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 paramyxovirus, the reason why this guy's 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 two 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 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 RNA 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 in 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 to 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 three days and
starts with a high fever and the three c's. Cough, Conjunctivitis or
inflammation and redness of the white part of the eye, and Carissa 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 colic 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 come to the exanthem phase which is
where red blotchy maculopapular rash spreads in a cephalocoddle progression, in other words, the exanthem starts at the head or cephalon and spreads to the
extremities or the ends of the body or caudal.
This rash fades after about four
days and leads into the recovery phase which can last for another 10 to 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 four
days before to four 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 six weeks and 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 two years
old is the development of subacute sclerosing pan-encephalitis which can happen
seven to ten years later and 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 a 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 immuno-compromised 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 enanthem or the complex
bots or the exanthema.
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 15months of age and again between 4 and 6years of age and it has an
impressive 95 vaccine efficiency 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 trans-placentally
and lasts until about 9months of age when measles does develop there isn't a specific
antiviral treatment instead the medications are generally aimed at treating
superinfections maintaining good hydration with adequate fluids and pain
relief.
Some groups are also given vitamin A
like young children in 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 a quick review of measles, measles
is an airborne pathogen that's highly contagious and causes cough conjunctivitis
and Carissa as well as complications like pneumonia and encephalitis and can be
prevented through vaccination.
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