Epidemiological and clinical aspects of snakebite in monagas state, Venezuela

J Navarro¹, A Caraballo², E Sánchez³ y A Rodriguez-Acosta⁴.

¹ Médico Jefe. Medicatura Rural Aguasay, Estado Monagas, Venezuela.- 

² Profesor Agregado. Universidad de Oriente, Facultad de Medicina,

Ciudad Bolívar, Venezuela.- 

³ Jefe de Laboratorio. Natural Toxins Research Center, Texas A&M University-Kingsville, Texas, USA.

⁴ Profesor Titular. Instituto de Medicina Tropical de la Universidad Central de Venezuela, Caracas, Venezuela. E-mail: rodriguf@ucv.ve

    Abstract: One hundred fifty-eight patients bitten by venomous snakes were retrospectively studied at Manuel Nuñez Tovar Hospital, Monagas state, Venezuela from January 1990 to December 1999. Most of these patients were rural workers: 124 (78%) males and 34 (22%) females, from one to more than sixty years old. One hundred and five (67%) patients were diagnosed as bitten by Bothrops and 53 (33%) by Crotalus snakes. One hundred twenty-one (76%) were bitten in the legs and 37 (24%) in the arms. January, April, May, September, October, November and December were the months of higher incidence of bothropic envenomations, while crotalic envenomations were March, August and December. This study showed that the prevalence of crotalic envenomations in the Monagas state was higher. Additional prospective epidemiological studies are needed for a better understanding of these findings.

Key Words: Bothrops, Crotalus, Lachesis, Monagas state, Ophidic accident, Venezuela.

    RESUMEN: Fueron estudiados retrospectivamente ciento cincuenta y ocho pacientes mordidos por serpientes venenosas en las historias médicas del Hospital Manuel Nuñez Tovar del estado Monagas, Venezuela desde enero de 1990 hasta diciembre de 1999. La mayoría de estos pacientes fueron trabajadores rurales: 124 (78%) hombres y 34 (22%) mujeres, en edades desde 1 hasta más de 60 años. Ciento cinco (67%) pacientes fueron diagnosticados con mordedura de serpientes del género Bothrops y 53 (33%) por Crotalus. Ciento veinte y un (76%) fueron mordidos en las piernas y 37 (24%) en los brazos. Los meses de enero, abril, mayo, septiembre, octubre noviembre y diciembre fueron los de mayor incidencia para el envenenamiento bothrópico, mientras el envenenamiento crotálico fue mayor en los meses de marzo, agosto y diciembre. Este trabajo mostró que la prevalencia del envenenamiento crotálico fue muy alta en comparación con otros estados del país.         Estudios adicionales en epidemiología prospectiva serán necesarios para un mejor entendimiento de los hallazgos observados en este trabajo.

Palabras Clave: Bothrops, Crotalus, Lachesis, Estado Monagas, Accidente ofídico, Venezuela.

Fecha de Recepción: 15/10/2003 Fecha de Aprobación: 14/10/2004

INTRODUCTION

    Envenomation caused by snakebite is a worldwide problem, especially in tropical regions⁽⁸⁾. Annual incidence rates may vary according to geographical region, from 4.8-125.7/10,000 in West Africa and 0.3-8.2/10,000 in New Guinea, to 1.4/10,000 in Brazil and 0.3/10,000 in the United States^(9-12). Most of snakebite cases occurring in the Western hemisphere are due to Viperidae family, also known as pit vipers. In South America, Viperidae are represented by the genera Bothrops (now subdivided into a number of new genera), Crotalus and Lachesis^(13-17).

    While dry season these snakes migrate to the river banks and also penetrate into the gallery and tropical forests. The snakes can be found resting on the bank stones or in humid caves near the rivers^(17,33).

    The main aim of the present work was to study the epidemiological and clinical aspects of snakebites in the Monagas State, Venezuela, in order to increase the ophidic accident knowledge in the national territory.

PATIENTS AND METHODS

    A retrospective survey was carried out from records of all patients bitten by venomous snakes admitted at Manuel Nuñez Tovar Hospital, Monagas State, Venezuela, from January 1990 to December 1999. This hospital is a reference hospital for a large area of the northeast region of the country. The majority of cases were referred because intensive care and dialysis facilities were available in this hospital. Antivenom is offered at this hospital and it also stocks hospitals in other major rural towns in the region, which allows mild and moderate cases to be treated in local medical facilities.

