Measles is one of the most contagious infectious diseases, and remains a leading cause of death, particularly among young children, especially in areas with low rates of vaccination. Measles is also called rubeola, which can easily get confused with German measles, which is also called rubella. Similar sounding names, but very different viruses.
Regular measles is caused by the measles virus. Seriously, the species is the measles virus. of the genus Morbillivirus, and family Paramyxoviridae. The reason why this guy is so contagious is that it's airborne, and spreads via tiny liquid particles that get flung into the air when someone sneezes or coughs, and can live for up to 2 hours in that airspace or nearby surfaces. If someone breathes in that air or touches a surface and then touches their eyes, their nose, or their mouth, they can become infected.
Measles is so contagious that if one person has it, 90% of nearby non-immune people will also become infected. Once the measles virus gets onto the mucosa of an unsuspecting person, it quickly starts to infect the epithelial cells in the trachea or bronchi. Measles virus uses a protein on its surface called hemagglutinin, or just H protein, to bind to a target receptor in the host cell, which could be CD46, which is expressed on all nucleated human cells. CD150, which is a protein that is used to bind to the epithelial cell, is also expressed aka signaling lymphocyte activation molecule or SLAM, which is found on immune cells like BRT cells and antigen presenting cells, or Nectin-4, a cellular adhesion molecule.
Once bound, the fusion or F protein helps the virus fuse with the membrane and ultimately get inside the cell. Now this virus is a single stranded RNA virus, and it's also negative sense, meaning it first has to be transcribed by RNA polymerase into a positive sense mRNA strand. After that it's ready to be translated into viral proteins, wrapped in the cell's lipid envelope and sent out of the cell as a newly made virus. Within days the measles virus spreads through local tissue and is picked up by dendritic cells and alveolar macrophages and carried from that local tissue in the lungs to the local lymph nodes. From there it continues to spread, eventually getting into the blood and spreading to more lung tissue as well as other organs like the intestines and the brain.
Now it typically takes 10-14 days from the time that the virus enters the body to the start of symptoms, and this is the incubation period. Once the symptoms start, we've entered the prodromal period, which typically lasts around 3 days, and starts with a high fever and the 3 C's, cough, conjunctivitis, or inflammation and redness of the white part of the eye, and choriza, swelling in the mucous membrane of the nose. Essentially a stuffy nose. One to two days later comes the enanthem, which is a rash on the mucous membranes that looks like salt grains on a wet background. These are called coplic spots and are these small white spots that are commonly seen on the inside of the cheeks opposite the molars.
After these initial prodromal symptoms comes the exanthem phase, which is where a red, blotchy maculopapular rash spreads in a cephalocaudal progression. In other words, the exanthem starts at the head, or cephalo, and spreads to the extremities, or the ends of the body, or caudal. This rash fades after about 4 days, and leads into the recovery phase, which can last for another 10-14 days, with the final symptom usually being a persistent cough. In general, infected people are most contagious starting from the final day of the incubation period through the prodromal and exanthem phase.
which roughly works out to be 4 days before to 4 days after the onset of the rash. Now the good news is that once all this is over and someone's recovered from measles, they have lifelong immunity. Since measles affects various organs like the lungs, the intestine, and the brain, it can lead to complications like pneumonia, diarrhea, and on rare occasions, encephalitis, all of which can lead to death. In addition, measles can suppress the immune system for up to 6 weeks, This can contribute to bacterial superinfections like otitis media and bacterial pneumonia. All of these complications are worst among young infants who typically have the highest rates of mortality during a measles outbreak.
Another severe and often fatal complication for children under 2 years old is the development of subacute sclerosing panencephalitis, which can happen 7-10 years later. This is thought to be caused by persistent measles virus infection. possibly due to an abnormal immune response or a mutated strain of the measles virus, which leads to chronic inflammation of the entire brain.
The symptoms of SSPE are initially pretty subtle, like for example mood changes, but eventually become severe and dramatic. and can include seizures, coma, and if left untreated, death. For people who are immunocompromised, for example people with HIV or AIDS, their immune mediated responses are impaired.
That being said, if they get measles, they might not develop some symptoms that are a result of the immune system responding to the measles virus, like the ananthem or the complex spots, or the exanthem, the rash. These people though also have higher rates of pneumonia and encephalitis, which contribute to a higher mortality rate. Diagnosis of measles is usually done via serology, looking for measles antibodies in the blood serum, and the disease is usually most likely to happen with unvaccinated individuals.
That said, the measles vaccine is a live attenuated immunization, essentially meaning it's been weakened, and it's given between 12 and 15 months of age, and again between 4 and 6 years of age, and it has an impressive 95% vaccine efficacy rate. which means that out of 100 cases of measles among unvaccinated people, 95 would have been prevented by the vaccine. In addition to the vaccine, another source of protection for young infants is their mother's anti-measles antibody, or immunoglobulin, which the fetus gets transplacentally and lasts until about 9 months of age. When measles does develop, there isn't a specific antiviral treatment. Instead, the medications are generally aimed at treating super infections, maintaining good hydration with adequate fluids, and pain relief.
Some groups are also given vitamin A, like young children and the severely malnourished, which acts as an immunomodulator that boosts the antibody responses to measles and decreases the risk of serious complications. Finally, in outbreak settings, measles vaccine can be given to household contacts, and measles immunoglobulin can be given to pregnant women and young infants to help prevent others from getting sick. Alright, so quick review of measles.
Measles is an airborne pathogen that's highly contagious and causes cough, conjunctivitis, and choriza, as well as complications like pneumonia and encephalitis, and can be prevented through vaccination. Helping current and future clinicians focus, learn, retain, and thrive. Learn more.