Friday, February 14, 2020

What to know about viruses

Viruses are microscopic organisms

They can infect animals, plants, fungi, and even bacteria.

Sometimes a virus can cause a disease so deadly that it is fatal. Other viral infections trigger no noticeable reaction.

A virus may also have one effect on one type of organism, but a different effect on another. This explains how a virus that affects a cat may not affect a dog.

Viruses vary in complexity. They consist of genetic material, RNA or DNA, surrounded by a coat of protein, lipid (fat), or glycoprotein. Viruses cannot replicate without a host, so they are classified as parasitic.

They are considered the most abundant biological entity on the planet

During this phase, they are roughly one-hundredth the size of a bacterium and consist of two or three distinct parts:

genetic material, either DNA or RNA
a protein coat, or capsid, which protects the genetic information
a lipid envelope is sometimes present around the protein coat when the virus is outside of the cell

Viruses do not contain a ribosome, so they cannot make proteins. This makes them totally dependent on their host. They are the only type of microorganism that cannot reproduce without a host cell.

After contacting a host cell, a virus will insert genetic material into the host and take over that host's functions.

After infecting the cell, the virus continues to reproduce, but it produces more viral protein and genetic material instead of the usual cellular products.

It is this process that earns viruses the classification of parasite.

Viruses have different shapes and sizes, and they can be categorized by their shapes.

These may be:

  1. Helical: The tobacco mosaic virus has a helix shape.
  2. Icosahedral, near-spherical viruses: Most animal viruses are like this.
  3. Envelope: Some viruses cover themselves with a modified section of cell membrane, creating a protective lipid envelope. These include the influenza virus and HIV.
  4. Other shapes are possible, including nonstandard shapes that combine both helical and icosahedral forms.

Wednesday, February 12, 2020

How 'good' viruses may influence health

Although the role of "good" viruses in human health is still relatively mysterious, we are slowly unraveling the importance of our viral visitors. In this special feature, we introduce a neglected section of the microbiome — the virome.

The role of bacteria and our microbiome in health and disease is at the forefront of medical research.

We are a long way from answering the many questions posed by recent findings, but it is now firmly established that without our personal fleet of "friendly" microorganisms — our microbiome — we would not thrive.

Medical science, however, does not sit on its haunches; its eyes are always fixed on the horizon, straining to describe the shape of things hidden in the far distance.

As we struggle to unpick the almost unbearably complex interactions between bacteria and health, the next challenge is already waiting in the wings: the role of the virome.

What is the virome?

When we hear the word "microbiome," we immediately think of bacteria, but technically, the microbiome is the sum of all microorganisms in a particular environment. Some scientists use the term to refer to the sum of the genetic material of these microorganisms.

So, aside from bacteria, the microbiome also includes viruses (the virome) and fungi (the mycobiome), among other visitors. To date, scientists have paid comparatively little attention to the virome or mycobiome.

Viruses have made themselves at home in a range of ecological niches in the human body, especially on mucosal surfaces, such as the insides of the nose and mouth and the lining of the gut.

In this feature, we will concentrate on the gut virome because it hosts the greatest number of viral occupants and has been investigated the most.

Of course, viruses are most famous for causing diseases, such as smallpox, hepatitis, HIV, and rabies. Because of the urgency associated with viral disease, this aspect has taken up the lion's share of researchers' time. However, many viruses do not have the slightest interest in human cells.

Introducing the bacteriophage

Scientists consider the virome to be "the largest, the most diverse, and the most dynamic part of [the] microbiome," and the majority of the viruses in our guts are bacteriophages. Wherever there are bacteria, there are bacteriophages in abundance.

As other researchers explain: "Phages are the most abundant life forms on Earth, being virtually omnipresent. [...] Some freshwater sources may contain up to 10 billion per [milliliter]."

Bacteriophages infect bacteria, commandeer their cell machinery, and use it to replicate their genetic material.

It is now abundantly clear that gut bacteria influence health and disease, so it is no surprise that viruses that infect gut bacteria may have a significant influence, too.
Phage therapy

From the 1920s to the 1950s, scientists investigated whether bacteriophages could be used to treat bacterial infections. After all, these viruses are adept at destroying human pathogens.

Scientists found that phage therapy was both effective and, importantly, free from side effects.

When antibiotics were discovered, phage therapy faded into the background. Antibiotics could be manufactured with relative ease, and they killed a broad spectrum of bacterial species.

However, with today's hi-tech capabilities and the fearsome backdrop of antibiotic resistance, interest in phage therapy may enjoy a resurgence.

One factor that makes phage therapy attractive is its specificity. Often, antibiotics wipe out a wide spectrum of bacterial species. Now that we know that "good" bacteria live in the gut, however, it is clear that this is not ideal.

Bacteriophages, meanwhile, only target a narrow range of strains within the same bacterial species.

Plus, they only replicate if their target bacteria are in the local area. Taken together, this means that they only attack the desired bacterium, and they continue to replicate until they have wiped out the infection.

Monday, February 10, 2020

There are fewer shark attacks but more unusual incidents

New data from the University of Florida’s International Shark Attack File (ISAF) — the world’s “comprehensive database of all known shark attacks” — show that unprovoked shark attacks remained infrequent in 2019.

Scientists in charge of ISAF define “unprovoked shark attacks” as attacks that take place in the shark’s natural territory and do not involve the human trying to initiate interaction.

ISAF data indicate that over the past decade, there have been 799 unprovoked shark attacks worldwide. Yet in 2018, and again in 2019, the numbers were remarkably low.

Last year, there were 64 unprovoked shark attacks in total, with only two more cases than in 2018, when scientists registered a total of 62 such attacks worldwide.

The number of registered attacks in 2019 is also 22% lower than the average of 82 cases per year over the 2014–2018 period.

Two of the shark attacks last year proved fatal, but this number, once more, is lower than the average of four shark attack-related deaths per year. Researchers are not quite sure what could explain this change.

“We’ve had back-to-back years with unusual decreases in shark attacks, and we know that people aren’t spending less time in the water,” says Gavin Naylor, director of the Florida Museum of Natural History’s shark research program.

“This suggests sharks aren’t frequenting the same places they have in the past. But it’s too early to say this is the new normal,” Naylor cautions.

U.S. still in the lead for shark bites

The ISAF report shows that one trend has remained consistent, however: Once again, most of the unprovoked shark attacks occurred in the United States, which registered as many as 41 such cases last year.

This number was, in fact, higher than the 32 unprovoked attacks that people reported in the U.S. in 2018 but lower than the 5 year average of 61 attacks per year.

Among the U.S. states, Florida led with 21 unprovoked shark attacks, and Hawaii followed with nine cases.

Other than the U.S., only Australia reported a relatively high number of unprovoked shark attacks last year: 11 cases. This country, too, however, saw a decrease from its recent 5 year average of 16 attacks per year.

The Bahama Islands followed, with two cases of unprovoked shark attacks in 2019.

The Canary Islands, Caribbean Islands, Cuba, French Polynesia, Guam, Israel, Mexico, New Caledonia, South Africa, and RĂ©union Island reported one case each.

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