Poisonous snakes of Oman
Most people associate snakes, scorpions and spiders with painful and possibly dangerous bites or stings, although a few may have actually encountered a dangerous snake.
Among rural populations, stories and myths about snakes abound, and many people have misconceptions regarding correct treatment of snakebites.
Although it is estimated that several hundred snakebites and perhaps the same number of scorpion stings are sustained every year in Oman, only a handful of individuals suffer serious effects and fatalities are rare.
The golden rule is 'Never interfere with or handle snakes or scorpions, unless it is certain they are dead!' Imported antivenoms for both snakebites and scorpion stings (manufactured using venoms from non-indigenous species) are available in larger hospitals, but their efficacy in Oman has never been evaluated.
A new programme to develop suitable snake antivenoms for use in Oman, using Omani terrestrial snakes, has recently been initiated by the College of Medicine, Sultan Qaboos University.
Snakes
The snake has a special significance for the medical profession. Asclepius, a 3rd century AD physician who lived in Greece, was renowned as an outstanding healer, and he was ultimately deified by the Ancient Greeks as their god of medicine. His staff, with a single snake coiled round it, has been adopted worldwide as the symbol of medicine (see logo for the World Health Organisation).
The rod with two snakes entwined, which is sometimes mistakenly used to symbolise medicine, represents the wand of Hermes, the mythical messenger of gods. Asclepius chose the snake motif because of its periodic re-emergence in a healthy new skin, apparently rejuvenated, following the shedding of its old, worn-out skin.
The classical association persists in the scientific names of snakes which are derived from Ancient Greek and Latin, often mixed together in a fascinating and totally illogical melange. For example, the scientific name of Burton's carpet viper is Echis (the genus), — employing the Ancient Greek word for viper — and coloratus (the species), — using the Latin adjective for coloured.
Terrestrial snakes occur worldwide in temperate and tropical climatic regions, while sea-snakes are largely confined to tropical seas (including the Gulf of Oman). Snakes are a successful, and often plentiful species, and they form a very valuable part of the ecosystem. They often have beautiful, patterned skins and their graceful and sinuous movements attract our admiration and awe. They are carnivorous and many feed on harmful pests like rodents. Only a few are dangerous to man. Snakes should never be harmed, but protected and treasured as a natural resource.
Venomous snakes in Oman
Although terrestrial snakes are widespread and often common in rural Oman, most people, even those who regularly camp in the desert, rarely see them. Snakes are deaf (the Indian snakecharmer who waves his flute from side to side is actually exerting a hypnotic effect on the cobra), but they are very sensitive to vibrations, and usually escape when they sense approaching footfalls.
Many species are nocturnal. Most Omani snakes that are encountered, belong to the Colubrinae family, for example the 'wadi-racer' (Coluber rhodoracis), a long, thin snake often seen swimming in pools in wadis, where it hunts for fish, and are mostly non-venomous, although they may bite if handled.
Only nine Omani snake species are truly dangerous, — six vipers (Viperidae): the Sind saw-scaled viper (Echis carinatus sochureki) of the sandy plains of northern Oman, and its close relative, the Egyptian saw-scaled viper (E. pyramidium) in Dhofar, Burton's carpet viper (E. coloratus) found usually in hilly regions; Gasperetti's horned viper (Cerastes cerastes gasperetti) which is present in sandy deserts, where it often lies buried in sand with only its eyes and nostrils above the surface; the falsehorned viper (Pseudocerastes persicus), of the northern mountains; and the sluggish, non-aggressive puff adder (Bitis arietans) which is confined to Dhofar.
The other two venomous species are the burrowing asp or mole viper (Atractaspis microlepidota) of Dhofar, a member of the Atractaspididae family, a rarely seen but greatly-feared species, which usually conceals itself in sand or soil, and the Arabian Cobra (Naja haje arabica), the sole Omani representative of the Elapidae family, confined to Dhofar, where it frequents hilly ground near water. Bites by the latter two snakes appear to be rare since they have not been reported.
Among these snakes, the majority of bites in Oman are caused by the Sind saw-scaled viper, an unusually aggressive snake, whose common name comes from its habit of rubbing opposing rows of scales on its skin together, producing a warning sawing or scraping sound, Burton's carpet viper, and occasionally Gasperetti's horned viper. All three may proceed over sand dunes by distinctive side-winding movements. Although in regional hospitals like Rustaq Hospital, up to a hundred snakebite patients are admitted annually (with no fatalities), in Sultan Qaboos University Hospital, a tertiary referral hospital, over the past eight years, only 25 cases of snakebite have been admitted with only one fatality.
