FMST Student Manual - 2008 Web Edition*

1.   TERMINOLOGY

Envenomation - an injury or illness caused by the poisonous secretion of an animal, such as a snake, spider, or scorpion, usually transmitted by a bite or sting.

Mortality rates - of all the deaths that occur annually due to envenomation injuries, the majority are caused by insects, followed by snakes, then spiders.  

2.   ACTIONS OF SNAKE VENOM

Snake venoms are complex chemical mixtures of proteins, which have mostly enzymatic properties.  The quantity, lethality, and composition vary with the species and the age of the snake, the geographic location, and the time of the year.  Venom is highly stable and is resistant to temperature changes, drying, and drugs. 

Hemotoxins - toxins that destroy red blood cells, disrupt blood clotting, and/or cause organ degeneration and generalized tissue damage.  An injury due to a hemotoxic agent is often very painful, and permanent damage, such as loss of an affected limb, is possible even with prompt treatment.

Neurotoxin - toxin that acts specifically on nerve cells, or neurons, usually by interacting with membrane proteins such as ion channels.  The effect of these neurotoxins is a paralysis in the affected area.

Some snake venom may include elements that produce both of these effects. 

3.   CLASSIFICATIONS OF POISONOUS SNAKES

Crotalidae Family (Pit Vipers)

These snakes take their name from the deep pit located between their eye and the nostril. (Figure 1.)  The pit is a highly sensitive organ capable of picking up the slightest temperature variance.  The Crotalids, or pit vipers, are usually much wider than their necks.  Most pit vipers are nocturnal.

Examples of Pit Vipers

Rattlesnakes - found from the U.S. through Central and South America

Saw-Scaled Viper - found from Pakistan, throughout the Middle East to Africa

Cottonmouth (Water Moccasin, Pilot Snake) - Found throughout the southern and eastern US (see figure 2)

Copperhead (Upland Moccasin) - found in the eastern U. S.

Habu - found throughout Southeast Asia, including Okinawa

Venom - hemotoxic

Characteristics

- Retractable fangs

- Heat sensing pit located below the nostril

- Large triangular shaped head (in relation to their body)

Signs and Symptoms of Crotalidae Bite 

- Excruciating pain at the site of the bite

- Presence of fang marks

- Tissue swelling at the site of the bite.  Swelling begins within 3 minutes and may continue for up to an hour with enough severity to break the skin

- Severe headache and thirst

- Bleeding from major organs that may appear as hematuria

- Destruction of blood cells and other tissue cells.  Discoloration of surrounding tissue.

- Tingling or numbness of face and scalp

- Muscle twitching (fasciculation)

Colubridae

The largest group of snakes worldwide.  Although there are many types of Colubridae, most are completely harmless to man.  Their venom is effective on cold-blooded animals (such as frogs and lizards) but not considered a threat to human life.  The Boomslang is the only one that has caused human deaths.

Examples  of venomous Colubridae

Boomslang - found throughout the African Savannah (see figure 3)

Venom - hemotoxic

Characteristics

- Fixed fangs in rear of mouth

- Large eyes and small pointed head 

Since both Crotalidae and Colubridae secrete hemotoxins, their signs and symptoms are the same although the bite of the Colubridae is not as painful as that of the Crotalidae. 

Elapidae Family

A group of highly dangerous snakes with powerful neurotoxic venom that affects the nervous system, causing respiratory paralysis.

Examples

- Coral Snakes - found in the southern US, through South America, and in parts of Asia  (see figure 4)

- Cobra - found from South Asia through Middle East and North Africa (see figure 5)

- Krait - found throughout South Asia, including Pakistan 

Venom - neurotoxic

Characteristics

- Fixed fangs

- Round pupils

- Head width is proportionate to body size

Signs and Symptoms of Elapidae Bite

- Stiffness, muscle aches, and spasms

- Respiratory paralysis and death

Hydrophidae (Sea Snakes)  (see figure 7)

For medical purposes, size, location, and species are irrelevant.  Determination of species is too difficult and dangerous to matter.  Sea snakes are found in all oceans except the Atlantic Ocean.

Venom - neurotoxic

Characteristics

- Fixed fangs

- Flat tail (for swimming) 

Signs and Symptoms of Hydrophidae Bite

- Since both Elapidae and Hydrophidae secrete neurotoxins, their signs and symptoms are the same.

- Persistent myths about sea snakes include the mistaken idea that they cannot bite effectively.  The truth is that although their teeth are small, about 1 inch, they are adequate to penetrate skin and they can open their mouths wide enough to bite a person’s thigh.  Envenomation from sea snakes is rare, due in most part to their temperament, but it does occur.  Without treatment, death from sea snake envenomation can occur within 12-24 hours.

