True or false coral snake: is it worth the risk? A Micrurus corallinus case report

Most tropical countries face morbidity and mortality induced by animal envenomation as a group of neglected diseases. Incidence of snakebites is over two million cases per year worldwide, with approximately 100,000 deaths, and non-estimated transient or permanent sequelae [1–4]. In Brazil, official data report approximately 27,000 accidents involving snakes per year, most of which caused by pit vipers (Bothrops, 71.41%), rattlesnakes (Crotalus, 7.03%), bushmasters (Lachesis, 3%) and true corals (Micrurus, 0.78%) [5, 6].

The genus Micrurus (the so-called true coral snakes) has a wide geographic distribution in Brazil. Micrurus corallinus and Micrurus frontalis are the two most frequent species, and Fig. 1 shows the distribution of the former in Brazilian coast [7]. Micrurus spp. have small to medium size, with short maxillary fangs (proteroglyph dentition) and are characterized by marked and attractive reddish coloration, presenting complete black, yellow or white rings around the body [8, 9]. The venom of these snakes generally present neurotoxic, myotoxic, nephrotoxic, hemorrhagic and edematogenic activities. Moreover, neuromuscular blockade comprises the systemic hallmark of envenoming by Micrurus spp. [10]. Due to resembling colors and rings, they are commonly mistaken for non-venomous snakes of families Dipsadidae, Colubridae and Aniliidae, altogether referred to as false coral snakes [10].

Coral snakes are generally not aggressive or prone to biting, and when confronted by humans they will most likely attempt to flee, so they bite only as a last resort [11]. Although uncommon, envenomation by Micrurus spp. in humans should always be considered serious. Therefore, public health systems ought to regard the antielapidic serum (AES) availability and administration, and its efficacy in neutralizing the venom toxins. Many people may have already heard: when facing a snake that resembles a coral snake, do not hesitate in considering it a true coral. Inadvertent manipulation of coral snakes when considering the animal to be a non-venomous specimen accounts for many cases of envenomation, which poses the question: is it worth to handle coral snakes unnecessarily? In this case report, we aim to describe such a case of envenoming by Micrurus corallinus that occurred in the city of Cachoeiras de Macacu, RJ, Brazil.

A 28-year-old Caucasian sailor man, born and living in Cachoeiras de Macacu, RJ, was in a recreational camp with a group of friends when he spotted a snake on the ground. A biologist present on the camp captured the animal with his bare hands believing it was a false coral snake (Fig. 2). The snake was photographed and imprudently manipulated by many people in the camp, including the patient, who was bitten on the back of the right hand, between the thumb and index finger around 1:00 p.m.

A few minutes later, the patient complained of mild local pain. During the afternoon, due to the beginning of visual disturbances, the friends of the victim took him to the city hospital, 20 km away from the camp. On admission, 6 h after the accident, he received 1000 mL of 0.9% NaCl saline solution and 500 mg hydrocortisone intravenously. Since the health unit did not have antielapidic serum (AES), the patient was transferred to the Hospital das Clínicas Constantino Ottaviano, in the city of Teresópolis, RJ, where he arrived around 8 h following the accident.

At that moment, the patient was presenting neurotoxic manifestations such as bilateral palpebral ptosis, diplopia, dysphagia and tongue paresthesia, in addition to low back pain. Vital signs were all within normal range (body temperature 36.7 °C, blood pressure 110/70 mmHg, pulse 78 bpm, and breathing rate 16 bpm). On the bite site (Fig. 3), there were no signs of local damage, such as edema or hyperemia. The patient received 100 mL of AES, divided into two doses of 50 mL each. Five vials (10 mL each) were sent from the Sul Fluminense University Hospital, Vassouras, RJ (140 km away) and the other five vials were from the Oswaldo Cruz Foundation, FioCruz, Rio de Janeiro, RJ (95 km away).

