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

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