(Signs and Symptoms)
is fast acting and is rapidly absorbed, attacking the central nervous system. By attacking the nervous system, the nerves that control breathing are paralysed and death is caused by respiratory failure.
The effects of a neurological bite usually manifest themselves within minutes after a bite due to the small molecular weight of the proteins being transported and absorbed rapidly by the body.
The victim experiences progressive weakness.
Death usually results between 5-15 hours, in severe envenomations however, death may occur in under an hour.
The majority of neurotoxic snakes usually belong to the family
Immediate symptoms of a Neurotoxic venom:
* A pins and needles sensation occuring at the bite site. This sensation usually spreads rapidly throughout the body, usually within 2-5 minutes after a bite.
* There may be minimal swelling around the bite site. Generally however this swelling does not progress further, and is usually restricted to the bite area.
* The bite itself is generally not painful, unlike cytotoxic venoms.
Other signs and symptoms of a neurotoxic venom:
* As with a
bite fang marks are usuallly a good indication of a potential envenomation. This could either be puncture marks at the site, or a scratch.
* A slight discolouration may be present due to the intra-tissue haemorrhaging.
* The pins and needles sensation manifests itself shortly after envenomation, and depending on the severity of the bite, spreads rapidly throughout the body.
* Although the bite itself is generally not painful, the victim usually experiences abdominal and muscle pain.
* Drooping eyelids (Ptosis). This occurs as the venom begins to paralyse the nerves which are then unable to communicate effectively to corresponding muscles. The "lesser" muscles are the first to be affected. In the case of Ptosis the levator and Mullers muscles (the muscles that control the eyelid), no longer respond due to the venoms' attack of the nervous system.
* Paralysis of neck muscles. This symptom causes the head to hang limply.
* As the neurotoxic venom continues its' onslaught on the nervous system the victim loses muscle coordination.
* Abdominal pain.
* Speech becomes affected usually within 20 minutes after a bite. This is often extremely frustrating as the victim is still concious but is unable to communicate effectively.
* Nausea and vomiting.
* Difficulty swallowing (Dysphagia). The nerves responsible for the "swallowing" action (glossopharyngeal, vagus, and hypoglossal nerves) are unable to function properly which leads to throat constriction. This is extremly painful.
* Increased salivation (saliva facilitates swallowing). This usually concides with dysphagia. The inability to swallow leads to an excessive production of saliva.
* Increased sweating. Sweating is controlled by the Sympathetic nervous system and is primarily a thermoregulatory mechanism. Because the neurotoxic venom neutralises the nervous system the body gets so called "mixed signals". As a result of this a victim usually experiences increased sweating.
* The venom attacks the motor neurons which causes muscle tremors (Fasiciculation).
* Mydriasis (dilated pupils). The two types of muscles that control the size of the iris are the circular and radial muscles. The radial muscles are innervated by the sympathetic nervous system. The stimulation of the venom causes the contraction of the radial muscle which leads to the pupils being dilated.
* Hallucination and confusion.
* Low blood pressure (Hypotension). A decrease in blood pressure means that not enough oxygenated blood reaches the various body parts which in turn prevents the adequate removal of waste products in the system. This inadvertedly leads to shock.
* Tachycardia (increased heart rate), or Brachycardia (decreased heart rate). There are two nerve systems that regulate heart rate (Parasympathetic, and sympathetic nerves) along with two sets of chemicals called adrenergic and cholinergic. These bind to receptors which can either raise or lower heart rate, and control blood pressure.
* Victims experience flaccid paralyses.
* Chest tightness.
* Respiratory distress.
* Respiratory muscle paralyses. This occurs when the thoracic diaphragm no longer contracts and relaxes. The contraction and relaxation of the diaphragm alters the volume and air pressure inside which contributes to the process of breathing (respiration). This is extremely serious and usually starts developing between 1-3 hours after envenomation.
* Oxygen deficiency in the tissue leads to the victim experiencing restlessness.
* Loss of control over bodily functions. The paralyses of sphincter muscles leads to incontinence of urine and faeces.
Click here to read about my personal account of a neurotoxic bite
Examples of Neurotoxic snakes that are classified as dangerous and life threatening:
King Cobra - ophiophagus hannah
Black Mamba - Dendroaspis polylepis
Forest cobra - Naja melanoleuca
Non spitting cobras
The extent of the signs and symptoms exhibited by a neurotoxic venom will vary depending on a number of factors.
Determining factors that will affect the symptoms shown include:
* Where the victim was bitten.
* Severity of envenomation.
* Snake species.
* Age of victim.
It is important to note that not all neurotoxic venoms are considered life threatening.
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