Texas coral snake (Micrurus tener) bites.

Background: The clinical features of bites from Texas coral snakes (Micrurus tener) have not been well studied. Our goal was to review the largest number of victims of Texas coral snakebites to determine their characteristics, effects, treatment, and outcome.

Methods: Retrospective case series of Micrurus tener exposures reported to the Texas Poison Center Network from 2000 to 2004.

Results: Eighty-two patients were included in the analysis. Most (57.3%) were 18 to 49-year-old men. Almost 90% had local swelling, pain, erythema, or paresthesias. Only 7.3% had systemic effects, and none of these were severe. Over half received coral snake antivenin, and 15.9% were given opioids for pain. No patient died and no patient required mechanical ventilation due to hypoventilation from the snakebite.

Conclusions: There were more local findings and less severe systemic effects than previously reported. Antivenin is not needed for most of these patients, and opioids may be administered safely.

Key Words: coral snake, snake bites, Micrurus tener, Micrurus fulvius tenere, Texas, venom

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In the United States, bites from coral snakes account for less than 2% of the total reported snakebites to people. (1-4) The majority of venomous snakebites are by pit vipers (rattlesnakes, cottonmouths, and copperheads). (3) Coral snakes differ from pit vipers in appearance, venom-delivery apparatus, venom composition, and venom effects. They can be identified by their black noses and the bright red, yellow, and black circumferential bands. (5) Their venom produces much less local tissue damage and hematological abnormalities than that of the pit vipers. However, peptides in the venom block postsynaptic acetylcholine receptors (4) and may produce severe delayed systemic effects, including paralysis, respiratory depression, and even death. (3,5-8) Coral snakes produce less venom than pit vipers, but the venom is more potent than that of all of US snakes except the Mojave rattlesnake (Crotalus scutulatus). (8)

Coral snakes are in the family Elapidae and are found in the southeastern United States, Mexico, Central and South America. (9) However, only two species (each having multiple subspecies) are responsible for all coral snake toxicity in the United States: Micrurus fulvius fulvius (Eastern coral snake) and Micrurus tener (Texas coral snake). (7) These two coral snakes were previously classified as subspecies of the same species. They have a similar appearance, but there are morphologic differences between them. The other coral snake in the United States does not envenomate people: Micruroides euryxanthus (Sonoran, Western, or Arizona coral snake). (5,7) It is estimated that the Eastern and Texas coral snakes together bite less than 150 victims every year. (4) The Eastern coral snake lives east of the Mississippi river in many southeastern states. The Texas coral snake is found only in parts of three states: southern and eastern Texas, southern Arkansas, and in Louisiana, west of the Mississippi river. (4) Most of the published coral snakebite knowledge has been limited to those pertaining to Eastern coral snakes. (4,6,7,9,10) No large case series of patients with Texas coral snake bites have been published. A review of the medical literature found less than twenty Texas coral snake victims. (2,5,11) The effects from Texas coral snakebites are believed to be similar to, but not as severe as those from Eastern coral snakes. (5) Our goal was to review a series of patients to determine the characteristics, effects, treatment and outcome of Texas coral snakebites.

Methods

This was a retrospective case review of patients with a bite from a coral snake referred to any of the six poison centers that make up the Texas Poison Center Network: Central Texas, North Texas, South Texas, Southeast Texas, Texas Panhandle, and West Texas Poison Center. A medical record is created for each human exposure and is stored in a secure electronic database. Follow-up telephone calls are made by the poison center specialist in poison information to the treating healthcare facility or to the patient.

The Texas Poison Center Network database of medical records was searched for all human exposures to coral snakes. Study inclusion criteria included human exposure, envenomation, coral snake regardless of subspecies, and occurrence between January 1, 2000, and December 31, 2004. A case was secondarily excluded if there was no follow-up call recorded, no treatment information or if the snake was later identified not to be a coral snake. Coral snakes were positively identified only by an expert, a treating physician, or by the detailed description told to the poison center staff. Local findings were defined as pain, swelling, erythema, paresthesias, and fasciculations. Systemic effects were defined as nausea, vomiting, dizziness, lethargy, salivation, euphoria, tremors, slurred speech, ptosis, diplopia, dyspnea, dysphagia, muscle weakness, respiratory depression, or seizures. A disruption of the skin was defined as a puncture wound, abrasion, or scratch. Local Institutional Review Board review was obtained before the study. The Wilson score method without continuity correction was used to calculate 95% confidence intervals for the main outcomes.

