Sometimes, even usually, evolution finds a “local maximum” of effectiveness. Where the solution an organism finds is not optimal but it’s good enough for the organism to survive, even win.
So yeah I’m sure evolution didn’t create something perfect in the disease here but it survives long enough, and kills few-enough people slowly enough in the wild to survive
Evolution is just a race to "good enough to consistently reproduce" and everything after the sufficient reproduction is irrelevant. Like the goats whose horns have to be cut or they'll eventually pierce their own brain.
Generally it's more advantageous for your own anatomy not to kill you without intervention, but they reproduce and that checks off the "good enough" box.
Evolution theory by itself doesn’t give us the ability to explain everything in a certain moment, but that’s only due to lack of knowledge on our part.
Consider that measles in itself comes originally from a animal but a mutation found itself be able to spread to humans. That, in and of itself, is the process of evolution.
So while it is not necessarily a useful lens to try to interpret a moment in time as many unknown factors are at play (for example the same gene that is important for mortality might also impact survival in certain environments, and therefore how contagious it could be), if we were to understand it’s history of every mutation that came and went, the environments it lived in, evolution theory would explain why the path looked like it did. And subsequently why it is like it is today.
1. We might not be the only hosts or place where it can survive. Measles seems to have mutated from a cattle virus.
2. Killing the host might be the virus' end-game, in which case it evolved to extinction. Mutations nor evolution don't have a goal. There's not always an advantage. I bet most changes aren't advantageous.
3. If you really want to see everything in terms of evolutionary change, the virus could even been seen as a tool in human evolution.
Evolution is a way to look at changes in and forces operating on living things. It is a property that emerges for human observers. Nature doesn't care about it.
The virus "cares" if it reproduces. There is often tension between the various levels of spreading mechanisms: for example airbourne spread diseases making you cough vs. the cough making the host feel poorly and not interacting with people or the cough killing the host really preventing further spread. There are plenty of optimum points between fast intense disease and asymptomatic disease.
Short term intense disease courses tend to only work for a short period of evolution for new infection mechanisms, the intensity makes them sensitive to any increased immunity which ends up halting the spread for more mild versions. Infectious diseases tend to lower in intensity over the long term.
"Once the measles virus contacts the mucosa lining the respiratory tract, it binds to SLAM (signaling lymphocyte activation molecule, also known as CD150) on the surface of macrophages and dendritic cells. These cells then take up the virus... These immune cells pass the virus on to other groups of immune cells, including B cells, T cells, thymocytes, and hematopoietic stem cells, which disseminate the virus to other organs during the incubation period.
"Immune amnesia
"The measles virus can deplete previously acquired immune memory by killing cells that make antibodies, and thus weakens the immune system, which can cause deaths from other diseases. Suppression of the immune system by measles lasts about two years and has been epidemiologically implicated in an increase in childhood mortality from other infectious diseases during this period. The measles vaccine contains an attenuated strain of the virus which does not deplete immune memory."
It can. It’s not common, from what I understand, but there are cases where it has put various autoimmune disorders into remission, either temporary, or permanent.
That said, you become far more likely to end up sick with a whole bunch of other stuff, which can then eliminate any benefits for the autoimmune disorders.
Oh, and there’s also a chance it will give you an autoimmune disorder.
