signs and symptoms of zika

measles (rubeola)author: tanner marshall, ms editor: rishi desai, md, mph measles is one of the most contagious infectiousdiseases, and remains a leading cause of death particularly among young children, especiallyin areas with low rates of vaccination. measles is also called rubeola, which caneasily get confused with german measles which is also called rubella—similar soundingnames 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’s so contagiousis that it’s airborne, and spreads via tiny

liquid particles that get flung into the airwhen someone sneezes or coughs, and can live for up to two hours in that airspace or nearbysurfaces. if someone breathes in that air or touchesa surface and then touches their eyes, their eyes, or their mouths, they can become infected. measles is so contagious that if one personhas it, 90% of nearby non-immune people will also become infected. once the measles virus gets onto the mucosaof an unsuspecting person, it quickly starts to infect the epithelial cells in the tracheaor bronchi. measles virus uses a protein on its surfacecalled hemagglutinin, or just h protein, to

bind to a target receptor on the host cell,which could be cd46, which is expressed on all nucleated human cells, cd150, aka signalinglymphocyte activation molecule or slam, which is found on immune cells like b or t cells,and antigen-presenting cells, or nectin-4, a cellular adhesion molecule. once bound, the fusion, or f protein helpsthe virus fuse with the membrane and ultimately get inside the cell. now this virus is a single-stranded rna virus,and it’s also a negative sense, meaning it first has to be transcribed by rna polymeraseinto a positive-sense mrna strand. after that it’s ready to be translated intoviral proteins, wrapped in the cell’s lipid

envelope, and sent out of the cell as a newlymade virus. within days, the measles virus spreads throughlocal tissue and is picked up by dendritic cells and alveolar macrophages, and carriedfrom that local tissue in the lungs to the local lymph nodes. from there it continues to spread, eventuallygetting into the blood and spreading to more lung tissue, as well as other organs likethe intestines and the brain. now it typically takes 10-14 days from thetime that the virus entering the body to the beginning of symptoms, and this is the incubationperiod. once symptoms start, we’ve entered the prodromalperiod 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 coryza—swelling in the mucous membrane of the nose, essentially a stuffy nose. 1-2 days later comes the enanthem which isa rash on the mucus membranes, that looks like salt grains on a wet background. these are called koplik spots and are smallwhite spots that are commonly seen on the inside of the cheeks opposite the molars. after these initial prodromal symptoms comesthe exanthem phase, which is where a red, blotchy, maculopapular rash spreads in a cephalocaudalprogression.

in other words, the exanthem starts at thehead (or cephalo), and spreads to the extremities or ends of the body (or caudal). this rash fades after about 4 days, and leadsinto the recovery phase which can last for another 10-14 days, with the final symptomusually being a persistent cough. in general, infected people are most contagiousstarting from the final day of the incubation period through the prodromal and exanthemphase, which roughly works out to be 4 days before to 4 days after the onset of the rash. the good news is that once it’s all overand someone has recovered from measles they have lifelong immunity.

since measles affects various organs likethe lungs, intestine, and brain, it can lead to complications such as pneumonia, diarrhea,and, on rare occasion, encephalitis—all of which can lead to death. in addition, measles can suppress the immunesystem for up to 6 weeks, and this can contribute to bacterial superinfections like otitis mediaand bacterial pneumonia. all of these complications are worst amongyoung infants who typically have the highest rates of mortality during a measles outbreak. another severe and often fatal complicationfor children under 2 years old is the development of subacute sclerosing panencephalitis, whichcan happen 7-10 years later.

this is thought to be caused by a persistentmeasles virus infection, possibly due to an abnormal immune response or a mutated strainof the measles virus, which leads to chronic inflammation of the entire brain. the symptoms of sspe are initially prettysubtle like for example, mood changes, but eventually become severe and dramatic, andcan include seizures, coma, and if left untreated, death. for people who are immunocompromised (forexample—people with hivaids), their immune mediated responses are impaired, that beingsaid if they get measles, they might not develop some symptoms that are a result of the immunesystem responding to the measles virus, like

the enanthem (or the koplik spots) or theexanthem (the rash). these people though also have higher ratesof pneumonia and encephalitis which contribute to a higher mortality rate. diagnosis of measles is usually done via serology—lookingfor measles antibodies in blood serum, and the disease is usually most likely to occuramong unvaccinated individuals. that said, the measles vaccine is a live attenuatedimmunization, essentially meaning it’s been weakened, and it’s given between 12-15 monthsof age and again between 4-6 years of age, and it has an impressive 95% vaccine efficacyrate, which means that out of a hundred cases of measles—among unvaccinated people—95would have been prevented by the vaccine.

in addition to vaccine, another source ofprotection for young infants is their mother’s anti-measles immunoglobulin which the fetusgets transplacentally and lasts until about 9 months of age. when measles does develop, there isn’t aspecific antiviral treatment, instead the medications are generally aimed at treatingsuperinfections, maintaining good hydration with adequate fluids, and pain relief. some groups are also given vitamin a, likeyoung children and the severely malnourished, which act as an immunomodulator that booststhe antibody responses to measles and decreases the risk of serious complications.

finally, in outbreak settings, both measlesvaccine and measles immunoglobulin can be given to household contacts and those at highrisk like pregnant women and young infants to help prevent others from getting sick. alright—so a quick review of measles: measlesis an airborne pathogen that’s highly contagious, and causes cough, conjunctivitis, and coryza,as well as complications like pneumonia and encephalitis, and can be prevented throughvaccination. thanks for watching, you can help supportus by donating on patreon, or subscribing to our channel, or telling your friends aboutus on social media.

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