July 9th, 2020

Viruses Mutate. What does that mean for us?

Viruses mutate. What does that mean for us?

In this course, you will learn that viruses can change over time as a result of mutations, and why this matters for public health.

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Microbes are all around us. Viruses are the smallest and simplest type of microbe. Viruses infect living cells. Some viruses infect cells in our body and make us sick.

Our body quickly recognizes and fights off most of the viruses around us, before they make us sick. But sometimes our body meets a virus that is new and unfamiliar.

Where do new viruses come from? Viruses can change over time as they develop mutations in their genetic material.

Genetic material is hereditary and contains instructions for life. The genetic material of a virus has the genes that determine how the virus looks and behaves.

Mutations can change small things about how a virus looks, how it causes sickness, how it spreads, whether our immune system can recognize it, or how difficult it is to treat.

For some viruses, mutations can build up as more and more infections occur. More infections mean more chances for mutations.

To learn more about virus mutations and how and why they happen, we need to look more closely at the genetic material of viruses.

Continue to learn more.

A virus has one mission: Make and spread more viruses. But first it has to copy its genetic material.

Viruses can use either DNA or RNA as their genetic material. Because of this, there are two basic different types of viruses: “RNA viruses” and “DNA viruses”.

A virus has to copy or replicate its DNA or RNA to make more viruses. But it can’t do this on its own - it must get inside a cell in a living thing first.

Getting inside a cell starts with the virus using special proteins on its surface to attach to other proteins on the cell.

A virus can only attach to and infect certain cells (like lung cells) in certain living things. Some viruses infect only humans. Others can infect both animals and humans.

After a virus attaches itself to a cell, it enters the cell and releases its DNA or RNA. Then the virus takes over - it’s the new boss in town.

The virus uses the cell’s copying machinery to replicate its own DNA or RNA. The copies get packaged into many new virus particles that leave the cell and spread to other cells.

But the replication process isn’t perfect. There can be mistakes, like typos, in the strings of letters in the copied DNA or RNA. These mistakes are called mutations.

Mutations happen in all living things, including us! As we reproduce, our children might have slight changes in their genes. But these changes rarely make much of a difference.


Viruses reproduce much, much more quickly, and produce many more copies, than we and other living things do. So they can collect more mutations. Mutations over time can slowly change a virus.

Recap
  • Viruses are the smallest microbes that carry genetic material - DNA or RNA.
  • New viruses can emerge when viruses create copies of their DNA or RNA inside of cells, but the copies have “typos” or mutations.

Mutations can be good or bad for a virus. A mutation might help a virus infect new types of cells. Sometimes, mutations allow a virus from animals to start infecting humans. This is called “spillover”.

A mutation might also work against a virus, making it less able to make copies. Some antiviral medicines are made to force viruses to gain many more mutations than usual.


Most mutations simply change the “looks” of the virus without changing how it behaves. Many critical mutations must occur to create a new “strain” that behaves very differently.

But some viruses change more quickly than others, creating new strains more often. Why is this? It has a lot to do with what kind of genetic material each virus uses.

DNA viruses like the chickenpox virus use DNA copy machinery in our cells to make more of themselves. This copy machinery works slowly and goes through “proof-reading”.

RNA viruses like the Influenza (flu) virus use different copy machinery than DNA viruses do. This RNA copy machinery is faster and sloppier and does not have proofreading.

Because of this, most RNA viruses get more mutations and change more quickly than DNA viruses.

To learn more, let’s compare two types of RNA viruses: coronaviruses and flu viruses.

The flu virus mutates very often. It has 8 RNA segments for its genetic material instead of one! This means more chances for mutations, but also for mixing-and-matching of segments into new viruses.


Imagine a person was infected by two strains of flu at once. Inside their infected cells, new virus particles could mix-and-match RNA segments from these two strains. A new type of flu could form.

We need a new flu shot every flu season because new flu strains always emerge that can escape our immune system. Their outer shells look different.

What about coronaviruses? With only one large piece of RNA, they mutate more slowly than flu viruses do. They also have their own type of proofreading that helps to prevent mutations.

The mutation rate of coronaviruses is slow enough for scientists to track it. This is good news. It gives scientists time to study the virus, learn more about it, and work towards a vaccine.

Vaccines are important for slowing or stopping the spread of viruses and helping to prevent new strains from emerging. If a virus can no longer infect people, it can’t replicate or mutate.

You can help to prevent virus mutations! Avoid spreading viruses: Wear a mask, wash your hands, and stay home if you are sick. Make sure to get your flu shot, and stay up to date on your vaccines!

Mutations might sound scary but science is on our side. Scientists make vaccines for new flu strains every year. Scientists are also studying mutations in the novel coronavirus to track it.

Summary

Other ways you can prevent virus mutations:

Keep your immune system strong so that you can fight off viruses before they replicate in your cells.

Protect animals and ecosystems.

Follow recommendations from CDC, healthcare workers and other experts.
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Adam Lauring, M.D., Ph.D.

Dr. Lauring is an associate professor at the University of Michigan, where his lab studies how RNA viruses evolve so quickly. His lab focuses on aspects of mutation rate and mutational tolerance in poliovirus, influenza, and other RNA viruses.

Katherine R. Spindler, Ph.D.

Dr. Spindler is a Professor at the University of Michigan. Her lab studies ways that viruses, such as mouse adenovirus, cause encephalitis. Dr. Spindler also co-hosts the weekly science podcast This Week in Virology.


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