Components of Venom and Mechanisms of action
The components of venom are cardiotoxin, hemotoxin, nephrotoxin, neurotoxin,
hyaluronidases, phosphodiesterases, phopholipases, glycosaminoglycans, histamine,
serotonin, tryptophan and cytokine releasers. Among all, the most potent is the
neurotoxin. There are two classes of neurotoxins (long chain & short chain polypeptide)
which are heat stable, have a low molecular weight and are responsible for causing cell
impairment in nerves, muscles, and the heart by altering sodium and potassium channel
permeability. The long chain polypeptide neurotoxin induces continuous, prolonged,
repetitive fi ring of somatic, sympathetic and parasympathetic neurons which results
in autonomic, and neuromuscular over excitation symptoms. It also prevents normal
nerve impulse transmissions. Further, it results in release of neurotransmitters viz.,
epinephrine, nor-epinephrine, acetylcholine, glutamate, and aspartate excessively. The
short chain polypeptide neurotoxin blocks the potassium channels.
Pathophysiology
The venom is produced by columnar cells of the venom glands. Scorpion venom
is water soluble, antigenic and positively charged. It is a heterogenous mixture and
this can be easily demonstrated by electrophoresis method. Also, the heterogenisity of
the venom explains the variable response to venom as observed in different people.
Normally injected venom is between 0.1 to 0.6mg. Generally most lethal scorpions
have a lethal dose (LD50) below 1.5mg. The potency varies with species causing mild
fl u to death with in an hour. Humans are much more sensitive than mice.
Once the venom is injected, it is distributed rapidly into the tissues. If the venom
is deposited into a vein, the symptoms develop within 4 to 7 minutes after injection,
with a peak concentration in 30 minutes. The half life of venom varies from 4.2 to 13.4
hours.
Symptoms and signs
Symptoms and signs are infl uenced by factors related to “3 Ss” viz., scorpion, sting
and the status of the patient.
Table No. 17: Infl uencing factors for symptoms and signs
Scorpion
• Species
• Age, size and
• nutritional status
• Stinging apparatus
(telson)
Sting
• Time of sting
• Number of stings
• Quantity of venom
injected (low dose –
adrenergic, high dose
– cholinergic)
• Depth of the sting
penetration
• Site of sting IV/SC/IM
• Components of venom
Status of the patient
• Age of the patient
• Health status
• Comorbid conditions
• Weight of the victim
• Physiological response
of the individual
• Sensitivity of
the systém to the
neurotransmitters and
toxins
Usual signs of scorpion sting are as follows
• Mydriasis
• Nystagmus
• Hyper salivation
• Dysphagia
• Restlessness
Usual mode of death is via
• Respiratory failure secondary to