On the neurotoxicity of caterpillars resulting in visual impairment

It was the hot dry Summer of 2018 when I got a message from a North American reader of The Toxicologist Today (right when I was sunbathing at a crowded beach whilst munching on 'Bolas de Berlim' like a very hungry caterpillar). After getting home for lunch there was a brief exchange of messages where I promised the kind reader I'd do the best I could to write a post on her afflictions, if she promised me she'd seek urgent medical advice. However, my mobile crashed. It crashed so hard that still today I cannot find the messages said person sent me, I cannot recall in what platform had we been having such brief chat, I cannot remember anything else but the fact that this person had a dog who had been playing with caterpillars and she has been (since then) with impaired vision, nausea and dizziness.

I remember expressing my deepest concern to this person and telling her time and time again that I am not a medical doctor, I am a Medical Information Specialist, a God damn good one :) but still, not a medical doctor... and definitely not a Guru Healer.

The person still asked me to inform her on any knowledge I had concerning studies covering the neurotoxicity of that specific caterpillar (still cannot precise which one) especially those with reported effects on the nervous system resulting in vision impairment.

Ai ai ai ai ai, we say in Portuguese when we are concerned about something that might prove serious. Once again I redirected the reader to her GP, stressing that if possible she should look for a speciality appointment after checking with the GP. But with very limited time in my hands and so many different projects still in progress, I could not really dedicate much time to said post... until now. I found about 30 minutes yesterday and today to do the best possible search within such time frame, even though I have no clue if the reader was talking about the Giant Silkworm Moth Caterpillar or the Oak Processionary Moth, or one of the many other that just inhabit this whole wide world. One thing I got to remember, the person was from the USA! So that will restrict the beasts to just those living and munchin' within them 3,797 million square miles that comprise the United States of America! Easy-Peasy :/

For the first time and because scientifically accurate referenced free information on the neurotoxicity of caterpillars resulting in vision impairment is not so much available out there, I had to resort to a couple of pages [1] [2] bearing no scientific references. If any of you find any inaccuracy, please let me know about it promptly so I can correct the article as best as possible. I looked for the most nasty caterpillars inhabiting the USA territory as I kind of recall the reader stating something in the lines of "my doctor told me it is unlikely that caterpillars affect our vision... it might be stress". Therefore, I decided to look for those that comprise the hardcore line of attack and I found these four:

Acharia stimulea (Eastern USA)

Megalopyge opercularis (Central America)

Automeris io (Southern US)

Lophocampa caryae (Central America)

After reducing the list of candidates to just four I had to look for any articles on envenomation causing blurry vision (and the like) that among all other symptoms was the one the reader was most concerned about. I found an article by Agarwal et al (2017) on Ophtalmia nodosa (inflammation of the eye when particles [could be caterpillar's hair] lodge in the conjunctiva, cornea or even iris. However, as the author puts it, this is a rare condition but a serious one that can result in loss of eye because of the constant inflammation within the vitreous humour. In the case-study they analysed there is a physical observation of the many caterpillar hairs that were present in the patient's eye where they used ultrasound biomicroscopy. This patient had blurring of vision and diminution of vision just like my reader reported, so the putative presence of caterpillar hairs in her vitreous humour could be another important thing for her to report to her doctor. In addition, this article also refers that their patient had some of the hairs removed and that the eye was "quiet for two months", but then the diminution of vision persisted when the inflammation returned after they stopped the anti-inflammatories (oral corticosteroids). The reason being that many other minute hairs can take months to years to be physically removed by movements of the ocular globe; moreover there are glands connected to the caterpillar's hairs that contain a toxin named thaumetopoein (an urticating protein) that induces inflammation. In this specific case, corticosteroids provided some peace but did not resolve the issue entirely as the hair still needed to be physically removed as thaumetopoein would always be causing inflammation to the area of contact. The NHS talks about the use of an antihistamine cream to antagonise the nefarious effects of thaumetopoein, as preferable approach [4].

In summary, caterpillar dermatitis (known as lepidopterism) can result in inflammatory ocular lesions when hairs come into contact with the different layers of the ocular globe, as discussed above. In fact, Rosen (1990) [5] actually discusses it so well in an article covering such matters and that deserves your uttermost attention. As the author suggests, there has been reports that these hairs can induce pruritus (itching), burning and painful dermatitis resulting in ocular lesions that can come with comorbidities such as neuropathy, convulsions, arrhytmia and dyspnea. Some of these same issues were reported by my reader!!!

It was indeed extremely difficult to find free information available in the Internet on these matters, but on Medscape one can read that when the ocular globe comes into contact with hairs from the M. opercularis (the puss caterpillar I already told you about) the resulting erucism (envenomation by caterpillars) might be counteracted by H1 and/or H2 blockers (antihistamines), but if there's pain the doctors might have to use narcotic analgesics [6].

That is the information I hope my reader is now glancing her eyes through. I honestly hope she is feeling much better and that she visited her doctor for a professional observation. For all of you who just reached this post, whatever reason brought you here, I hope you found useful info.

[1] 5 of the world's most toxic caterpillars, SunnyScope, [https://www.sunnysports.com/blog/5-worlds-toxic-caterpillars/], last update unknown, last visited on the 20th of September 2018.

[2] Stinging caterpillars of the United States, The Ark in Space, [http://www.arkinspace.com/2011/05/stinging-caterpillars-of-united-states.html], last visited on the 21st of September 2018, last update on the 12th of June 2016.

[3] Agarwal, M., Acharya, M. C., Majumdar, S., Paul, L. (2017). "Managing multiple caterpillar hair in the eye". Indian Journal of Opthalmology, 65(3), pp. 248-250.

[4] Health warning over invading moth, NHS, [https://www.nhs.uk/news/heart-and-lungs/health-warning-over-invading-moth/], last updated on the 4th of August 2010, last visited on the 21st of September 2018.

[5] Rosen, T. (1990). "Caterpillar dematitis". Dermatologic Clinics, 8(2), pp. 245-252.

[6] Caterpillar envenomation, Medscape, [http://misc.medscape.com/pi/iphone/medscapeapp/html/A772949-business.html], last visited on the 21st of September 2018, last update unknown.