Category Archives: animal attack

Komodo dragons: Myth vs Reality

The Komodo dragon is a creature that inspires fear and mysticism in many. It’s got all the characteristics of a good monster movie: only found on rare tropical islands, large, and possessing magical saliva that can kill. First identified by the west in 1910 by Dutch sailors, they reported the lizards could spit fire and reached 7m in length. In reality the lizard can only get up to 3m and can weigh 70kg, and none have been identified as either breathing or spitting fire.

Komodo dragon (Varanus komodoensis), Komodo National Park, Indonesia

This review comes after a zoo worker was bitten on the hand by a small Komodo dragon. She had transient hypotension, and a retained tooth on xray. This was not removed, and after loose approximation (Ed. note: never do this), she was discharged on antibiotics. Thankfully the tooth came out on its own, and she did not develop a deep space infection. After this case report, the authors decided to do a literature review, knowing that it would help them get published.

Many of us are taught in school that Komodo dragon saliva is a possibly venomous, potentially fatal concoction of particularly virulent bacteria, including E. Coli, Staphylococcus, Streptococcus, and Pasteurella. These bacteria live in the rotting flesh that they leave in their mouth. But what is that based on?

It turns out, not much. The “facts” we have in textbooks, zoos, and medical literature are based on one guy’s book written in 1981. While Walter Auffenberg was the Jane Goodall of Komodo dragons, moving to the island and studying them in their natural habitat, his results haven’t been widely reproducible. And, more importantly, komodos don’t carry rotting flesh in their mouth. They fastidiously clean their teeth and gums. Now, perhaps the water buffalo does die of sepsis after being bitten, but if it does, it’s because it runs into murky water with fresh wounds, and not from bacteria in the mouth of the lizard. So, the “bacteria as venom” concept is just as dead in the water as the buffaloes.

So what about the venom aspect? The author of that study (Fry) was able to identify glands in the lower jaw that could potentially be venom glands. Furthermore, the extract of those glands does in fact contain proteins that inhibit blood clotting similar to snake venom. However, there isn’t any evidence that the venom actually affects the prey or is secreted in any significant amount during bites. The teeth lack venom grooves present in every other venomous animal (including the shrew). On the plus side, the author did come up with the “grip, rip, and drip” model of lethality from komodos.

Then why do animals die after being bitten by a large, reptilian predator? For the same reasons they die after being bitten by any large animal. Direct trauma, blood loss, and hypovolemic shock (and by eating).

Our findings are also in accord with the view that the killing technique of V. komodoensis is broadly similar to that of some sharks and Smilodon fatalis (saber cat). Despite obvious anatomical differences, these unrelated predators kill or are thought to have killed (respectively) large prey by using relatively weak bite forces amplified by sharp teeth and postcranial input.

They have strong neck muscles and serrated teeth, so after they bite they pull away, tearing holes in the prey that then bleeds to death. Is it possible that venom can increase this bleeding? Sure, but it’s also possible that it doesn’t.

So then why did this patient become hypotensive? Likely a vasovagal response. And given that the bite was on the hand, it’s appropriate to put the patient on antibiotics. But maybe we can finally stop propagating the magical thinking associated with komodo dragons.

Bitten by a Dragon
http://www.wemjournal.org/article/S1080-6032(16)00100-9/abstract

Further enjoyable reading
National Geographic
http://phenomena.nationalgeographic.com/2013/06/27/the-myth-of-the-komodo-dragons-dirty-mouth/
A central role for venom in predation by Varanus komodoensis (Komodo Dragon) and the extinct giant Varanus (Megalania) priscus
http://www.pnas.org/content/106/22/8969.full

Animals attacks aren’t really that bad, after all

At least, not according to the CDC WONDER database. When you take 9 years of data from said database, you get a whopping 1802 deaths. That comes out to just a hair over 200 deaths per year. Now, the article says they used ICD-10 codes W53-59 and X20-29 as their inclusion criteria, so take from that what you will.

Of the 1802 deaths, 1088 (60%) were from nonvenomous species, and specifically, 655 (36% of the total) were from farm animals. Thus, farm animals account for nearly as many deaths as venomous animals. Guess which one we spend more time on with teaching. When’s the last time you saw a board question that involved cattle?

The authors also break down the statistics by gender, race, age, and regional geography. The gender and race of the most commonly injured shouldn’t surprise anyone (white, male), but the ages might. We are taught that often it is young, intoxicated men are on the receiving end of most bites, but this data shows the overwhelming majority of those killed are >35 years old. The only group with more deaths at a young age(<9) is those killed by dogs, sadly. Children under 9 make up 46% of dog related deaths, despite making up only 10% of the total deaths.

Now, the question is, is this an example of the problems with ICD-10, or just a problem with reporting in general? Clearly more than 200 people are killed per year by animals, so how do we accurately assess the true risks? Based on this data we should put as much emphasis on agricultural education as we do on venomous species. Now, a significant majority of the farm animal injuries occur in rural areas, but so do most of the venomous animal injuries that don’t involve hymenoptera (~28% of the total). And yet we clearly devote a larger proportion of our teaching towards exotic, venomous animals. This even differs from the perceived over-emphasis on critical care, as knowing the exact thing to do in a time stressed situation can have a mortality benefit. Rarely is that true in the case of a venomous species, apart from anaphylaxis.

As the authors propose, we should as a specialty spend more effort on teaching agricultural safety as well as dog safety in homes with children. We already do a fair amount of teaching and community outreach with regards to anaphylaxis and hymenoptera, which is another significant cause of mortality. However, we could always do more with regards to preventable deaths.

Fatalities from venomous and nonvenomous animals in the United States (1999-2007)
http://www.ncbi.nlm.nih.gov/pubmed/22656661