The report of this case aims to raise some questions, the most important of which is: is it worth to classify a coral snake as non-venomous, even if you are a specialist? The Brazilian literature [6, 10, 12, 13] describes accidents with coral snakes as rare, even when cases with non-venomous species are considered. Due to their non-aggressive behavior, most accidents involving coral snakes are the result of incorrect or reckless handling of these snakes, so that hands and fingers are more frequently affected [14–16]. Elapid envenoming is a public health problem in several regions of the world. The high diversity of Micrurus species in Brazil should raise concern for human accidents, because genomic variations in individuals of different species within the same genus are significant and relevant, especially when we analyze the differences in the proteins that compose the venoms [17, 18]. Such variations directly affect the immunogenicity and the different physiological changes caused in cases of envenoming.

Micrurus venoms have several pharmacological actions, the most common being neurotoxic, myotoxic, edematogenic and hemorrhagic [10]. Remarkable presynaptic actions of phospholipases A₂ or postsynaptic effects of three-finger toxins (3FTx) provoke neuromuscular blockage, with variable effects in contraction capacity and muscle strength. Intense muscular paralysis reaching diaphragm is the cause of death in cases of expressive Micrurus envenomation [19, 20]. Some previous observations described that some coral snake venoms are able to damage skeletal muscle fibers and induce myonecrosis [21]. In the present case, plasma CK activity did not change significantly to suggest relevant myotoxic activity, which, besides the limited neuromuscular effect observed, indicates that the amount of venom (e.g., snake age) or the size of the victim are important in the observed outcomes.

Officially, AES in Brazil is manufactured by the Butantan Institute in São Paulo, and by the Ezequiel Dias Foundation in Minas Gerais. It is produced based on the venoms of M. corallinus and M. frontalis. These species are relatively common in populous regions in Brazil, such as South and Southeast, which facilitates the collection of specimens to obtain the venom (Fig. 1). However, studies with venoms from different Micrurus species have shown that they present a variety of toxins in their composition. For example, M. corallinus venom presents higher amounts of PLA₂ than 3FTx [22], which could diminish or even significantly limit the protective capacity of the standard AES when used in accidents caused by different species of snakes of this genus [19, 21, 23, 24].

Another relevant issue is the distribution of specific antivenom. Snakebites are on the World Health Organization list of neglected tropical diseases. Due to the lack of knowledge on the biological, clinical and epidemiological aspects related to the problem, accidents with venomous snakes do not generally count with a structured and diffuse plan of assistance [25]. According to Brazilian Ministry of Health, elapid accidents that present neurological symptoms are characterized as potentially serious, so that serum therapy is strongly recommended, using 10 vials (100 mL) of AES administered intravenously in a single dose [26]. The treatment described in this reported case was inappropriate since the serum therapy was divided into two doses of 50 mL due to the lack of the whole dose in the hospital. Moreover, administration of corticosteroids, although not strictly contraindicated, is not part of the primary approach to elapid envenomation. The patient stayed in the hospital long enough to avoid venom redistribution from the snakebite site [27].

Finally, we would like to emphasize this issue: why expose yourself to the risk of touching or handling a coral snake by judging it as non-venomous? In North America, there is a popular rhyme that many people know that has for decades been a popular way of telling them apart: “red-on-yellow, kill a fellow” and “red-on-black, venom lack.” The idea is that “true” coral snakes can be identified by red bands touching the yellow ones. It may be helpful in telling coral snakes apart from non-venomous species in the USA, for example, but the color pattern is not the same for all Micrurus species. Therefore, the rhyme rule cannot be considered reliable in all South America, for instance, nor for all species, even though the rule could be correctly applied to the case herein described. Therefore, unless this is part of your work (e.g. as a biologist or herpetologist), and especially if you are in a recreational camp with a group of friends, it is safer to consider the Brazilian rule of thumb: “when you spot a coral snake, always consider it to be a true one”.

The care and treatment provided by the medical team in Hospital das Clínicas Constantino Ottaviano was satisfactory to revert the clinical picture of the envenoming, even with serum therapy performed in two steps, and following corticosteroid injection. In face of the risk to human health, due to potentially serious neurotoxicity, it is essential to guide professionals so that occupational accidents could be minimized with the use of proper equipment, and, especially, to educate the general population on the subject.