Measles – one of the most contagious human pathogens known to science – can kill you. This deserves to be said clearly.
Overall, between one and three children in a thousand unvaccinated children infected with measles die, but the mortality rate depends heavily on a given person’s living and health conditions before they contract the disease.
In 1990, measles and vitamin A deficiency were still considered the leading causes of childhood blindness in most low-income countries. In 2004, the WHO estimated that around 100,000 children lost their sight each year due to the virus.
As disease control expert Dr Peter Strebel explained to VaccinesWork earlier this year, in a context of poverty – which is often accompanied by poor nutritional status and household overcrowding – the results are much worse. In such circumstances, as well as in humanitarian emergencies, the virus is expected to 15% of victims.
All people who do not die (by definition) survive their infection. But survival is not always synonymous with a return to perfect health. Some of the people who survive measles live with permanent disabilities that disrupt their lives. A very small, unlucky minority will die, years after first contact with the disease, from a rare and sudden degenerative brain condition. A majority of them will remain more vulnerable to other diseases after being confronted with the virus, the consequence of a phenomenon linked to measles called “immune amnesia”, which also constitutes a significant epidemiological risk factor in terms of population.
How is the virus spread?
A person has measles. When coughing, it spreads viral material into the air in the form of aerosolized droplets, which can remain airborne for two o’clock. An unvaccinated and “immunely naive” person inhales these droplets and their respiratory system sucks them up.
The virus first infects immune cells in the lining of the lungs. These infected cells travel to the lymph nodes where the virus spreads to other immune cells – those responsible for producing antibodies that remember old pathogens. It commandeers the “machines” of these cells and uses them to replicate itself at high speed. The measles virus then becomes systemic and spreads aggressively throughout the body. In an interview with Wired, Roberto Cattaneo, a molecular biologist at the Mayo Clinic, estimated that just about a week after breathing in measles droplets, some 50% of the body’s memory cells become infected, seriously damaging the sick person’s defenses. against other bacteria and viruses. Deaths from measles are often linked to co-infection by other microbes, most often through a measles-associated pneumonia.
The virus travels through the windpipe, killing certain cells along the way which, as it spills into the airways, causes coughing – sending virus-laden droplets out into the world.
As it travels through the blood, the virus infects the capillaries of epithelial cells, triggering the immune system to release chemicals that attack the invaders but also damage the host cells. L’measles rash on the skin is the visible witness.
By a similar process, the virus causes conjunctivitis in the eye – this is an inflammation of the conjunctiva, a membrane rich in blood vessels. More rarely, the cornea can also become infected in a process called keratitis.
In about one in a thousand cases, the virus enters the brain where it can cause dangerous inflammation of the brain parenchymaor brain tissue.
Loss of eyesight
In 1990, measles and vitamin A deficiency were still considered to be the main causes of childhood blindness in most low-income countries. In 2004, the WHO estimated that on the order of 100,000 children lost their sight every year due to the virus. Vaccination and vitamin A supplements have improved the situation, but the risk of this life-altering disability remains high in communities suffering from vitamin A deficiency and whose rates of vaccination are low.
“In some ways, infection with the measles virus puts the immune system into default mode. » The body definitively “forgets” how to fight against the pathogens with which it is familiar. It can learn again – but learning means surviving another infection, another threat – potentially, at the population level, surviving another epidemic.
Measles can causeulceration of the corneal epithelium, leaving the eye vulnerable to bacterial infection – and secondary infection can cause scarring of the cornea, partially or completely damaging a child’s vision. If a healthy cornea is as transparent as a window, a scarred cornea looks like frosted glass. Tragically, corneal scarring is often caused or exacerbated by misguided and unscientific attempts to treat or soothe the uncomfortable eye inflammation common with measles.
The risk to a child’s eyes is particularly serious if, due to an inadequate diet, the child is deficient in vitamin A. When measles infects the lining of the intestine, it can lead to loss of proteins that carry vitamin A around the body, meaning that an already vulnerable child’s vitamin A levels may drop.
“If a child has an acute, severe deficiency, the cornea can simply melt,” Dr. Clare Gilbert, an ophthalmologist and professor of international eye health, told VaccinesWork. Following a process of liquefactive necrosis of the cornea, the contents of the eye can come out “and it’s a real disaster”, explains Clare Gilbert. “They end up going totally and permanently blind after that. »
Hearing loss
Measles can precipitate hearing loss in two ways: first, through ear infections, which are common with measles but do not often cause permanent damage. The second is due to a lesion resulting from inflammation of the brain linked to measles, or encephalitis.
As measles-related hearing loss primarily affects children under the age of five, it is likely to have significant developmental consequences, potentially affecting speech acquisition.
According to a 2021 article in Nigeria, hearing loss due to measles is widely underreported, which means it’s hard to say for sure how common it is. According to estimates, before widespread vaccination in the United States, approximately 5 to 10% cases of profound deafness were linked to measles.
Other lasting neurological deficits, from paraplegia to intellectual disability
In addition to deafness, encephalitis can cause other forms of lasting disability. The mortality rate for measles-related encephalitis is approximately 10-15%. Approximately 25% of people who survive measles-related encephalitis will suffer permanent neurological damageranging from motor deficits such as paraplegia to convulsive disorders, including deafness and intellectual disability.
Delayed death: subacute sclerosing panencephalitis
Sometimes years pass before the measles virus takes its toll. More common in poor countries that in rich countries, subacute sclerosing panencephalitis (SSP) is nevertheless extremely rare, and strikes approximately 4 to 11 people per 100,000 measles infections.
PSS is a disease that occurs years after primary infection with measles. Typically, patients contracted measles young – usually in early childhood – and appeared to recover from the infection. But a particular mutant of the virus persisted, latent, in the brain.
Much later, usually when patients are between five and fifteen years old, they begin to change. At first, the change is vague, hard to pin down – headaches, forgetfulness, mood swings, drop in grades at school. However, over time, they will suffer from muscle spasms, loss of speech, difficulty walking. Within one to three years after diagnosis, patients enter a vegetative state and then die. There is no treatment to counter the progression of the disease once it has started, but vaccination against measles is a reliable means of prevention.
Immune amnesia
The phenomenon called immune amnesia generated by measles is not uncommon and can therefore be dangerous on a large scale. Not only does the attack on the immune system by the measles virus make the body vulnerable to other bacteria and viruses for the duration of the infection, but it can also destroy previously acquired immunity against other agents. pathogens, putting people at higher risk of contracting other illnesses, even after clearing the measles virus from their body.
In a landmark study, published in 2019 in the journal Science, Michael J. Mina, of Harvard, and his coauthors found that “measles caused the elimination of 11 to 73 percent of the antibody repertoire in individuals… And it is worth noting that these effects on the immune system were not observed in infants vaccinated against measles, mumps and rubella (MMR). »
“In some ways, infection with the measles virus puts the immune system into default mode,” Mansour Haeryfar, professor of immunology at Western University in Canada, told the BBC. The body permanently “forgets” how to fight against pathogens with which it is familiar. It can learn again – but learning means surviving a new infection, another threat – potentially, at the population level, surviving another epidemic.
Credit: Gavi/2021/Asad Zaidi
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