- Merlin Tuttle’s Response to Exaggerated Disease Warnings Featured by the Wildlife Society
- Bats Spread Viruses Across Species
Still unproven supposition is presented as fact, and it is assumed without supporting evidence that spreading viruses across species is always bad.
Bats in fact have one of our planet’s finest records of living safely with humans. Despite intense efforts to link Ebola to bats, “No clear case of bat-to-human transmission of Ebola has ever been proven.” (G. Vogal, Science, 2014, vol. 344:140). Nevertheless public health virologists have so frequently speculated that this and other so-called “emerging diseases” are of bat origin, that unproven hypotheses are becoming entrenched as “fact” in the public mind.
Throughout most of human history bats and people have shared dwellings, from caves to thatched huts. Only recently have we begun living mostly in modern buildings which exclude bats. With such long association, one might logically expect bats and people to have co-evolved unusual resistance to each other’s pathogens, a possibility that hasn’t been investigated.
Those attempting to scare us can’t explain how millions of people still hunt and eat bats every year without documented harm or how colonies of hundreds of thousands of bats that live in cities from Africa to America continue to have an impeccable safety record. It is even more difficult to explain how hundreds of bat researchers like me have survived close, career-long association with bats on every continent where they occur, often surrounded by millions at a time in caves, without a single one of us contracting one of these so-called “emerging diseases.” Like veterinarians, we are vaccinated against rabies to protect against defensive bites from animals we handle, but that has been our only protection.
Put in perspective, mortality from our much beloved dogs dwarfs any associated with bats (http://www.who.int/mediacentre/factsheets/fs373/en/). However most of us have had sufficient experience to understand that we are unlikely to be harmed by a dog, and we’d be irate if anyone distorted the facts about dogs as is done for bats.
As documented in Juan Enriquez and Steve Gullans’ new book, Evolving Ourselves (Penguin Group/Random House, 2015), our current understanding of viruses is miniscule. More than 99 percent of viruses remain undiscovered by scientists, and despite our inordinate fears, most are likely benign or even essential to our very survival. Failure to understand the beneficial ones may one day be our undoing. Yet as Enriquez and Gullans point out, “it is hard to get grants to study the nice viruses.” It is far easier to scare us into funding studies of the bad ones, and given the already widespread superstitious fear of bats and the unknown it isn’t surprising that those who profit from our fears love to pick on bat/virus combinations!
When even a few new viruses are discovered in bats they are typically announced as though bats are therefore uniquely dangerous. Lots of new viruses can be found wherever we look. Enriquez and Gullans cite a 2013 study in which 478 relatively abundant viruses were discovered in a single human being, most of them new to science.
It is easy to become prematurely frightened when we are told that a newly discovered virus from a bat is related to deadly ones like SARS and Ebola. However, given the infancy of our knowledge of virus taxonomy, such claims can be highly misleading. All life is related to some extent. We don’t confuse ourselves with chimpanzees just because our genomes are 96 percent identical. And we don’t even know that viral relationships are always bad. Some may even help convey resistance to those we fear.
Most viruses are likely benign, and many may be essential to our very survival. Unfortunately it is far easier to obtain grants hypothesizing already feared and misunderstood animals like bats as potentially dangerous harbingers of rare, but scary viruses like SARS and Ebola. And these are made even more sinister by referring to them as “emerging pathogens,” though available evidence suggests they’ve been here for a very long time, simply unnoticed due to being rare and limited to remote areas.
Recent speculation by public health virologists has netted millions of dollars in grants to search for deadly viruses in bats, and given that viruses are exceedingly abundant in all living creatures, they’ve been easy to find. However, the same premature speculation that sells media readership and gains big research grants today, may also damage the credibility of a whole generation of much needed public health virologists. Diverted funds are urgently needed to fight far more serious, largely preventable killers like cancer (http://www.who.int/mediacentre/factsheets/fs297/en/) and childhood obesity (http://www.who.int/features/factfiles/obesity/en/).
For me, well documented experience trumps speculation. It’s time for the Wildlife Society, as a much admired, science-based guardian of wildlife, to take a stand in defense of far too carelessly maligned bats, and I would be happy to help.
