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



**********



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 wildlife control 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 coral snakes 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: dborys@swmail.sw.org



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%)