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PBS NewsHour

Why do honeybees die when they sting?

Colonies of bees have been disappearing since 2006. Photo by Flickr user Andreas

It is only the female honeybees, or the worker bees, that sting. Photo by Flickr user Andreas

We return to our Just Ask feature, where experts tackle your questions on science and technology.

Why do honeybees die when they sting?

When a honeybee stings, it dies a gruesome death. The bee’s stinger is structured in such a way that once it punctures human skin, the bee can’t yank it out without self-amputating. As the honeybee tries to pull out the stinger, it ruptures its lower abdomen, leaving the stinger embedded, pulling out instead a string of digestive material, muscles, glands and a venom sac. What results is a gaping hole at the end of the abdomen.

Bee sting

“It’s kind of like bleeding to death, except bees don’t have blood,” said Eric Mussen of the University of Davis. Mussen is an apiculturist, a fancy word for beekeeper. “It’s fake, clear insect blood.”

The honeybee stinger is hollow and pointed, like a hypodermic needle, Mussen said. It contains two rows of lancets, or saw-toothed blades. These blades are barbed in shape, and face outward like a harpoon.

 A honeybee stinger magnified 650x, from Rose-Lynn Fisher's book, BEE. Image by Rose-Lynn Fisher

A honeybee stinger magnified 650x, from Rose-Lynn Fisher’s book, BEE. Image by Rose-Lynn Fisher

As a bee stings, the blades alternate, “scissoring together into your flesh,” said Mark Winston, biologist and author of “Bee Time: Lessons from the Hive.” It looks — and works — like a screw anchor, meaning that once in, the stinger can’t retract. Muscles connect the stinger to a venom sac, from which a cell-destroying toxin is pumped into the hole.

Bee screw copy

The scent of the venom released from the honeybee signals a threat to the hive. And weirdly, it smells like bananas. That’s because the “alarm pheromone” of honeybees contains isopentyl acetate – which is potassium.

But lets back up. It is only the female honeybees, also known as the worker bees, that sting. Each hive contains some 60,000 worker bees, followed by a few hundred male drones and a single female queen bee.

science-wednesday

Worker bees are like disposable soldiers for the colony: their sole function is to gather nectar, pollinate, and defend the base. They are all infertile females. The queen lays all eggs and the drones fertilize them.

The queen bee only stings when fighting for dominance against another queen, Winston said.

And while the hornet and the wasp are known for being more aggressive, honeybees are more docile, and typically only attack when threatened.

“A wasp or a bumblebee can sting again and again, but the honeybee only gets you once, and it’ll get you good,” Mussen said.

The post Why do honeybees die when they sting? appeared first on PBS NewsHour.

This is how you get Ebola, as explained by science

A
         colorized, magnified electron microscope image of the Ebola virus growing out of an  infected VERO 46 cell. Image by NIAID

A colorized, magnified electron microscope image of the Ebola virus growing out of an infected VERO 46 cell. Image by National Institute of Allerfy and Infectious Diseases

This post was originally published on Aug. 21 and updated on Sep. 30 to reflect the latest numbers from the World Health Organization.

As of Sep. 30, the Ebola virus had killed more than 3,000 people in the West African countries of Liberia, Sierra Leone, Guinea and Nigeria, according to the latest numbers released by the World Health Organization.

As the virus spreads and medical workers feverishly battle to contain it, we wanted to know, how exactly is this virus transmitted from human to human?

What is Ebola?

Illustrations
         by Ruth Tam

Illustrations by Ruth Tam

Ebola is one of the world’s most virulent diseases. It comes from an extended family of viruses called Filoviridae, which also include the deadly Marburg virus. It is a swift and effective killer, known to kill up to 90 percent of those it infects. And it is a “hemorrhagic fever virus,” which means it causes fluid to leak from blood vessels, resulting in a dangerously low drop in blood pressure.

Understanding Ebola requires an understanding of viruses and how they work. “Viruses,” science writer Carl Zimmer writes in his book “A Planet of Viruses”, “can replicate themselves, despite their paltry genetic instructions, by hijacking other forms of life. They… inject their genes and proteins into a host cell, which they [manipulate] into producing new copies of the virus. One virus might go into a cell, and within a day, a thousand viruses [come] out.”