I do recognize that Kobilinsky warns that bats are valuable and shouldn’t be killed. However, as one who has engaged in extensive world travel on behalf of bats for more than 55 years, I have repeatedly met people who have exterminated large bat colonies due to unfounded fear of disease. And no group of mammals is more uniformly beneficial nor persecuted and endangered than the flying foxes, represented in Kobilinsky’s story by an exceptionally sinister photo, which itself will counter a thousand words.
On seeing scary speculation, you can be of great assistance to bats by simply letting editors know you do not approve. Here are some talking points that may be useful in setting the record straight.
Bat Disease Counterpoints
Merlin Tuttle1, Luis Viquez-R2, Bernal Rodriguez-Herrera3, Rodrigo Medellin2
Viral taxonomy is in its infancy. Of the millions of viruses believed to exist, only a few thousand have been identified and described. New ones can be found wherever they are looked for, even on our own bodies. In fact it has been estimated that a single teaspoon of seawater likely contains a million viruses (Bergh et al. 1989; Suttle 2005). Many are benign or beneficial, probably essential to the very survival of life on earth. On the other hand, bats suffer from an unfounded, seriously bad reputation. Not only are bats essential for many ecological processes and for various aspects of human well-being, they have also not been proven to be the maligned carriers of as many diseases as recent articles have implied. The points below will provide the basis for a better understanding of bats and the infectious diseases they have been accused of spreading:
We are currently finding more viruses in bats because millions of dollars are being spent disproportionally looking for them in bats. Though much has been said about coronaviruses being discovered in bats worldwide, these often benign entities are also widely distributed in other animals, from birds to whales. Furthermore, contrary to repeated assertions, Olival and associates (2012) demonstrated that bats host only 4.5 percent of known Emerging Infectious Diseases (EIDs). Rodents, ungulates, primates and even horses hosted more human EIDs than bats.
Available evidence indicates that “emerging” viruses are not new. They have been here for millions of years, but are only now being discovered. Describing them as EIDs simply adds an unnecessary level of fear. Their diversity is high in bats because 20 percent of the world’s mammals are bats, and because they are the most ecologically diverse of all mammals. These viruses have long, co-evolved histories of reliance on specific host species or groups, reducing the probability of spillover to humans.
Much of what has been implied simply cannot be justified by current knowledge. There is no scientific basis for claims that “hoards of deadly diseases lurking in bats,” are ready to spill over to humans. There is also no evidence that humans are living in closer association with bats today than in the past. Bat literature contains numerous examples of major decline of bats, and modern humans increasingly live in homes that are less suitable for bat colonization. Reports that newly discovered viruses are closely related to others that are known to be human pathogens seem meaningless when we consider both the infancy of viral knowledge and the fact that compared nucleotide for nucleotide, the human genome differs from that of chimpanzees by only 1.23 percent. We may be closer relatives to chimpanzees than some of these so-called “closely related” viruses are to each other. We also do not yet know that some of these bat-associated viruses are not weak varieties that could help convey immunity to more virulent versions. Finally, all 1,300 bat species are frequently discussed as though they were one apparently universal species, implying that rare, but scary viruses from some of earth’s most remote regions might be found in anyone’s back yard.
Empty warnings of potentially devastating pathogen outbreaks aside, bats have an outstanding safety record. Throughout the Old World tropics, where the most feared pathogens reside, many thousands of humans hunt and eat bats, and extract guano from bat caves. While these are all likely unsustainable practices, they are not triggering any of the pandemics now hypothesized. This is additionally true for the thousands of bat researchers who have handled and closely observed bats over decades of time before so-called EIDs were even discovered.
It is appropriate to study potential pathogens and to warn people not to handle unfamiliar animals, but there appears to be no justification for singling out bats as especially dangerous while ignoring the fact that our own pet dogs account for more human mortality annually than EIDs have in all recorded history.
Bergh, Ø., Børsheim, K.Y., Bratbak., G., Heldal, M. 1989. High abundance of viruses found in aquatic environments. Nature 340:467-468
Suttle, C.A. 2005. Viruses in the sea. Nature 437:356-361.
Olival, K.J., J.H. Epstein, L.F. Wang and H.E. Field. 2012. Are bats exceptional viral reservoirs? Pp. 195-212 in New Directions in Conservation Medicine: Applied cases of ecological health. Oxford Univ. Press, USA, Oxford, ISBN 9780199909056.
University of Texas
Institute of Ecology, UNAM
University of Costa Rica