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Bat Rabies Risk in Perspective

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Bat Rabies Risk in Perspective
By Merlin Tuttle

 

If public health warnings were based on actual risk, rabies from bats would be near the bottom of the list. On a global scale 99 percent of human rabies comes from dogs, killing more than 60,000 humans annually.1 In contrast, transmission from bats is exceedingly rare. Colonial species, the ones typically found in buildings, rarely become aggressive even when rabid2 and normally bite only in self-defense if handled.3 Even in Latin America, home of the common vampire (Desmodus rotundus), rabies transmission from bats to people is uncommon, normally restricted to people sleeping in open areas, unprotected by mosquito nets.2

 

The United States and Canada average just one or two cases per year,4,5,6 and it is unlikely that additional preventative efforts could further reduce such an already rare event. States with so-called “passive” rabies prevention programs, where they simply warn of animal bite risks and vaccinate pets and people reporting bites, suffer no higher rabies mortality than states with “active” surveillance and prevention programs supported by large budgets.7

 

The 1.5 million Brazilian free-tailed bats living in the center of Austin, Texas provide an excellent example how bats and humans can safely coexist at great mutual benefit when conservationists and public health officials cooperate in providing a balanced message. By simply posting small signs warning visitors not to handle bats, millions have observed the spectacular bat emergences close-up over the past 35 years without a single individual being attacked or contracting any disease. The bats consume tons of insects nightly and attract millions of tourist dollars each summer. 8

 

Millions of tourists have watched free-tailed bat emergences from the Congress Avenue Bridge in Austin, Texas over the past 35 years without harm. Small signs simply warn the visitors not to handle the bats.
 
Over the last century, human rabies has become rare in developed countries, mostly due to domestic animal vaccination. In the United States as recently as 1955 domestic animals, especially dogs, accounted for most rabies cases. Due to the success of dog vaccination, canine rabies declined from 47 percent in 1955 to less than two percent by 1994. As domestic animal transmission sharply declined, the number of cases caused by wildlife remained low, but attracted far more public health attention despite its continued rarity.9,10      
           
In 1995 the U.S. Center for Disease Control and Prevention (CDC) began to advocate a new policy, emphasizing that 34 percent of bat-transmitted rabies cases had “no history of bat exposure whatsoever” and that bat bites are difficult to detect.5 By 1996 the CDC Advisory Committee on Immunization Practices was advising consideration of post-exposure prophylaxis for “persons potentially exposed to bats even where a history of physical contact cannot be elicited,” unless prompt diagnosis excluded rabies.11-13

This policy was based on the hypothesis that undetected bat bites are a significant source of the few remaining cases of human rabies. However, justification was based on highly unreliable reporting of transmission events. Most human rabies cases had been diagnosed only after the victim was incoherent or dead,14 and often were listed as having no bite history, based solely on a lack of coherent testimony from the victim.15 Furthermore in recent decades, though monoclonal antibody tests have attributed each human case to a rabies variant associated with a specific mammal species, each variant can be transmitted by a variety of other mammals, not just the one from which it originated.16 For example a human could contract a bat rabies variant from a domestic cat.

 

When I reviewed a list of human rabies records for the U.S. (from 1985 to 2014), 17 this was an obvious problem, one that is well-recognized. 18 There was no evidence that “no reported bite histories” differed among rabies cases ascribed to be of bat versus dog or wild carnivore origin. The only case listed as being from a raccoon variant had “No known animal exposure,” 17 and the single case traced to a skunk variant also remains a mystery.19 It appears that the lack of a bite history has been inappropriately emphasized in bats.14

 

In a much publicized case in New York, Dr. Stephen Frantz, who officially investigated the case for the New York State Department of Health, discovered from family members that the brother of an 11-year-old, animal loving girl with a postmortem diagnosis of bat rabies, had found and caged a grounded bat in her home.20Because she was diagnosed postmortem and could not be questioned, CDC’s Morbidity and Mortality Reports stated, “She had no known history of contact with a bat.”21 Direct questioning likely would have revealed  handling and a bite.

 

A further complicating factor involves the sometimes extended latency between the time of a bite and the onset of symptoms, which can occur years later, long after even a coherent person might forget an exposure.22

 

The observed inconsistency of data interpretation is difficult to justify. Even websites that provide otherwise accurate and valuable information too often greatly exaggerate the idea of undetected bites from bats. For example, the New York State Department of Health claims that “All but one of the people who died of bat rabies in the U.S. were unaware of a bat bite.”23 It is tempting to wonder if such unjustified statements may be designed to promote lucrative post-exposure rabies prophylaxis.

