Category Archives: insect

How persistant is permethrin?

Malaria and other mosquito-borne infections are a significant cause of morbidity and mortality for many countries, and visitors to those countries are certainly not immune. While travelers certainly do not want to experience illness during or after a trip, the military has an even more vested interest in keeping soldiers healthy. Considering that  more troop casualties result from these infections than there are from direct combat, it is easy to understand why this is such an important area of study for the military.

Applying repellent to clothing is appealing to everyone, as it does not need frequent re-application, often has less of an odor, and has less skin irritation. A side benefit of clothing based repellent is that it is usually advertised as lasting through “many” washes, thus allowing one to apply the product before a trip and possibly not need to carry it with them. But like many commercial products, the validity of those claims is not easy to find out, and often you have to take the company at their word.

The authors of this study set out to determine exactly how effective permethrin-impregnated army uniform cloth was at repelling or killing mosquitoes after multiple washings.

Surprisingly, permethrin stays on the fabric through a large number of washes. Even more surprising, it remains somewhat effective, even after 55 washings. Of course, they weren’t using commercial washing machines, instead agitating with glass rods in beakers, so external validity may vary.

However, how effective it is depends on what you’re asking for. For knockdown (ie, a mosquito landing on the fabric falls off due to toxicity), it goes from 98.3% to 23.3% after 20 washings. 24 hour mortality, on the other hand, remained 100% after 24 hours even after 55 washes. One hour mortality drops after only 10 washes. For repellency, the rate of mosquitoes landing on the sleeves increased from 32% at 0 washes to 51% at 55 washes, both of which were below the 86-87% landing rate of the controls.

Then they go into scanning electron microscopy and energy-dispersive X-ray spectroscopy analysis of the cloth that basically shows that there are measurable permethrin levels on the cloth after 55 washes. This leads you to the logical assumption that the effect is still from the permethrin.

So there you go. Permethrin works, even after washing. You can save some money by not needing to reapply it after every wash, and maybe only every 10 or so (depending on how you’re washing it). Don’t use your dryer though, as you have to air dry the product based on this study. Also make sure not to use fabric softener. This does not preclude use of topical agents on exposed skin, but the combined use can significantly reduce your exposure to mosquito-borne illnesses (or simply itchy bites). 

Knockdown and repellent effect of permethrin-impregnated army uniform cloth against Aedes aegypti after different cycles of washings.
http://www.ncbi.nlm.nih.gov/pubmed/24595642

Ants as sutures?

You’ve probably heard of it, or seen pictures of it on various internet feeds. But how many references have you seen in the medical literature? They’re sparse at best, which is part of the reason I haven’t written about them yet.

Does this mean that their use hasn’t been recognized in the medical literature? Far from it. This paper from 1925 discusses much of the history (to that point) of using ant heads as wound closure devices. What may surprise you is how long it has been in the literature. You may also be surprised that it was written by an ichthyologist, who apparently just found this interesting and decided to publish it in JAMA.

The use of ants as sutures likely dates from prehistoric times. It seems fairly easy to go from “this big ant bit me and it pinched the skin” to “lets use this to close wounds”, but most facts that seem simple after being established generally weren’t. Since we have no evidence of the first use, we have to go to the first recorded use. This falls to the Artharva Veda, circa 1000 BC. However, they weren’t using ants for skin wounds, they were using them to suture intestinal wounds after surgeries. It goes without saying that they probably didn’t start with that, so it had likely been in practice for some time prior.

It is possible, then, that the use of ants in surgery in the Mediterranean was learned from the Indian practices. Arabian medicine had translated the Hindu literature by 600 AD, and many recorded uses into the middle ages were from Arabic physicians. From there it spread into parts of Europe. The use in surgery persisted until the early Renaissance.

What made them stop? This article contends that a few high-ranking surgeons decided against them for a myriad of reasons. Theodoric rejected Arabian medicine, de Chauliac felt that they were rejected by the body, di Vigo felt they were obsolete, Fabricius felt the mandibles relaxed too much after the ants died (and were also hard to source in winter), and Purmann ridiculed them in his books. Most of these manuscripts were published (or republished) around 1500. Gut suture had also become more common by then, and was much easier to obtain.

Their use in skin continued in austere environments. As South America was explored, use of ants by native peoples was noted from the 1800s on. Concurrent use was still occurring in Algeria and noted by the French Foreign Legion. Their use was also described in Greece in 1896, as wounds were still being dressed by barbers according to local customs. That one comes from the Journal of the Linnaean Society of London, so you may have missed it on your feedly.

So why don’t we see articles discussing it now? Because it’s an established fact at this point. You’d be hard pressed to get more than a case report out of using ants as sutures, unless you were going to write a review article. And since much of the literature (including this article) isn’t accessible on pubmed, it becomes a scavenger hunt to get enough sources. The author of the paper had to look at the originals at the New York Academy of Medicine. Many are written in other languages, so you have to trust that the translation is correct (or translate the original yourself) before citing it.

Now, if you want to use ants to close a wound, you’ll want the right kind. Generally you would ask locals what they’ve used in the past, as naming species is unlikely to help you. Driver ants, army ants, and bullet ants are a few of the types that have mandibles big enough to close a decent skin wound.

