Name: how virus mutations drive outbreaks
Uploaded: 2019-03-11T09:21:24.000Z
Duration: 36 s
Channel: JoVE

K12 Standards

Louisiana Student Standards for Science

High School

Life Sciences

from-molecules-to-organisms-structures-and-processes

From Molecules To Organisms: Structures And Processes

HS-LS1-8

Viral Mutations

- [Instructeur] Lors de la réplication, les viruspeuvent aussi évoluer génétiquement en raison de mutations,des modifications permanentes du matériel génétique. 
Des erreurs plus spontanées se produisent lorsque l'ARNest présent car la réplication nécessitel'enzyme transcriptase inverse, qui ne relis pas,ce qui augmente les chances d'évolution rapideet de résistance aux médicaments. 
C'est le cas du virus de l'immunodéficience humaine ou VIH,ce qui le rend si difficile à combattre.

Quan, Chuansong, Weifeng Shi, Yang Yang, Yongchun Yang, Xiaoqing Liu, Wen Xu, Hong Li et al. « Nouvelles menaces du virus de la grippe H7N9 : propagation et évolution des variantes à haute et basse pathogénicité avec une grande diversité génomique dans la cinquième vague », Journal of Virology 92, n° 11 (1er juin 2018) : e00301-18. [<a href="https://doi.org/10.1128/JVI.00301-18 » target="__blank">Source</a>]

mutations virales

Une mutation est un changement dans la séquence des bases de l’ADN ou de l’ARN dans un génome. Certaines mutations se produisent lors de la réplication du génome en raison d’erreurs commises par les enzymes de polymérase répliquant l’ADN ou l’ARN. Contrairement à la polymérase de l’ADN, la polymérase d’ARN est sujette à des erreurs parce qu’elle n’est pas capable de “ relire ” son travail. Les virus avec des génomes basés sur l’ARN, comme le VIH, accumulent donc des mutations plus rapidement que les virus avec des génomes basés sur l’ADN. Parce que la mutation et la recombinaison fournissent la matière première pour l’évolution adaptative, les virus à base d’ARN peuvent rapidement développer une résistance aux médicaments antiviraux.
 
 <h4>Comparer les mutations nous permet de reconstruire l’évolution</h4>
 
 Un objectif majeur dans la biologie moderne est de révéler l’histoire de l’évolution en comparant les séquences génomiques. Une application pratique importante de ces analyses est l’étude de l’évolution des virus pathogènes. Le séquençage des génomes est devenu si rapide et peu coûteux qu’il est maintenant possible d’étudier les origines et l’évolution continue des virus au cours d’une épidémie.
 
 Par exemple, en 2013, une nouvelle souche de grippe aviaire appelée H7N9 a émergé en Chine causant des maladies respiratoires graves chez l’homme. En comparant les mutations dans les virus isolés de l’homme et de plusieurs espèces aviaires, les chercheurs ont pu démontrer que l’ancêtre de cette souche grippale provenait probablement des populations de canards domestiques chinois avant d’être transmise aux poulets. La souche ancestrale s’est ensuite recombinée à d’autres virus aviaires pour générer la souche H7N9 qui a infecté les humains. Ces analyses ont identifié les marchés de volailles vivantes comme la source probable d’infections humaines. En outre, tout en étudiant l’évolution de la souche H7N9, les chercheurs ont trouvé une autre souche de grippe aviaire qui peut probablement infecter les humains. Ces travaux montrent comment les analyses évolutives des mutations peuvent fournir des informations essentielles aux épidémiologistes pendant une épidémie.

Mutations virales

Une mutation est un changement dans la séquence des bases de l’ADN ou de l’ARN dans un génome. Certaines mutations se produisent lors de la réplication du génome en raison d’erreurs commises par le ...

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how virus mutations drive outbreaks

Virus mutations can change how quickly a virus evolves and spreads. A mutation is a change in the sequence of bases in DNA or RNA. Some mutations happen when the genome is copied. They are caused by errors made by polymerase enzymes, which replicate DNA or RNA.

RNA viruses often change faster than DNA viruses because RNA polymerase does not proofread its work. That means RNA-based genomes, such as HIV, can gather mutations more quickly. Mutation and recombination give viruses the raw material for adaptive evolution. As a result, RNA-based viruses can sometimes evolve resistance to antiviral drugs.