All viruses contain “attachment proteins,” which, as the name suggests, attach to host cells through the cells’ “receptor sites.” This is how they invade healthy human cells.

EbolaWhile some virus particles are shaped like spheres, the particles that make up Ebola are filament-like in structure, giving them more surface area to potentially attack a greater number of cells. Each Ebola virus particle is covered in a membrane of these attachment proteins, or glycoproteins.

“[The virus] has a tremendous number of glycoproteins, which can increase its ability to affect cells,” said Richard Cummings, chair of Emory’s Dept. of Biochemistry and director of the National Center for Functional Glycomics. “It’s extremely infectious in that regard.”

Imagine Ebola’s glycoproteins as giant oak trees with branches and leaves, said Erica Ollmann Saphire, a structural biologist at the Scripps Research Institute. The Ebola virus has its own critical receptor site, which lies beneath these branches and leaves to avoid detection from the immune system. Each glycoprotein can attach itself to a host cell in a number of different ways, but once its branches fasten themselves to a host cell’s molecules, that host cell pulls in the attachment protein, slicing off its leaves and branches and exposing the trunk, the virus’s receptor site.

“The previously hidden receptor rearranges itself and spring loads like a spear fishing rod,” said Saphire. “It uncoils, springs forward and penetrates the membrane, driving itself into the cytoplasm.”

science-wednesday

The cells then internalize the virus, and Ebola’s race against the human immune system begins.

How Ebola moves from person to person

Ebola spreads through direct contact with infected bodily fluids or tissue. The virus can be transmitted when an infected person’s vomit, blood or other fluids contact another person’s mouth, eyes or openings in their skin, said Dr. Ameesh Mehta, an infectious disease doctor at Emory University.

Even after a person has died, the virus persists. In West Africa where funeral rites include washing, touching and kissing corpses by family members, putting the dead to rest can be just as deadly as caring for a living patient.

“Contact with any aspect of it is considered very dangerous,” Cummings said. “Any physical contact.”

BloodEbola’s sucker punch is its speed of replication. At the time of death, a patient can have 1 billion copies of the virus in one cubic centimeter of blood. In comparison, HIV, a similar virus, has the same rate at the time of death. But unlike HIV, which only infects two types of immune cells, Ebola first infects white blood cells that disable the body’s ability to destroy foreign substances,  then seizes nearly every cell type.

“It’s a systemic viral infection throughout your body as opposed to an infection of just your immune system,” Saphire said. “Patients may die before they’re able to mount much of an immune response.”

This process takes anywhere from two to 21 days (though it’s typically between four to 10 days). When the immune system begins breaking down, the symptoms begin to show.

Patients experience fevers, headaches and fatigue early on. After the virus overwhelms healthy cells, they burst, causing a chemical release leading to inflammation. Their remains are taken over by other cells, perpetuating the virus. As the symptoms worsen, patients suffer from bloody diarrhea, severe sore throat, jaundice, vomiting or loss of appetite.

Infected cells that haven’t yet burst carry the virus through the bloodstream to invade different parts of the body like the lymph nodes, spleen and liver. When infected cells attach themselves to the inside of blood vessels, it weakens them, causing fluids to leak. This triggers the uncontrollable bleeding for which Ebola is known, though it only happens for about 50 percent of patients and occurs mostly inside the body.

In fatal cases, blood pressure plummets after blood vessel damage, and death from shock or multiple organ failure occurs within six to 16 days.

The path ahead

Saphire is part of a large, multi-site team made up of 25 laboratories that’s mapping Ebola’s glycoprotein to better understand and defeat the virus. Among the potential strategies they’re studying is an antibody cocktail called ZMapp, an experimental drug that drew media attention after its use on two U.S. aid workers and three Liberian doctors. First developed by the U.S. Army Medical Research Institute for Infectious Diseases a decade ago, this “Ebola serum” potentially works to neutralize the virus by preventing its rearrangement and flagging it for destruction by the immune system.

