An epidemiological review of scorpion stings in Venezuela: the Northeastern region

An epidemiological review of scorpion stings in Venezuela: the Northeastern region

L. DE SOUSA

, P. PARRILLA-ALVAREZ , M. QUIROGA

1 Grupo de Biomedicina Aplicada (GBA), Centro de Investigaciones en Ciencias de la Salud (CICS), Universidad de Oriente, Núcleo de Anzoátegui, Puerto La Cruz, Venezuela; 2 Postgrado en Biología Aplicada, Escuela de Ciencias, Universidad de Oriente, Núcleo de Sucre, Cumaná, Venezuela and 3 Laboratorio de Alacranología, Escuela de Medicina, Universidad de Oriente, Núcleo de Bolívar, Ciudad Bolívar, Venezuela.

ABSTRACT: In Venezuela, the restricted manner of works on scorpion envenoming has contributed little to the real magnitude and knowledge of this subject in our country. The lack of basic scorpiofauna knowledge, distribution, clinical manifestations, and especially of specific treatments justify multidisciplinary studies. The purpose of these studies is to obtain information that allows the elaboration of a preventive plan. This paper demonstrates the magnitude of scorpion envenomings in Venezuela.

KEY WORDS: Scorpionism in Venezuela, Tityussp.

INTRODUCTION

VENEZUELAN SCORPIONS: THEIR ENVIRONMENT, BIOLOGY, AND TOXINOLOGY. The Venezuelan territory corresponds zoogeographically to the neotropical region. This region is influenced by the Andean, Caribbean, and Amazonian subregions (52). The latter providing the most influence during approximately six months, and especially between April and October (46), due to intertropical front with masses of humid air and annual recurrent migrations, which condition the macroclimate of almost all Venezuela. These factors lead to a variety of environmental conditions in Venezuela, which characterize a series of ecological areas that range from tropical scrub desert to Amazonian forest and high mountainous areas. These environmental characteristics determine a high animal biodiversity, with several medically important zoological groups related to their possible toxicity: Anura, Aranea, Hymenoptera, Lepidoptera, Myriapoda, Pisces, Serpentes, and Scorpionida. Some of these groups are located in urban and rural areas, leading to frequent interactions, causing from mild to serious envenomings that can lead to death.

The zoological group with the highest diversity is the Phylum Arthropoda, subdivided into Subphylum Mandibulata and Chelicerata, which includes the Arachnida class that in turn contains the Scorpionida order. This order includes nine families of scorpions: Bothriuridae, Buthidae, Chactidae, Chaerilidae, Diplocentridae, Ischnuridae, Iuridae, Scorpionidae, and Vaejovidae (96,97). The Buthidae is the widest distributed in the world, and at the same time contains species of clinical and epidemiological importance (97). This family has approximately 25 of the 1,500 known species whose venom can kill humans (50,97). These arthropods live in the tropical, subtropical, and temperate regions of the Earth (50), a taxonomical group with great plasticity, and physiological and ethologic adaptability to adverse ecological conditions (97).

In the Americas, the toxins of the Tityus and Centruroides genera cause the most cases of scorpion envenoming (6,29,97), and they are responsible for serious and fatal accidents. The composition of their venom is complex, containing peptides of low molecular weight responsible for physiological alterations seen in experimental animals and in humans. Some of the toxins in the venom can help in the understanding of ionic channel dynamics (11,17,81). They selectively act in the plasma membrane sites, modifying mechanisms of ionic selectivity fundamental to cellular homeostasis (4,5,11,81,92). So far, four classes of toxins that interact with the ionic channels have been identified and described. The ones that recognize sodium and potassium channels have been the most intensely studied (4,5,81).

In Venezuela, the study of the scorpiofauna began in 1952 when Scorza started studying Venezuelan scorpions, followed by Dagert in 1957, and Esquivel and Machado-Allison between 1968 and 1969. Since 1970, González-Sponga has carried out several taxonomical studies, describing approximately 96 new species, representing 78.7% of the 1999 Venezuelan known scorpiofauna. He has also described five new genera: Auyantepuia (Scorpionida: Chactidae), Taurepania (Scorpionida: Chactidae), Vachoniochactas (Scorpionida: Chactidae) (33), Cayooca (Scorpionida: Chactidae) (37), and Mesotityus (Scorpionida: Buthidae) (34).

