Ebola: Bats Prematurely Blamed

Ebola: Bats Prematurely Blamed
By Merlin Tuttle
1/14/16

If public health concerns were based on actual threats to human mortality, diseases speculated to be spread by bats would take a distant back seat. Even our beloved dogs are many times more dangerous than bats (1). Real killers, like consumption of over processed and contaminated foods dwarf any risks associated with animals (2).

Yet we squander millions of scarce public health dollars on witch hunts for rare diseases in bats, when those funds could save far more human lives if spent on reducing already proven killers such as obesity and environmental toxicants linked to escalating rates of cancer, heart disease, dementia and diabetes.

An adult male straw-colored fruit bat (Eidolon helvum), the species most often blamed for Ebola.

In recent years speculation linking scary diseases to bats has gained unprecedented media headlines and grants.

Discoveries of dozens of new viruses in bats have been announced as though they were major breakthroughs in human disease prevention (3). By comparison a recent study discovered hundreds of previously undescribed viruses in a single human (4). Given our minuscule knowledge of viruses, new ones can be found wherever we look. And since all life on earth is related at some level, it’s easy to claim scary sounding relationships that may be irrelevant or even beneficial to public health (5).

For most of human history we shared caves, then thatched huts and log cabins with bats. Only in recent decades have humans begun living in buildings that exclude bats. So it stands to reason that we should have evolved extraordinary resistance to each other’s diseases. And that appears to be the case.

While media headlines scream of bats as dangerous reservoirs for a wide variety of diseases (6), I and hundreds of other bat researchers remain in good health, despite countless hours of close contact, often surrounded by thousands or even millions of bats in caves. Like veterinarians we are vaccinated against rabies because we are sometimes bitten in self-defense by the animals we handle. However for people who simply don’t handle bats, the odds of contracting any bat-borne disease are close to zero.

Hunters kill millions of bats annually for human consumption throughout the Old World tropics. Yet no resulting disease epidemics have been documented from such unsustainable use.

Those wishing to scare us about bats are ignoring an incredible safety record. Throughout the Old World tropics, where the most feared pathogens reside, many thousands of people hunt and eat bats each year, and others work long hours extracting bat guano for fertilizer from their caves. Yet there is still no proof that the “potentially devastating pathogen outbreaks” we’ve been warned about have ever been caused by bats.

The search for an Ebola reservoir provides an enlightening example of how a race for lucrative, grant- getting headlines can bias science, harm public health and destroy valuable bat populations. Colonial bats are by far the easiest mammals to quickly sample in large numbers, making them tempting targets for quickly publishable virus research. However, after spending millions of dollars disproportionately testing large numbers of bats, there is still no scientifically credible evidence linking bats to Ebola (7).

Despite failure to find the virus in any bat species examined, during the summer of 2014 media headlines worldwide claimed that the two-year-old toddler, considered to be the “index case,” likely got Ebola from a straw-colored fruit bat (8). No one has ever been able to explain how this child may have contacted a three-foot-wingspan bat that never enters buildings without anyone knowing it, nor how thousands of Africans hunt and eat these bats without documented harm. Straw-colored fruit bats were simply believed guilty!

Some of these guano miners photographed lived in excellent health well into their eighties and nineties despite spending huge amounts of time with the bats in Rakang Cave in Thailand.
Thousands of people spend most of their lives in caves extracting bat guano for fertilizer with no disease outbreaks known to have been associated.

By December of 2014 researchers concluded that the same child likely was infected by playing near a free-tailed bat roost, again with no credible substantiation. Few, if any animals other than bats were tested and no Ebola virus was found. Nevertheless the bats were burned and their roost permanently destroyed (9).

In December of 2015 researchers reported that the straw-colored fruit bats, which had been blamed for years, were so highly resistant to Ebola infection that they were an unlikely reservoir. They further noted that “infectious Ebola viruses have never been recovered from bats” (7).

Due to exaggerated media speculation, supported by woefully biased and inadequate science prematurely reported, bats are now erroneously “known” as the source of Ebola, the most recent discovery having received minimal coverage. Simply saying that bats are beneficial can’t save them from those who increasingly fear and kill them. It’s time to end the bat witch hunt and put public health dollars back where they belong.

Read more about Ebola…

 

Straw-colored fruit bats roosting in Kenya.

 

