What’s the Difference Between Pandemic, Epidemic and Outbreak?
By Rebecca S.B. Fischer
The coronavirus is on everyone's minds. As an epidemiologist, I find it interesting to hear people using technical terms – like quarantine or super spreader or reproductive number – that my colleagues and I use in our work every day.
But I'm also hearing newscasters and neighbors alike mixing up three important words: outbreak, epidemic and pandemic.
Simply put, the difference between these three scenarios of disease spread is a matter of scale.
Small, but unusual.
By tracking diseases over time and geography, epidemiologists learn to predict how many cases of an illness should normally happen within a defined period of time, place and population. An outbreak is a noticeable, often small, increase over the expected number of cases.
Imagine an unusual spike in the number of children with diarrhea at a daycare. One or two sick kids might be normal in a typical week, but if 15 children in a daycare come down with diarrhea all at once, that is an outbreak.
When a new disease emerges, outbreaks are more noticeable since the anticipated number of illnesses caused by that disease was zero. An example is the cluster of pneumonia cases that sprung up unexpectedly among market-goers in Wuhan, China. Public health officials now know the spike in pneumonia cases there constituted an outbreak of a new type of coronavirus, now named SARS-CoV-2.
As soon as local health authorities detect an outbreak, they start an investigation to determine exactly who is affected and how many have the disease. They use that information to figure out how best to contain the outbreak and prevent additional illness.
Bigger and spreading.
An epidemic is an outbreak over a larger geographic area. When people in places outside of Wuhan began testing positive for infection with SARS-CoV-2 (which causes the disease known as COVID-19), epidemiologists knew the outbreak was spreading, a likely sign that containment efforts were insufficient or came too late. This was not unexpected, given that no treatment or vaccine is yet available. But widespread cases of COVID-19 across China meant that the Wuhan outbreak had grown to an epidemic.
International and out of control.
In the most classical sense, once an epidemic spreads to multiple countries or regions of the world, it is considered a pandemic. However, some epidemiologists classify a situation as a pandemic only once the disease is sustained in some of the newly affected regions through local transmission.
To illustrate, a sick traveler with COVID-19 who returns to the U.S. from China doesn't make a pandemic, but once they infect a few family members or friends, there's some debate. If new local outbreaks ensue, epidemiologists will agree that efforts to control global spread have failed and refer to the emerging situation as a pandemic.
Terms Are Political, Not Just Medical
As of this writing, the World Health Organization classifies the risk of global COVID-19 spread as "very high," the highest level in their risk classification scheme and one step below an official pandemic declaration. This means that the WHO remains hopeful that, by taking aggressive steps now, containment of localized outbreaks may still be possible.
But I and other scientists and public health officials are already calling this a pandemic. The official numbers count an excess of 100,000 cases in almost 100 countries, and community spread has been documented in the U.S. and elsewhere. By the classical definition, it's a pandemic.
A formal declaration of COVID-19 or any other infectious disease as pandemic tells governments, agencies and aid organizations worldwide to shift efforts from containment to mitigation. It has economic, political and societal impacts on a global scale.
Formal declaration needn't incite fear or cause you to stockpile surgical masks. It doesn't mean the virus has become more infectious or more deadly, nor that your personal risk of getting the disease is greater. But it will be a historical event.
Reposted with permission from The Conversation.
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The ghoulishly named ogre-faced spider can "hear" with its legs and use that ability to catch insects flying behind it, the study published in Current Biology Thursday concluded.
"Spiders are sensitive to airborne sound," Cornell professor emeritus Dr. Charles Walcott, who was not involved with the study, told the Cornell Chronicle. "That's the big message really."
The net-casting, ogre-faced spider (Deinopis spinosa) has a unique hunting strategy, as study coauthor Cornell University postdoctoral researcher Jay Stafstrom explained in a video.
They hunt only at night using a special kind of web: an A-shaped frame made from non-sticky silk that supports a fuzzy rectangle that they hold with their front forelegs and use to trap prey.
They do this in two ways. In a maneuver called a "forward strike," they pounce down on prey moving beneath them on the ground. This is enabled by their large eyes — the biggest of any spider. These eyes give them 2,000 times the night vision that we have, Science explained.
But the spiders can also perform a move called the "backward strike," Stafstrom explained, in which they reach their legs behind them and catch insects flying through the air.
"So here comes a flying bug and somehow the spider gets information on the sound direction and its distance. The spiders time the 200-millisecond leap if the fly is within its capture zone – much like an over-the-shoulder catch. The spider gets its prey. They're accurate," coauthor Ronald Hoy, the D & D Joslovitz Merksamer Professor in the Department of Neurobiology and Behavior in the College of Arts and Sciences, told the Cornell Chronicle.
What the researchers wanted to understand was how the spiders could tell what was moving behind them when they have no ears.
It isn't a question of peripheral vision. In a 2016 study, the same team blindfolded the spiders and sent them out to hunt, Science explained. This prevented the spiders from making their forward strikes, but they were still able to catch prey using the backwards strike. The researchers thought the spiders were "hearing" their prey with the sensors on the tips of their legs. All spiders have these sensors, but scientists had previously thought they were only able to detect vibrations through surfaces, not sounds in the air.
To test how well the ogre-faced spiders could actually hear, the researchers conducted a two-part experiment.
First, they inserted electrodes into removed spider legs and into the brains of intact spiders. They put the spiders and the legs into a vibration-proof booth and played sounds from two meters (approximately 6.5 feet) away. The spiders and the legs responded to sounds from 100 hertz to 10,000 hertz.
Next, they played the five sounds that had triggered the biggest response to 25 spiders in the wild and 51 spiders in the lab. More than half the spiders did the "backward strike" move when they heard sounds that have a lower frequency similar to insect wing beats. When the higher frequency sounds were played, the spiders did not move. This suggests the higher frequencies may mimic the sounds of predators like birds.
University of Cincinnati spider behavioral ecologist George Uetz told Science that the results were a "surprise" that indicated science has much to learn about spiders as a whole. Because all spiders have these receptors on their legs, it is possible that all spiders can hear. This theory was first put forward by Walcott 60 years ago, but was dismissed at the time, according to the Cornell Chronicle. But studies of other spiders have turned up further evidence since. A 2016 study found that a kind of jumping spider can pick up sonic vibrations in the air.
"We don't know diddly about spiders," Uetz told Science. "They are much more complex than people ever thought they were."
Learning more provides scientists with an opportunity to study their sensory abilities in order to improve technology like bio-sensors, directional microphones and visual processing algorithms, Stafstrom told CNN.
"The point is any understudied, underappreciated group has fascinating lives, even a yucky spider, and we can learn something from it," he told CNN.
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