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

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Life Sciences

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From Molecules To Organisms: Structures And Processes

HS-LS1-8

Viral Mutations

During replication, viruses can also evolve genetically due to mutations, permanent changes in the genetic material.

More spontaneous errors occur when RNA&nbsp;is present and replication requires the reverse transcriptase enzyme, which does not proofread, leading to a higher chance of rapid evolution and drug resistance.

This is the case for human immunodeficiency virus, or HIV, which makes it so hard to combat.

viral mutations

A mutation is a change in the sequence of bases of DNA or RNA in a genome. Some mutations occur during replication of the genome due to errors made by the polymerase enzymes that replicate DNA or RNA. Unlike DNA polymerase, RNA polymerase is prone to errors because it is not capable of &ldquo;proofreading&rdquo; its work. Viruses with RNA-based genomes, like HIV, therefore accrue mutations faster than viruses with DNA-based genomes. Because mutation and recombination provide the raw material for adaptive evolution, RNA-based viruses can quickly evolve resistance to antiviral drugs.

<h4>Comparing Mutations Allows Us to Reconstruct Evolution</h4>

A major goal in modern biology is to reveal evolutionary history by comparing genome sequences. An important practical application of these analyses is the study of evolution in disease-causing viruses. Genome sequencing has become so rapid and inexpensive that it is now possible to investigate the origins and ongoing evolution of viruses during a disease outbreak.

For example, in 2013, a new strain of avian influenza called H7N9 emerged in China that caused severe respiratory illness in humans. By comparing the mutations in viruses isolated from humans and several bird species, researchers were able to show that the ancestor of this flu strain probably originated in Chinese domestic duck populations before it was transmitted to chickens. The ancestral strain subsequently recombined with other bird viruses to generate the H7N9 strain that infected humans. These analyses identified live poultry markets as the likely source of human infections. Furthermore, while investigating the evolution of the H7N9 strain, researchers found an additional strain of avian flu that can likely infect humans. This work demonstrates how evolutionary analyses of mutations can provide critical information to epidemiologists during an epidemic.

A mutation is a change in the sequence of bases of DNA or RNA in a genome. Some mutations occur during replication of the genome due to errors made by the ...

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KEY TERMS AND CONCEPTS

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...

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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