Eciton burchelli ants

The image to the left shows a bunch of the wrong type of ants, and one that is suitable, even though they’re the same species of army ant. Once you’ve found a suitable ant, pinch the wound closed, and hold the ant by the thorax (using something other than your fingers preferentially). You’ll want to be incredibly careful with the bullet ant, as it has the most painful sting of any hymenoptera, hence the name. The mandibles will usually be open in a defensive position if you’re holding it. Once the mandibles are near the skin, the mandibles will clamp shut, holding the wound closed. Then lift up the thorax and pinch off the body, leaving just the head and mandibles. Repeat as needed to close the wound, and there you have it. 

You’ll of course want to irrigate the wound with water clean enough to drink prior to closure, as has been discussed before here. Also, don’t try to suture intestines with ants. That is well beyond what I would recommend in the wild.

Stitching Wounds with the Mandibles of Ants and Beetles
http://jama.jamanetwork.com/article.aspx?articleid=236062

What to do for bug bites?

Face it. Except for the very lucky, few of us are able to escape biting insects. After getting bit, the range of reactions is immense; from no reaction to anaphylaxis. Thankfully, most simply have mild pruritis and urticaria. But how are we supposed to treat these?

This review article from the UK lays out the evidence behind all the common treatments for bug bites. Here is a summary:

  • Oral antihistamines are recommended, but data is lacking. A review consisting mostly of multiple studies from one group in Finland showed them to be effective.
  • Use non-sedating antihistamines during the daytime, and sedating ones as night.
  • Topical antihistamines don’t work well, can cause sensitization, and aren’t recommended for longer than 3 days.
  • Topical corticosteroids are poorly studied but may be effective.
  • Topical corticosteroids shouldn’t be used on broken skin or on the face.
  • Oral corticosteroids are used for severe urticaria, but no studies have been found to support this.
  • Use the lowest dose for the shortest time possible for oral corticosteroids.
  • OTC analgesics can be used for pain, but topical anesthetics can cause sensitization.
  • Calamine isn’t the slightest bit effective, so don’t use it.
  • Counter-irritants (such as dilute ammonium) may be effective based on one double blind RCT.
  • Topical antiseptics after bites are probably overkill.
  • Generalized symptoms or redness/swelling over 10cm should be referred to an allergist.
  • Secondary infections should be treated with antibiotics.
  • Treat anaphylaxis appropriately.

Nothing earth shattering here, but maybe this will prevent unnecessary topical treatments which are often ineffective and possibly harmful. I do wish more people would recommend loratidine or cetirizine for this instead of diphenhydramine. The sedating effects as well as the duration of effect would tend to recommend the newer, now OTC agents, but I still see most everyone giving patients prescriptions for Benadryl®.

Management of simple insect bites: Where’s the evidence?
http://dtb.bmj.com/content/50/4/45.full

Asian giant hornet

You may have recently seen news stories about Vespa mandarina “terrorizing” parts of China. What is interesting about this species is that due to their size, their venom has significant effects in addition to the typical hymenoptera anaphylaxis. Yes, most deaths are still from anaphylaxis, but the venom can cause acute renal and hepatic failures, as well as rhabdomyolysis.

This article describes a case report of a Japanese man who received multiple stings while in his yard. He was hypotensive and tachycardic, and as such received epinephrine. In addition to the epi you’re thinking of, he also received intrathecal epinephrine. He also received glycyrrhizin, an active component of licorice roots, commonly used in Japan for hepatitis and skin lesions. Apparently anaphylaxis is included in the “skin lesion” category. They also put gentamicin/steroid ointment on the stings. In spite of this treatment, the sting lesions became hemorrhagic, then necrotic. He also developed rhabdomyolysis and hepatitis.

In writing the case up, the authors did an Ichushi (Japan) literature search to find other cases of organ failure after Vespa stings. They ended up finding 14, and using their case came up with a grand total of 15. All of them had hepatitis and rhabdomyolysis, but surprisingly, 3 did not have anaphylaxis. Thirteen of the 15 had some degree of skin necrosis or hemorrhage, however. Six patients died, and when the data were analyzed, this correlated well with number of stings. Strangely, organ injury did not correlate as well, per the authors.

A Medline search was also performed, but they were unable to find any papers with photographic evidence. The few reports they found simply described the lesions, and some sounded similar to their experiences in Japan. Using written descriptions, they were able to find 15 more cases of wasp stings that had cutaneous manifestations and organ failure. There were also reports of bee sting cases in Zimbabwe, the United Kingdom, and Brazil with similar syndromes.

The authors agree with the Good Samaritan Regional Poison Center recommendation of admission for any pediatric, elderly, and patients with comorbidities if they have more than 50 stings. This seems like a good rule to follow for patients with a significant number of stings from any wasp, hornet, or bee. They also recommend being on the lookout for multiple organ failure if any of the stings become hemorrhagic or necrotic, as this implies either a stronger than usual venom, or a weaker than usual immune response. This seems like a reasonable clinical approach.

Cutaneous hemorrhage or necrosis findings after Vespa mandarinia (wasp) stings may predict the occurrence of multiple organ injury: A case report and review of literature
http://www.ncbi.nlm.nih.gov/pubmed/17952752