    Distribution of cases in time, place, sex, age, occupation, site of bite, month when the bite occurred, time delay in reaching the hospital and the snake species involved, based on the epidemiological information accessible in the hospital records were reviewed. Diagnosis on snake identification, when this was brought by the patient, and/or by clinical manifestations was made. Statistical calculations using the EPI-INFO software package (Centers for Disease Control, Atlanta, GA and the World Health Organization, Geneva, Switzerland) were performed.

RESULTS

    The records of 158 cases were available for the study period. The patients came from 13 municipalities in Monagas state, mainly of the cases (54 of 158, 34%) were coming from Maturín municipality. Most of the bites (107 of 158, 67%) occurred between 6:00 am and 12:00 m. Males (124 of 158, 78%) were more bitten than females and 105 individuals (66%) were bitten by Bothrops snakes; 53 (33%) by Crotalus as shown in Table 1. The age distribution of the study population is shown in Table 2.

 

    In 120 cases (75%), the snake was captured and identified as B. colombiensis (58), B. atrox (26), and C. vegrandis (36). Diagnosis was based on clinical findings in 38 cases (24%). The legs were the most common site of bite (121 of 158) (76%), (Table 3).

    The time interval between being bitten and admission to the hospital ranged was less than 6 hours in 79% of the cases (Table 4). The distribution of the patients according to the severity of the envenomations and the snake species involved is shown in Table 5.

 

    Most of the patients were rural workers (52%), housekeepers (5%) and others (43%) as shown in Table 6.

    January, April, May, September, October, November and December were the months of higher incidence of bothropic envenomations, while crotalic envenomations were March, August and December, as shown in Table 7.

DISCUSSION

    Manuel Nuñez Tovar hospital had admitted cases of snakebite from many municipalities of the Monagas state, Venezuela. It is liable that some of these cases were referred because they were moderate to severe, and thus required special care.

    In Venezuela, the notification of envenomation cases is mandatory. At present, there is antivenom available for early treatment in several Health Centres of Monagas state. Early administration of antivenom proved to be effective in terms of the patients better course and prognosis, as it was observed in this study^(17-19).

    The distribution of cases by age, sex, time of day and anatomical site was consistent with other studies^{(3-5,8,12,15,18,19, 25-28,30)}.

    The results showed that snakebites were more frequent among young rural workers during their routinely tasks, which allows us to classify them as "work accidents". Most of the workers were bitten in the legs which, agree with the literature descriptions^(6,12,20-22). Crotalic envenomations were considered moderate to severe mainly when compared with bothropic envenomations as it has been described by other authors^{(12,18,20,21,23)}.

    In Monagas state, the prevalence of crotalic envenomations was higher, when compared with other Venezuelan regions⁽³²⁾.

    Monagas state is a tropical region of 28,900 km² situated at 9º 30' N, 63º 10' W.

    Savannah climate prevails together gallery and tropical rainforest environment, with an average annual precipitation of 1400 mm, a mean temperature of 28ºC, a relative humidity of 80%. The town’s main economic activities are livestock raising as well fruit, cassava, maize, orange, sorghum and pine production and processing. Some patients bitten by venomous snakes (97%) were working in the development of oil palm plantation (Elaeis guineensis Jacq.) and Caribbean pine (Pinus caribea) in several regions of the state. This new circumstance on the epidemiological problems may arise when forests are cleared and cultivated for commercial tree plantations. It has been reported changes in abundance and behaviour of other biological species induced by land use during the study of an oil plantation⁽²⁴⁾. In some regions of the state, species such as Crotalus vegrandis, autochthonous of Venezuela⁽³¹⁾, its environment in the last 20 years has changed from dry savannah, with scarce alimentary supplies, producing small populations of snakes to a vast caribbean pine forests rich in food resources that has increased the snake presence. If this serpent, in the past ate small lizards that were available only occasionally; now with the wild mice invasion, these reptiles have changed the frequency and quality of their food⁽³²⁾.

    Most of the crotalic envenomations occurred in March, August and December, months, which the harvests of oil palm, seed of the pine and beginning and end of the rainy period. Monagas state economy and geography, in addition to environmental changes may have contributed to the procreation of snakes of Crotalus genus. Consequently, the incidence of crotalic envenomations observed has increased. Prospective epidemiological studies will be required for a better understanding of these findings.

Acknowledgements

    This paper is dedicated In memoriam of Dr. Alejandro Caraballo who passed away when this work was finishing.

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