Clinical trials for ZMapp are set to begin in 2015, but according to Saphire, doses for “experimental compassionate therapy,” treatment provided to critically-ill patients before the drug has been approved, could be ready in three months.

“The central dogma of molecular biology is that sequence dictates fold, which dictates function,” Saphire said. “But Ebola does more with less. While the human genome has 20,000 kinds of genes, Ebola has seven, and by rearranging its protein structure, it can carry out far more than seven functions.”

Transformers

Ebola, Saphire explained, remodels its molecules “like a Transformer: those toys that unfold and refold to change between a robot and a truck,” she said. “We don’t typically expect molecules in biology to do that. We expect proteins to have one particular form – just the robot. If you didn’t know that the Ebola robot would also refold into a truck, you would design all your drugs against the robot structure.”

In addition, due to its extreme nature, there are far fewer human studies on Ebola than other similar viruses.

“Ebola patients are often too sick to consent to research,” Mehta said. These cases are occurring in poor environments where it’s hard to collect the samples to really understand the pathogens. But hopefully science catches up with the clinical phenomenon.”

While the recent outbreak is not expected to reach far beyond West Africa, researchers like science writer Richard Preston fear the beginning of a more deadly and longer-lasting epidemic if the virus finds its way to metropolitan areas like Lagos, Nigeria, which has a population larger than the state of New York.

Despite Ebola’s pervasive spread, Cummings says the biggest misconceptions are that Ebola is easily transmitted and that the outbreak in West Africa could reach global levels.

While one should still exercise caution, Cummings says the requirement of transmission of fluids makes the disease more difficult to get if you’re not directly treating patients.

“It is more controllable than people realize.”

What are your questions about Ebola? Leave them in the comments below, and we’ll get them answered for you shortly.

The post This is how you get Ebola, as explained by science appeared first on PBS NewsHour.

What made Japan’s deadly volcanic eruption so unpredictable?

volcano

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JUDY WOODRUFF: In Japan, rescue efforts at the Mount Ontake volcano have been hampered by toxic gases and fears of another eruption.

On Saturday, more than 250 people were out hiking and enjoying a nice fall day, when a surprise eruption littered the mountain with falling Boulders, thick smoke and piles of ash. At least 36 people were killed. And questions have been raised as to why there wasn’t more warning.

Here to help us understand what’s happening, our science correspondent Miles O’Brien, and Thomas Wagner of NASA, who is an expert on volcanoes.

And we welcome you both.

Miles, to you first.

Why was it — was this as unexpected as we’re reading?

MILES O’BRIEN: It was, Judy. This was what’s called a phreatic eruption, which means it was shallow and involved some hot water essentially.

Steaming water that entered into a crevice and came in contact with magma, which of course is many thousands of degrees, causes like an instantaneous flash like you would have in your oven, and caused that pyroclastic flow to come out.

This is not the kind of thing that all those sensors which are on that volcano — and Japan has well-sensored volcanoes — this is not the kind of thing that they predict well.

JUDY WOODRUFF: And, Thomas Wagner, when it comes to predictability, they’re not always this unpredictable, are they?

THOMAS WAGNER, NASA: No. It depends on what’s going on in the volcano.

Like, in a place like Hawaii, you have got big bodies of magma moving around. They cause the volcano to deform and tilt. But eruptions are difficult things. You can think of a volcano like a big crazy plumbing system in a big old building.

JUDY WOODRUFF: And you were talking me that there are many different kinds of volcanoes active right now around the world, but they’re operating at different speeds.

THOMAS WAGNER: Right.

And some volcanoes, like the Japanese volcanoes, have a lot of water dissolved in the magma, and they have more explosive eruptions, just like if you shook up a soda and took the top off, whereas that Hawaii, you don’t have a lot of water and you get more lava flows.

JUDY WOODRUFF: So, Miles, clearly, these deaths, 36 deaths, tragic. But for the volcano itself, how significant an eruption is this?

MILES O’BRIEN: Well, this is — scientists will be looking very closely at what may lie ahead here.

If you will hearken back to 1980, Mount Saint Helens, before the huge eruption there, there was a series of these phreatic eruptions, these eruptions involving boiling water. And they were viewed as a precursor to the eruption which we ultimately saw which caused such devastation in that part of the world.