In Venezuela, there are four families (Buthidae, Chactidae, Diplocentridae, and Scorpionidae) (39) that include 19 genera and 122 species (Table 1). This number is not definitive because there are wide extensions of the country to be explored, and at present, information on the distribution of Venezuelan scorpiofauna is still in process. In this sense, González-Sponga (44) is describing new species. Yústiz (104) is characterizing the scorpiofauna in Lara State in the Westerncentral region, and Quiroga (86) in the Northeastern region of Venezuela. Manzanilla-Puppo (56) is studying the scorpiofauna and its relationships to different environments within the Henri Pittier National Park, and providing knowledge from morphometry studies on the analysis of the trichobothriotaxy of Rhopalurus laticauda, as well as drawing up ecological distribution maps of this species in different environments of Venezuela (52,53,55).

In Venezuelan scorpiofauna, the family Chactidae is the most abundant, with 52.6% of all the genera and 59% of all the species. The second most abundant family is the Buthidae, with 7 genera (36.8%) and 46 species (37.7%). Within this, the medically important individual Tityus genus has the highest number of species known, 36 (29.5%) (Table 1).

Of the nine Administrative Regions of Venezuela (62), the Coastal Northcentral (1.82% of the whole national territory), which includes the capital, is the most densely populated area of the country. This region has 22.2% of the Tityus genus (8 species) followed by: the Andes (19.4%), Southern (16.6%), Northeastern (13.9%), and Westerncentral (11.1%) (Table 2).

Scorpions can be found in almost all terrestrial ecosystem of varying climates and altitudes. They are basically found in three of the four climatic types, as per Koeppen: Type A - rainy warm, Type B - dry warm, and Type G - high temperate. At present, there is no current information for Type H - high mountainous cold. They can be found in the following vegetal formations (35,52): the coast vegetation, the savannas, thorn bushes, tepuyan shrubs, deciduous forest (tropical dry forest), semi-deciduous, evergreen, including the cloudy forests and the gallery woods. In these habitats, they live in a variety of microhabitats, such as under stones, in cracks, decomposing trees, in epiphytes such as bromelias and orchids, especially in environments where the ground is very humid. In their natural environment, some species such as the Chactas genus dig galleries. In the Amazonas State a specimen of Tityus filodendron was collected in a bromelia 15 meters above the ground (35). Rhopalurus laticauda shows adaptations to various microhabitats that can be seen by the coloration of the specimens (52,53,55).

In Venezuelan scorpiofauna, sexual dimorphism is present to some extent, with no reports of parthenogenetic species, such as Tityus serrulatus (35,50,96,97). A single fecundation allows a female to give birth several times, which is a process of natural compensation due to the generally smaller number of males against females (35). In this sense, this agrees with our field collections in a mountainous town in the north of Anzoátegui State, where we captured four females to each male.

In the laboratory of the School of Medicine, Universidad de Oriente, Venezuela, the scorpions Rhopalurus laticauda and Tityus caripitensis have been kept in captivity to study their biology, ethology, feeding, and venom-producing gland histology. Their venoms were extracted to study their biological activity, pharmacology and immunology, and hystopathological alterations in experimental animals (54,60,72,78) (82-86). This laboratory developed a new feeding method for scorpions in captivity using Rhopalurus laticauda. This method is based on the administration of an artificial medium that contains amino acids, lipids, carbohydrates, vitamins, and minerals (Medium 199®, GIBCO Laboratories), and it is a successful substitute for the diet of Periplaneta americana. This artificial diet is shown to be effective in maintaining scorpions for venom extraction, with no risk of administering polluted material, such as pathogenic organisms, pesticides, or insecticides. It is easy to control the quantities and quality of this diet. Rhopalurus laticauda, maintained in captivity with artificial or natural feeding, shows a reduction in the ponderal evolution curve, venom production, and dry weight (84). However, no alteration in venom quality and potency is observed. The captivity survival rate of some adult specimens of Rhopalurus laticauda has been approximately 3 years. In toads, this scorpion venom produces spontaneous quick abdominal muscle contractions, without constant rhythm or frequency (32).

Specimens of a new Tityus genus species (Tityus caripitensis) (82) were collected in Punceres and Bolívar municipalities in the Centralnorth region of Monagas State. They arrived at our laboratory with acari parasites. These arthropods are the most common scorpion ectoparasites (97). In the laboratory, females produced an average of 22 newborns, with birth duration generally over 60 minutes. Approximately 5.57 days post-birth, embryonic veil detachment occurred, and in 12.58 days they descended from the mother's back. At this time, specimen weight was from 25.5 to 50.7 mg (54). During growth, they undergo periodical ecdysis, with exoskeleton substitution (97). With Tityus caripitensis, the fourth change of post-embryonic development can be reached in five months.