4.   DIAGNOSING A SNAKE BITE

Fang Marks - fang marks may be present as one or more well defined punctures, or as a series of small lacerations or scratches, or there may not be any noticeable or obvious markings where the bite occurred.  The absence of fang marks does not exclude the possibility of envenomation (especially if a juvenile snake is involved).  However with rattlesnake envenomation, fang marks are invariably present and are generally seen on close examination.  Bleeding may persist from the fang wounds.  The presence of fang marks does not always indicate envenomation; rattlesnakes, when striking in defense, will frequently elect not to inject venom with the bite, resulting in a “dry bite.” 

Manifestations of signs and sypmtoms of envenomation are necessary to confirm diagnosis of a snake venom poisoning.

5.   TREATMENT OF A SNAKE BITE

- Most definitive care for envenomation is anti-venom.

- Keep the victim calm and reassured.  If possible, allow the limb to rest in a neutral position level with the victim’s heart.

- Locate the bite site.  If the bite is on the hands or feet, immediately remove any rings, bracelets, watches or any constricting items from the extremity.

- For bites on the extremities, wrap extremity with three to six inch Ace bandage past the knee or elbow joint to immobilize it.  Leave the fang marks exposed. 

- Apply a splint.

- Check distal pulses.

- Monitor and CASEVAC.

- THINGS YOU SHOULD NOT DO:

- DO NOT cut or incise the bite site.

- DO NOT apply ice or heat to the bite site.

- DO NOT apply oral (mouth) suction.

- DO NOT remove dressings/elastic wraps.

- DO NOT try to kill snake for identification as this may lead to others being bitten.

- DO NOT have the victim eat or drink anything.

6.   PREVENTION OF SNAKE BITES

LEAVE THE SNAKE ALONE!!  This is the best way to avoid a snakebite.  Most snakes will only bite if threatened.  Most snake bites occur when the victim is attempting to catch, kill, or play with a snake.  Keep hands out of areas that you cannot see (i.e. holes, under rocks, and under logs).

7.   ARTHROPOD ENVENOMATION

Arthropods are the largest species of animals and include insects (bees wasps, ants), arachnids (spiders), crustaceans (crabs), and others (scorpions).  Arthropods are characterized by the possession of a segmented body with appendages on each segment.

Bee, Wasp, and Ant Stings - primary effect is from the strong histamine reaction they cause.

Signs and Symptoms

Bee/Wasp stings - Honey bees only sting once and leave the stingers and venom sac embedded in the skin.  Wasps, hornets, and bumble bees can sting multiple times.

- Pain

- Itching/burning sensation

- Wheal (raised, inflamed skin)

- If patient is allergic, monitor for anaphylactic reaction

Ant bite - some species of ants, especially the fire ant, can bite repeatedly (see figure 8).

- Pain

- Itching/burning sensation

- Vesicles on skin

- If patient is allergic, monitor for anaphylactic reaction

- Multiple bites can produce the following signs and symptoms: 

- Diarrhea

- Generalized edema

- Hypotension due to vasodilation 

Treatment

- Stingers should be removed immediately to prevent more venom from entering the victim.  Remove the stinger by scraping across the skin with a knife blade or similar object.  Do NOT use tweezers to grasp stinger, this only injects the remaining venom into the victim.

- Apply ice to the affected area

- Apply Hydrocortisone Cream 1% to affected area BID (twice a day)

- For anaphylaxis:

- Benadryl injectable 50mg SQ

- Epinephrine 0.3-0.5mg 1:1000 SQ

Prevention

- Leave them alone

- Avoid nesting sites

- Personnel with known allergies should carry an Epi-pen or Ana-kit

Millipedes, Centipedes, and Caterpillars    

Millipedes - some millipedes secrete a toxin on their skin, other large species can squirt secretions from distances up to 32 inches. They secrete their toxin as a defensive mechanism.

Signs and symptoms  

- Secretions in the eye can cause immediate pain, lacrimation, and blurry vision.

Centipedes - any centipede whose fangs can penetrate human skin can cause local envenomation.  Contrary to popular folklore, centipedes do not inject venom with their feet or head.  Their injury is caused by a bite.

Signs and symptoms

Caterpillars - venomous caterpillars have venom in hollow hairs all over their bodies.  Their venom is purely defensive.  There are too many different types of caterpillars to describe.  Your best bet is to leave them alone!

- Leave them alone

- Avoid known nesting sites and hives

- Shake out sleeping bags and clothing and check boots before putting them on.      

Spiders and Scorpions               

Black Widow Spider - glossy black with a red hourglass on the underside of the abdomen.  All Black Widow Spider’s can bite but only the female bite is poisonous and all have a red hourglass pattern on abdomen (see figure 12). 

Signs and Symptoms

- Initial pain is not severe, but severe local pain rapidly develops

- Pain gradually spreads over the entire body and settles in the abdomen and legs

- Weakness

- Sweating

- Excessive salivation

- Rash may occur

- Tremors

- Nausea/vomiting

- Respiratory muscle weakness combined with pain may lead to respiratory arrest

- Anaphylactic reactions can occur but are rare

- Symptoms usually regress after several hours and are usually gone in a few days

Treatment

- Clean site with soap and water

- Intermittent ice for 30 minutes each hour

- Supportive care and antibiotics if needed

Brown Recluse Spider - they are small, light brown, and have a dark brown violin design on the top of their thorax (see figure 13).

