Stingray Envenomation

Stingray venom is highly complex chemically. For example, analysis of Potamotrygon motoro (ocellate river stingray), has shown the presence of hyaluronidase, cystatin, and calglandulin. The hyaluronidase present is unique to stingrays and differs from the hyaluronidase found in the venom of bony fish species. There is large variation in the composition of stingray venom, even among related freshwater species.[4]   

In rodent models, it has been discovered that P motoro venom causes both neurogenic and inflammatory pain. Neurokinins, calcium, and histamines are among the neuroinflammatory mediators in the venom that contribute to the extreme pain associated with P motoro stings.[5] Kirchhoff et al found from analysis of 5 stingray venom transcriptomes that toxins present in these venoms responsible for hyperalgesia primarily activate the inositol-3-phosphate receptor cascade. This activation causes the release of intracellular calcium. There was also evidence for synergistic activity among toxins, with tumor proteins and nerve growth factors working in unison to activate pain-signaling pathways.[6]

According to the National Capital Poison Center, there are approximately 1500-2000 stingray injuries reported in the United States each year.[7] More detailed statistics are unavailable, but several international surveys of local incidence have been undertaken. A survey of 392 marine toxicology cases reported to a South African poison control center from 1995-2014 revealed 36 (9.2%) were regarding stingray envenomations.[8]  A separate survey of 300 adults living in the Tapajos River Basin of Brazil revealed that 19 (6.3%) respondents had experienced stingray injuries in the past 12 months.[9]

Following is an example of discharge instructions that could be given to patients after treatment of stingray injuries.

Because so many areas of water are nearby, many types of injuries associated with being in or near the water are encountered. These injuries may occur while fishing, walking on the beach, playing in the surf, diving, or working with a home aquarium.

Stingrays often cause lacerations and puncture wounds when the tail whips up and thrusts its barbed spine into the victim, depositing venom (poison). The pain is severe immediately and worsens over the next hour. The pain may last 48 hours. Although rare, deaths have occurred from stingray injuries.

As soon as possible, the wound should be soaked for 30-90 minutes in very hot water (as hot as can be endured without causing burns). The heat inactivates the poison and dramatically relieves the pain. The physician may prescribe pain medication. Also, because the risk of infection is very high, antibiotics are given to prevent infection.

Despite the best of care, any wound can develop infection or other complications. If any of the following occur, it is recommended that patients call their own doctor, the referral physician, or clinic (If a physician cannot be contacted, return to the ED is advised.):

• Wound drainage increases, shows pus, or develops a foul odor

• Wound bleeds heavily

• Wound becomes more sore or swollen

• Wound develops increasing redness, or red streaks develop

• A fever develops

• Wound does not appear to be healing properly

• Any other new or worsening symptoms that are of concern

The wound may bleed freely and the patient may have systemic symptoms, including the following:

• Syncope

• Nausea

• Vomiting

• Diarrhea

• Diaphoresis

• Muscle cramps

• Fasciculations

• Abdominal pain

• Seizures

• Hypotension

Puncture wounds can cause injury to large vessels, and exsanguination following laceration of lower extremity arteries has been reported. Pseudoaneurysm of the superficial femoral artery has been reported following stingray envenomation.[10]

Stringray wounds are shown in the images below.

Typical stingray puncture wound on a foot, approximately 60 minutes after injury. Photo by John L. Meade, MD.

Stingray barb in forearm. Photo by John L. Meade, MD.

The most frequent complication seen with stingray injuries is bacterial infection. The infection may originate from the stingray barb, the surrounding water, or debris that enters the wound, such as sand. In 1 recorded case, an iatrogenic infection developed after a sting to ankle was treated with application of a chewed unknown plant root and attempts to suck the venom out by mouth. Sepsis ensued, and the wound culture grew normal oral flora. Treatment using intravenous antibiotics, surgical debridement, and vacuum dressing was successful, but this case underscores the importance of avoiding oral suction on any wound.[11]

Necrotizing fasciitis from Photobacterium damsela resulted in a stingray laceration case from Florida.[12]

In a rare case from Costa Rica, a 12-year-old male experienced a stingray injury to the spine with fracture of the posterior elements of the C6 vertebra. The patient suffered significant neurologic impairment, presenting with a complete asymmetric right C6/left T1 American Spinal Cord Injury Association (ASIA) A examination, loss of anal sphincter tone, and priapism. He made a good recovery over the following 3 months. This case illustrates a stingray injury instance in which the chief medical concern is not envenomation but penetrating injury from the barb.[13]  

Note that some patients have experienced refractory pain after stingray envenomation. There is at least 1 reported case of regional anesthesia, specifically an ultrasound-guided sciatic popliteal nerve block, being used to treat hyperalgesia in the setting of stingray envenomation.[14]

If a patient has demonstrated any sign of systemic effect, it should be addressed quickly.