The histological study of Tityus caripitensis venom-producing gland by optical microscopy shows that it is composed of two lobes containing striated muscle tissue in its medial region. Its epithelium is simple, cylindrical, and pseudo-stratified, formed by secretory and non-secretory cells, which are arranged in five folds or pleats of increasing thickness towards the distal part of the gland. In the central axis, it contains some fibroblasts and cells with eosinophilic granulations, characteristic of mast cells. The secretory cells are of two types, some with fine granules and others with course granules. The excretion conduct is single with cylindrical ciliated epithelium (82,85).

Sublethal doses of Tityus caripitensis venom injected intramuscularly in mice produce histological alterations. In the studied organs, the following general features were observed: tissue degeneration, vascular congestion, hemorrhage, and inflammatory infiltrate. Heart fibers, renal tubules, hepatocytes, and testicle germinal cells were seriously affected, showing nuclear and cytoplasmic alterations, in many cases compatible with hydropic degeneration (60).

Although historically in Venezuela, Rhopalurus laticauda was the first scorpion whose venom biological activity was investigated (70), most of the attention has been directed at the Tityus genus. The study of Tityus venom is relatively recent in comparison with some Brazilian species, such as Tityus serrulatus (31). However, the toxicity of Tityus discrepans venom, found especially in the Federal District and Miranda State in the Coastal Northcentral region of the country (39), has been determined [2.5 mg/mouse kg in 24 hours intravenously (10) and 8.8 mg/mouse kg in one hour subcutaneously (77)]. Its components, according to the chromatographic pattern with Sephadex G-50, are of four fractions denominated as Tdf-I, Tdf-II, Tdf-III, and Tdf-IV with different pharmacological effects (15-17). Tdf-III causes pancreatitis in experimental animals without muscarinic effect. Tdf-I fraction contains peptides of 48 KD with a reversible curarizing action, so far unknown in other species of this genus (15,17,92). Tdf-II, the most abundant fraction, contains neurotoxins that affect the sodium channel, causing clinical effects in experimental animals, and Tdf-IV contains toxins that block the potassium channel (15,16,17,92). The chromatographic pattern (Sephadex G-50) of Tityus ivic-nancor venom, a species of the Westerncentral region of Venezuela described by González-Sponga (41), contains three fractions: Tin-I, Tin-II, and Tin-III. Fraction Tin-II is the most abundant and lethal for mammals, representing 73% of the total venom (17,48). The venom LD50 of this species is 8.9 mg/mouse kg in one hour subcutaneously (77), and for Tityus caripitensis (82) 14.6 mg/mouse kg subcutaneously in one hour (77).

One of the generally fatal complications of Tityus envenoming is acute lung edema. Experimentally, Tityus discrepans venom produces ultrastructural changes in several organs (7,8,87). Some relationship has been suggested between the experimental clinical manifestations that appear as a toxic response to this venom and alterations or cellular and sub-cellular changes in the lung system of the murine model. These changes are probably similar to those seen in human envenoming (87). The venom of this species is capable of producing acute lung edema in vivo, but has no effect on isolated lung. In vivo, it possibly involves the activation of clotting factors and the formation of microcoagula, so there is not a direct action of the venom on lung tissue (14,18,19). D´Suze et al. (20) have proposed the substitution of the term "lung edema in scorpionism" for "scorpion venom respiratory distress syndrome".

EPIDEMIOLOGY OF SCORPION ENVENOMATION IN VENEZUELA: AREAS OF POTENTIAL RISK. From a geographical point of view, scorpions are widely distributed. The family Buthidae has the widest distribution (Figure 1a) followed by the Chactidae (Figure 1b). Within the Buthidae, Rhopalurus laticauda is geographically dominant in the Venezuelan scorpiofauna (Figure 1c) followed by scorpions of the Tityus genus (Figure 1d).

Some of them are located in areas of dense human population in the north of the Venezuela (Figure 2) (35,39,40). So far, Tityus scorpions inhabit 63% of the Venezuelan states.

Although scorpion envenoming in Venezuela has not reached the same magnitude as in Mexico with 250,000 cases and several hundred fatalities every year (1), it is gradually increasing. If we consider the distribution data of the Tityus genus with the distribution of Venezuelan population calculated in 1995, this genus is present in municipal areas (38,39,41,43,44) with an estimated population of 9,703,479 inhabitants. It can therefore be suggested that 45% of the human population is at potential risk of Tityus scorpion envenoming. González-Sponga reports that even in areas of low population density, its presence poses a potential danger (35).

