What causes the Ebola virus to be so infectious and deadly?

Mudassir Ali
Mar 10, 2020 06:41 PM 0 Answers
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Mudassir Ali
- Mar 10, 2020 06:41 PM

Ebolaviruses (note there are several, including one that is not human pathogenic and another we don’t know much about – my answer is mainly about Zaire and Sudan ebolaviruses, the big two human pathogenic viruses) are not very infectious, as they need direct contact with bodily fluids. While haemorrhagic fevers by their haemorrhagic nature tend to encourage that through profuse bleeding, ebolaviruses by far aren’t among the top of the list when it comes to virulence. For comparison: based on the first outbreak, Yambuku, EBOV has an R0 of 2 or thereabouts – every case creates two more cases. Measles has an R0 between 15–20, and yet there are people convinced it’s a harmless childhood disease. I can’t even.

But deadly they are. Until recently, CFRs (case-fatality ratios) of 60–80% were common. There are multiple reasons for EBOV’s lethality. Perhaps the most important of these is that ebolaviruses circumvent the human immune system’s part designed specifically against viral infections (interferons) through the EBOV viral protein VP24 blocking karyopherin alpha.And then there’s the fact that it causes disseminated intravascular coagulation (DIC), which is hard to manage even in the best settings. Paradoxically, patients clot too much and too little at the same time. None of that benefits the virus in any sense. It’s a byproduct of glycoprotein GP release, which the virus produces to burst apart cells full of newly replicated copies of itself. There’s no single factor for why ebolaviruses are so lethal – they are, rather, making the best of less than a dozen homocistronic genes by clever reuse. They’re multi-millennia-old predators, and they’ve had time to evolve while also having a reservoir host, a safe haven to retreat to and attack again. And that’s what makes it truly scary to me.

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