A humane alternative to the measurement of the lethal effects ( ld50) of non-neurotoxic venoms using hens' eggs

Abstract

The accurate measurement of venom lethality is the basis of clinical treatment of snakebite and of much venom-related research. Lethality tests are necessarily carried out in animal models and the results extrapolated to man. While we may be confounded by the obvious limitations of this approach, we can improve the situation by using a non-sentient living system, such as the very early developmental stage of the chick embryo, as an alternative to lethality testing in mammals. The continuing need for lethality testing of venoms and their isolated components, which underpins the development and assessment of antivenoms, currently accounts for thousands of mice annually; this is becoming increasingly unacceptable, first because of the amount of suffering caused and second, because of the high cost incurred. We describe here the use of 4–6 d old chick embryos as a system for estimating venom lethality. The shell-less yolk sac membrane offers a vascular system which develops before intact nervous reflex arcs are functional and therefore the embryo is incapable of experiencing pain. Venom is applied to the membrane on a filter paper disc and its effects on vascular and cardiac function are easily observed throughout the 6 h experiment. Eight venoms tested on eggs and by conventional ld 50 assays in mice were compared. A highly significant correlation was obtained suggesting that this simple and inexpensive test would be a far more acceptable alternative for non-neurotoxic venoms.