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TWiV 891: LLOV in the time of Ebola

21 April 2022 by Vincent Racaniello

Elke, Adam, and Gabor join TWiV to discuss their work on Lloviu virus, a filovirus, including recovery of infectious virus from a DNA copy of the genome and from Schreiber’s bats in Hungary.

Hosts: Vincent Racaniello, Rich Condit, Kathy Spindler, and Brianne Barker

Guests: Elke Muhlberger, Adam Hume, and Gabor Kemenesi

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Show notes at microbe.tv/twiv

Filed Under: This Week in Virology Tagged With: ebola virus, filovirus, host range, Lloviu virus, Schreiber's bats, spillover, viral, virology, virus, viruses, zoonosis

More filoviruses in bats

31 January 2019 by Vincent Racaniello

Ebola dishThe family of viruses known as the Filoviridae (filo, from the Latin for thread) is well known for the ebolaviruses, which cause the hemorrhagic disease that regularly erupts in Africa. As Earth’s virome is slowly revealed, other filoviruses are discovered.

[Read more…] about More filoviruses in bats

Filed Under: Basic virology, Information Tagged With: ebolavirus, filovirus, hemorrhagic fever, Mengla virus, minigenote, spillover, viral, virology, virus, viruses

TWiV 415: Ebola pipettors and the philosopher’s clone

13 November 2016 by Vincent Racaniello

Jeremy Luban, Aaron Lin, and Ted Diehl join the TWiV team to discuss their work on identifying a single amino acid change in the Ebola virus glycoprotein from the West African outbreak that increases infectivity in human cells.

You can find TWiV #415 at microbe.tv/twiv, or listen below.

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Filed Under: This Week in Virology Tagged With: adaptation, amino acid, ebola virus, filovirus, glycoprotein, mutation, NPC1, spillover, viral, virology, virus, viruses, zoonosis

Increased infectivity of Ebola virus glycoprotein from West Africa

3 November 2016 by Vincent Racaniello

filovirionWhen viruses cross species, serial transmission may lead to the selection for mutations that confer improved replication or transmission in the new host. Identifying such mutations in human viruses is extremely difficult: we cannot conduct the appropriate experiments in humans, and often do not have viral isolates spanning the time from spillover through prolonged circulation. The 2013-2016 outbreak of Ebola virus in West Africa is unique because viral genome sequences were obtained early and throughout the epidemic. The results of two new studies (link to paper one, link to paper two) suggest that some of the observed mutations increase infectivity for human cells. The impact of these mutations on infection of humans, and their role in the West African outbreak, remain unknown.

Many mutations have been identified among the many hundreds of genome sequences obtained during the recent Ebola virus epidemic. One stands out: a mutation that leads to a single amino acid change in the viral glycoprotein, from alanine to valine at position 82 (A82V). This change arose early in the outbreak (it was first observed in Guinea in March 2014) and was subsequently found in most of the isolates. It has never been observed in previous Ebolavirus outbreaks.

The effect of the A82V change on viral infectivity was determined by building pseudotyped viral particles – in this case, HIV particles with the Ebola virus glycoprotein. Human cells in culture were infected with pseudotyped viruses with the Ebola virus glycoprotein with either alanine or valine at position 82. Infectivity was measured by quantifying the production of a protein from the HIV genome. The results show that A82V increases infectivity by twofold. The effect is also observed in cells from non-human primates, but not from rodents, dogs, or cats. However, the A82V change decreased infectivity in bat cells.

The A82V change is located at the binding site of the Ebola virus glycoprotein with the cell fusion receptor, NPC1. It appears to increase the fusion activity of the viral glycoprotein.

Other amino acid changes in the Ebola virus glycoprotein were also observed to increase infectivity in human cells, and decrease infectivity in bat cells.

The pattern of increased infectivity in primate cells, and decreased infectivity in bats, is consistent with the hypothesis that the outbreak virus came from bats, and after circulation of the virus in humans, it lost some ability to infect bat cells while becoming better at infecting human cells. However there is still no solid proof that bats are a reservoir of Ebolaviruses.

What does increased infectivity have to do with infection of humans? The idea is that the mutation increases the efficiency of virus entry into cells, and hence increased viral gene expression is observed. Fewer viruses needed to infect a cell, the better chance of initiating an infection. But is the two-fold increase observed in cells enough to impact infection in humans?

The assays used in these papers measure protein production from an HIV genome. The experiments need to be repeated using bona fide Ebola virus, to make sure that the mutations have the same effect. The changes might have impacts on other stages of viral replication. Furthermore, the impact of the changes in the viral glycoprotein should be assessed in animal models, to determine if improved infectivity has any impact on pathogenesis and transmission. Ultimately, we can’t prove that these mutations have any effect in humans – the needed experiments cannot be done.

I’m curious about why the A82V change was not seen in previous Ebola virus outbreaks. Those were in different parts of Africa – could the changes be driven by population genetics, ecology, or other factors? It will be important to determine if the same change is selected in future outbreaks.

The authors are sufficiently cautious in their conclusions. From paper #2:

Despite the experimental data provided here, it is impossible to clearly establish whether the adaptive mutations observed were in part responsible for the extended duration of the 2013–2016 epidemic. Indeed, it seems likely that the prolonged nature of the outbreak in West Africa was primarily due to epide- miological factors, such as an increased circulation in urban areas that in turn led to larger chains of transmission.

From paper #1:

Our findings raise the possibility that this mutation contributed directly to greater transmission and thus to the severity of the outbreak. It is difficult to draw any conclusions from this hypothesis, though…

As I feared, press coverage of these findings has been inaccurate. For example, a BBC headline proclaims “Ebola adapted to easily infect people”. Even the journal Cell, which published both papers, made an incorrect conlcusion: see the screen capture below from the journal website.key mutations ebola virusBoth Cell and the BBC might have taken too literally the unfortunate title of one of the papers,  “Human adaptation of Ebola virus during the West African Outbreak.” The results suggest adaptation to human cells, not to humans. The title of the second paper is sufficiently careful: “Ebola virus glycoprotein with increased infectivity dominated the 2013-2016 epidemic”. But that’s not a BBC headline.

Filed Under: Basic virology, Commentary, Information Tagged With: adaptation, ebola virus, filovirus, glycoprotein, outbreak, pseudotype, spillover, viral, virology, virus, viruses, zoonosis

TWiV 394: Cards in a hand

19 June 2016 by Vincent Racaniello

Vincent and Alan speak with Erica Ollmann Saphire about her career and her work on understanding the functions of proteins of Ebolaviruses, Marburg virus, and other hemorrhagic fever viruses, at ASM Microbe 2016 in Boston, MA.

You can find TWiV #394 at microbe.tv/twiv, or listen or watch the video below.

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Filed Under: This Week in Virology Tagged With: cryoEM, ebolavirus, filovirus, marburg virus, protein, protein structure, structural biology, viral, virology, virus, viruses, X-ray structure

TWiEVO 5: Looking at straw colored fruit bats through a straw

20 February 2016 by Vincent Racaniello

TWiEVOOn episode #5 of the science show This Week in Evolution, Sara Sawyer and Kartik Chandran join Nels and Vincent to talk about how the filovirus receptor NPC1 regulates Ebolavirus susceptibility in bats.

You can find TWiEVO #5 at microbe.tv/twievo, or you can listen below.

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Filed Under: This Week in Evolution Tagged With: bat, ebolavirus, filovirus, host-virus conflict, NPC1, positive selection, receptor, viral, virology, virus, virus entry, viruses

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by Vincent Racaniello

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