Results

Patient Demographics

There were 96 records regarding human exposure to coral snake venom in the Texas Poison Center database that met the inclusion criteria. This represented only 2.3% of all snakebites in Texas. Of these, fourteen calls were excluded due to duplication, misidentification of the snake, or no follow-up information. The medical records for the remaining 82 patients were analyzed. The number of calls for each of the study years from 2000 to 2004 was 16, 8, 20, 22, and 16. Over 85% of the bites occurred during the seven months from April to October (Fig. 1). Most patients were male (85.4%). There were 17 (20.7%) children (Fig. 2). The calls usually came quickly after the bite occurred. Most (90.2%) of the calls had the time of the bite recorded, and all were within 24 hours of the bite. Of these, 70.3% were within 1 hour of the bite, and 91.9% were within three hours.

Snake Factors

In 22 cases (26.8%), the snake was positively identified as a coral snake by the study criteria. Half (n = 11) received antivenin. Of those 60 without a positive identification, 50 (83.3%) had some local effects (pain, swelling, or paresthesia). Only 24 (29.3%) had the snake biting behavior noted. Ten (41.7%) of these stated the snake held on for a few seconds or more. Fourteen (58.3%) stated the snake let go quickly after the strike and did not "hang on" or "chew." Of those 14 who received only a quick strike, 13 (92.9%) had a mild local reaction, and one patient had a moderate local reaction. Four of these 14 patients received coral snake antivenin.

[FIGURE 1 OMITTED]

Bite Location

Of those who had the bite location recorded (89.0%), most (94.5%) were bitten on the upper extremity. Forty-six (56.1%) were bitten on a finger. Four patients (5.5%) were bitten on the foot or ankle. Only 29 cases recorded whether or not the victim was handling the snake before the bite. Of these, 79.3% were handling the snake.

Local Signs and Symptoms

Examination of the bite site revealed ten patients (12.2%) who had no visible skin disruption at the bite site. Three of these ten patients had local effects and one had systemic effects. For the 68 patients (82.9%) who had a wound at the bite site, 86.8% had local effects and 7.4% had systemic effects. Only eleven (13.4%, 95% CI: 7.7-22.4%) of the 82 patients had no local or systemic signs or symptoms. Seventy (85.4%, 95% CI: 76.1-91.4%) of the 82 patients had some abnormal finding at the bite site. Thirty-eight patients (46.3%, 95% CI: 36.0-57.1%) noted localized swelling, and 3 (3.7%) had significant swelling. Thirty-five (42.7%, 95% CI: 32.5-53.5%) patients reported some pain, and 13 (15.9%) reported more than mild pain that required multiple doses of medication. This pain frequently radiated up the arm or to the chest. Twenty-four patients (29.3%) were noted to have both pain and swelling, and two patients (2.4%) had both significant pain and significant swelling. Other local findings were erythema, paresthesia, numbness, and a small area of ecchymosis (Table 1).

Systemic Effects

Only six patients (7.3%, 95% CI: 3.4-15.1%) had systemic effects. These were all men from 17 to 51 years old who were bitten on the hand or finger. Four of the six stated the snake "held on" for a few seconds. They all received antivenin. All except one of these also had local effects (pain, swelling, or erythema). The exception was a man who went to the hospital almost 12 hours after being bitten because he was having joint pain and generalized fatigue but had no skin disruption at the bite site. Another patient, who had a chronic seizure disorder, presented within 30 minutes of the bite with status epilepticus. He had endotracheal intubation at arrival to the healthcare facility. The next day, he was extubated and discharged home. The systemic effects of these two patients were probably not the result of the snakebite. The other four patients presented with one or more of the following symptoms: mild shortness of breath, fatigue, nausea, vomiting, facial flushing, muscle jerking, weakness and dizziness. All these systemic effects occurred within three hours of the bite. None of these four patients had a severe systemic reaction to the snakebite, although all (except the late presenter) received coral snake antivenin within eight hours of the bite.

[FIGURE 2 OMITTED]

Hospital Length of Stay

Seventy-nine (96.3%) were treated in a healthcare facility such as a hospital emergency department. Hospital observation was the most common treatment. Seventy-two had their hospital discharge time recorded or estimated. For those who were hospitalized for a known time, 66.7% were discharged within 24 hours (Fig. 3).