To simplify the potential risk for scorpion envenoming, data were grouped according to the Administrative Regions of Venezuela (62) (Table 3). The total population has been calculated for each region and its municipalities with distribution of the Tityus genus. With these data, index 1 is obtained, reflecting the potential risk of scorpion envenoming. In this sense, the most important regions are the Coastal Northcentral (0.75) and the Northeastern (0.66). Considering the indexes for regions and relating them with the general index for Venezuela (0.45), index 2 is obtained, where it could be suggested that the inhabitants of the Coastal Northcentral region have a potential risk factor 1.70 times higher than the rest of the Venezuela population. This is followed by the Northeastern region at 1.50.

From these results, we can say that the Venezuelan public health problem from scorpion envenoming is endemic and regional in character. The more dangerous areas due to the Tityus genus are the mountainous and foothill areas of: 1. western of Venezuela, the Coro and the Andean Systems (western branch or Sierra of Perijá and eastern branch or Merida Mountain Range, continuing towards the Lara and Yaracuy States); 2. northcentral, the Coastal Mountain Range; 3. eastern, the Paria System and the Eastern Solid (the Turimiquire Sierra made up of the Bergantin Solid and the Caripe Solid); and 4. southern, the Guayana Solid. In some of these areas, deaths have occurred in: the metropolitan area of Caracas (39,88), Los Teques and surroundings (39), the northcentral Monagas State (28,30,47,61,101), the Sucre State (26,27), the south zone of Lake Maracaibo, and the Trujillo, Táchira (39), Merida (61), and Lara States (57).

In general, González-Sponga (35) has qualitatively defined five endemic areas for scorpion envenoming: 1. Maracaibo and surroundings, Zulia State (habitat of Rhopalurus laticauda); 2. Ciudad Bolívar, San Félix, and Puerto Ordaz in Bolívar State (habitat of Rhopalurus laticauda); 3. Táchira State (habitat of Tityus funestus and partly of Tityus nematochirus); 4. Barcelona, Puerto La Cruz (Anzoátegui State), and Cumaná (Sucre State) (Rhopalurus laticauda); 5. the Northcentral region of Venezuela, comprising the Carabobo State, north of Aragua State, Miranda State, and the Federal District (habitats of Tityus discrepans that causes serious envenomings in the surroundings of Caracas and nearby areas). The addition of a sixth area in Lara State has been proposed (57). Although the Oriental Solid has been previously reported as an endemic area for scorpion envenoming in northeastern Venezuela (39), our team has recently characterized quantitatively, ecologically, and geographically this macroregion located in the Turimiquire Sierra and its foothills (Turimiquire Subregion) in Anzoátegui, Monagas, and Sucre States. It has been determined that in these the frequency of scorpion envenoming is increasing (26,28). We have also determined the mortality levels for scorpion envenoming in the region (27,59). According to data, there are four large endemic areas for scorpion envenoming by the Tityus genus in Venezuela (Figure 3).

In the tropics, scorpions are active all year long, although they are more active during the hotter months (97). Envenoming can occur in forest region, rural areas, or in the city from both non-toxic species, such as Rhopalurus laticauda or toxic species, such as the Tityus genus. Puerto La Cruz-Barcelona (Anzoátegui State), the coastal cities of northeatern Venezuela are according to Holdridge, tropical very dry forest, and according Koeppen of dry warm climate Typo B: Bshi [semi-arid with xerophyte vegetation or spinous bushes, with more evaporation than precipitation]). This area is the habitat of Rhopalurus laticauda (35,39,52) of low toxicity (70) and the most commonly distributed in Venezuela (35,52,54). Our experience indicates that Rhopalurus laticauda appears with more frequency in human dwellings between February and April, active fundamentally at night, especially after the 20:00 hours. The 31 specimens of Rhopalurus laticauda brought to our laboratory by community members were collected from inside dwellings. Of these, 6 (19.4%) were responsible for bites. The highest incidence occurred during the first three months of the year, with the highest peak in March. This coincided with the highest frequency within dwellings (Figure 4). Recently, three specimens of Tityus scorpions were captured in these coastal cities inside buildings and in the municipal market inside a sack of tubers. Also, three specimens of the Tityus genus, which have been involved in moderately serious envenomings, have been included in our laboratory collection. One of these specimens caused envenoming in a 53 year-old woman. This species, Tityus discrepans, is generally distributed in Caracas, the Federal District (39), located approximately 350 km far from Puerto La Cruz, and Barcelona. In this sense, we suppose that specimens of the Tityus genus captured in these cities have been brought from distant areas. González-Sponga states that the scorpions can end up in human dwellings by being brought in boxes, construction materials, and in many cases, in bunches of bananas. In Caracas, a scorpion was captured on the tenth floor of a building (35). In the Northcentral region of Venezuela, the high frequency of accidents in children less than 6 years suggests that Tityus discrepans has intra-domiciliary habits (90).

