Health care | Infectious Diseases | Patient care | Policy

Required Reading: Bat-Related Human Rabies

Posted by Paul Sax on April 17th, 2008

A group of researchers in Canada have done infectious diseases experts a big favor — they’ve summarized a staggering amount of useful data on bat-related cases of human rabies in a paper just published in Clinical Infectious Diseases.

(Note to non-ID specialists: infectious diseases doctors spend a lot of time answering questions about rabies in general and the vaccine and bats in particular. I’m fairly certain that being a bat expert was not listed in my job description when I signed up for this field, but maybe that’s because there was no job description.)

This paper should be required reading for all ID docs. Whether the news is reassuring or terrifying will depend on whether you’re a glass half-full or half-empty type of person. Here are some of the key points:

  • Bat-related human rabies is incredibly rare: Since 1950, there have been 56 cases of bat-variant rabies in the United States and Canada, for an average annual incidence of just under one case per year. In several years, there were no cases; in the worst year on record (2001), there were five cases.
  • The overall incidence rate of bat rabies in humans is 3.9 cases per billion person-years. Your odds are better — much better – of winning a huge payout in the lottery, but you don’t need to be a statistician to figure out that neither one of these events (bat rabies or lottery bonanza) is particularly likely.
  • Of the 56 people with bat-variant rabies, 31 (or 55%) had direct contact with a bat (i.e., they were either bitten by one or touched by one), and 6 others (11%) found bats in their home (including 2 in the room where they slept). And here’s the creepy part: 19 (34%) reported no bat exposure whatsoever.
  • Many states have never had a case of bat-related rabies, including Massachusetts (hooray!) and large chunks of the Midwest and Southwest, including both Dakotas, Nebraska, Kansas, Wyoming, Colorado, Arizona, Utah, and others. Among remaining states, most have had 1 case, but California and Texas have not been so lucky, leading the way with 8 and 7 cases, respectively.

The paper has other fascinating non-epidemiologic information for ID docs who may want to brush up on their bat facts, including that the behavior of rabid bats “is not always dramatically altered.” Some rabid bats “may simply become disoriented, lose their flying ability, and appear clumsy.” (Who knew?) Bat bites, furthermore, leave puncture marks <1 mm in diameter, and bat scratches are usually <1 cm long — hence explaining those 19 cases with “no” bat exposure. In all likelihood, they just didn’t notice the small bite or scratch.

All of which leads to the key question of how we can get from a small number of human rabies cases per year down to zero. One possible solution, of course, is to administer the rabies vaccine to anyone with even potential (as opposed to reported) bat exposure. Indeed, in 1999 (and just updated here), the Advisory Committee on Immunization Practices from the CDC recommended administration of rabies vaccine to:

“…persons who were in the same room as the bat and who might be unaware that a bite or direct contact had occurred (e.g., a sleeping person awakens to find a bat in the room or an adult witnesses a bat in the room with a previously unattended child, mentally disabled person, or intoxicated person).”

This has always struck me as a somewhat bizarre recommendation given the inappreciable nature of bat bites and scratches — why does seeing a bat flying around your child’s room mean that this same bat hasn’t flown around your room too? And if you awake to find a bat flying around your room, but your significant other sleeps through the bat visit, should you get the vaccine but your soundly sleeping partner skip it? These are rhetorical questions.

My opinion: some, if not most, of our prevention strategies for bat rabies are really about trying to do something rather than nothing — a completely understandable human impulse given that the survival rate for human rabies is practically zero. After all, no one wants to be the ID doctor who advised against the rabies vaccine when the first-ever case of bat-related human rabies happens in Illinois (or Massachusetts, for that matter). But I don’t think we should be fooling ourselves that recommending rabies vaccine for these possible bat exposures is going to have much of an impact on the rate of bat rabies in humans, which is already reassuringly low …

… or is it? (Key dramatic music here.)



13 Comments »

1

Name: Michael Koski

Submitted on April 17, 2008 @ 10:17 am

Great article! I am hoping you will let me post it as a resource on my website? I won’t make any changes, and will credit you, and link back.

I am a bat exclusion professional. Everyday I run into people with various levels of fear regarding bats. All my employees get the pre rabies vaccination - then follow up shots if/when we get bit.

There is one additional thing that can be done if you have contact with a bat (or wake up with it in the room). As I explain in my article “What to do with a Bat in the House” (http://www.GetBatsOut.com/batinhouse.htm) - the bat itself can be tested for rabies. This often saves hundreds or even a couple thousand dollars for family rabies shots, and provides considerable peace of mind.

Michael

2

Name: Paul Sax

Submitted on April 17, 2008 @ 1:04 pm

>>I am hoping you will let me post it as a resource on my website?

That would be great, thank you.

Thanks also for the reminder about getting the bat tested — can be very reassuring and save lots of time/$.

Just have to make sure the bat has health insurance before bringing it in.

(That was a joke.)

3

Name: Joe

Submitted on April 17, 2008 @ 4:21 pm

Vote for clinton…that bat will have health insurance whether it wants it or not!