Venom - neurotoxic 

Signs and symptoms

- Painless bite.  Most often, the victim does not know they have been bitten.

Treatment

- Cold compresses intermittently

- Provide supportive care as necessary

- Refer to Medical Officer as it is necessary to excise all the indurated (hardened) skin and fascia before healing will begin

- Tetanus prophylaxis and antibiotics are necessary to control secondary infection

- Anaphylactic reactions may occur 

Scorpion Envenomation - these arthropods inhabit warm climates around the world and number greater than 650 species.  Fifty species can cause serious disease in humans (see figure 15).  The most dangerous scorpions in the US inhabit Arizona and portions of California, Texas, and New Mexico.  The size and shape of these arthropods can be both intimidating and frightening, but envenomation, although potentially painful, very rarely produces mortality in humans.

Venom - neurotoxic

Signs and Symptoms

- Erythema and edema

- Local pain and/or paresthesia (an abnormal touch sensation such as burning or prickling often in the absence of external stimulus) at site of sting.

- Cranial nerve dysfunction - blurred vision, wandering eye movements, hypersalivation, trouble swallowing, tongue twitching/spasms, problems with upper airway, and slurred speech.

- Somatic skeletal neuromuscular dysfunction - jerking of extremity(ies), restlessness, and severe involuntary shaking that may be mistaken for a siezure.

Diagnosis

- Positive “Tap Test” - excruciating pain when tapping on the affected area.  This is the only true way to diagnose a scorpion sting.

Treatment

- Based on the level of envenomation

- Ice applied to the site for 30 minutes each hour until symptoms subside

- Oral analgesics

Prevention

- Wear shoes

- When in the field, bedclothes, sleeping bags, and shoes should be shaken out prior to use.

- Many scorpions inhabit brush and debris piles in search of prey.   If you come in contact with this type of material, it is wise to wear gloves.

- Remove wood and rubbish piles around camp

- Cracks and recesses in rural desert dwellings should be filled 

8.  ANAPHYLACTIC SHOCK

Definition - life threatening reaction to an allergen.  This reaction may have a rapid and severe onset. Without immediate emergency medical care, the patient may die.

Causes - exposure to an allergen that causes hypersensitivity reaction.  Such exposure can be introduced to the body by the following:

- Injections (tetanus antitoxin, penicillin)

- Stings (honeybee, wasp, yellow jacket, hornet)

- Ingestion (medications and foods such as shellfish, chocolate, peanuts,etc.)

- Inhalation (dusts, pollen)

- Absorption (certain chemicals)

Signs and Symptoms

All signs & symptoms get progressively worse:

- Skin (Itching, redness, and hives)

- Respiratory depression

Treatment

- Maintain ABC’s

- Diphenhydramine Hydrochloride (Benadryl), which is an antihistamine drug with anticholinergic (drying) and sedative effects.

Indications

- Skin allergies or urticaria (rash)

- Anaphylactic reaction

- Food allergies

Contraindications

- Hypersensitivity to diphenhydramine hydrochloride and other antihistamines of similar chemical structure

Dosage and Administration

- A single injection of 25-50mg IM

- Epinephrine Injection (Ana-Guard) - the most valuable drug for the emergency treatment of severe allergic reactions.

Indications

- Allergic reactions that may be caused by exposure to pollen, food, insects or drugs.

- Severe, life-threatening asthma attacks characterized by wheezing, dyspnea, and inability to breathe.

- Other symptoms may include bronchoconstriction, wheezing, sneezing, hoarseness, urticaria, erythema, and pruritis.

Contraindications

- Must not be used if there is a hypersensivity to any of the components.

- Cardiogenic or hemorrhagic shock

Dosage and Administration

- Epinephrine Injection 1:1000 is contained in a sterile, 1mL syringe, designed to deliver two doses of 0.3 mL or (0.3-0.5ml) each.

- Epi-pen autoinjector

- Intended for subcutaneous or intramuscular use

- Repeat in five minutes if no improvement

- Fluid Resuscitation

- Documentation of the amount of medications and the times they were given is necessary in order to prevent an overdose of medication.

- CASEVAC

REFERENCES

Tropical Medicine (7^th ed.), Pgs 877-888

Wilderness Medicine (3^rd ed.), Ch 28, pgs 680-884, 704-705; Ch 31, pgs 743-768

Hospital Corpsman NAVEDTRA 14295, Pgs 5-12

Poisonous Snakes of the World, NAVMED P-5099 Pgs 83, 107, and 117

REV: July 2008

Envenomation Review

1.  List 5 pit vipers.

2.   List the signs and symptoms associated with the neurotoxin secreted by a coral snake.

3.   List the appropriate treatment for secondary infections associated with a Brown Recluse bite.

4.  What are the two medications required to treat anaphylaxis?  Which is the most valuable?