Wednesday, October 31, 2018

Vampire Bats: Why horses should be afraid of vampires--and not just on Halloween

Vampire bats in South and Central America love horse hooves. They frequently feed at the coronet, where the blood is close to the surface. Besides being creepy, vampire bats are the leading reservoir of rabies virus in Central and South America and have recently been identified as a host that easily spreads bartonella bacteria. Newly deforested landscapes are now home to domestic livestock; vampire bat populations have flourished with the captive animals so easily available to bite. Officials in Texas are now warning that common vampire bats have crossed the Rio Grande into the United States.

Until recently, most of us only thought about vampires once a year, on October 31. But that is about to change. While Count Dracula may be a figment of literary imagination, the real-life inspiration for his story is alive and well and spreading rapidly through recently deforested regions of South and Central America.

Horses, horseowners and horse professionals: Consider yourselves warned. Like the killer bees who paved the path, vampire bats may be headed your way. And they're bringing dangerous diseases with them.

As the population (and geographic range) of the common vampire bat (Desmodus rotundus) expands, so do the warnings from public health officials of the genuine risks to horses, commercial livestock, and even humans who may be bitten by the tiny mammals, thanks to the common but potentially deadly viral disease and bacterial infections the bats may spread as they bite.

Vampire bats have long been a nighttime nuisance to horse and cattle owners in large areas of Latin America, but their impact has only ramped us since the relatively recent changes in the ecosystems there. In 2011, the Centers for Disease Control reported the first human death from a vampire bat in the United States, but it turned out that the victim had been bitten while in Mexico and contracted rabies that led to his death in the United States.

Of the three species of vampire bats, the common vampire bat is the one making the news; it has recently begun to expand its range northward toward the Lower Rio Grande Valley of Texas, according to a document released through Texas A&M's University Agrilife Extension.

Here's an introduction to vampire bats from the Smithsonian:

Written records of vampire bats attacking horses at night in the tropics goes back to colonial Spaniard records: Francisco Montejo, the Spanish conqueror of the Yucatan peninsula, wrote, "A great plague of bats (which) attacked not only the beasts of burden but the men themselves, sucking their blood when they were asleep." The great evolutionary biologist George Darwin documented a vampire bat attack on one of his expedition horses in Chile in the early 1800s.

Today, the United Nations warns that cattle and horses in 18 countries are threatened by vampire-borne paralytic rabies, although seven report that vaccination programs are succeeding in stemming the problem.

Professor Heather Proctor of the University of Alberta points out a vampire bat bite found on a horse in Mexico in the morning. Bats will only attack in the darkest part of the night, and will not come out if the moon is full. (Heather Proctor photo)

A vampire usually bites a horse on the withers or neck, if the horse is lying down, but it is especially common for the bite to be in the coronet area, where the bat finds a plentiful supply of blood, when a horse is standing. The Food and Agriculture Organization (FAO) of the United Nations used night vision technology in a closed paddock. They record 49 biting incidents; 27 were on the interdigital region of standing cattle and 22 were on various body parts of cattle that were lying down.

According to official reports in Peru, vampire bats kill about 500 cattle a year by infecting them with rabies; no statistics are available on horses. Recently researchers from the University of Glasgow, with funding from the Wellcome Trust and Royal Society, reported that the actual number of cattle rabies cases is about four times the number reported.

The bats are being studied extensively, both because of the health risk of diseases they may spread, and because the mechanism of their locomotion and their actual biting adaptations are fascinating and may hold medical benefits for human and veterinary medicine in the future.

How can a vampire help us? The vampires are uncanny opportunists and a boon to the study of locomotion. In their normal gait, they move along the ground in a four-beat walk, but when they need to speed up, they use their wings like crutch-like super-limbs that sends them bounding forward in a unique gait seen only in vampire bats. An unusual thumb aids their ability to run.

A vampire bat lives solely on blood, which is largely liquid; it does not even require water intake to survive. However, its survival depends on a daily meal of blood.

Most people are acutely aware that vampires have very sharp teeth, but the vampire brain is highly developed to detect the regular sound of a sleeping animal’s breathing.

They are also equipped with thermoreceptors, which detect heat and help the bat make a beeline to a spot on the horse or cow where blood is close to the surface--think of it as “venogram vision”. 

This image shows how tiny a vampire bat really is. Notice the thumbs on the tips of its wings; they are used to thrust the bat forward when it is ready to leap onto its prey. Photo courtesy of USDA.

Scientists suggest that the bat has some ability to anesthetize the area with its saliva before it bites; animals often sleep through a vampire attack and never stir.

The vampire does much more than simply bite its host and suck blood. First of all, it is a tiny animal, and it is biting a horse covered with hair. The bat’s sharp teeth begin shaving the hair around the bite target; the underside of the tongue is channeled to create canals that carry blood quickly into the waiting, empty stomach.

But why does the blood keep flowing? Why doesn’t it clot? Researchers at Norwegian University of Science and Technology and the University of Copenhagen say that the chemical content of the bat’s saliva acts as an anticoagulant. The stream will stop when the bat leaves. Research is ongoing to find a way to utilize vampire bat saliva proteins to create a new anticoagulant medication for stroke victims.

When the bat does leave, it will be well-fed; a vampire bat typically sucks half its body weight in blood.

Vampire bats can be messy eaters. (USDA photo)

The final surprise is that it will remember if it has found an ideal host, and it will use a unique form of on-board GPS to return the next night to the same animal, particularly when horses are in small pens or stalls and likely to be in the same location.