Antivenin

Forty-five (54.9%) patients were treated with "North American coral snake antivenin. The antivenin administration time was noted in 86.7% of the cases. Seventeen had antivenin given within three hours of the snakebite. All but three patients (51.2%) had the antivenin initiated within eight hours of the bite. One person received antivenin 16 hours after the bite. One patient was administered only half a vial of antivenin due to an adverse reaction. Thirty-nine patients (86.7%) received three to five vials of antivenin. The maximum dose was six vials. Five patients (11.1%) had an adverse reaction to the antivenin. Three patients had lip and/or tongue swelling, one had a pruritic rash, and one had anaphylaxis.

Thirty-seven (45.1%) victims did not receive antivenin. Nine of these (24.3%) were bitten by a confirmed coral snake and had skin breakage. Thirty-one victims (83.8%) who did not receive antivenin had a local reaction (pain, swelling, erythema, or paresthesias). Two patients had severe pain. None of these patients had any systemic reactions. All thirty-four patients treated in a healthcare facility were discharged within 36 hours.

[FIGURE 3 OMITTED]

Other Treatments

Thirteen patients (15.9%) received opioid medication (usually morphine) for pain, 14.6% had antihistamines, and 8.5% had antibiotics. Other treatments included steroids, nonopiate pain medication, anti-emetics, and benzodiazepines. Local wound care and IV fluid administration were common treatments.

Outcome

Patients were followed by the poison centers after the bite to determine outcome. Over 92% were followed for six hours, and 78.0% were followed for 24 hours or more. Most (84.1%) had no effects or only mild effects from the snakebite. This included those with only minor local effects (swelling, pain, erythema) and those with minor systemic effects (nausea, fatigue, dizziness, other). No patient had severe local or systemic effects. No patient had paralysis, diplopia, or required intubation due to paralysis, and there were no deaths (0%, 95% CI 0-4.5%).

Discussion

Before the introduction of the North American coral snake antivenin in 1967, there was about 1 death every few years from the Eastern coral snake. (1,7,8,10,12) The number of deaths from Texas coral snakes during this time is unknown. Although the coral snake antivenin is indicated for both the Eastern and Texas coral snake regardless of symptoms, (3) it is believed that the bites from the Eastern are more severe than those of the Texas. (5) There have been no reported deaths from coral snakebites in the United States from 1967 to 2005. (4) Only a few descriptions of patients bitten by Eastern coral snakes have been published. (4,6,7,9,10) They have described the following characteristics: swelling, paresthesias, nausea, vomiting, dizziness, lethargy, salivation, euphoria, tremors, slurred speech, ptosis, diplopia, dyspnea, dysphagia, muscle weakness, respiratory depression, and seizures. There are even fewer published reports of Texas coral snakebites. In 1960, Stimson and Engelhardt (11) stated none of the nine coral snake patients in Texas had serious effects from a coral snakebite. Parrish and Khan (5) reported that none of the five patients bitten by Texas coral snakes had any serious symptoms, but at least one had "minimal swelling." Norris and Dart (2) reported on a patient bitten by a Texas coral snake who had only paresthesias.

Our study confirms many characteristics of Texas coral snakebites that have been based on Eastern coral snakebite studies. Very few snakebites occurred in late fall and winter. (6) Most bites occurred on the finger or hand, probably due to the small size of the snakes' mouths. (5,6,8) Many occurred while the victim was handling the snake. (5,6) As in previous studies, most victims were adult men. (5,6) Visible wounds (puncture, scratches, or abrasions) from the bite are common. (5,6) However, a wound does not have to be present to have envenomation. (2) None of our patients had the severe tissue damage seen with pit viper bites, but not seen in previous coral snake studies. In fact, some patients (13.4%) had no local or systemic signs or symptoms. (6) Previous studies report minor swelling and no pain. (5,10) The majority of our patients did not have swelling noted, and most of the remainder had only minor swelling. Most patients had no pain reported. No patient died or had permanent neurologic sequelae. These are the same results reported by Kitchens and Van Mierop (6) in the largest Eastern coral snake study published to date. Of note, 35% of the patients from that study that received antivenin developed a drug reaction, including one with anaphylaxis. Only 11% of our patients had an adverse drug reaction to the antivenin. This low rate is probably due to the frequency that steroids and antihistamines were administered prophylactically before the antivenin.