In Brazil in recent years, the alarming spread of the highly toxic species Tityus serrulatus into new areas is undoubtedly related to human colonization (50,51,98,103). There, the effects of human activity and environmental changes have allowed the expansion and colonization of this opportunist species, by modifying its habits, invading human dwellings, and displacing less dangerous autochthonous species (50). Their original savanna habitat was restricted to an area of Minas Gerais State, but since 1980, they have invaded Brasília (50) and São Paulo State (103). In Brasilia, between 1971 and 1975, Tityus fasciolatus represented 93% of the total scorpiofauna. At the present time, Tityus serrulatus has became the predominant species with 70% of the current scorpiofauna (50). Similar to Brasilia, Tityus serrulatus has displaced Tityus bahiensis (a less toxic species) in São Paulo State (103). These results suggest competition between different species with the prevalence of Tityus serrulatus, possibly due to its parthenogenetic reproduction, ease of adaptation to human dwellings, and some other biological peculiarities that give it an opportunist character invading and colonizing altered environments (50,51,103).

According to Lourenço et al. (51), there are three factors that favor transformation of an area into an area of important scorpion colonization: 1. expansion of human population; 2. rapid expansion of toxic opportunist species to modified habitats, changing their behavior to the extent that they can live inside human dwellings; and 3. high human population density, coinciding with abundant scorpion population density, increasing the probability of envenoming. These factors are in accordance with our findings that the Tityus genus can be found in ecological areas differing from their natural habitat. This suggests that we may be in the process of being colonized by this genus due to human activity in a non-correspondent habitat. According to González-Sponga, in the Northeastern region of Venezuela, the Tityus genus is found in green forests during only part of the year (tropophilous forest) (35). In this Venezuelan tropophilous forest, there is a significantly high human population, which is subjected to strong intervention by man.

Scorpionism in peripheral areas of cities has increased (36). This may be due to ecological alterations during the urbanization process of areas naturally occupied by scorpions, especially by the Tityus genus. This has allowed these arthropods to invade, colonize, and adapt to the new niches, such as human dwellings, thus increasing the possible contact with man, especially at the beginning of the rainy season (36). In the metropolitan area of Caracas and surrounding towns between 1990 and 1995, 44.5% of the envenomings occurred between April and June. Most envenomings occurred in an intra-domiciliary form, mainly in towns that are 1,000 m above sea level (9).

Scorpionism is not considered a public health problem in Venezuela, with frequent statements that scorpion stings are not dangerous. Of the 122 species of scorpions described in Venezuela up to 1999, 29.5% correspond to the Tityus genus, so the remaining 70.5% could be implicated in accidents without important consequences. Rhopalurus laticauda may be responsible for a large number of stings, however, it produces only local pain, due to the low venom power and toxicity (LD50=30 mg/mouse kg intravenously in 24 hours) (70). Additionally, from ten specimens, the average yield of venom is 1.78 to 1.83 mg dry weight (84). Thanks to this species, the general notion among inhabitants is that scorpion stings are innocuous. In contrast, specimens of Tityus caripitensis produce an average of 1.06 mg of venom (75) with an LD50 of 5 mg/mouse kg in 24 hours, intravenously (73,74,83). For other latitudes, Tityus serrulatus or Tityus bahiensis produce 1.1 and 0.9 mg respectively (12) and Androctonus australis hector between 1.5 and 2 mg (65).

Although there are not detailed national records of morbidity, scorpionism is important in some Venezuelan regions, such as the Federal District, and the states of Lara, Merida, Miranda, Monagas, Sucre, Trujillo, and Zulia (3,23,25,26,35,57) (61,66,68,69,80). The most recent works indicate an increase in envenomings (21,24,26,28,57,66,69). On the other hand, it is believed that scorpionism does not represent a problem in Venezuela. However, in the whole country according to official data, 91 patients died of scorpion envenoming between 1980 and 1990 (64). This represented the third highest cause of death due to envenomings and toxic reactions caused by plants and venomous animals (Table 4). Although mortality due to scorpion stings was in third place, age discrimination results placed the under 15’s in second place. In the under 5’s, the mortality median was not significantly different from that of snakebites for this age group.

