News: Bats & Viruses — Friend or Foe?

Bats & Viruses — Friend or Foe?

Tell the truth. The bat picture creeps you out. You are not alone. But in reality, bats truly are some of our best friends. They gobble thousands of disease-spreading bugs a night. But they also carry viruses that can be deadly to humans. So, bats — friend or foe?

There are over 1,300 species of bats, living in all but the coldest regions on the planet. Mostly nocturnal, bats are social creatures that can live 35 years or more. Bats are mammals like us, and they give birth to about one pup a year. They are fastidious about grooming themselves and pretty shy.

Belonging to the animal group Chiroptera, fossils of bat relatives date back about 52 million years. Although clumsy looking fliers, bats are highly maneuverable in the air. Their aerodynamic wing structure allows them to make snap changes to the position and shape of their wings in response to airflow or prey. Bats locate dinner and navigate the sky through "echolocation." Bats emit sounds (that we can't hear) that bounce off objects, giving the bat the ability to locate prey and navigate the terrain.

Bats chirp more frequently when close to prey.

Should You Be Afraid of Bats?

Called a "keystone" species, bats provide specialized services including seed-dispersal, insect eradication, and pollination. While many bats eat insects, others eat fruit or pollen. Still other bats eat plant nectar, fish, frogs, and larger fruits. But then there are the vampire bats.

Of the over 1,000 species of bats, only three drink blood for nourishment. These are the common vampire bat, the white-winged vampire bat, and the hairy-legged vampire bat. Vampire bats give bats altogether, a poor reputation. And because they look like flying rats, bats have a bit of a problem with brand management.

It is also true that bats carry a large number of worrisome viruses. A recent study published in Virus Evolution took tissue samples from 19,192 bats, humans, rodents, and non-human primates from 20 different countries and analyzed the samples for the presence of coronaviruses (CoV). Coronaviruses are the family of pathogens responsible for serious emergent infections including Severe Acute Respiratory Syndrome (SARS) and Middle East Respiratory Syndrome (MERS).

In 2002, the SARS-CoV emerged in China and spread to 27 countries, infecting more than 8,000 people, and killing 774. The outbreak is considered the first pandemic of the 21st century. The MERS-CoV emerged in 2012 in the Middle East. Though camels were spreading MERS during the outbreak, bats are the evolutionary beginning for both coronaviruses.

In analyzing the viral samples collected over a five-year time span, the scientists at the Mailman School of Public Health at Columbia University found that 98% of the animals harboring CoV are bats, specifically, 282 different species of bats.

The likelihood of these viruses "jumping" to humans is the subject of ongoing research, and researchers believe, after sequencing the viral DNA, that bats viruses from Latin American countries are less likely to impact humans than those in Africa or Asia. The research team stresses their analysis is "not to create alarm or incite the retaliatory culling of bats." The authors note harming bats could have unintended consequences that raise the likelihood of disease transmission, given that "most of the … viruses detected in this study are unlikely to pose any threat to humans."

Although less than 1% of bats carry rabies, don't touch a dead bat, or a bat acting aggressively or strangely, day or night. It could be one of the unlucky few with rabies. Rabies is a virus spread through saliva from a bite or a scratch. If you are bitten or scratched by a bat, try to trap it in a container for testing and get help immediately. Rabies is curable if treated in time. Otherwise, it is usually fatal.

The study also notes the important ecological niche occupied by bats and the importance of their well-being to human society around the world.

The endangered Hawaiian Hoary Bat. Image by Frank Bonaccorso/USGS

The Benefits of Bats

Did you know the Hawaiian Hoary Bat is Hawaii's state land mammal? Many bats are threatened, and the US Department of the Interior notes habitat loss or disease endanger at least 13 species.

With the spread of a fungal infection called "white-nose syndrome," millions of insectivore bats across the US have died.

The fungus, Pseudogymnoascus destructans, emerged in 2007 and infects the face, ears, and wings of hibernating bats. Researchers think the fungus came to North America from Europe or China, where bats have adapted to the fungus without being harmed. With no natural resistance, North American bats have little defense. The US Geological Survey estimates that the population of bats in the northeastern US has declined by approximately 80% since white-nose syndrome emerged. Because bats do not reproduce quickly, the fungal infection could be devastating — to more than just bats.

Map showing the spread of white-nose syndrome from 2006 forward. Image via White-nose syndrome.org

Let's run through some of the advantages of bats:

  • By controlling insects, bats give farmers a big assist. The USGS estimates bats save between $3 billion and $53 billion dollars a year in reducing crop loss due to insect pests. Those figures do not include the value of bats that eliminate damaging forest insects for the timber industry. According to the National Park Service, the number of insects eaten nightly by a bat is equivalent to a "teenage boy eating 200 quarter-pound burgers" in a night. Given the rise in mosquito-vectored infections like West Nile and Zika virus in humans, bats are our front line defense against potentially devastating disease.
  • Enjoy a Margarita now and then? Next time you and your friends gather around a salted-rim, raise your glasses to the Mexican Long-Nosed Bat and the Lesser Long-Nosed Bat that pollinate the plant Agave tequilana, which is refined to make tequila. But, given habitat destruction along their migratory pathways, and newer methods of raising Agave, both these bats are now endangered.
The rare and beautiful Mexican long-tongued bat. Image via USFWS
  • Bats are important plant pollinators in tropical and subtropical zones. If you enjoy avocados, mangos, figs, bananas, and even cacao (that means chocolate), you are already a bat fan.
  • Plants and humans rely on bats for plant seed dispersal.
  • Bats occupy an important tier in the food chain. As they consume insects, higher level predators eat them, including larger birds of prey, and animals that attack bats as they sleep.
  • Poop from bats, called "guano" is a great fertilizer because of its high nutrient value.
  • Long envied by engineers for their in-flight maneuverability, bats are now the model for robotic bat-drones.
Check out the Caltech robotic bat

You can reduce the mosquitoes in your neighborhood by putting up a bat box and growing night-blooming plants like you might find in a Moon Garden. For organic gardeners, bats offer free, natural pest control.

Inside and out, bats are complicated, essential partners in the environment. Under terrific threat from white-nose syndrome in North America, bats need our help to understand their value to our health and assist them to keep theirs.

Cover image by Stihler Craig/US Fish and Wildlife Service

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