Scientists also use mutations to trace how viruses evolve over time. By comparing genome sequences, researchers can reconstruct evolutionary history. This is especially useful during disease outbreaks because genome sequencing is now fast and inexpensive. It helps scientists study where a virus came from and how it is changing.

The 2013 H7N9 avian influenza outbreak in China is one example. By comparing viruses from humans and several bird species, researchers found that the ancestor likely came from domestic ducks in China before spreading to chickens. That ancestral virus later recombined with other bird viruses to form the H7N9 strain that infected humans. The analysis also pointed to live poultry markets as the likely source of human infections and revealed another avian flu strain that may also infect humans.

How Virus Mutations Drive Outbreaks

what are viruses?

How Viruses Infect Cells and Multiply

Viruses infect cells and make new copies by using a host cell’s own machinery. A virus is a tiny infectious particle with an RNA or DNA genome inside a protective protein coat. It cannot reproduce on its own, so it must enter a cell to make more viruses. After infection, the virus sheds its protein coat and uses the host cell to transcribe and translate its genetic material. The cell then assembles many new viral particles. In many cases, these new viruses rupture the host cell and kill it.

viral structure

How Virus Shapes Help Infection

Viruses have specific structures that help them infect host cells and trigger immune responses. Each virus has a core that contains either a DNA-based or RNA-based genome. That core is surrounded by a protective protein coat called the capsid. The capsid is made of smaller subunits called capsomeres. The capsid and the genome-containing core together are called the nucleocapsid. Viruses are often grouped by capsid design. Most viruses have either icosahedral or helical capsids, but some have...

lytic cycle of bacteriophages

How Phages Infect and Burst Bacteria

Bacteriophages, or phages, are viruses that infect bacteria. They have a distinctive head-tail shape. In the lytic cycle, a phage first attaches to the outside of a bacterial cell. Tail proteins bind to specific receptor proteins on the bacterium’s surface. After attachment, the phage tail injects its DNA genome into the bacterial cytoplasm. The phage then uses the bacterium’s cellular machinery to make proteins needed for replication and dispersal. When phage replication is complete, some of...

lysogenic cycle of bacteriophages

Prophage Integration in Bacteria

The lysogenic cycle shows how bacteriophages can infect bacteria without killing the host right away. In this cycle, the phage genome joins the bacterial genome. The integrated phage DNA is called a prophage, and the bacterium copies it each time it replicates. Some prophages can switch back into the lytic cycle. This change can happen after DNA damage or even without an obvious outside trigger. When the prophage is induced, the phage begins making new virus particles again. Prophages can...

retrovirus life cycles

How Retroviruses Replicate in Host Cells

Retroviruses replicate by copying their RNA genome into DNA inside a host cell. After entry, the viral enzyme reverse transcriptase makes a double-stranded DNA copy from the single-stranded RNA genome. The viral DNA is then carried into the nucleus and inserted into the host genome by integrase. Once integrated, the retroviral DNA is transcribed whenever the host genome is transcribed. This produces new viral RNA that can be copied and used again. The new RNA moves into the cytoplasm, where it...

viral recombination

How Viruses Swap Genes and Spread

Viral gene swapping can happen when more than one virus infects the same cell. After the viruses break open and expose their genomes for replication, matching regions can pair up and exchange sequences. This process is called recombination. Viruses with segmented genomes can also swap whole segments, which is called reassortment. These changes can help create new diseases. Some diseases can infect more than one species. Pigs can be infected by some human and bird viruses, along with the...

viral mutations

Virus mutations can change how quickly a virus evolves and spreads. A mutation is a change in the sequence of bases in DNA or RNA. Some mutations happen when the genome is copied. They are caused by errors made by polymerase enzymes, which replicate DNA or RNA. RNA viruses often change faster than DNA viruses because RNA polymerase does not proofread its work. That means RNA-based genomes, such as HIV, can gather mutations more quickly. Mutation and recombination give viruses the raw material...

key terms and concepts

Learn how RNA and DNA virus mutations differ, why RNA viruses evolve fast, and how genome sequencing helps track outbreaks like H7N9 influenza.

How Virus Mutations Drive Outbreaks | JoVE K12

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How Virus Mutations Drive Outbreaks

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