In several countries, scorpion envenoming is considered a major public health issue. Recently, an alarming increase has been observed in several tropical and subtropical countries, such as Brazil, Mexico, Tunisia, and Morocco (6,50,51). For 1988 and 1989, the mortality rate due to scorpion envenoming in Brazil was respectively 0.29 and 0.20 per million inhabitants (2). From our calculations, from deaths due to scorpion envenoming registered at MSAS (64) in 1988 and 1989 (9 and 5 cases respectively), there is a mortality rate of 0.52 and 0.28 per million inhabitants, slightly higher than those from Brazil in the same years.

In some hospitals, scorpion envenoming is responsible for higher morbidity than other venomous animals, reaching 39% (26,69). Pancreatitis is the most frequent complication (69,91,101), with rare occurrences of pancreatic pseudocyst (90) or hemorrhagic pancreatitis (95), toxic myocarditis (49), and neurological complications, such as aphasia and hemiparesis (58), hemiplegia, and facial paralysis (22). The clinical cholinergic manifestations by muscarinic activation is present in most of the envenomed patients (66,68,90,91). Cardiovascular complications are the most severe, and when present they are usually fatal, even though patients are treated in intensive care units (88). Generally, death occurs due to heart failure and acute lung edema, which when established are usually irreversible (68,91,101).

Some patients, especially those that do not receive prompt specific treatment with scorpion antivenom, evolve to heart arrhythmia, lung edema, and untreatable cardiogenic shock (61). Several works in Venezuela indicate the importance of the prompt treatment with scorpion antivenom (66,68). In a retrospective study in Merida State, of 64 children referred to the Hospital of the Los Andes University, two died. They had received antivenom five hours after the bite (61).

IMPLICATIONS OF SCORPION ENVENOMING IN VENEZUELA: THE NORTHEASTERN REGION. With the aim of contributing to basic knowledge on scorpion envenoming as a public health problem, epidemiological characteristics have been studied since 1990 in the states of Anzoátegui, Monagas, and Sucre in the Northeastern region of Venezuela (13,21-25) (26-28,59,100,101). This region covers 84,000 km , representing 9.1% of the Venezuelan territory, with approximately 10.9% of the population. At the moment, the criteria to define an endemic macroregion for scorpionism inside the Northeastern region are being studied (28). The data suggest its presence covering the Turimiquire Sierra or Oriental Solid (administratively called Turimiquire Subregion) of approximately 5,040 km2 (62,63,67) and the adjacent foothills. The macroregion, in turn, can be subdivided into several microregions some of clinical, some of epidemiological, and some of toxinological importance, and others that combine all three criteria. The space distribution of scorpion envenoming in Monagas State in 1996 indicates that the highest rates are in the municipalities that comprise the Turimiquire Subregion and its foothills(28). In this State, as part of the Turimiquire Sierra are the municipalities of Acosta (20.3 envenomings per 10,000 inhabitants), Caripe (12.1 envenomings per 10,000 inhabitants), Piar (7.2 envenomings per 10,000 inhabitants), and Cedeño (4.3 envenomings per 10,000 inhabitants); in the foothills, the municipalities of Punceres (25.8 envenomings per 10,000 inhabitants) and Bolívar (14.5 envenomings per 10,000 inhabitants) (28); and in Sucre State, the municipality of Montes (11.76 envenomings per 10,000 inhabitants) (26,28). These data suggest and define the presence of the endemic macroregion These municipalities show an increased epidemiological importance due to scorpion envenoming, since they are distribution areas of the Tityus genus. Scorpion envenoming is seasonal, dynamic, and variable throughout the year in these areas (21,25).

This physiogeographic and ecological area denominated Turimiquire Subregion shows different forests, such as the green forests during part of the year, denominated tropophilous forest or tropical dry forest. This forest with an annual mean temperature between 25 and 28°C, annual mean precipitation between 1,000 and 2,500 mm, vegetation with trees from 30 to 40 meters high, a low level of epiphytes, and a well-developed herbaceous stratum occupies the foothill areas of the Turimiquire Subregion and represents one of the habitats for the Tityus genus, as well as the ever green forests (pluvial forest and cloudy forest) (35).

Of the three states that form the Northeastern region, Anzoátegui contributes the smallest number of cases. However, there is a small area, not densely populated in the northeast (inside the Turimiquire Subregion) where scorpion envenomings of medical importance occur. The envenomings from this small area are serious, sometimes fatal. Nationally, Anzoátegui State is not mentioned as an endemic area of importance for scorpion envenoming, but low official registration is not necessarily proof that this is not a problem. Only the presence of the genus Tityus makes the area susceptible to the serious envenoming. Although the magnitude of scorpion envenoming in this state (45) can not be compared with Sucre (13,23,24,26) and Monagas States (25,28,59,100,101), it is still of major importance. An example of the seriousness of scorpion envenomings within the Turimiquire Subregion in Anzoátegui State was shown (22) when we described the case of a 9 year-old boy who developed acute lung edema, hematological alterations, upper digestive hemorrhage, and direct left hemiplegia (pyramidal type motor deficiency). Computerized tomography showed a cortico-subcortical right front-temporal parietal encephalomalacia lesion due to an ischemic cerebrovascular accident of the right cerebral hemisphere. Other patients from that same ecological area have been hospitalized with heart arrhythmia characterized by bradycardia and bundle branch blockade (data not published). Also, two children who died from scorpion envenomation in the north of Anzoátegui State since1990 came from that same area.

