The culprit in millions of bat deaths since 2006? A 'vampire' fungus.

White-nose syndrome is nearly as lethal to bats as the Black Plague was for humans.

  • White-nose syndrome has killed at least 6.7 million bats, though this estimate was made in 2012, and the current figure is almost certainly much higher.
  • Bats serve a crucial role in our ecosystem and economy, and white-nose syndrome is already pushing many species to the brink of extinction.
  • Researchers and scientists are working hard to develop novel methods to cure white-nose syndrome; a few methods have shown promise, but none have yet been deployed in the field.

The fungus Pseudogymnoascus destructans was certainly well named. As it continues to spread across North America, the P. destructans has been precisely destroying a critical part of the ecosystem: bats. Between 2006 and 2012, the fungus killed 6.7 million bats. When it takes hold, the fungus kills between 70 percent and 90 percent of the bat population on average, sometimes completely eradicating a given colony.

No accurate estimates have been made for after 2012, but, if the trend has persisted, then the number is almost certainly millions more.

North America first encountered the fungus in February 2006 in upstate New York after a caver took a photograph of a bat with an unusually white, fuzzy nose. P. destructans primarily affects the skin and tends to cluster around the nose, giving the disease its common name: white-nose syndrome.

Why is white-nose syndrome so deadly?

A group of bats with white-nose syndrome. Flickr user Government of Alberta

Although the exact mechanism behind its lethality is unclear, researchers have found that bats with white-nose syndrome have skin damage, particularly on their wings. The infection also knocks bats' physiology out of whack; infected bats have high levels of carbon dioxide and potassium in their blood, which affects their heart function.

The deaths, however, are most clearly linked to the odd behavioral changes that take place. White-nose syndrome only appears to affect hibernating bats, who normally don't do too much during the winter. But bats with white-nose syndrome go into a flurry of activity when they're supposed to be resting, flying around during the day in freezing temperatures. One study found that infected bats used twice as much energy as healthy ones, burning up the fat reserves they need to survive the winter.

Why do bats matter?

From a conservation perspective, any animal threatened with extinction is a tragedy. But what are the practical impacts of this plague? When we look at the role of bats in our ecosystem, their disappearance would have major impacts.

Bats make up a full fifth of all mammals on the planet. Fortunately, only hibernating species are affected by white-nose syndrome, but their disappearance would still wreak havoc on the ecosystem. Bats eat insects: In fact, a single little brown bat (which are affected by white-nose syndrome) can eat 1,000 insects in an hour. This service — which we currently get for free — is actually incredibly valuable to the agricultural industry. Were bats not around to eat these pests, it could cost the agricultural industry between $3.7 billion and $53 billion per year.

Not only that, but bats contribute to the spread of plant life. They distribute seeds from fruits and, alongside birds, bees, and other insects, serve as crucial pollinators. Three-quarters of our food crops rely on animal-mediated pollination, including many fruits and vegetables. Furthermore, pollinated plants are foundational elements of the food chain and provide habitats for other animals. If a large segment of the bat population were to disappear, it would have cascading effects for the rest of the ecosystem.

So far, the northern long-eared bat, the gray bat, and the Indiana bat have been listed as endangered or threatened with extinction due to white-nose syndrome. The population of little brown bats, previously one of the most common species in North America, is just 1 percent of what it was prior to the arrival of P. destructans. So, it's clear there's a major problem here. What have we been doing about it?

Reasons to be optimistic

Bat wing under UV light

Turner et al., 2018

A bat wing under UV light. The orange specks are P. destructans, which causes white-nose syndrome.

