What's the Difference Between A Dead and Live Virus?

iStock/Rost-9D
iStock/Rost-9D

Franklin Veaux:

There is none, because viruses aren't alive.

A virus straddles the fuzzy boundary between living and dead. That's why biologists and doctors talk about "inactivated" or "attenuated" viruses, not "dead" viruses.

It's helpful to think of a virus as a machine. In fact, in a lot of ways, it's a machine that's simpler than your car. What's the difference between a living and a dead car? None, because cars aren't alive.

Cars can be working or not working. You can, for example, pull the spark plug wires, or drain the gas tank, or fill the intake manifold with Silly Putty, and a working car will become a not-working car, even though they look pretty much the same.

Inactivated viruses are a bit like not-working cars: some part of the machinery has been changed or damaged to make it not work.

You can inactivate viruses by heating them so the protein coat is damaged, or the genetic material is destroyed. You can hit them with radiation to destroy the genetic material. You can break the virus into pieces.

Your body's immune system does not recognize the entire virus. It looks for and recognizes certain parts of the virus, called "antigens" or "antigen subunits." As long as just that part is intact, it doesn't matter how badly damaged the rest of the virus is.

By way of comparison, if you open the hood of a car, melt the engine into slag, and then close the hood, people walking down the street will still recognize it as a car. They'll see it and say "yep, that's a car," even though the engine is totally destroyed. You can take the wheels off and people will still say "yep, that thing I'm looking at is a car."

Your body will look at the outer shell of a virus and say "yep, that's a virus," even if the genetic material is completely destroyed (or entirely removed altogether). You can take parts of the virus off and your body will still say "yep, that thing I'm looking at is a virus."

This post originally appeared on Quora. Click here to view.

Why Does Hand Sanitizer Have an Expiration Date?

Hand sanitizer does expire. Here's why.
Hand sanitizer does expire. Here's why.
galitskaya/iStock via Getty Images

The coronavirus pandemic has turned hand sanitizer from something that was once idly tossed into cars and drawers into a bit of a national obsession. Shortages persist, and people are trying to make their own, often to little avail. (DIY sanitizer may not be sterile or contain the proper concentration of ingredients.)

If you do manage to get your hands on a bottle of Purell or other name-brand sanitizer, you may notice it typically has an expiration date. Can it really go “bad” and be rendered less effective?

The short answer: yes. Hand sanitizer is typically made up of at least 60 percent alcohol, which is enough to provide germicidal benefit when applied to your hands. According to Insider, that crucial percentage of alcohol can be affected over time once it begins to evaporate after the bottle has been opened. As the volume is reduced, so is the effectiveness of the solution.

Though there’s no hard rule on how long it takes a bottle of sanitizer to lose alcohol content, manufacturers usually set the expiration date three years from the time of production. (Because the product is regulated by the Food and Drug Administration, it has to have an expiration date.)

Let's assume you’ve found a bottle of old and forgotten sanitizer in your house somewhere. It expired in 2018. Should you still use it? It’s not ideal, but if you have no other options, even a reduced amount of alcohol will still have some germ-fighting effectiveness. If it’s never been opened, you’re in better shape, as more of the alcohol will have remained.

Remember that sanitizer of any potency is best left to times when soap and water isn’t available. Consider it a bridge until you’re able to get your hands under a faucet. There’s no substitution for a good scrub.

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Why Are Sloths So Slow?

Sloths have little problem holding still for nature photographers.
Sloths have little problem holding still for nature photographers.
Geoview/iStock via Getty Images

When it comes to physical activity, few animals have as maligned a reputation as the sloth. The six sloth species, which call Brazil and Panama home, move with no urgency, having seemingly adapted to an existence that allows for a life lived in slow motion. But what makes sloths so sedate? And what horrible, poop-related price must they pay in order to maintain life in the slow lane?

According to HowStuffWorks, the sloth’s limited movements are primarily the result of their diet. Residing mainly in the canopy vines of Central and South American forests, sloths dine out on leaves, fruits, and buds. With virtually no fat or protein, sloths conserve energy by taking a leisurely approach to life. On average, a sloth will climb or travel roughly 125 feet per day. On land, it takes them roughly one minute to move just one foot.

A sloth’s digestive system matches their locomotion. After munching leaves using their lips—they have no incisors—it can take up to a month for their meals to be fully digested. And a sloth's metabolic rate is 40 to 45 percent slower than most mammals' to help compensate for their low caloric intake. With so little fuel to burn, a sloth makes the most of it.

Deliberate movement shouldn’t be confused for weakness, however. Sloths can hang from branches for hours, showing off some impressive stamina. And because they spend most of their time high up in trees, they have no need for rapid movement to evade predators.

There is, however, one major downside to the sloth's leisurely lifestyle. Owing to their meager diet, they typically only have to poop once per week. Like going in a public bathroom, this can be a stressful event, as it means going to the ground and risking detection by predators—which puts their lives on the line. Worse, that slow bowel motility means they’re trying to push out nearly one-third of their body weight in feces at a time. It's something to consider the next time you feel envious of their chill lifestyle.

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