Jungle Medicine Survival Guide: Evading Leeches, Bullet Ants, and Mosquito Bites

22 November 2023

Contributor

Dr. Will Duffin – Joint Medical Director & GP

Will is a jobbing Devon based GP, educator and adventure addict. He has provided medical cover for dozens of very different expeditions and projects; including commercial high-altitude treks in The Himalayas and The Andes, a luxury Trans-Siberian private train, a reality TV show in the South Pacific and he has worked with UNICEF out in forgotten corners of Myanmar.

Spend a night in the jungle and you will be lulled to sleep by a symphony of clicking bats, shrieking birds, and buzzing insects. It’s a reminder of just how alive this precious ecosystem is. Having said that, it can be hard to appreciate this when you’re tucked up in your Hennessy hammock, the rain hammering on your tarp, the humidity is 90% and you’re lying there itching ribbons of skin off your legs in a frenzy of fingernails. Here are my top 3 least favourite ‘bitey things’ that I do my best to avoid in the jungle and some of the key medical considerations.

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Leeches

Whilst these little blood suckers are a right up there on the nuisance scale, unlike mosquitos, they rarely transmit disease. When they latch, they cunningly inject a local anaesthetic, which is why they can be hard to notice. Top tip – spot each other for leeches when you’re in a group. They also inject an anticoagulant, and this is why the area bleeds so much when you remove them. The bite can lead an open wound which risks becoming infected if not dealt with properly. The risk of infection is increased if the leech is removed by squeezing, salt or burning as these methods cause the leech to regurgitate its stomach contents (1). The best method of removal is to either wait or scrape. They do normally drop off after they’ve had their fill within about 40 minutes, although most people don’t have that level of composure. A preferred option is to locate where the mouth is at the skin, stretch the skin taught, and use a flat edged tool (like a credit card) or your fingernail to carefully scrape them off sideways. It’s prudent to dress the wound afterwards and a few drops of betadine (antiseptic) won’t go amiss. Leeches are truly bizarre little creatures. Fun fact, they have 10 eyes, 6 hearts and 32 brains…!! (2) They hunt prey (including humans) through mechanoreceptors (detecting vibrations) and working along CO2 gradients. That’s right, the b****** can literally sense you breathing! (3)

A leech on my wrist in Malaysian Borneo. Look at the mess it made when removed! The anticoagulant makes things look much worse than they are.

Bullet Ants

If you want to experience a deep drilling pain that you can feel right down to your bones, then go get yourself bitten by a bullet ant. These are not your regular ants. Endemic to South America, they live in colonies at base of trees and look more like wingless wasps. And boy do they pack a punch. The pain is caused by a small neurotoxic peptide called poneratoxinthat commonly lasts for 12-24 hours or more. Fortunately, the toxin does not cause systemic or dangerous effects (4). Management is focused on symptom relief. Consider issuing strong opioids for analgesia (Co-Codamol or Oxycodone), an oral antihistamine and a topical steroid cream for associated itch, alongside a hefty dose of reassurance.

Mosquitos

It’s impossible to leave out the mozzies because they are ubiquitous to any tropical environment. They are a particular nuisance around dawn and dusk, except for the Ades mosquito which is a daytime biter. They are vectors of serious tropical diseases, including malaria, dengue and zika. Oral malaria prophylaxis is an essential part of pre-departure planning and needs to be tailored to resistance patterns of the destination country. The emphasis on any jungle expedition is firmly on bite avoidance. DEET based products still perform the best in head-to-head studies comparing the wide range of chemical insect repellents. Maximum protection is with 30% DEET, avoid the stronger formulations which will completely trash your clothes. Long sleeves at dusk and dawn and sleeping under bed nets are a must. Heavy rain and wind offer a welcome reprieve as the insects seek shelter.

If you’re thinking of venturing into the jungle, please don’t let this list put you off. If you take one moment to contemplate the bolts of light piercing the rich green canopy, the magnificent buttress roots, and the bright red bloom of a Rafflesia, then like me, you’ll be hooked too!

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