system amnesia’ makes it all the more so.
So what exactly does that mean? It turns out that not only does the disease significantly weaken your immune system for some time, it also wipes your immune system’s memory. Essentially, it erases the history of infections from your body and causes it to forget how to fight off sicknesses it already learned to. And this amnesia can last for a few months up to a few years.
This has been verified by a pair of studies published in Science and Science Immunology which looked into blood samples from unvaccinated children before and after they were infected with the virus. However, the mechanism was first identified in a 2012 study published in PLOS Pathogens. While previous studies had already identified that the measles virus would attack immune cells, this study was able to pinpoint the process.
The research team partly led by Rik de Swart, a virologist from Erasmus University Medical Center, was able to do this by capitalizing on a basic fact known of viruses. This ‘viral necessity’ is that “to multiply and spread, a virus has to invade a cell, hijacking the machinery to copy itself.” So the team modified the measles virus to encode for a fluorescent protein, making the virus ‘light up’ as it spreads across the host. They were able to track the virus at different stages of the disease, monitoring its invasion of the cells.
This modified measles virus was injected into a group of monkeys, which revealed that the virus particularly infects immune memory cells. These are the cells that keep a record of the infections your body has already fought off in order to lessen repeat encounters. It was discovered by tracking which specific cells the virus would infect, and it turned out that all of the monkey’s lymphoid tissues — which is where the immune system cells are — began to glow green due to the added fluorescent protein.
But it wasn’t just the infection that wiped out the immune memory cells. As the immune system worked to eradicate the virus, the ‘viral constellation’ similarly vanished. This means that “by infecting memory cells, the virus not only wiped out some of the body’s immune recollections, it essentially turned the system against itself by forcing healthy immune cells to kill off their infected comrades.”
“If the virus didn’t kill those memory cells already, the immune system would finish the job off,” de Swart explains.
While the experiment was conducted on macaques, the team concludes that a similar mechanism happens with humans. But it is not sure exactly how much of our immune memory is cleared.
Harvard’s Michael Mina was intrigued by the findings of this study and pushed the subject by asking: “If measles is essentially chewing up all of our immune cells, does that have a long-term impact on our immune memory?” In his own study for Science in 2015, he explored this question by using data sets from the United States, Denmark, England, and Wales.
These data sets covered a period from before and after the 1960s’ widespread measles vaccination and compared the presence of childhood disease. Its analysis showed that in populations where measles flourished, up to half of the childhood deaths were caused by infections following their contraction of measles. Moreover, it indicated that these effects lingered for up to 3 years in the affected population.
Throughout all the data sets the number of measles cases remained the best and most consistent predictor of non-measles deaths over a span of 3 years. Meaning to say, even 3 years after a child contracted measles they would continue to have a weaker immune system and a higher risk of death from infections. However, the researchers warned that the conclusions were simply based on temporal relationships and would need further evidence.
This is where the newer pair of studies from Science and Science Immunology becomes relevant. The team behind this study focused on unvaccinated children between four and 17 years old in the Netherlands. The students’ blood was sampled before and after a measles outbreak in 2013, revealing the intricacies of how the measles virus attacks.
Science Immunology’s study was mainly concerned with the blood’s B cells, which are a type of immune cell. Its primary function is to identify invaders and trigger attacks. The B cells of the infected individuals were shown to take some time to completely recover after the sickness. Meanwhile, the Science study cataloged the antibodies or invader-neutralizing proteins in the blood samples. Doing so indicated that there was an 11% to 73% decline in the antibody array for around 2 months after the infection.
So what can be done to manage this harm? The studies found that it was re-exposure to viruses and similar invaders which helped repopulate the lost antibodies best. Still, the best answer to something like this is to prioritize prevention. Prevention of infection from the measles virus can only be done through vaccination, which is on a steady decline.
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