 

Researchers meeting at the 29th Annual North American Symposium on Bat Research, on October 30, 1999, passed a resolution stating that they “find no credible support for the hypothesis that undetected bites by bats are a significant factor in transmitting rabies to humans.” The resolution further stated that bats are seldom aggressive and that humans typically feel and recognize bat bites, while noting that any animal bite should receive immediate medical evaluation.15,24

 

CDC’s over emphasis on the difficulty of bite detection has left health professionals little alternative but to recommend vaccination for anyone reporting having been near a bat. In the first five years following acceptance of CDC’s bat policy, the State of New York’s post-exposure vaccination rate due to bat-human encounters, mostly “fly-bys,” steadily rose from 131 in 1995 to 1,755 by 2000, an increase of more than a thousand percent!25 In that period, the cost for a post-exposure treatment averaged approximately $2,000 in the U.S. By 2002 the average cost had risen to $3,688, 18jumping to commonly exceed $10,000 by 2013.26

 

The following example demonstrates how the policy is often carried out. In 2013, a New York bicyclist ran into a flying bat at dusk. The bat simply bounced off his chest.  He removed his shirt, searched in front of a lamp, and found no evidence of a bite or scratch. However, faced with health department warnings of potential death, he opted for post-exposure rabies treatment. Vaccine, immunoglobulin and varied hospital and doctor bills totaled more than $16,600.27 One can only imagine how such unnecessary costs inflate insurance rates.

 

As the CDC’s vague policy is currently administered, prophylaxis is frequently advised simply because a bat has flown by without known contact. In 1998, at Camp Dudley, a boy’s camp that had been in operation for close to a century without a single child contracting rabies, an emergency was declared when the local health department heard that bats sometimes flew through open cabin windows. Fifty-two boys were vaccinated at a cost of roughly $100,000.7 At today’s prices, the cost for a similar incident could exceed $832,000, though the practice continues.

 

Dr. Stuart Updike, a medical school professor volunteering his services at Camp Dudley at the time of the incident, was outraged at such misappropriation of public health funds, as were many other professionals. They wanted to know how such expenditures could be justified.7

 

Independent studies reached the same conclusion. If implemented in their respective areas, the CDC bat-rabies policy could lead to outrageous misappropriation of public health funds with minimal impact in saving human lives.4The State of Oregon calculated that CDC’s bat rabies policy (at 1998 prices) would cost $2,400,000 annually to prevent just one human case every 75 years.28 A similar analysis in Canada concluded that following CDC’s policy would cost $2 billion to prevent a single case every 84 years.4 These studies agree that, though human exposure to bats is common, bat-associated rabies transmission is extremely rare. Canada’s National Advisory Committee on Immunization, based on these findings, opted not to follow CDC’s recommended bat policy. They no longer advise vaccination when there has been no direct contact.4

 

Those who profit from public fear often report that most human rabies in America comes from bats while conveniently omitting mention of its extreme rarity. Unfortunately, risks from bats “have been grossly magnified and carried far out of proper perspective by sensation-seeking reporting, designed to prey on deep-rooted cultural phobias” which continue to fuel public fear of bats.10

 

The CDC’s policy, though lucrative for the rabies and pest control industries,7 results in major misappropriation of public health dollars and causes greatly exaggerated fear and intolerance of these generally harmless and highly beneficial animals.8 Dr. Brendon Brady, Chairman of the Board for Finger Lakes Community Care in New York commented, “I am outraged that the Health Department policy is wasting millions to prevent the rarest disease in New York.”29

 

Given the consequences of a wrong decision, it is appropriate to take each possible exposure to rabies extremely seriously, so I sympathize with public health professionals forced to make potentially life and death decisions in an area in which most have little or no experience. However, simply being near or even touching a rabid animal is not considered to be an exposure, and the CDC should make this clearer regarding bats. An exposure requires a bite or contact between an open wound or mucous membrane with saliva or nervous tissue from an infected animal.30,31

 

Though rabies is relatively rare in humans, the disease is almost invariably fatal once diagnosable symptoms appear. It can be effectively prevented through prompt vaccination following an exposure (as well as through pre-exposure vaccination). All who risk bites from handling wild animals should obtain pre-exposure vaccination and have titers checked at two-year intervals.4

 

Unprovoked bites from bats simply flying by are so rare that in more than 55 years of studying bats worldwide, often surrounded by thousands at a time in caves, I still have not been able to personally document such an event. Since bats normally avoid humans, and because aggressive behavior is so rare in bats, I’d recommend having any bat that lands on a human be captured and tested for rabies.