Why are vampire bats in the news now? First of all, researchers are finally able to study the bats better, thanks to GPS and motion capture technologies. But on a larger scale, the population is both increasing and spreading because of deforestation in South and Central America. The increased number of horses and cows on open land that was once forest means that there are many more -- and easier -- meals for the bats, and their populations have grown right along with the increase of domestic livestock on newly cleared land.

World human and veterinary health officials are concerned about the vampire bats’ switch to domestic livestock from their former wildlife hosts as the forests have disappeared. Control of bovine paralytic rabies spread by vampire bats is of particular concern; millions of dollars’ worth of cattle are lost each year under current conditions.

In 2014, the British charity World Horse Welfare noted problems with horses being bitten by vampires in the remote Guaymi Indigenous Reserve in southern Costa Rica, an area it identified as also in need of farrier education. In some regions, being bitten by a vampire is associated with witchcraft by local communities; a witch is usually identified as the cause rather than the tiny bat.

Research published in September reported the high likelihood of vampire bats to be behind the spread of bartonella, bacteria that cause endocarditis, a potentially life-threatening illness in humans and domestic animals. In tests conducted by Montana State University researchers in Peru and Belize, 67% of tested bats were found to be Bartonella carriers.

Warfarin-based bat poisons are used in Central and 
South America to kill the bats when they 
return to feed on the same horse or cow. (photo 
courtesy of Professor Proctor)
Linda Gray, a transplanted New England horseowner living in Costa Rica, shared her experience--and advice--with vampires with The Hoof Blog: “These pesky little guys bite your horse in places where they can't be reached – behind the front leg, on the back of the neck, on the tips of the ears, etc. You'll notice a coagulated bloody trail on your horse in the morning.

“When they bite, they drink the horse's blood and pee at the same time,” she continued. “The urine marks the spot for the bat, and allows him to come back the next night and find the same spot to feed again.”

What’s a horseowner to do?

“Go to the vet store and ask for "Vampirisan", which is a small jar containing pink, Vaseline-like substance. It is relatively inexpensive. A small jar will last you quite a long time.

“When your horse has been bitten by a vampire bat, clean the area of the bite with alcohol very thoroughly. Remove all traces of blood and bat pee, to eliminate the odor that marks the spot for the bat's return.

“In the late afternoon or early evening, put a tablespoon-sized smear of Vampirisan over the original bat bite. Use surgical gloves, to avoid getting the poison on your fingers.

“The bat will come back to the original location of the bite, find the Vampirisan, eat it, and die (somewhere else, thankfully). You may have to do this a couple of nights in a row to get all the bats, but generally once you kill them, they won't come back for months.”

Biology professor Heather Proctor of the University of Alberta shared stories and photos from her encounters with horses bitten by vampire bats in Mexico during a research expedition. She also described using a product called Vampiracida, which she described as “a warfarin-containing cream”. (Warfarin was commonly used as a rat poison for the past 100 years and, for the past 50 years, has been used in human medicine as a blood thinner under the name of Coumadin.

“When bats returned to feed on open wounds the next evening they also ingest some warfarin. Then, because vampire bats frequently share their blood meals with roost-mates via regurgitation, the anti-clotting agent would not only affect the bat that fed on the wound directly but also its friends and relatives.”

Remember that bats are an important part of the ecosystem and they have been badly affected by disease in the United States. Most bats are completely harmless and are important to insect control. But no one will blame you if you leave the lights on in the barn tonight.

Horse hoof photo courtesy of Imgur contributor. "Happy Halloween" image of flying common vampire bat kindly loaned by bat researcher José Gabriel Martínez Fonseca. Thank to all the researchers and to Linda Gray for their contributions to this article.

More about vampire bats:

Greenhall, A. M. and Schmidt, U. (2018). Natural history of vampire bats. CRC Press.

Mendoza, M.L.Z., Xiong, Z., Escalera-Zamudio, M., Runge, A.K., Thézé, J., Streicker, D., Frank, H.K., Loza-Rubio, E., Liu, S., Ryder, O.A. and Castruita, J.A.S., 2018. Hologenomic adaptations underlying the evolution of sanguivory in the common vampire bat. Nature ecology & evolution, 2(4), p.659. (Open Access, free to read and/or download)

More reader-friendly information from the Norwegian research
More about vampire bat locomotion research:

Riskin, D. K., Parsons, S., Schutt, W. A., Carter, G. G., & Hermanson, J. W. (2006). Terrestrial locomotion of the New Zealand short-tailed bat Mystacina tuberculata and the common vampire bat Desmodus rotundus. Journal of Experimental Biology, 209(9), 1725-1736. (Open Access, free to read/download)

Riskin, Daniel K.; Hermanson, John W. (2005). "Biomechanics: Independent evolution of running in vampire bats". Nature. 434: 292.

More about vampire research in public health:

Becker DJ, Bergner LM, Bentz AB, Orton RJ, Altizer S, et al. (2018) Genetic diversity, infection prevalence, and possible transmission routes of Bartonella spp. in vampire bats. PLOS Neglected Tropical Diseases 12(9): e0006786.

Benavides JA, Rojas Paniagua E, Hampson K, Valderrama W, Streicker DG (2017) Quantifying the burden of vampire bat rabies in Peruvian livestock. PLoS Negl Trop Dis 11(12): e0006105.

Vampire Bats in Texas: Ecology, Signs, and Managing Damage to Livestock by John M. Tomeček and Michael J. Bodenchuk, April 2017, available through Texas A&M AgriLife Extension Service.

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