Category Archives: antivenom

Death by caterpillar or: Consider zebras, but don’t memorize them

I’ve given lectures on lepidoptera before.  There are between 200-3500 envenomations from lonomia spp reported every year in Brazil, but they’ve increased yearly since 2000. This is most likely from increased time in the rain forest by loggers and people recreating, but it was originally described in rubber tree tappers. The giant silkworm moth caterpillar is particularly noted, because they’re the only one reported to cause hemorrhagic syndromes and acute renal insufficiency. The envenomation syndrome is severe enough that fatalities were noted prior to creation of antivenom in Brazil.

Thankfully, this case report doesn’t involve a fatality. What it does involve is the basis of the article, namely delayed presentation. The patient was envenomated, and 24 hours later noticed bleeding from his gums and his other scratches. He waited another 3 days to present for medical treatment. Thankfully, as if it was a snake, the patient brought some caterpillars with him to be identified as Lonomia spp. Initial labs showed “blood incoagulability”, which meant that it was outside the range of normal values of prothrombin activity and clotting times. These values changed ever so slightly by day 6, and on day 8 the patient had a headache, so he was finally treated with antivenom. Thankfully the CT of his head did not show intracranial hemorrhaging. His clotting time returned to normal after antivenom, and he was discharged on day 12.

The venom appears to be a procoagulant that causes thrombin formation, leading to DIC via prothrombin and factor X activators. Due to the moth larval stage living in colonies, often the venom load in the patient is high as the injury is usually from either stepping on or puttting their hand on multiple individual caterpillars.

The antivenom is of equine origin, and is an F(ab)2 product. It’s only recommended for moderate and severe cases, such as the one mentioned in the case report. There’s not a significant amount of evidence for premedication, it is common in Brazil to give antihistamines and steroids.

Of note, while there is danger of misidentification of the condition in Brazil, where it is at least heard of if not common, the risk is even greater in the returning traveler. This is clear in this fatal case report from Canada in 2008. This doesn’t mean that lonomia envenomation should be at the top of your differential for every coagulopathy, but being aware of it may help with those future zebras that come up in travelers. And you should especially be knowledgeable about it if you practice in Brazil.

Severe Hemorrhagic Syndrome After Lonomia Caterpillar Envenomation in the Western Brazilian Amazon: How Many More Cases Are There?
http://www.wemjournal.org/article/S1080-6032(16)30271-X/abstract

No really, snakes can hurt you after they’re dead

Even though we have all (hopefully) been taught that dead snakes can still envenomate people, apparently it hasn’t been reported much in the literature. I say this because this case report is in press as of 18 Nov 2016.
Southern Copperhead
In this instance a young man killed a copperhead by cutting it into three pieces. While holding the piece containing the snake’s head, “his right index finger brushed against the fang and was inadvertently punctured.” I’m sure all of us think that is exactly how this happened. Pain and swelling followed, so the patient went to his local hospital where he received 4 vials of antivenom.
There was further progression of the swelling and ecchymosis, so another 4 vials were administered. The patient was then transferred to a tertiary center “with concern for compartment syndrome of his hand.” Another 2 vials were given and the hand was elevated, and no operative intervention was done. Of note, his labs showed he did not have a bleeding diathesis, but readers of this blog already knew that.
I wish I didn’t have to say it, but sadly some people out there still believe that fasciotomies are required after snake bites. Truthfully, based on the evidence, the best treatment is antivenom and elevation, not surgeries that can cause complications and haven’t been shown to give benefit.
This paper does note that there have been multiple case reports of envenomations by dead rattlesnakes or rattlesnake heads. One even had been freeze-dried, bought at a gift shop, and used as a tie tack. Almost all of those required antivenom. This is an interesting thought, as recently deceased snakes likely retain the ability for the venom gland to contract reflexively. Envenomation from a freeze-dried snake has to be retained protein on the fang itself, as the ducts aren’t functioning anymore. This particular episode is the first documented case involving a copperhead that required antivenom.
So it is more than just an old wives tale. Dead snakes can still evenomate you, even if they’ve been dead for quite a while. So stay away from the pointy ends of snakes, and stop killing them for crying out loud.

Clinically Significant Envenomation From Postmortem Copperhead (Agkistrodon contortrix)
http://www.wemjournal.org/article/S1080-6032(16)30225-3/abstract