eli5: rabies – It is said that birds cannot be infected with rabies, because they are not mammals. On the other hand they have a nervous system like us. Does the difference come from blood-brain barrier or what? It seems like they are not more complex than us.
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If you ask this question in a search engine there are some good answers.
The ELI5 version is that a virus always has a specific way it infects its “hosts”. Usually this is done by “binding” to something in some kind of cells in an animal.
The best ELI5 way to describe this I can think of is to imagine you build a weird structure with a hole in it out of LEGO bricks. That’s a cell. For a virus to “bind” to the cell, it needs to have a structure shaped exactly like that hole. If it does not have that structure it cannot “bind” to the cell so it cannot infect the cell.
Rabies binds to a very specific cell structure in the nervous system of mammals. Birds are not mammals, and part of their differences include that their nervous system has slightly different cells with a different structure. So rabies can’t bind to their nerve cells thus they can’t be infected.
If we think about it like computers, it’s like mammals are a PS5 and birds are an XBox One. They’re both complicated machines. There are some games that run on both. But those games are different versions of the same thing with slightly different code: if you put a PS5 game onto an XBox One you can’t play it and vice versa.
Could rabies evolve to infect birds? Probably. It’d have to change the structure it “binds” to. Nothing’s stopping nature from trying that to see what happens. But it’s possible that the changes needed for the virus to make that change alter so much of its DNA the new bird-affecting strain might not be able to infect mammals and its effect on birds might not be as severe as it is on mammals. Then it’d be a different disease we wouldn’t call “rabies”.
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