Coral snake bites (Micrurus spp.) in Brazil: a review of literature reports

CONTEXT: In the Americas, the main representatives of the family Elapidae are coral snakes of the genus Micrurus, of which 33 species are in Brazil. They are the smallest cause of venomous snakebite in Brazil. We analyzed literature reports of coral snake bites in Brazil from 1867 to 2014, and provide a brief review of case series and reports of coral snake bites in the Americas in general.

METHODS: Only reports with clinical descriptions of envenomation were included. The variables recorded included identification of the offending snake, patient's age, sex, bite site, clinical manifestations, treatment, including antivenom and anticholinesterase drugs, and general evolution of the cases. 30 published reports describing bites caused by Micrurus spp. in Brazil were identified and involved 194 distinct cases. Since no information on the clinical manifestations was available in 44 cases, the analysis was restricted to 25 reports (150 cases).

RESULTS: Most patients were from southern (61.3%; primarily Santa Catarina state, 60%) and southeastern (20%) Brazil and were male (70.7%), with a median age of 27 years (interquartile interval = 18 to 40 years). The offending snakes were described in 59 cases (M. corallinus 36, M. frontalis 12, M. lemniscatus 5, M. hemprichi 2, M. filiformis 1, M. ibiboboca 1, M. spixii 1 and M. surinamensis 1); in 22 cases only the genus (Micrurus spp.) was reported. Of the 143 cases in which the bite site was recorded, most involved the hands (46.2%) and feet (26.6%). The main clinical features were local numbness/paresthesia (52.7%), local pain (48%), palpebral ptosis (33.3%), dizziness (26.7%), blurred vision (20.7%), weakness (20%), slight local edema (16%), erythema (16%), dysphagia (14.7%), dyspnea (11.3%), inability to walk (10.7%), myalgia (9.3%), salivation (8%) and respiratory failure (4.3%). Fang marks were described in 47.3% of cases and 14% of bites were classified as asymptomatic. A slight increase in total blood creatine kinase was reported in 3 children, suggesting mild myotoxicity. Therapeutic procedures included coral snake antivenom (77.3%), anticholinesterase drugs (6%), and mechanical ventilation (3.3%). Two patients reported in 1933 developed paralysis/respiratory failure and died 6 h and 17 h post-bite. Four more deaths probably caused by coral snakes were reported (2 in 1867, 1 in 1959, 1 in 1962), but no clinical information was available.

DISCUSSION: Neuromuscular blockade was the hallmark of systemic envenomation by Micrurus spp., with signs of myasthenia such as weakness and ptosis that may evolve to paralysis and respiratory failure. Local features, mainly numbness/paresthesia and pain, were frequently reported, with the pain being intense in some cases. Although myotoxicity has been detected in experimental studies with Micrurus spp. venoms, few human reports described laboratory findings compatible with myotoxicity.

CONCLUSION: Most coral snake bites reported in Brazil were caused by M. corallinus and M. frontalis, with several patients showing signs of acute myasthenia. Serious complications such as paralysis with respiratory failure were observed but comparatively rare. The deaths occurred where respiratory support (mechanical ventilation) was unavailable when needed.