No specific antidote is available, and supportive care is recommended, including use of analgesics.

An easy and important initial treatment that can be started (sometimes at the scene of the injury) is immersion of the injured extremity in hot water (preferably 110-115°F). The water should be as hot as the patient can tolerate but should not cause burns. The water should be exchanged for more hot water as it cools, for an immersion duration of 30-90 minutes.

Very little has been written about the toxin left in wounds after a stingray injury. It is known that the stingray toxin is a protein and is very sensitive to heat. The patient should obtain very rapid symptomatic improvement with heat as the poison denatures and becomes neutralized. Some thought exists that the protein does not truly denature but that some sort of gateway effect occurs on the nerve conduction. Whatever the mechanism, heat is a rapid, effective treatment to reduce pain almost instantaneously.

In addition, some practitioners also infiltrate the wound with a local anesthetic, such as lidocaine (lignocaine)[15] or the longer-acting bupivacaine. Oral or parenteral narcotics may also be given if the patient is suffering severe pain. The effectiveness of hot water immersion may eliminate the need for local anesthetic infiltration.

After the toxin has been deactivated by the hot water, attention to local wound care should begin because it is not uncommon for part of the stinging apparatus to break off in the wound.

Obtain a plain radiographic image of the injured area to look for retained barbs or other foreign material. Explore the wound thoroughly and irrigate it. Perform any necessary debridement.[16]

Remove any foreign body from the wounds, including the spine and sheath from the stingray stinger (if present), as well as any dirt or sand.

As with other potentially contaminated wounds, consider allowing the wound to heal without closure. Because most of the wounds are small, this usually is not an issue. If the wound is very large or gaping, consider loose primary closure.

Address the patient's tetanus immunization status and administer a booster as needed.

Give patients explicit instructions regarding attention to local wound care and advise them to watch for infection. Requesting that the patient seek a wound check in 2-3 days (with a family doctor or at the ED) is not unreasonable.

It is especially vital that the patient understands that for any sign of infection with Vibrio organisms, time is of the essence in returning to the ED for immediate care.

Infection is not common but, if it occurs, is likely to result in high morbidity because of injury location and the possible infecting agents in the water environment. Staphylococci and streptococci remain the most common infecting agents and must not be ignored. However, pathogens of specific concern to such envenomations are Vibrio species in saltwater and Aeromonas species in freshwater. Optimal coverage should include staphylococci, streptococci, and pathogens expected in the involved water (freshwater or saltwater). Such antibiotics include quinolones (eg, ciprofloxacin, levofloxacin), doxycycline, trimethoprim/sulfamethoxazole (Bactrim, Septra), cefuroxime or other late-generation cephalosporins, an aminoglycoside, or chloramphenicol.

As 1 study[17] showed a significant number of patients returning to the emergency department with wound infections when prophylactic antibiotics were not administered at initial presentation, many physicians choose to treat the wounds associated with stingray envenomations prophylactically with a short course (~5 days) of oral antibiotics.

Prescribing oral narcotics for patients to use as needed upon discharge is appropriate.

Class Summary

Antibiotics are used in the treatment of uncomplicated infections and wound prophylaxis. Empiric antimicrobial therapy must be comprehensive and should cover all likely pathogens in the context of the clinical setting.

Levofloxacin (Levaquin)

Levofloxacin is first-line treatment for infections caused by Vibrio species found in saltwater. It is indicated for Staphylococcus aureus and infections caused by multidrug resistant gram-negative organisms.

Cefixime (Suprax)

By binding to one or more of the penicillin binding proteins, cefixime arrests bacterial cell wall synthesis and inhibits bacterial growth. It is an advanced-generation cephalosporin.Its advantages include a once-per-day dosing schedule and broad spectrum. A disadvantage is relatively high cost.

Cephalexin (Keflex)

Cephalexin is a first-generation cephalosporin, which is usually effective against Staphylococcus and Streptococcus species. It is inexpensive and readily available, but it has no real efficacy against Vibrio species.

Doxycycline (Bio-Tab, Doryx, Vibramycin)

Doxycycline inhibits protein synthesis and, thus, bacterial growth, by binding to 30S and, possibly, 50S ribosomal subunits of susceptible bacteria. It covers Vibrio species well, although coverage is not as good for Staphylococcus and Streptococcus species. Generic versions are inexpensive.

Trimethoprim and sulfamethoxazole (TMP-SMZ, Bactrim, Septra)

This combination inhibits bacterial growth by inhibiting the synthesis of dihydrofolic acid. It is an inexpensive combination agent that covers Vibrio and some Staphylococcus and Streptococcus species.

As with doxycycline, many individuals can develop photosensitive skin rashes while on the medication. (This is important if the patient is on vacation or lives at the beach and is likely to get significant sun exposure while on the medication.)