Easy questions to
askvery difficult to answer succinctly and simply. Snake venom is saliva,
a highly modified saliva, and is produced by modified saliva glands.
The proteinaceous nature
of snake venom was established by Napoleon Bonaparte's brother, Lucien
in 1843. Proteins constitute the major portion of venom's dry weight90%
or more. Snake venom is a cocktail of hundreds, sometimes thousands, of
different proteins and enzymes.
Many of these proteins are
harmless but a percentage of them are toxins. The makeup of these toxins
varies widely from species to species. This complexity accounts for the
widely differing effects of snakebite.
Venoms are rich in hydrolithic
enzymes, a complex mix of polypeptides, nucleases, peptidases, etc., which
help digest the snake's prey. Some of them also enhance or contribute to
the toxic effect of the venom. As early as 1949 it was shown that an enzyme
from the Bothrops species produces a vasodilation resulting from the production
of a hypotensor neuropeptide, bradykinin. This had important consequences
for man leading to drugs for the control of blood pressure.
were first produced a century or more ago. Albert Calmette demonstrated
that it was possible to "hyper-immunize" an animal against snakebite by
graduated and increased regular dosage of that animal with the venom of
that snake. He further demonstrated that a second animal could be saved
after snakebite by introducing the serum of the immunized creature. This
discovery is still the basis of the production of modern anti-venoms.
The proteins that
can kill or immobilize prey vary and differ in their effect and the percentages
in which they are present in venom.
||Block neuromuscular transmission
by linking, like curare, onto the cholinergic receptor found on the skeletal
||Blocks some of the central
nervous system's cholinergic receptors.
||Notexin, ammoclytoxin, beta-bungarotoxin,
||Block neuromuscular transmission
by keeping nerve ends from liberating acetylcholine. Could interact with
a potassium canal sensitive to voltage.
||Dendrotoxin, toxins I and
||Increase amount of acetylcholine
liberated by nerve ends. Could interact with a potassium canal sensitive
||y-Toxin, cardiotoxin, cytotoxin
||Disturb the plasma membranes
of some cells (cardiac fibres, excitable cells...) and lead to their lysis.
Lead to cardiac arrest.
||Lead to muscular degeneration
by interacting with a sodium canal dependent on voltage.
||Leads to muscular degeneration.
||Mucrotoxin A, hemorrhagic
toxins, a, b, c, ..., HT1, HT2
||Lead to very serious hemorrhages
by altering the vessel walls.
A few modern modifications
have been introducedsuch as the neutralization of the venom with formaldehyde
before use on the animal. This removes a lot of the earlier suffering such
The animal of choice is the
horse. Increasing doses of venom are injected until the animal becomes
hyper-immunized and thereafter blood is drawn and the serum removed. The
rest of the blood is transfused back into the animal.
The serum then passes through
various stages of refinement before it is released for use on humans. It
contains immunoglobulins and these are digested by pepsin to isolate the
antigen that neutralizes the venom.
These antivenoms are very
safehowever they are an animal protein derivative and a small percentage
of people react dangerously to it. They display a hyper-allergic reaction
which leads to anaphylactic shock which can kill. In a hospital situation
a cocktail of anti-histamines and hydro-cortisones would be administered
prophylactically. Then a small test sample of antivenom is administered
and the reaction to it noted before a full dose is injected or preferably
dripped into the patient in an intravenous solution.
The production of serum from
a single venom is known as a "monovalent" anti-venom and is efficacious
only on the snake from which the venom comes. When a cocktail of venoms
is used in the hyper-immunisation process the serum produced is a "polyvalent"
serum and is effective against a range of venoms. However the addition
of each venom causes a loss of efficiency and potency in the anti-venom
as a whole. So a delicate balance of like venoms is usually used to produce
an antivenom against the known snakes of a given area.