In Montes municipality (Sucre State), scorpion stings have shown epidemic character. Between 1991 and 1993, 77% of the evaluated months reached high risk levels (13,21). Later on, when looking at the epidemic characteristic for 1994 and 1995, 95.8 of this period was considered of high risk (24). The monthly endemic curve, built with data between 1980 and 1990, shows that from 1991 and 1996, 74% of the months were epidemic (the number of monthly cases was above the 75 percentile) (26). Between 1980 and 1996, the lowest incidence rate was recorded in 1982 with 2.1 per 10,000 inhabitants and the highest value in 1995 with 14.7 per 10,000 inhabitants. This difference indicated a 500% increase in this municipality (26).

The evaluation of mortality due to scorpion envenoming in Sucre State between 1990 and 1997 indicates that there were 21 fatalities from scorpion stings. These deaths occurred in 11 (73.3%) of the 15 municipalities that make up the state, and 67% of deaths occurred between 1994 and 1997. Most of these events (71.4%) involved children less than 6 years (median age = 4 years old). The yearly mean mortality rate for the state was 0.35 per 100,000 inhabitants. The higher yearly mean mortality rates were recorded in the municipalities of Benítez (1.82 deaths per 100,000 inhabitants), Libertador (0.89 deaths per 100,000 inhabitants), and Montes (0.71 deaths per 100,000 inhabitants). In Benítez, this rate was in the 95 percentile, while in Libertador and Montes, these were between the 75 and 95 percentile (27). These results ratify the importance of scorpionism in this region as a serious public health problem, placing Sucre State as an endemic area for serious and potentially fatal scorpion stings (27).

In Monagas State, specifically in its northcentral area, the municipalities of Bolívar, Caripe, Cedeño, and Piar have been identified as endemic areas, and the Acosta municipality as a hyperendemic area (25,100,101). The incidence rates in the Acosta municipality between 1987 and 1993 ranged from 13.02 to 23.30 cases per 10,000 inhabitants, significantly higher than those recorded in Caripe that ranged between 2.49 and 7.39 (25). Recently, the municipality of Punceres has been identified as a new hyperendemic area in Monagas State (59). Its incidence rate for 1996 was 25 cases per 10,000 inhabitants, which is not significantly different from the other hyperendemic municipality, Acosta, with an incidence rate of 20.3 per 10,000 inhabitants (28,59). In some of these municipalities (Punceres and Bolivar), the participation of Tityus caripitensis (82) has been confirmed in some serious envenomings (101). Preliminary results of our research team indicate that the number of inhabitants per square kilometer, the altitude, and the ecological area act as risk factors that increase the probability of scorpion stings (59). This reveals that the importance of scorpion envenoming in Monagas State increases from the south (savanna areas) towards the north (foothill and mountainous areas). Also from the tropical very dry forest to the tropical dry forest, and from the humid and very humid pre-mountainous forest to the low mountainous humid forest.

Fatal envenomings in Monagas State are mainly in the north. Between 1990 and 1996, 12 children died from scorpion envenoming (59) due to heart failure and acute lung edema, with one case of lung hemorrhage (59,101). Of the 10 municipalities that form this state, 6 (60%) recorded deaths from envenoming. The yearly mean mortality rate was 0.32 deaths per 100,000 inhabitants. The highest number of deaths occurred in 1993 (4 deaths; 0.75 deaths per 100,000 inhabitants) distributed in a decreasing order in the municipalities of Caripe (2 deaths; 6.57 per 100,000 inhabitants), Libertador (1 death; 4.65 per 100,000 inhabitants), and Bolívar (1 death; 3.48 per 100,000 inhabitants) (59).

As well as children, who are the group of higher risk and clinical and epidemiological importance, there have been cases of severe toxicity observed in adults (69,101). Adults stung in the north of Monagas State showed electrocardiographic alterations characterized by early auricular and ventricular contractions, elevation of ST segment, presence of J point and prominent U wave, infradislevel of ST segment, and sinusal tachycardia. Some of these dysfunctions suggest a syndrome of early repolarization and primary repolarization such as ischemia (101). The most frequent complications in this area are acute pancreatitis and acute lung edema (30,101).

