Later On

A blog written for those whose interests more or less match mine.

Why do human beings keep getting diseases from bats?

with 3 comments

Trevor Klee has an interesting post at the 21st Night blog:

Humans get a surprising number of very infectious diseases from bats. We get SARS (including the recent COVID-19/SARS-CoV2), Ebola, rabies, and possibly mumps. These are all incredibly infectious, deadly diseases.

This seems weird because human beings aren’t in particularly close contact with bats. They’re nocturnal, don’t have large city populations (for the most part), and humans don’t eat them that often. It should be harder for diseases to pass from them to us. They’re also not very similar to us genetically, so their diseases shouldn’t be able to leap to us so easily.

Part of the answer is that bats are very social creatures. When one bat gets a virus, they pretty quickly pass it onto the other bats in their colony. However, that’s also true of goats and cows, who don’t seem to pass on infectious diseases to us as often.

The more important part of the answer is that bats are “reservoirs” of some particularly virulent viruses. Bats live with long-term infections of SARS or Ebola and are seemingly ok with it. While humans and other mammals either have to clear these viruses from their body or die, bats do not. They will just keep on keeping on, sometimes shedding the virus, sometimes not. It’s more likely that the bat will shed the virus during stressful times (i.e. when it’s in a cage and about to get eaten).

That’s what seems to have happened with COVID-19. A bat shed the SARS-CoV2 virus at some point, probably in a wildlife market. The virus at this point was not in state where it could infect humans. However, viruses can both mutate (change shape) and recombine (swap parts) rapidly. Coronaviruses are especially good at recombining.

The SARS-COV2 virus was shed from a bat (possibly from its saliva or droppings), seems to have recombined with a coronavirus in a pangolin (who was probably in a cage right next to it), and then was in a form where it could be transmitted to a human. . .

Continue reading. There’s much more, and it’s intriguing. Later in the article:

In other words, bat cells just continually assume they’re under attack and never stop fighting viruses, regardless of whether they’ve detected any. This is surprising. Interferon is a really powerful molecule, and continually producing it should have the same effect on a cell as continually putting a factory on red alert. It should make the cell run much worse, and cause a lot of collateral damage.

After all, when this sort of immune system overreaction happens in humans, humans get serious disorders, like Multiple Sclerosis and Lupus. Bats do not tend to get these. In fact, many bat species live around 20 years on average, which is not only way longer than it should have with its overactive immune system, but is exceptionally long for such a small animal. To give a comparison, rats live a year or two, as do rabbits.

So, how do bats live so long with a hyperactive immune system? Well, the answer seems to be that . . .


Written by LeisureGuy

10 April 2020 at 2:49 pm

3 Responses

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  1. Opossums are immune to rabies, so this should be heavily explored if not already so.


    10 April 2020 at 2:54 pm

  2. Mostly immune to rabies, but not absolutely so. Interesting that they are also immune to some snake venom.


    10 April 2020 at 3:52 pm

  3. I did not know about the snake venom resistance, but according to what I read, it’s allegedly total invulnerability to rabies. I’ll check on Wiki & update with results.


    10 April 2020 at 4:22 pm

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