Measles Erases Immune Memory, Stifling Protection from Other Infections

Measles virus has long occupied a top spot on a list of most dangerous pathogens, for in addition to spreading easily, it can temporarily cancel immunity against other infectious diseases. A powerful vaccine has vanquished measles since 1963, offering close-to-lifetime immunity. But the disease is returning, thanks to vaccine hesitancy and apparent lack of knowledge of basic biology.

I was too young to remember having measles. But my mother told me I was very sick for a month, and was a day away from being hospitalized for encephalitis when I finally began to improve.

Circa 1960, everyone got measles. In a room full of vulnerable individuals, some 90 percent will quickly become infected, as the virus wafts in droplets dispersed in the air, hanging around for up to two hours. Having the telltale spots, however, conferred lifelong immunity.

Measles vaccine isn’t quite as effective as protection from natural infection, but it is safe and has saved many lives. A booster can return protection, as many people in fear of a resurgence are now doing. The vaccine is typically administered with vaccines against mumps and rubella (German measles), the MMR. I remember my sister being held down to get her triple vaccine, then given in two shots in the arms, which DNA Science covered here.

It’s Back
Symptoms of measles begin ten to twelve days after inhalation of viral particles. In addition to the telltale red rash are high and persistent fever, congestion, cough, runny nose, watery eyes, and small red, white, and blue lesions in the mouth and cheek lining called Koplik spots.

Measles usually clears up with supportive care. However, brain damage or death occurs in 2 or 3 cases out of every thousand.

Alas, measles is back, cases as of this writing in the hundreds. The widening pool of new cases provides an opportunity for the virus to once again do what viral (and all) genomes do – mutate (change sequence) and recombine (swap parts).

So far, the “wild type” (most common variant) virus hasn’t mutated enough to change its serotype (surface molecule pattern), but it has started down that path. A deadly disease that was once eradicated is free now to reinvent itself into, perhaps, a more infectious or deadly strain. But at the same time, bringing back measles will beckon return of other infectious diseases.

Immune Amnesia
Once an infection has passed, the pathogen leaves a mark on the host’s immune system, in the form of white blood cells – aka lymphocytes, or T and B cells.

“Helper” T cells, when encountering a pathogen after the initial infection, stimulate B cells to produce antibodies, which are proteins that directly attack the virus or bacterium. Another subset of T cells, called memory cells, enable a rapid immune response should the person encounter the pathogen again. The immune response includes memory B cells too, at the ready to pump out antibodies.

Measles virus stifles this pre-existing protection from other infections. This “immune amnesia“ reminds me of the common nightmare of waking up the morning of a final exam and realizing you’ve never gone to class, done the assigned reading, or have forgotten everything – you are woefully unprepared.

“The immune memories that you have acquired are priceless, built over many years and from countless exposures to a menagerie of germs. Measles virus is especially dangerous because it has the ability to destroy what’s been earned: immune memory from previous infections,” wrote Ashley Hagen, MS for the American Society for Microbiology in 2019, recently republished in light of measles’ resurgence.

The Virus
Measles virus is a long, single strand of RNA wound within clusters of proteins that fuse and attach the virus to cells of its only host – US. The virus belongs to genus Morbillivirus and more specifically, family Paramyxoviridae,

A cascade of events sets up the attack on immune memory. Inhaled measles viruses enter macrophages near the tiny air sacs of the lungs. Macrophages are large, blobby cells that move about and scavenge the body, enveloping and destroying dust, debris, worn out cell parts, and pathogens.

The infected macrophages wander over to nearby lymph nodes. Here, they disgorge measles viruses that then enter memory T and B cells. These cells then not only mass-produce measles virus, but the B cells lose the ability to make and release antibodies against other pathogens encountered in the past. This shutdown of immune memory can last up to 3 years. That’s why, before measles vaccine became available, some kids would recover from the disease but succumb to a different infection.

Fortunately, vaccine protects against this “measles-induced immune amnesia.” And that’s good, because vaccine hesitancy is likely to offer other pathogens a new niche.

I think the returning viruses are canaries-in-the-coal-mine heralding the true epidemic – of a profound and infectious ignorance of science.

(Photo credit: CDC/NIP/Barbara Rice)