This study contradicts some findings from other studies of the Eastern coral snake. These studies state that most Eastern coral snakes hang on to their victims for several seconds. (5,6) Although this factor was not well recorded in our study, more than half of the patients who noted the bite characteristic stated the snake let go of the skin immediately. Apparently, these snakes can inject enough venom with a quick strike to cause a moderate local reaction. Our patients were older than those of previous studies. (5,6) Several authors report the death rate for coral snakebites that do not receive antivenin is 10 to 20%. (2,4,5) This seems extremely unlikely for victims of Texas coral snakebites since none of our 37 patients who did not receive antivenin developed any systemic findings. Neurologic findings are common with the Eastern coral snake. (3,5,6,9,10) None of the Texas coral snakebite victims developed neurologic findings other than paresthesias. Respiratory paralysis requiring mechanical ventilation occurs in some patients bitten by the Eastern coral snake. (6,9,10) This has not been recorded with the Texas coral snake. Some authors have suggested that over 20% of Eastern coral snakebites are "dry bites" causing no envenomation to the victim. (6,13) However, only about 6 to 13% of victims of Texas coral snakes have dry bites, depending on the definition used. We found a much higher fraction of patients with local pain and swelling than have been reported for the Eastern coral snake. (2-8) Others have stated that all coral snake victims should be hospitalized for 48 hours, and none should receive morphine. (5,6) About 70% of our patients were discharged from the hospital within 24 hours of the bite, and 15.9% received opioids for pain.

Our study verifies many concepts pertaining to Texas coral snakebites. These bites produce less severe effects than bites from the Eastern coral snake. (5) They seldom, if ever, cause death or paralysis. (5) Our study contradicts many previous beliefs about Texas coral snakes. Texas coral snakes frequently do not chew or hang on when they bite. However, they may envenomate without chewing. Frequently, there are local minor signs and symptoms (pain, swelling, erythema, or paresthesias). These rarely may be more than minor, but the pain and swelling resolves within 24 hours. The paresthesias may last for weeks. Bites from Texas coral snakes do not produce severe systemic symptoms, even without the administration of antivenin, and antivenin is not needed for every bite.

This retrospective study of patients reported to Texas poison centers has several limitations. Not all coral snakebites in Texas were reported to the Texas poison centers. Victims who did not seek medical care may not have called the local poison center. In addition, treating physicians may not have called the poison center, allowing that some patients with serious envenomations not be included in this study. However, this is the largest study of North American coral snakebites, and the findings should remain valid, even if additional patients are later found. Since this study was retrospective, only the data collected for routine poison center use was reviewed. If the data was not reported, collected or recorded accurately or completely, the results could be invalid. Only 22 of the snakes involved were positively identified as coral snakes by the study's criteria. Some bites could have been from snakes other than the Texas coral snake. The scarlet king snake (Lampropeltis triangulum elap-soides), which looks similar to the coral snake ("Red on Black, Venom Lack" and has a red snout), is nonvenomous. However, since none of the victims had a serious systemic effect, the removal of a few patients bitten by nonvenomous snakes would not affect the major results. Some of the snakes could have been other venomous pet snakes such as a different species of Micrurus (Eastern coral snake or Mexican coral snake). Since these are thought to have more serious effects than the Texas coral snake, this limitation should not affect the major results. The major limitation of the study is the fact that over half of the patients received antivenin. This was not done randomly, and the patients that received the antivenin were likely more poisoned than those who did not receive it. The administration of the antivenin may have prevented serious progression of the effects of the venom in this group. But it remains remarkable that in this study, none of the patients (with or without antivenin) developed serious neurologic or respiratory problems.

Conclusion

Poison Center data of 82 patients with bites from Texas coral snakes were analyzed and revealed that most were men, age 18 to 49 years old, bitten on a finger. A skin disruption at the bite site was noted for over 80%, and almost 90% had local swelling, pain, erythema, or paresthesia. Only 7.3% had systemic effects, and none of these were severe. Over half received coral snake antivenin, and 15.9% were given opioids for pain. No patient died and no patient required mechanical ventilation due to hypoventilation from the snakebite. This review of Texas coral snakebites found more severe local findings, and less severe systemic effects than previously reported. Antivenin is not needed for most of these patients, and opioids may be given safely.