References

  1. Banyard, A.C. et al. 2013. Control and prevention of canine rabies: The need for building laboratory-based surveillance capacity. Antiviral Research, 98(3):357-364.
  2. Montiero, C.A. et al. 2011. Increasing consumption of ultra-processed foods and likely impact on human health: evidence from Brazil. Public Health Nutrition, 14(1):5-13. CDC. 2015. Foodborne germs and illnesses. http://www.cdc.gov/foodsafety/foodborne-germs.html.
  3. For example. Gilbert, N. 2011. West Africans at risk of bat epidemic: Ecologists hope to avert public health disaster without a cull. Nature doi:10.1038/news.2011.545. http://www.nature.com/news/2011/220911/full/news.2011.545.html. Anonymous. 2012. New virus to fear? Bat flu could affect humans. http://www.nydailynews.com/life-style/health/bat-flu-pose-risk-humans-evidence-virus-proving-not-animal-flu-discovered-article-1.1030409. Anonymous. 2012. Bats may carry up to 66 new species of virus linked to measles and mumps, scientists say. http://www.nature.com/ncomms/journal/v3/n4/full/ncomms1796.html.
  4. Minot, S. et al. 2013. Rapid evolution of the human gut virome. Proc. National Acad. Sci. USA, 110(30):12450-55.
  5. Enriquez, J. and S. Gullans. 2015. Evolving Ourselves (see Viruses: The Roadrunners of Evolution, pp 99-103). Random House, Penguin Group.
  6. For example. Arnold, C. 2014. Contagion: Hordes of deadly diseases are lurking in bats and sometimes jumping to people. Can we prevent a major pandemic, asks Carrie Arnold. NewScientist, 8 Feb.:45-50. Grant, B. 2014. Lurking in the shadows: Bats harbor diverse pathogens, including Ebola, Marburg, SARS, and MERS viruses. The Scientist, http://www.the-scientist.com/?articles.view/articleNo/41537/ title/Lurking-in-the-shadows/#articleCommentForm.
  7. Ng, M. et al. 2015. Filovirus receptor NPC1 contributes to species-specific patterns of ebolavirus susceptibility in bats. http://elifesciences.org/content/4/e11785.  Aizenman, N. 2016. Five mysteries about Ebola: From bats to eyeballs to blood. National Public Radio, January 14. http://www.npr.org/sections/goatsandsoda/2016/01/14/462964602/five-mysteries-about-ebola-from-bats-to-eyeballs-to-blood.
  8. For example. Lewis, K. and J. van dere Kleut. 2014. Ebola outbreak traced back to toddler and fruit bat. Health,http://wjla.com/news/health/nih-scientist-ebola-outbreak-traced-back-to-single-animal-bite-to-single-human–106590. Vidal, J. 2014. Ebola outbreak traced to toddler’s contact with infected fruit bat. The New Zealand Herald.http://www.nzherald.co.nz/world/news/article.cfm?c_id=2&objectid=11313653.
  9. Saez, A.M. et al. 2014. Investigating the zoonotic origin of the West African Ebola epidemic. EMBO Molecular Medicine, 7 (1):17-23.

 

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5 thoughts on “Ebola: Bats Prematurely Blamed

  1. My son is writing a speech about bats. This is the first article we’ve found questioning the premise that bats carry more infectious diseases than any other animal. Yet they don’t even show up on the Gates’ foundation’s graphic of animals who kill humans. Your article throws doubt about the charge that bats carry and transmit ebola. What about Marburg, Nipa, Hendra and Sars? Is there any proof they carry these diseases? Is there any evidence they transmit to humans? If so, why are bats omitted from the Gates graphic?

    1. There is reasonably clear evidence for flying fox transmission of Hendra and Nipa to horses and pigs respectively. Hendra has reached humans only through horses, but Nipa also on rare occasion appears to have gone directly to humans via fecal contamination of open palm juice containers that attract hungry flying foxes. I remain unconvinced on the data supporting bats as the culprits behind SARS. There is also some evidence but no proof for SARS. The case for bats being important reservoirs for Ebola is based mostly on bad science and remains far from credible. Bats are one of a wide variety of well documented reservoirs for rabies.

      To put this all in perspective all the so-called emerging diseases (Hendra, Nipa, SARS, Marburg and Ebola) are among the rarest sources of human mortality. Rabies, not considered to be “emergent,” comes mostly from dogs. Worldwide 99% of human rabies cases are transmitted by dogs. In fact, though we’ve heard a great deal about the recent Ebola outbreak killing some 11,000 people over a two-year period, in that same period an estimated 120,000 people died of dog-transmitted rabies, yet somehow rabies warnings typically focus on bats, while rabies from dogs is largely ignored by media who understand that dogs are much loved. Hendra, Nipa, SARS, Marburg and Ebola combined have killed fewer than 15,000 humans over the several decades of their known existence.

      Within the next several days, we’ll be releasing a book review blog that will provide further clarification. Thanks for your interest. -Merlin Tuttle

      1. Thank you, that is very clarifying. Most internet sources, including bat advocacy groups, leave the impression that bats definitively carry all these diseases and leave one with the assumption that they transmit them to humans. There is even a video blaming human incursion into bat territory, eating of bats and guano collecting for transmission of these diseases to humans.

        Aren’t licensing laws that require vaccination in the developed world the reason we don’t hear much about dogs as transmitters of rabies? Of course, rabies can be spread by all kinds of small predators, so the focus on bats is misplaced regardless.

        1. Yes, most developed countries now require dog vaccination against rabies. Nevertheless warning people as though bat are far more dangerous than dogs remains irresponsible. In the latest year of reporting for the U.S., dog attacks killed more than 40 people, while none died of any cause related to bats. Going way back averaging human mortality caused by dogs versus bats, dog attacks kill more than 20 compared to 1.5 per year who die from bat rabies. We are warned that most human rabies in America comes from bats, but health representatives seldom admit that they are referring to a number that is close to zero! Those who do the most to frighten us are also those who profit most from our fear (exterminators, sellers of over-priced vaccine, those depending on inflated rabies budgets or grants). CDC’s claiming people can be bitten without knowing it has dramatically increased vaccine sales. Canada, who usually follows CDC guidelines, conducted its own investigation found such advice counterproductive and opted not to follow CDC recommendations involving bats. To understand the extent of exaggerated advice on rabies (and often other diseases as well), one only has to follow the money trail. Merlin Tuttle

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