Fortunately, it's not all doom and gloom. Researchers are hard at work trying to find a cure for white-nose syndrome, though no silver bullet has yet been found. Researchers Jonathan Palmer, Kevin Drees, Jeffrey Foster, and Daniel Lindner compared the fungus's genetic code to some similar strains and noticed a glaring weakness. In an interview with the Washington Post, Lindner said, "[P. destructans is] something that has evolved for millions of years in the dark. Its ability to repair damage caused by UV light [...] seems to be entirely lacking in this fungus. […] I'd go as far as to say it's a vampire fungus. It doesn't go up in a puff of smoke, [but] it's gone down an evolutionary path so far that it's really a creature of the dark." They found that only a few seconds of UV exposure is sufficient to kill the fungal infection, but the problem is how to treat bats en masse in the wild.

Other treatments are looking at using antifungal bacteria, such as Rhodococcus rhodochrous, which has shown promise in preventing the P. destructans from gaining a foothold and has even reduced the amount of fungus on already-infected bats. But again, the issue is how to treat an entire species. And, even if some mass delivery system of UV radiation, anti-fungal bacteria, or another treatment were developed, there is always the risk that the treatment could be worse than the cure. Scientists are accordingly moving cautiously, not wanting to worsen an already bad situation. With any luck, though, the future will be one with bats in it.

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Are modern societies trying too hard to be clean, at the detriment to public health? Scientists discovered that a microorganism living in dirt can actually be good for us, potentially helping the body to fight off stress. Harnessing its powers can lead to a "stress vaccine".

Researchers at the University of Colorado Boulder found that the fatty 10(Z)-hexadecenoic acid from the soil-residing bacterium Mycobacterium vaccae aids immune cells in blocking pathways that increase inflammation and the ability to combat stress.

The study's senior author and Integrative Physiology Professor Christopher Lowry described this fat as "one of the main ingredients" in the "special sauce" that causes the beneficial effects of the bacterium.

The finding goes hand in hand with the "hygiene hypothesis," initially proposed in 1989 by the British scientist David Strachan. He maintained that our generally sterile modern world prevents children from being exposed to certain microorganisms, resulting in compromised immune systems and greater incidences of asthma and allergies.

Contemporary research fine-tuned the hypothesis, finding that not interacting with so-called "old friends" or helpful microbes in the soil and the environment, rather than the ones that cause illnesses, is what's detrimental. In particular, our mental health could be at stake.

"The idea is that as humans have moved away from farms and an agricultural or hunter-gatherer existence into cities, we have lost contact with organisms that served to regulate our immune system and suppress inappropriate inflammation," explained Lowry. "That has put us at higher risk for inflammatory disease and stress-related psychiatric disorders."

University of Colorado Boulder

Christopher Lowry

This is not the first study on the subject from Lowry, who published previous work showing the connection between being exposed to healthy bacteria and mental health. He found that being raised with animals and dust in a rural environment helps children develop more stress-proof immune systems. Such kids were also likely to be less at risk for mental illnesses than people living in the city without pets.

Lowry's other work also pointed out that the soil-based bacterium Mycobacterium vaccae acts like an antidepressant when injected into rodents. It alters their behavior and has lasting anti-inflammatory effects on the brain, according to the press release from the University of Colorado Boulder. Prolonged inflammation can lead to such stress-related disorders as PTSD.

The new study from Lowry and his team identified why that worked by pinpointing the specific fatty acid responsible. They showed that when the 10(Z)-hexadecenoic acid gets into cells, it works like a lock, attaching itself to the peroxisome proliferator-activated receptor (PPAR). This allows it to block a number of key pathways responsible for inflammation. Pre-treating the cells with the acid (or lipid) made them withstand inflammation better.

Lowry thinks this understanding can lead to creating a "stress vaccine" that can be given to people in high-stress jobs, like first responders or soldiers. The vaccine can prevent the psychological effects of stress.

What's more, this friendly bacterium is not the only potentially helpful organism we can find in soil.

"This is just one strain of one species of one type of bacterium that is found in the soil but there are millions of other strains in soils," said Lowry. "We are just beginning to see the tip of the iceberg in terms of identifying the mechanisms through which they have evolved to keep us healthy. It should inspire awe in all of us."

Check out the study published in the journal Psychopharmacology.