 

The vast majority of bats are not rabid, and most bats found flying around indoors are merely lost youngsters looking for a way out. However, any bat found in an unusual location, especially one that is grounded and easily approached, is more likely than others to be sick. On average about five percent of such bats test positive for rabies, and the proportion doubles for those that initiate direct contact with a person.4

 

An animal with the “furious” form of rabies doesn’t seem likely to just take a quick, painless nip and flee. No policy can be both cost-effective and 100 percent foolproof. However, based on personal experience, I support the Canadian policy which “recommends vaccination when there is direct contact and a bite, scratch, or mucous membrane exposure cannot be ruled out.” It further advises that post-exposure prophylaxis “should depend on whether direct contact with the bat occurred and not on the rabies status of the bat.”4

 

The following recommendations are prudent. In case of a bite or other suspected exposure. Immediately: 1) capture the animal for rabies testing; 2) wash the wound or area of contact with soap and water or alcohol; and 3) seek medical evaluation. A bat in your home is generally catchable. If it is flying around don’t flee and later wonder where it hid.  Watch it till it lands. Then approach slowly to avoid frightening it back into flight. Trap it beneath an old coffee can or similar container in one hand while holding a piece of cardboard in the other. Gently clamp the container over the bat, and slide the cardboard behind, trapping it inside.3 If it hasn’t been in contact with anyone (or an unvaccinated pet), simply release it outdoors. If there has been a possible rabies exposure call your local animal control or health department for instructions on having it tested. Testing a suspect animal is far less costly than post-exposure prophylaxis!

 

I do understand that those who love animals may not want to see a bat killed. But before allowing one that may have infected a person with rabies to go free, consider the alternatives. Someone could die, not to mention the fact that associated publicity could get hundreds or even thousands of other bats killed. If you truly love bats, don’t risk becoming a statistic that can be used against them.

 

Note: For advice on medical issues, please consult your family physician. Merlin Tuttle’s Bat Conservation website or Bat Conservation and Management's website does not contain medical advice and is not intended as a substitute for such information.

 

 

References

 

