STINGRAYS

Blotched Fantail Ray at a depth of 19 meters, Wolf Rock, off Double Island Point (Rainbow Beach), Queensland, 4 August 2006, (Australian Museum)

Introduction

Rays are the largest type of venomous fish.

They are among the commonest causes of fish-related injury and/or envenoming worldwide.

Stingrays are usually placid animals that are non-threatening to humans except if disturbed.

Injury is usually the result of traumatic contact with the stinging barb(s) of the animal’s tail.

Although stingrays do have venom in their tail, the trauma of the injury is usually more important than any venom mediated effects.

These traumatic injuries can be highly lethal, the most famous recent example being that of the death of Australian Wildlife adventurer, Steve Irwin in 2006.

There is no specific antivenom, treatment is supportive, surgical and antibiotics for wound infections.

Biology

Rays are flat-bodied cartilaginous fish of the same class as sharks (Elasmobranchii).

Kingdom: Animalia.

Phylum: Chordata.

Class: Chondrichthyes

Subclass: Elasmobranchii

Order: Myliobatiformes

Suborder: Myliobatoidei

Families (8): Hexatrygonidae, (Six gill stingrays)

Plesiobatidae, (Deep water stingrays)

Urolophidae, (Stingarees)

Urotrygonidae, (Round rays)

Dasyatidae, (Whiptail stingrays)

Potamotrygonidae, (River stingrays)

Gymnuridae, (Butterfly rays)

Myliobatidae, (Eagle rays)

Habitat

Rays are found in temperate and tropical waters worldwide.

Numerous species of are found in waters all around Australia.

They are also found in freshwater systems in tropical regions around South America, Africa, and South East Asia.

Pathophysiology

Although stingray barbs do carry venom, it is generally not highly toxic to humans.

Far more dangerous is the penetrating injury caused by the barb itself.

The sharp bony spine produces a laceration and simultaneously leaves venom in the wound.

The stingray tail may bear one or more spines.

Barb (or spine):

The barb of the stingray, (Gan et al 2008).

The spine is a stiletto-like bilaterally serrated structure that can cause severe lacerations or puncture wounds.

It contains backward-pointing, serrated barbs that consist of a hard bone-like cartilaginous material called vasodentin. It has two ventrolateral grooves lined with venom-secreting glandular cells. The spine structure is enveloped in an integument that rips open when a target is struck. Venom then flows down the ventrolateral grooves of the spine and into the wound.

The spine including its integumentary sheath may break off within the wound, necessitating removal of these as retained foreign bodies.

Venom:

Stingray venom is not well understood.

It contains a large number of both protein and non-protein components, including:

● Thermolabile toxic proteins (including phosphodiesterases and nucleotidases).

● Various degradative enzymes such as hyaluronidases

● Some non-protein components such as serotonin

There are however many other substances present that have not been characterized.

There do not appear to be any anticoagulant, hemolytic, or neuromuscular-blocking agents.

Clinical Features

Physical injury:

Stingrays usually rest on the bottom of the water where they like to feed on molluscs, marine worms and crustaceans living within the sand and most commonly cause an injury when they are unwittingly trodden on. This makes the stingray reflexively whip its highly manoeuvrable tail upward and into the person's foot or ankle.

Injuries to the hands can occur if the fish are handled.

Rarely if divers swim too closely to the animal they can sustain injuries to the neck, chest or abdomen that can cause serious trauma or death.

The venom may cause local tissue necrosis requiring surgical debridement and leading to prolonged healing times.

Secondary infection is also an important complication of spine wounds, especially in wounds that penetrate joint spaces or tendon sheaths, or wounds that are not appropriately cleaned or debrided.

Infecting organisms can include:

● Marine species, such as Vibrio species or Aeromonas species.

● Skin organism: Streptococcus/ Staphylococcus.

● Clostridium in necrotic wounds.

Envenomation:

The major effects of stingray venom include:

1. Local pain:

● This effect is immediate and intense.

● Local pain may last up to 48 hours.

2. Slowly developing local necrosis:

3. Systemic venom effects:

Systemic effects are uncommon and may in fact be secondary to severe pain.

Reported effects have included:

● Nausea/ vomiting

● Diaphoresis

● Tachycardia

● Agitation.

More seriously:

● Hypotension

● Weakness

● Arrhythmias

Investigations

Investigations are done for secondary complications of venom and/ or the trauma inflicted by the barb.

Imaging is done to examine foreign bodies or the complications of penetrating injury.

Blood tests:

● FBE

● U&Es/ glucose

● Troponin.

ECG:

● For arrhythmias or cardiac injury.

Plain radiology:

Stingray barb embedded in the heal of a 37 year old male.

● May be used to detect retained spines.

● CXR for possible haemopneumothorax

Ultrasound:

● May be used to detect retained spines where these are suspected and plain radiology has not detected these.

CT Scan/ CT angiography:

● For penetrating injuries to the neck, chest or abdomen/ pelvis.

Echocardiography:

● For any suspected cardiac injury.

Wound swabs for M&C:

● For late presenting infected wounds.

Management

1. First aid:

● ABC:

♥ Attend to any immediate ABC issues.

♥ Initial treatment is as for a penetrating injury.

♥ Apply local pressure for any bleeding

● Wash wound:

♥ Wash and irrigate wound as required.

● Warm water immersion:

♥ Immerse injured part in hot water (about 45 degrees, or as hot as the victim can tolerate).

♥ This should be to a maximum duration of around 90 minutes.

♥ An unaffected limb must be used to check tolerance of the temperature first.

● Spine removal:

♥ The spine can be removed if very superficial, but in general should not be removed if it is more deeply embedded.

● Pressure immobilization bandaging (PIB) is not recommended.

2. Analgesia:

● Titrate IV opioid analgesia as clinically required.

● Regional nerve block anaesthesia is a further option for severe local pain.

♥ Adrenaline should be avoided with local anesthetic injections as it may delay microvascular clearance and increase the risk of local necrosis.

3. Trauma:

● Resuscitate as required for any penetrating thoracic or abdominal injuries

● The spine and its integumentary sheath may break off within the wound, necessitating removal of these as retained foreign bodies.

4. Venom effects:

● Treat symptomatically as required.

5. Tetanus immunoprophylaxis as clinically indicated.

6. Antibiotics:

For established infection:

● Doxycycline is used for vibrio infections

● Ciprofloxacin is used for Aeromonas species

There is controversy over prophylactic antibiotics but they should be considered with:

● Larger wounds

● Wounds with retained foreign material

● Delayed presentations.

See latest Antibiotic Therapeutic Guidelines for further prescribing details.

Disposition:

An observation period of 4 hours for systemic signs and symptoms has been suggested before discharge.

Surgical consultation will be required for deep injuries, injuries to the chest or abdomen, or with retained spine material.

Microbiology and Infectious Disease referrals may be required for more serious established wound infections.

References

1. Geoffrey K Isbister, Managing injuries by venomous sea creatures in Australia. Aust Prescr. 2007; 30: p.117–21.

2. Cook MD et al. Stingray Envenomation, The Journal of Emergency Medicine, Vol. 30, No. 3, p. 345 - 347, 2006.

Dr J. Hayes February 2014.