Great article.

4

Name: Kaz mawji

Submitted on May 2, 2008 @ 3:24 pm

Does this artcle apply to bats in NON-european countries also? Do bats go for pets too?

5

Name: Paul Sax

Submitted on May 3, 2008 @ 7:47 am

This is an paper about bat-related human rabies in the USA/Canada.

As for whether they “go for pets”, not sure I understand your question … do you mean do people have bats for pets? Or do bats attack pets (such as dogs and cats) too? Regardless, I think you’ve surpassed my bat knowledge with either question!

6

Name: c.

Submitted on May 4, 2008 @ 9:35 am

thanks dr. sax, this was a very interesting article. thanks to mr. koski, too, for mentioning the possibility to test the bat.

i think the following questions is somewhat related to Kaz mawji’s question: does this article apply to all bats in north america or only to blood sucking bats? (are there any of those in the US??)

i’m trying to relate the key points of your article to medical practice in central europe.

c.
(medstudent)
austria, europe

7

Name: Rich

Submitted on September 20, 2008 @ 10:56 am

I plucked a dark leaf out of the radiator of my car — only to discover that it was, in fact, a smashed bat.
Aside from the wriggling horrors, I have been concerned about the possibility of exposure to rabies. How quickly after contact would symptoms develop (and what would they be?).

Would you recommend shrugging it off? Thoughts?

Thanks very much…..

Rich

8

Name: Deborah Watkins

Submitted on February 10, 2009 @ 4:16 pm

Excellent article, Dr Sacks! Bat lovers everywhere thank you!

I am a trained bat rehabilitator that lives in Texas. I am vaccinated, in case anyone is wondering. It is required for me to do what I do.

Rabies is a blood-borne disease. I can all but guarantee (being a statistician, I don’t GUARANTEE anything! ) that those people who contracted rabies were indeed BITEN by the animal that gave it to them.

And yes, if a bat would bite a human, it would bite your family pet. But this I know: bat are NOT agressive, even when rabid. If you were bitten (or your pet was), it is likely that you accidently trapped the bat somehow (rolled on it or it was trapped in blankets or the dog house). Bats will avoid contact with other animals with every effort they have (vampire bats excluded)!

As Dr Sacks explained, rabid bats get clumsy and disoriented (this is from the encephalitis that comes with the progression of rabies - they are in SEVERE pain) - but do not get agressive. And no, it does not have to be a vampire bat. (By the way, vampire bats are restricted almost exclusively to the far south regions of the northern hemisphere, and are EXTREMELY rare in the US (any we might find in the US were probably brought here - they did not come here on their own)).

As for the gentleman that found the “leaf” on his car. Unless you had an open wound and touched that to the bat’s mouth AND it was still moist… It is practically impossible that you have “been exposed”. I hope that helps.

NO ONE SHOULD EVER touch a bat with their bare hands. If you encounter one, please put on gloves and if you must attempt to catch it, do so with a towel - this protects the bat as well, and makes it less likely you will crush it. Better yet, get out of the area and call a Bath Rehabilitator immediately. If no one has touched the bat, there is no reason to KILL IT for testing.

Please see http://www.batworld.org to find a Bat Rehabilitator in your area.

Again, many thanks to Dr Sacks for this very comforting and informative article.

Bless you!
Deborah

9

Name: Paul Sax

Submitted on February 11, 2009 @ 5:10 pm

What a great comment. Thank you!

10

Name: Amy

Submitted on February 23, 2009 @ 12:12 am

based on the summaries of the articles, would you say it would be recommended to vaccinate a child who was accidentally scratched by a cat, if you found a dead and torn apart bat in the area the cat had been soon after the scratch happened? is it too farfetched to imagine that the cat could still have had live rabid material on its mouth or claws and then scratched it into the child? The first bat is gone - was not much left - but another dead bat was found a few days later (cat still in the area, not known if the cat killed this one) and was sent for testing. awaiting results. no way to know when the bat was killed; could have been right before the scratch or could have been the night before. the cat climbed up the child’s winter coat before the scratch. child is 8 and had no direct contact with the bat itself.

what do you think? thanks for the information and for your time!

11

Name: Amy

Submitted on February 23, 2009 @ 12:15 am

also- according to my local health dept. no bats tested have come back positive in my town in recent years, though there have been one or two in a town about an hour away.

12

Name: Paul Sax

Submitted on February 23, 2009 @ 5:08 pm

I’d say the risk is pretty darn low … one must always contact the local health dept for “formal” advice, glad you did this!

Paul

13

Name: Amy

Submitted on February 23, 2009 @ 5:40 pm

thanks for the feedback. :) the health dept. just plain does not think my daughter could have been exposed this way. local walk-in clinic told me they probably wouldn’t do the series based on the curcumstances, but to see what the 2nd bat revealed. Pediatrician said the same, and that even though it was VERY unlikely, I would pretty much be “stuck” giving her the rabies series if it came back positive. still waiting and worrying, but a bit less. thanks again!

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