Nonvenomous chicken snake (Spilotus pullatus)

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Snakebite
The odds are small, but potentially lethal: a snakebite. Worldwide approximately 20.000 deaths occur per year due to venomous snakes. Recently I met Luis, a biologist in Mexico who is specialized in snakebites en currently empowers people to protect the habitat of sea turtles around Seybaplaya. In this article the prevention and treatment of snakebites will be discussed, thereby focusing on Mesoamerica.

Prevention
Prevention of snakebites is no rocket science. Stay away from snakes- and snake charmers, if a snake feels frightened: make sure there’s an escape route, wear proper shoes, be careful with swimming, walking and climbing in places with dense foliage, use a light at night and make sure your sleeping bed is of the ground or in a closed space. It is important to have information on the nearest hospital and availability of antiserum in a country.

A bite
Even when a snake bite does occur, there’s no need to panic. Of all snakes worldwide, only a small portion can inject lethal venom, and dry bites occur in about 50% of the times. Make sure you have some know-how of local venom snakes, so you can recognize the potential lethal ones. Medical important snake distribution can be found on this WHO page. Medical important groups in Mesoamerica are
Elapidae: coral snakes (Micrurus) and
Pit vipers:
– Bothrops (Bothrops)
– Copperheads/cantils (Agkistrodon)
– Bushmasters (Lachesis) and
– Rattlesnakes (Crotalus).

In other parts of the world there are three other important groups: Vipers (Viperidae), Colubridae (Colubridae), and Burrowing asps/vipers (Atractaspis). In South-East Mexico there are four snakes with lethal venom:

Yellow Lips: Mexican Cantil (Agkistrodon bilineatus)              Mexico, Central America

Tropical rattlesnake (Crotalus tzabcan)                                    Mexico, Belize, Guatemala

Yucatán hognose pit viper (Porthidium yucatanicum)            Mexico

Coral snake (Micrurus diastema)                                              Mexico, Belize, Guatemala

First Aid Snakebite
Assess scene safety
Reassure the bitten person
Treat major bleedings
Remove tight clothes, jewelry
Immobilize the patient and the injured extremity

Evaluate risk, plan evacuation
Treat pain, NSAID’s can exaggerate bleedings(!)
Consider Pressure-Immobilization (PI)*
Identificate, but don’t try to catch or kill the snake
Avoid traditional methods:
– don’t use a tourniquet
– no incision, suction, herbs, etc.

*Controversial. Pressure-Immobilization (PI) is advised in case of neurotoxic snakes. The idea is to prevent the spreading of venom by draining the veins and lymph canals. Don’t apply in case of mainly necrotoxic snake bites.

Clinical Features
A patient should be observed for at least 24h. Symptoms can develop in a short period of time, but often take some hours. Different snake families and species have different kinds of venom, thereby inducing different symptoms. The following features can be seen:

– general: vomiting, nausea, edema, stomach ache and headache
– necrotoxines: local pain, swelling, blistering, lymph node enlargement, tissue damage, necrosis
(vipers, pit vipers, burrowing asps)
– hemotoxines: clotting disorders
(vipers, pit vipers, colubrids)
– neurotoxines: descending paralysis (ptosis, ophthalmoplegia, respiratory insufficiency)
(elapids, pit vipers)
– cardiotoxines: shock and arrhythmia
(vipers, pit vipers, burrowing asps)
– myotoxines: rhabdomyolysis (coca-cola urine), kidney injury
(sea snakes, vipers, pit vipers)

Anti-venom?
Anti-venom is not always available, expensive, the snake species can be unknown en administration involves risks. Indications for administration are signs of systemic envenomation as described above or rapidly spreading local envenomation. Ideally, anti-venom is  administered IV, IM is also possible. The choice of an appropriate venom depends on the identification of the species, geography and clinical symptoms. Polyvalent venom is often available to cover multiple snakes. Adrenaline is a must in the medical kit when administering anti-venom, to deal with an anaphylactic reaction. Antihistamine and hydrocortisone as well. The following flowchart (Oxford Handbook Wilderness Medicine) can help decision making in the field:

Complications:
Complications which can occur include (hypovolemic) shock, respiratory insufficiency and acute kidney injury. These should be treated according to the ABCDE-method. A tetanus-booster is advised and antibiotics are only indicated in case of infected wounds. Surgical measures may be necessary in case of necrosis and compartment syndrome (rare). Until 14 days of administration of anti-venom, serum disease can develop.

Although a snakebite can be deadly, the odds of a lethal bite are small, especially in travelers. Most lethal bites have been documented in locals working on the lands in tropical regions. Venomous bites in a low-resource setting acquire rapid evacuation in a short time frame, to reassure the health of the patient. Recently researchers discovered a method to identificate the snake species by the bite site (by PCR DNA sequencing). This is quite promising, since identification of the snake is of vital importance.

Do you want to aquire more experience with snakebites, scorpion bites, dehydration and hyperthermia, infectious diseases and improvised trauma managament in a wilderness setting? Consider taking a course African Wilderness Medicine.

Literature:
Oxford Handbook of Tropical Medicine (2014)
Oxford Handbook of Expedition Medicine (2015)
The Treatment of Snake Bites in a First Aid Setting: a systematic review (2016) – Avau et al.
Snakebites Worldwide management (UpToDate)