  1. Jackson, A.C. 2014. Rabies: Neurology. Pp 235-250 in Neglected Tropical Diseases and Conditions of the Nervous System. (M. Bentivoglio, E.A. Cavalheiro, K. Kristensson and N.B. Patel, eds.), Springer, New York and London, 391 pp.
  1. Kuzmin, I.V. and C.E. Rupprecht. 2015. Bat lyssaviruses. Pp 47-96 in Bats and viruses: A new frontier of emerging infectious diseases (L.F. Wang and C. Cowled, eds.), J. Wiley & Sons, New Jersey, 368 pp.
  1. Tuttle, M.D. 2005. America’s Neighborhood bats (2nd rev. ed.). Univ. Texas Press, Austin, 98 pp.
  2. National Advisory Committee on Immunization. 2009. Canada Communicable Disease Report, Volume 35:ASC-7, 28 pp.
  3. De Serres, G. F. Dallaire and M. Cote. 2008. Bat rabies in the United States and Canada from 1950 through 2007: Human cases with and without bat contact. Clin. Infect. Dis., 46(9):1329-1337.
  4. Monroe, B.P., P. Yager, J. Blanton, M.G. Birhane, A. Wadhwa, L. Oreiari, B. Petersen and R. Wallace. 2016. Rabies surveillance in the United States during 2014. JAVMA, 248(97):777-788.
  5. Tuttle, M.D. 1999. Rabies economics vs. public safety. Bats, 17(2):3-7.
  6. Tuttle, M.D.2013. Threats to bats and educational challenges. Pp 363-391 in Bat evolution, ecology and conservation. (R.A. Adams and S.C. Petersen, eds.). Springer, New York, Heidelberg Dordrecht, London, 547 pp.
  7. Cockrum, E.L. 1997. Rabies, Lyme Disease and Hanta Virus. Fisher Books, Tucson, Arizona, 146 pp.
  8. Brass, D.A. 1994. Rabies in Bats: Natural history and public health implications. Livia Press, Ridgefield, Conn., 335 pp.
  9. Centers for Disease Control and Prevention (CDC). 1994. Human rabies, Alabama, Tennessee and Texas 1994. Morbidity and Mortality Weekly Report, 44(14):269-272.
  10. Centers for Disease Control and Prevention (CDC). 1995. Human rabies, Washington 1995. Morbidity and Mortality Weekly Report, 44(34):625-67.
  11. Fitzsimmons, T.D., W.J. Pape and R.E. Hoffman. 1996. Bat bites and human rabies prophylaxis, Colorado, 1977-1996. https://www.researchgate.net/publication/291110739_Bat_bites_and_ human_rabies_prophylaxis_Colorado_1977-1996.
  12. Centers for Disease Control and Prevention (CDC). 1991. Epidemiologic notes and reports human rabies—Texas, Arkansas, and Georgia, 1991. Morbidity and Mortality Weekly Report, 40(44):765-769.
  13. Olnhausen, L.R. and M.R. Gannon. 2004. An evaluation of bat rabies prevention in the United States, based on an analysis from Pennsylvania. Acta Chiroptologica, 6(1):163-168.
  14. Centers for Disease Control and Prevention (CDC). 2014. Human rabies—Missouri, 2014. Morbidity and Mortality Weekly Report, 65(10):255-256.
  15. Zoonosis Control Branch. Texas Department of State Health Services. 2015. Rabies in humans in the U.S.: 1950 – present. https://www.dshs.texas.gov/WorkArea/linkit.aspx?LinkIdentifier= CDC Centers for Disease Control and Prevention. 2011. Learning about bats and rabies.             http://www.cdc.gov/rabies/bats/education/22id&ItemID=8589998639.
  16. Dato. V.M., E.R. Campagnolo, J. Long and C.E. Rupprecht. 2016. A systematic review of human bat rabies virus variant cases: Evaluating unprotected physical contact with claws and teeth in support of accurate risk assessments. Plos One, http://dx.doi.org/10.1371/journal.pon.0159443.
  17. Centers for Disease Control and Prevention (CDC). 1988. Human rabies, California, 1987. Morbidity and Mortality Weekly Report, 37(19):305-308.
  18. Frantz, S. Personal Communication
  19. Centers for Disease Control and Prevention (CDC). 1993. Human rabies—New York, 1993. Morbidity and Mortality Weekly Report, 42(41):805-806.
  20. Shankar, S.K., A. Mahadevan, S.D. Sapico, M.S.G. Ghodkirekar, R.G.W. Pinto and S.N. Madhusudana. 2012. Ann. Indian Acad. Neurology,15(3):221-223.
  21. New York State Department of Health. https://www.health.ny.gov/diseases/communicable/ zoonoses/rabies/docs/bigbatbook.pdf.
  22. Griffiths, T.A. 2000. A resolution concerning bat bites and rabies. Bat Res. News, 41(1):1.
  23. Eidson, M, Y. Hagiwara, R.J. Rudd and L.A. McNutt. 2011. Bat rabies and human postexposure prophylaxis, New York, USA. CDC Emerging Inf. Dis. J., 17(12):Dec 2011.
  24. Blanton, J.D. and M.G. Stobierski. 2013. Rabies postexposure prophylaxis surveillance in the United States. Council of State and Territorial Epidemiologists Annual Conference, Conference Paper. https//www.researchgate.net/publication/267887379_Rabies Postexposure Prophylaxis_            Surveillance in the United States.
  25. Dempster, M. 2012. The costs of not dying from rabies. The Billfold, Nov. 2 issue, 5 pp.
  26. Cieslak, P.R., E.E. Debess, W.E. Keene and D.W. Fleming. Occult exposures to bats in Oregon: Implications for rabies post-exposure prophylaxis. International Conference on Emerging Infectious Diseases. Atlanta, Georgia, Volume 58 (Abstract).
  27. Tuttle, M.D. 2000. The media blitz that threatens bats. Bats, 18(3):5-8.
  28. CDC Centers for Disease Control and Prevention. 2011. When should I seek medical attention? http://www.cdc.gov/rabies/exposure/.
  29. CDC Centers for Disease Control and Prevention. 2011. What type of exposure occurred? http://www.cdc.gov/rabies/exposure/type.html .


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Article date 1/20/17 - Reprinted by Bat Conservation and Management with permission

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