You’re getting one last Halloween post, because, of course, we haven’t talked about bats!
Bats are the second largest order of mammals after rodents, and the only mammal capable of true flight. There are 1,500 species of bats, and they range in size from a 5-inch wingspan to a whopping 5-foot wingspan. They are mammals, so they are warm-blooded, have live young, nurse their pups, and have fur. Amazingly, they absorb oxygen, not only in their lungs, but across the patagium, the thin membrane of skin that makes up their “wings”. Most bats eat insects or fruit; only a very few drink blood. What’s lovely about bats is they serve an important function in suppressing mosquito populations (and I love anything that eats mosquitoes), pollinating flowers and dispersing seeds. They can, however, function as reservoirs for many pathogens, notably rabies. Some cultures see them as symbols of wisdom, long life, and rebirth, while other cultures see them as harbingers of doom, or agents of witchcraft.
Let’s talk about the vampire bat, since it is Halloween season. Vampire bats feed on large mammals (cows, horses, humans), and smaller animals like birds. They can sense deep steady breathing, and thus target sleeping prey. They make a tiny bite with specially grooved canine and incisor teeth, biting away a small flap of skin, and lap up the seeping blood (like little puppies lapping up milk…). Most animals are unaware they have been bitten, so tiny are the bat and the bite.
Here’s where it gets fascinating. The bat saliva contains a complex array of anti-coagulants, that is, substances that keep blood from clotting. So, bats can continue to drink until they are engorged. Even though they are tiny, vampire bats can drink up to an ounce of blood at a time, and the wound they create will continue to ooze blood for hours after they leave.
First, a refresher on how blood clots. We want our blood to stay liquid, and not clot too easily, but we want a quick clot when there is an injury. The clotting process that has evolved is complex and multi-faceted. First, when there is a cut or injury, tiny platelet cells in the bloodstream rush to the site, change shape, and stick to the injured tissue, creating a temporary plug. These platelets release chemicals that activate other clotting factors. These clotting factors trigger a chain reaction (called the coagulation cascade) to make fibrin. Fibrin forms a mesh over the platelet plug, making a stable clot.
In 1967, British researcher Dr. Christine Hawkey isolated a substance in bat saliva that keeps platelets from sticking together. In 1995, Dr. Raphael Apitz-Castro, a biochemical researcher from Caracas, Venezuela, isolated another anticoagulant in vampire bat saliva that binds and inhibits Factors IX and X in the coagulation cascade. Since he isolated it, he got to name it: Draculin!! Seriously! I love this guy!
Work by various researchers in the 1990s led to isolation of another protein in bat saliva that dissolved fibrin and thus dissolved clots. In 1999, Desmoteplase, based on that protein, was genetically engineered. It was chemically similar to the well- known “clot-buster” t-PA, currently used in stroke treatment. Clinical trials using Desmoteplase in stroke patients were encouraging, but ultimately it was not better than products already on the market, so commercial use was abandoned.
The saliva of the vampire bat harbors a whole arsenal of unique substances. We just read about three, and there are many more being studied. I hope some of this research bears fruit. How great would it be to be able to give patients Draculin!?
I know you want to ask me about bats and rabies. I’ve written a lot about rabies recently, so I will only say that yes, bats can carry rabies. In the South, less than 1% of bats carry rabies. However, among bats submitted for testing, up to 20% were positive. People don’t always know they have been bitten, and the bites are tiny, so even if you just find a bat in the room with you, you’ll need rabies prophylaxis. Call your doctor or health department or Poison Control. I was once camp doctor at Camp Sea Gull on the North Carolina coast. A small colony of bats was found living in the rafters of a cabin there. Because we were concerned one or more of the boys may have had an unknown bite, all 24 boys and their counselors had to receive rabies prophylaxis, which is a series of 5 shots over 2 weeks. The camp leaders did a wonderful job of making it fun and special, with ice cream parties, movies, and air conditioning for those boys on the night of their shots and special t-shirts (neon green with bats, “I got batty at Camp Sea Gull”) for just those boys. They were almost envied. And all of them were fine.
On a lighter, non-medical note, I have bat-related information for those of you who are tequila drinkers. Tequila is having a moment. It has surpassed whiskey as the second-best-selling spirit and is poised to challenge vodka for the top spot. George Clooney, Dwayne “The Rock” Johnson, Kendall Jenner, Matthew McConaughey, and Michael Jordan have all launched their own tequila brands. Tequila is made by shredding the heart of the blue agave plant, extracting the juices, then fermenting, distilling, and aging it. A blue agave plant lives about twelve years, thrusting up a giant flower stalk just before it dies. But agave growers cut and harvest the agave just before it flowers, when the plant is at its sweetest. The next plant that grows in that spot is a clone. What does this have to do with bats?
Long-nosed bats and agave plants have a mutually beneficial relationship. Long-nosed bats have a particularly long muzzle and tongue and can reach deep within the agave flower to get the nectar. Like hummingbirds, they go flower to flower, loading up on nectar and pollen. Pregnant bats need the sweet nectar from the agave plants before they make their annual migration from central Mexico to the US Southwest, before birthing their pups. The agaves depend on these migratory bats to pick up the pollen and disperse it to help propagate new plants, and maintain the diversity of the agave population. With cultivation for tequila, these plants are harvested before they flower, so these bats are becoming endangered. And the agave is losing its biodiversity.
What can you do? Try to buy small batch tequila with “bat friendly” on the label. Those growers are letting their agave flower to help the plant and the bats. Or switch to mezcal, which is just like tequila, except it is made from wild agave plants that are allowed to flower, which is much more sustainable.
So, now I hope next time you see a bat flitting around in the dusk, you’ll cast a friendly eye upon it.