Krait - Venom

Venom

Bungarus contains some species which are the most venomous Asiatic land snakes based on their LD₅₀. They have highly potent neurotoxic venom which can induce muscle paralysis. Clinically, their venom contains mostly pre-synaptic neurotoxins. These affect the ability of neuron endings to properly release the chemical that sends the message to the next neuron. Following envenomation with bungarotoxins, transmitter release is initially blocked (leading to a brief paralysis), followed by a period of massive overexcitation (cramps, tremors, spasms), which finally tails off to paralysis. These phases may not be seen in all parts of the body at the same time. Since kraits are nocturnal they seldom encounter humans during daylight hours, so bites are rare, but a bite from a krait is potentially life-threatening, and should be regarded as a medical emergency.

Typically, victims start to complain later of severe abdominal cramps accompanied by progressive muscular paralysis, frequently starting with ptosis. As there are no local symptoms, a patient should be carefully observed for tell-tale signs of paralysis (e.g. the onset of ptosis, diplopia and dysphagia) and treated urgently with antivenom. There is frequently little or no pain at the site of a krait bite, which can provide false reassurance to the victim. The major medical difficulty of patients envenomated are the lack of medical resources (especially intubation supplies and mechanical ventilators in rural hospitals) and the ineffectiveness of the antivenom.

Once at a healthcare facility support must be provided until the venom is metabolised and the victim can breathe unaided, especially if there is no species-specific antivenom available. Given that the toxins alter acetylcholine transmission which causes the paralysis, some patients have been successfully treated with cholinesterase inhibitors such as physostigmine or neostigmine, but success is variable and may be species dependent as well. If death occurs it typically takes place approximately 6 to 12 hours after the krait bite, but can be significantly delayed. Cause of death is usually respiratory failure i.e. suffocation via complete paralysis of the diaphragm. Even if patients make it to a hospital subsequent permanent coma and even brain death from hypoxia may occur given potentially long transport times to get medical care.

Mortality rates caused by bites from the members of this genus vary from species to species: according to University of Adelaide Department of Toxicology, bites from the banded krait has an untreated mortality rate of 1—10% while that of the common krait is 70—80%. Several websites state that there is a mortality rate of 50% even with treatment, but no specific species is given and there is no original source in the medical literature for this statement.In common with those of all other venomous snakes, the death time and fatality rate resulting from bites of kraits depend on numerous factors, like the venom yield and the health state of the victim.

The polyvalent Elapid Antivenom is effective in neutralizing of the venoms of Bungarus candidus and Bungarus flaviceps and rather effective in the neutralization of the venom of Bungarus fasciatus. In this last case, the monovalent Bungarus fasciatus antivenom is also moderately effective.