References

1. Parrish HM. On the incidence of poisonous snakebites in Florida: analysis of 241 cases occurring during 1954 and 1955. Am J Trop Med Hyg 1957;6:761-764.

2. Norris RL, Dart RC. Apparent coral snake envenomation in a patient without visible fang marks. Am J Emerg Med 1989;7:402-405.

3. Gold BS, Barrish RA, Dart RC. North American snake envenomation: diagnosis, treatment, and management. Emerg Med Clin N Am 2004;22:423-443.

4. German BT, Hack JB, Brewer K, et al. Pressure-immobilization bandages delay toxicity in a porcine model of eastern coral snake (Micrurus fulvius micrurus) envenomation. Ann Emerg Med 2005;45:603-608.

5. Parrish HM, Khan MS. Bites of coral snakes: report of 11 representative cases. Am J Med Sci 1967;253:561-568.

6. Kitchens CS, Van Mierop LH. Envenomation by the Eastern coral snake (Micrurus fulvius fulvius). JAMA 1987;258:1615-1618.

7. McCollough NC, Gennaro JF. Coral snake bites in the United States. J Fla Med Assoc 1963;49:968-972.

8. Wingert WA, Waisnshel J. Diagnosis and management of envenomation by poisonous snakes. South Med J 1975;68:1015-1026.

9. Ramsey GF, Klickstein GD. Coral snake bite: report of a case and suggested therapy. JAMA 1962;182:949-951.

10. Mosely T. Coral snake bite: recovery following symptoms of respiratory paralysis. Ann Surg 1966;163:943-948.

11. Stimson AC, Engelhardt HT. The treatment of snakebite. J Occup Med 1960;2:163-168.

12. Parrish HM. Deaths from bites and stings of venomous animals and insects in the United States. Arch Intern Med 1959;104:198-207.

13. Russell FE, Carlson RW, Wainschel J, et al. Snake venom poisoning in the United States experience with 550 cases. JAMA 1975;233:341-344.

David L. Morgan, MD, Douglas J. Borys, PharmD, Rhandi Stanford, PharmD, Dean Kjar, BS, and William Tobleman, MD

From the Central Texas Poison Center, the Department of Emergency Medicine, Scott and White Memorial Hospital, Texas A & M System Health Science Center, Temple, TX.

Reprint requests to David L. Morgan, MD, Department of Emergency Medicine, Scott and White Memorial Hospital, 2401 South 31st Street, Temple, TX 76508. Email: [e-mail]

Preliminary data from the study was presented at the North American Congress of Clinical Toxicology annual meeting in Orlando, FL, September, 2005.

Accepted June 9, 2006.

RELATED ARTICLE: Key Points

** Only a few studies have described the clinical effects of coral snake bites in the US, and most of these were limited to the Eastern coral snake.

** Texas coral snake bites frequently produce local effects in many patients.

** Texas coral snakes bites rarely produce systemic findings. Texas coral snakes require antivenin only in the unlikely event of severe systemic effects.

** This study is limited by its retrospective nature and reliance on nonprofessional identification of the snake.

RELATED ARTICLE: Recommendations for Texas Coral Snake Bites

1. Attempt to identify the snake ("Red on Yellow, Kill a Fellow", black snout).

2. Do not incise the wound or suck venom from the wound.

3. Provide wound care and fluids. (These bites will not have the severe local tissue damage and ecchymosis seen with pit viper bites.)

4. Use pressure-immobilization bandage on the extremity. (4)

5. Administer pain medication (opioid or other) as needed.

6. Observe for 8 hours to assure no anaphylaxis to the venom and no worsening signs and symptoms of envenomation.

7. No antivenin is needed for only mild swelling and mild pain.

8. No need to prophylactically treat the bite of a Texas coral snake with antivenin.

9. Consider 3 to 5 vials of coral snake antivenin for systemic effects or progressive local effects.

*These recommendations do not apply to those patients bitten east of the Mississippi River.

Table. Local findings

Puncture/scratches  68 (82.9%)
Swelling            38 (46.3%)
Pain                35 (42.7%)
Erythema            19 (23.2%)
Paresthesia         10 (12.2%)
Numbness             3 (3.7%)
Ecchymosis           1 (1.2%)
None                11 (13.4%)