So volcanoes are in some sense predictable, but in some sense not. You can see a lot of the warning signs. It’s very difficult to know when they’re going to blow. Think of the island of Montserrat. And that island dealt with evacuations. Half the island is now completely evacuated, but it lingered in a state of near eruption for many, many years.

There were many questions to scientists, saying to them, why can’t you figure this out better?

JUDY WOODRUFF: And, Thomas Wagner, just continuing with that, is it easy to predict when it settles down by watching it?

THOMAS WAGNER: No, because you get different kinds of eruptions.

 

And so like that’s why, in some cases, we look use satellites to look at how a volcano deforms. In other cases, we will actually have people go out and map the old deposits around a volcano to figure out what its history is and where you might be likely to get another eruption.

And the hazards are different, too. In this case, we had a phreatic eruption. In some cases, a tiny eruption melts snow on top and makes a mud flow. One of those killed 20,000 people in South America in the ’80s. And sometimes you get lava flows. And that’s why it’s important to sort of understand the particular hazards around the volcano you’re on.

JUDY WOODRUFF: And, Miles, you talked about what scientists learn from this. What are scientists looking at here?

MILES O’BRIEN: Well, what they’re going to do, and as we — as I mentioned, the Japanese have a well-sensored volcanic system, if you will, as well as great ability to predict earthquakes as well.

This is a nation that kind of lives on the knife edge when it comes to seismic activity and volcanoes. So they will be looking at those sensors, seeing what was damaged, putting in the types of devices that will allow them to further analyze it.

At the time of the hike, it was considered safe to be there. It was level one out of a scale of one to five, on the safe end for hikers to be in proximity of that volcano. Perhaps over time, they will not be as generous with that rating, as they consider the possibility that this could be a precursor to something bigger.

JUDY WOODRUFF: And, very quickly, Thomas Wagner, here in the U.S., nothing quite like this?

THOMAS WAGNER: No.

We have like Mount Rainier. We have all the Cascade Volcanoes. The USGS, though, has a great program monitoring those and studying those. And there are really good maps of the hazards that people should make themselves aware of.

JUDY WOODRUFF: Well, this is certainly — if you didn’t have a reason to do that before, you do now.

Thomas Wagner with NASA and our own Miles O’Brien, we thank you.

THOMAS WAGNER: Thank you.

MILES O’BRIEN: You’re welcome, Judy.

 

The post What made Japan’s deadly volcanic eruption so unpredictable? appeared first on PBS NewsHour.

World’s wildlife population shrinking at alarming rate, report says

Species, like the red-eyed tree frog of Central America, could be threatened by shrinking habitat. Photo copyright Philippe
         Kok

Species, like the red-eyed tree frog of Central America, could be threatened by shrinking habitat. Photo copyright Philippe Kok

The world population of vertebrate species has been cut in half over the past 40 years, according to a report released Tuesday.

The Living Planet Report, compiled by the World Wildlife Fund in partnership with the Zoological Society of London, points to human activities as the primary reason for the decline.

The report calculates the Living Planet Index, which measures population trends in more than 3,000 wildlife species. Globally, the number of vertebrate animals has decreased by 52 percent since 1970.

This number is worse than previous estimates, which drew heavily from data on species living in North America and Europe. The report accounts for wildlife in South and Central America, which showed a decline of 83 percent.

Freshwater animals, such shorebirds and fish, also saw their populations plummet. Their decline of 76 percent was nearly double the rate of loss for land or marine species. The study identifies habitat loss, pollution and invasive species as the main causes.

The report also takes a detailed look at how humans’ activity impacts the environment. At our current rate of consumption, it says, humans need the resources of 1.5 earths.

“A range of indicators reflecting humanity’s heavy demand upon the planet shows that we are using nature’s gifts as if we had more than just one Earth at our disposal,” writes the WWF International Director General, Marco Lambertini in the report’s foreword. “By taking more from our ecosystems and natural processes than can be replenished, we are jeopardizing our future.”

The post World’s wildlife population shrinking at alarming rate, report says appeared first on PBS NewsHour.