Anatomy of a Virus
By: Dr. Amy Jones, DO, Ob/Gyn
Scientists estimate that there are roughly 10^31 viruses at any given moment. That’s a one with 31 zeroes after it! If you were somehow able to wrangle up all 10^31 of these viruses and line them end-to-end, your virus column would extend nearly 200 light years into space. To put it another way, there are over ten million times more viruses on Earth than there are stars in the entire universe.
Does that mean there are 10^31 viruses just waiting to infect us? Actually, most of these viruses are found in oceans, where they attack bacteria and other microbes. It may seem odd that bacteria can get a virus, but scientists think that every kind of living organism is probably host to at least one virus!
What is a virus?
A virus is a tiny, infectious particle that can reproduce only by infecting a host cell. Viruses "commandeer" the host cell and use its resources to make more viruses, basically reprogramming it to become a virus factory. Because they can't reproduce by themselves (without a host), viruses are not considered living. Nor do viruses have cells: they are basically just packages of nucleic acid and protein and are much smaller than a single cell in our bodies.
Still, viruses have some important features in common with cell-based life. For instance, they have nucleic acid genomes based on the same genetic code that's used in your cells (and the cells of all living creatures). Most viruses have either RNA or DNA as their genetic material. Also, like cell-based life, viruses have genetic variation and can evolve. So, even though they don't meet the definition of a living organism, viruses seem to be in a "questionable" zone.
How are viruses different from bacteria?
Even though they can both make us sick, bacteria and viruses are very different at the biological level. Bacteria are small and single-celled, but they are living organisms that do not depend on a host cell to reproduce. Because of these differences, bacterial and viral infections are treated very differently. For instance, antibiotics are only helpful against bacteria, not viruses.
Bacteria are also much bigger than viruses. The diameter of a typical virus is about 20 – 300 nanometers. This is considerably smaller than a typical E. coli bacterium, which has a diameter of roughly 1000 nanometers. Tens of millions of viruses could fit on the head of a pin.
The structure of a virus
There are a lot of different viruses in the world. So, viruses vary a ton in their sizes, shapes, and life cycles.
Viruses do, however, have a few key features in common. These include:
- A protective protein shell, or capsid
- A nucleic acid genome made of DNA or RNA, tucked inside of the capsid
- A layer of membrane called the envelope (some but not all viruses)
Let's take a closer look at these features.
The exterior layer is a membrane envelope. Inside the envelope is a protein capsid, which contains the nucleic acid genome.
What is a viral infection?
In everyday life, we tend to think of a viral infection as the nasty collection of symptoms we get when catch a virus, such as the flu or the chicken pox. But what is actually happening in your body when you have a virus?
At the microscopic scale, a viral infection means that many viruses are using your cells to make more copies of themselves. The viral lifecycle is the set of steps in which a virus recognizes and enters a host cell, "reprograms" the host by providing instructions in the form of viral DNA or RNA, and uses the host's resources to make more virus particles.
For a typical virus, the lifecycle can be divided into five broad steps (though the details of these steps will be different for each virus):
Steps of a viral infection:
- Attachment. Virus binds to receptor on cell surface.
- Entry. Virus enters cell by endocytosis. In the cytoplasm, the capsid comes apart, releasing the RNA genome.
- Replication and gene expression. The RNA genome is copied (this would be done by a viral enzyme, not shown) and translated into viral proteins using a host ribosome. The viral proteins produced include capsid proteins.
- Assembly. Capsid proteins and RNA genomes come together to make new viral particles.
- Release. The cell lyses (bursts), releasing the viral particles, which can then infect other host cells.
COVID-19 (Coronavirus Disease 19)
So let’s talk more specifically about COVID-19, which is responsible for a global pandemic.
COVID-19 is caused by SARS CoV-2, or severe acute respiratory syndrome coronavirus 2, because it’s genetically similar to the SARS coronavirus which was responsible for the SARS outbreak in 2002. Coronaviruses that circulate among humans are typically benign, and they cause about a quarter of all common cold illnesses.
In COVID-19 what happened is that there was a coronaviruses circulating among bats, which are a natural animal reservoir, that seems to have mutated just enough to start infecting an intermediate host - the pangolin, an animal that looks like a cross between an anteater and an armadillo. In late 2019 the coronavirus mutated again and started causing disease in humans. The outbreak began in China, but has since spread around the world.
It is currently thought that COVID-19 has a fatality rate of between 0.8% and 3.5%. As a point of comparison, the flu typically causes a fatality rate of 0.1%, so even based on this data COVID-19 is still 8 to 35 times more deadly than the flu. Similarly, the fatality rate is higher in the elderly and in people with hypertension, diabetes, cardiovascular disease, chronic respiratory disease, and cancer.
Based on the current data, over 80% of the patients with COVID-19 have a mild infection, and some people don’t develop any symptoms at all. For others, they can develop symptoms that can range from mild symptoms like fever, cough, and shortness of breath, all the way to serious problems like pneumonia. Severe lung damage can cause acute respiratory distress syndrome, or ARDS, which occurs when the lung inflammation is so severe that fluid builds up around and within the lungs. The severe infection can cause septic shock, which happens when the blood pressure falls dramatically and the body’s organs are starved for oxygen. ARDS and shock are the main cause of death for people with the infection, and again this is most likely to occur in those over the age of 60, smokers, and people with other medical conditions like heart disease.
In addition to causing disease, coronaviruses can spread quickly. Usually the virus spreads when people cough or sneeze, and tiny droplets containing the virus are released. These droplets can land on another person’s mouth, nose, or eyes, and that allows the virus to enter a new person.
Once a person is infected, symptoms develop about 5 days later. This is called the incubation period. There is debate about how much asymptomatic people or presymptomatic - people that are in the incubation period - are spreading the disease, and it may be much more than what was originally thought.
Treatment is focused on supportive care, however medications are in clinical trials and we will likely have an approved vaccine by 2021. In the meantime, the best strategy is prevention. This includes careful hand washing, avoiding traveling to crowded places when possible, avoiding touching your face and social distancing.
While on lock down we suggest you connect with loved ones and spend some of your time developing a self care regimen. Stay tuned for more on self care in our next V News drop. Until then check out our maintenance care items or share a eGift card with someone one special.
Disclaimer: This is not medical advice, does not take the place of medical advice from your physician, and is not intended to treat or cure any disease. Patients should see a qualified medical provider for assessment and treatment.
