Chapter-i origins Why are snakes called reptiles? What is a reptile?
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- Bu səhifədəki naviqasiya:
- Range Status within its distribution range Potency of venom Incidence of bites
- What are the three important families of venomous snakes in India
- What are the other principal venomous snakes of India which are not ‘common’ throughout most of India (For clarification on ‘common’ see Q A 217).
- Based on the same or similar criteria as in Q A 220 what snakes can be considered as the most dangerous snakes of the world
- Are new-borns of venomous snakes dangerous
- What is meant by a ‘mildly venomous’ snake
- What is meant by a ‘dry bite’
- What are the different groups of toxins present in snake venom
- How is potency of snake venom measured
- What is the principal difference between the venom of the vipers and the venom of cobras and kraits and the venom of sea snakes
- Why is it dangerous to handle a recently dead venomous snake
- Can repeated injections of snake venom make a man immune to snakebite
- What are the symptoms of bite by different venomous snakes
- In the case of a snake bite, is absence of fang marks or pain or swelling an assurance that there is no envenomation
[Sourced mostly form Whitaker and Captain : Snakes of India : The Field Guide, 2004] N.A. : Information not available.
The elapidae (cobras, kraits and coral snakes), the viperidae (vipers including pitvipers) and the hydrophidae (sea snakes).
There is no one-word answer to this because the degree of danger posed by a snake depends on various factors:
If we consider sea snakes, the hook-nosed sea snake (Enhydrina schistosa) may be reckoned as the most dangerous sea snake for India (also worldwide). It is the most widespread on the Indian coast, it is the commonest in its range and it has the most potent venom. Though sea snakes are generally reluctant to bite, this one is more ready to do so than others. Fatalities are known, but the comparative data for sea snakes is not available. As is the case with all sea snakes, occasions for confrontations with humans are limited mostly to fishermen. No one land snake of India qualifies to be counted as ‘the most dangerous’ going by all the criteria listed above. The honours have to be shared by four snakes. The position is as follows:
b) The commonest within its range the spectacled cobra and c) Occurrence in areas with the densest the monocled cobra taken human population together .
for confrontations with humans kaouthia)
(Bungarus caeruleus)
(Daboia russelii) g) Frequency of fatal or life-threatening envenomation by bites : The saw-scaled viper (Echis carinatus) Thus the Indian cobra (i.e. the spectacled cobra and the monocled cobra), the common krait, the Russell’s viper and the saw-scaled viper are together known as the “Big Four” venomous snakes of India.
Here again, the situation may differ from country to country or region to region depending on various factors. But, generally speaking, the following is the position:
Yes. They have venom glands, venom and fully functional fangs. It may appear paradoxical, but the venom of new-born and small juveniles is more potent than that of adults of the same species. This is Nature’s way of making up for the smaller quantity. A young snake is also more irritable than an older one.
Some snakes such as the cat snakes, vine snakes and estuarine snakes used to be described until recent times as ‘non-venomous’. This was not strictly correct. It is true they do not have glands producing venom and hollow or grooved front fangs for venom delivery. But they have large grooved teeth in the back of the upper jaw (hence called rear-fanged or back-fanged) which can deliver toxic saliva to its prey from the Duvernoy’s gland. This can paralyse the prey species. In humans, their bites can cause local symptoms but no serious complications or death. This is sometimes referred to as salivenomation. The Duvernoy’s gland is a modified salivary gland, but different in structure from a venom gland which too is a modified salivary gland. It varies in size from species to species.
When the snake bites a non-prey species like humans, the intention is rarely to kill. The venom is a precious resource for the snake, being an aid to capture its prey and an enzyme to digest it and, therefore, the snake does not expend more venom than what is strictly necessary. Even when it bites a prey, it usually injects only just enough venom to paralyse it. The snake then allows the prey to run away and tracks it down by smelling the scent trail and finally captures it when it has become incapacitated. In the case of a human victim when the snake bites as a reflex action when it is trodden upon or otherwise hurt, a large quantity of venom may, perhaps, be injected. But, often, it is only a defensive action and the intention is only to warn in which case the venom may be insignificant in quantity or nil. A bite with little or no venom injected is known as a ‘dry bite’. It is estimated that, in Indian conditions, nearly 50 % of bites are ‘dry bites’. In seasnakes ‘dry bites’ are as high as nearly 70 %. But this may vary depending on the species. Cobra bites are in many cases ‘dry’. But few bites of the saw-scaled viper are ‘dry’. It is estimated that only 10 % of saw-scaled viper bites are ‘dry’.
The venom of a snake is not just one kind of toxin. It is a cocktail of toxins with different properties and different effects on the body of the victim. These toxins are enzymes and 25 such enzymes have been isolated. The toxins are broadly as follows:
There are also components whose functions we still do not know.
A large number of mice are injected with a measured quantity of venom. The percentage of mortality within 24 hours is found out. The lethal dose for 50 % of the mice is specified as ∟D50 and this is expressed in ‘milligram of venom per kilogram of mouse’. For instance, a spectacled cobra’s (Naja naja) venom’s ∟D50 is 0.28. This means that the lethal dose of venom for 50 % of mice of a given sample is 0.28 mg for kg of mouse. The ∟D50 figures for different species of snakes will give an idea of the comparative potency of their venom. For instance, the ∟D50 for king cobra (Ophiophagus hannah) venom is 0.90 whereas for spectacled cobra, it is 0.28. This means that the potency of the king cobra’s venom is only about one-third of that of the spectacled cobra.
The venom of the vipers is haemotoxic and attacks the tissues and blood. The blood loses its ability to coagulate. There is profuse bleeding internally and externally and this is the principal cause of death. The venom of the cobras and kraits is neurotoxic i.e. damaging or destroying nerve tissue. Death is due to respiratory failure. The venom of sea snakes is predominantly myotoxic i.e. damaging the muscles. The venom’s site of action is at the neuro-muscular junction. But, these are not water-tight compartments. For instance, viper venom can cause neurotoxic effects also.
Even after death, the jaws may sometimes snap shut in a reflex action and if a body part of the handler gets caught inside the mouth, a venomous bite may be the result. Such reflex action in dead snakes, and even in severed heads, has been noticed even one hour after the snake’s death.
Though such claims are occasionally heard, no controlled experiments have been conducted in the matter, or are, indeed, possible for obvious reasons. While, theoretically, such immunity may be thought possible, this is unlikely to be achieved in practice because of the likelihood of even mild doses causing serious complications forcing the research to be abandoned, the uncertainty in determining when the immunity built up is adequate, the uncertainly of how long the immunity will last and the probability that, at some stage, the tolerance threshold may unwittingly be crossed leading to fatal results. Also, and not the least, is the possibility of someone getting entangled with the law on homicide or attempted suicide. Moreover, the slow accumulation of venom in the blood, even if it does not prove fatal, can have very serious consequences in course of time. The case of Ram Chandra, the famed ‘Taipan Man’ of Australia, is a pointer (See Q & A 332).
No. There can be envenomation even in such cases. In all cases of snakebite, except where the snake is positively identified as non-venomous or only mildly venomous, all precautions should be taken and a watch kept for symptoms of envenomation which may set in later.
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) The most widespread in distribution The Indian cobra i.e.