In the Northeastern region of Venezuela, the presence of the following species of the genus Tityus have been confirmed (Table 5): Monagas State - Tityus arellanoparrai and Tityus monaguensis in Caripe municipality (39), Tityus surorientalis in Sotillo municipality (38), and Tityus caripitensis (83) in Bolívar and Punceres municipalities; and Sucre State - Tityus tamayoi in Montes municipality (39). and Tityus nororientalis in Bolívar, Mejía, Montes, and Ribero municipalities (38). Patients from these areas, although asymptomatic, must be considered as potentially serious cases of scorpion envenoming. This indicates that patients must be submitted to strict medical surveillance, which will be even higher if the patient belongs to higher risk groups.

CONTROL OF SCORPION ENVENOMING. Scorpion envenoming in our country must be addressed by the government in order to reduce its impact on the population. From the 1991 serious problem of envenomings in Aparecida municipality, São Paulo State, Brazil, Spirandelli-Cruz et al (98,99) proposed a program for scorpion accident control. These authors state that a good control program for an endemic region should be observed all year long, especially before or during the higher risk periods. Since scorpion envenoming is of a seasonal character (6,25,59,100) similar to other venomous animals, especially snakes (94), it is possible to predict the higher incidence periods and take the pertinent measures. A good scorpion control program should be implemented in our endemic regions, similar to that proposed by Spirandelli-Cruz et al (98,99). This must include the identification of the etiologic agent, the study of the conditions that favor contact with humans, as well as the actions and proposals for its control. Educational measures are the most difficult to implement (98). These authors recommend that there should be a continuous and uninterrupted surveillance for several years to verify these measures.

Chemical control can be used in endemic areas where scorpions invade human dwellings. In vitro assays demonstrate that lambda-cyhalotrin (10 mg/cm ) is lethal to scorpions. Intramural application of this pyrethroid at a dose of 50 mg/cm in corners and lower parts of walls was lethal to Tityus valerae (89). Biological control with Beauveria bassiana, an entomopathogenic fungus, is not effective against Tityus valerae topically or by ingestion (89). However, natural predators can be used (35,97-99), especially in rural communities.

In Venezuela, efforts have been made to develop toxoids for the prevention of serious envenoming by the genus Tityus. The experimental results demonstrate that these toxoids are inmunogenic (75-79). There is a high cross-reactivity between the sera obtained from mice treated with toxoids produced from the venom of Tityus discrepans, Tityus ivic-nancor, and Tityus caripitensis (70 to 100%). Formaldehyde eliminated venom toxicity, increased its antigenicity, and did not alter its capacity of inducing a protective response in mice (79). As a toxoid is not being implemented at present, it is important to install scorpion anti-envenoming centers in the endemic areas. In this way, patients can be quickly and appropriately treated, with the administration of specific scorpion antivenom. The Venezuelan antivenom serum is made at the Biotechnology Center of the Pharmacy Faculty of the Universidad Central de Venezuela from the venom of Tityus discrepans (71). It is of high quality, and so far there have been no serious adverse reactions seen.

Based on experience from Australia, where bandages have been applied to compress lymphatic circulation as part of first aid treatment to victims of Elapidae snakes, this technique has been proposed to avoid the absorption and distribution of scorpion venom, since the peptides in these venoms, especially the most toxic fractions, reach the systemic circulation by means of the lymphatic circulation (93).

It is thought that the prevention of scorpionism also requires actions of civilians. A non-governmental association has been established, named the "Isabel Cecilia Itriago Viso" in memory of the 6 year-old girl victim of scorpion envenoming (102). This association promotes prevention measures, organizes workshops and symposia with specialist researchers to update the health personnel in relation to treatment of scorpion envenoming.

ACKNOWLEDGEMENTS

We express our gratitude to Professor Víctor Castro (INDESA) for his help in the digitalization of the images. This work was Cofinanced by FUNDACITE-Anzoátegui (PI-015/95; L.D.S.), Consejo de Investigación, Universidad de Oriente (CI-1-0403-0799/97; L.D.S.), and CONICIT (Fortalecimiento de Centros de Investigación: F-97001400; C.I.C.S.).

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Received 22 October 1999

Accepted 22 October 1999

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Publication Dates

• Publication in this collection
  22 Sept 2000
• Date of issue
  2000

History

• Accepted
  22 Oct 1999
• Received
  22 Oct 1999