Most snakebites occur during summer when snakes are active. In cold weather, being polkilothermic (body temperature depending on the ambient temperature), they are sluggish and drowsy.
There are nine species of sea-snakes, all highly venomous, present around the coasts of Oman. However they are not aggressive. These snakes feed on fish, and their mouths are relatively small making it difficult for them to bite humans. Fishermen often catch them in their nets, and usually pick them up and throw them back into the sea, but serious bites appear to be rare since they are not reported.
Snakebite
Snakes require venom to immobilise their prey and promote their subsequent digestion (for example viper venom prevents blood clotting and breaks down tissues), and when they bite in self-defence, frequently significant envenomation does not occur.
In Oman, most snakebites occur when people are walking in sandals or barefoot in rural areas at night, without a torch, or working bare-handed with crops. Most bites are immediately painful. As a rule, the snake escapes, and the anxious victim cannot describe the snake accurately.
Local treatment is often inappropriate, for example, the wound may be sucked, or incised, and a tourniquet may be applied.
These practices are ineffective, and tourniquets may cause ischaemia and even gangrene of a limb if left too long. None of these measures are recommended. Instead the patient should be reassured, the bitten limb immobilised in a splint with light bandaging, and the patient transported directly to hospital.
At hospital, if there are signs of envenomation (swelling and bruising around two fang marks, with signs of impaired blood clotting in viper bites; mild swelling around two fang marks, and neurological signs eg drooping of the eyelids (ptosis), in cobra bites), then antivenom is indicated. If local signs are trivial, and there are no systemic signs (eg hypotension, nausea, vomiting, bleeding), venom is withheld and the patient is kept under observation until he or she can safely be discharged.
Snake antivenom
Snake antivenom is manufactured overseas using horses which are injected with a series of increasing quantities of venom from one species of venomous snake. The horse develops antibodies to the venom, and becomes tolerant to large amounts of venom, becoming immune. Because the snake species is rarely identified in snakebite, the process is repeated with venom from a second, or more snakes present in the same region, and finally, the combined antibodies are extracted from the horse serum, purified, and preserved.
The final product of pooled antibodies against various snake species is called polyvatent antivenom, and can be administered directly intravenously to the patient. The greatest danger is an anaphylactic reaction to the horse protein, (sudden collapse, shock, respiratory distress), and we always have adrenaline ready to counteract it. In Oman, available polyvalent antivenoms offer some protection to most but not all venomous land snakes, but none protect against sea-snake bites. (In Australia, where sea-snake bites are more prevalent, an effective polyvalent sea-snake antivenom is available).
Snakebite research in Oman
Current research in venomous snakes of Oman is underway in the Department of Medicine in SQU in collaboration with the Venom Research Laboratory of the Liverpool School of Tropical Medicine, in England.
The first project is to develop a bedside snake-antigen detection test, so that by testing tissue fluid from the site of the bite, and also serum or urine from the patient, the species is identified, even if the victim never saw the snake. The second project is to collect representative terrestrial venomous snakes, keep them in vivaria, obtain venom by 'milking' their venom glands, and subsequently in Liverpool, manufacture monovalent and polyvalent antivenoms specific for Omani snakes.
This is preferable to making venoms from non-indigenous snakes, because the venom from, say, a Sind saw-scaled viper in Oman, may differ significantly from that of a viper of the same species in Pakistan or Egypt. It is anticipated that the latter project will take three or more years.
Prevention of snakebite
In Oman, where much of the population live in rural areas and practise subsistence agriculture or animal husbandry, and wear sandals, it is impossible to eliminate snakebite, but children and adults should be urged to wear foot protection and carry torches when walking in the dark. Everyone should be encouraged to avoid handling or trying to harm snakes (i.e. with a stick). All snakes should be regarded as potentially dangerous.
The author is Associate Professor in Infectious and Tropical Diseases, Department of Medicine, College of Medicine, SQU. His current research interests include evaluation and treatment of snakebite in Oman, and the development of snake antivenoms specific for indigenous species. He has worked in many countries (Papua New Guinea, Australia, USA, Tanzania, Zimbabwe, Saudi Arabia) where venomous snakes, scorpions and spiders occur.
Oman Observer 24th August 2002
