Page 841 - Clinical Small Animal Internal Medicine

74 Diseases of the Neuromuscular Junction 809

Snake Envenomation muscular blockade when there is a facilitatory release
VetBooks.ir There are four families of snakes that produce venom of neurotransmitter leading to complete cessation of
neurotransmitter release. The Elapidae family, such as
which causes neuromuscular blockade: Atractaspididae
(African mole viper), Colubridae (bloomsang, twig the coral snake, produce at least three neurotoxins
(taipoxin, beta‐bungarotoxin, and notexin). These
snake), Elapidae, and Viperidae. The Elapidae have three toxins have phospholipase A 2 activity and damage syn-
major subfamilies: Elapidae (cobras, mambas, coral aptic vesicles. There is also a change in the morpho-
snakes), Hydrophiinae (sea snakes), and Laticaudinae logic structure of the motor axon terminal, including a
(sea kraits). The Viperidae have two major subfamilies: decreased number of synaptic vesicles. The clinical
Crotalinae (pit vipers, copperheads, cotton mouths, and signs of snake envenomation are of a progressive neu-
rattle snakes) and Viperinae, the “Old World” vipers romuscular weakness with cranial nerve involvement,
(carpet vipers, adders, desert vipers). with death usually resulting from respiratory paralysis.
The pit viper toxin that causes neuromuscular weak-
ness is the Mojave toxin. It causes a presynaptic block If the snake can be identified then the use of antivenin
has a positive effect on outcome, especially the coral
of ACh release which can then lead to complete neuro-
snake.

Further Reading

Dewey C. A Practical Guide to Canine and Feline critical care management. J Vet Emerg Crit Care 2011;
Neurology, 2nd edn. Ames, IA: Iowa State University 21(3): 193–208.
Press, 2008. Shelton GD. Myasthenia gravis and disorders of
Khorzad R, Whelan M, Sisson A, Shelton GD. Myasthenia neuromuscular transmission. Vet Clin North Am Small
gravis in dogs with an emphasis on treatment and Anim Pract 2002; 32(1): 189–206, vii.