The use of hens' eggs as an alternative to the conventional in vivo rodent assay for antidotes to haemorrhagic venoms.

One of the tests used routinely for the preclinical assessment of antivenom efficacy is the WHO-approved rodent intradermal skin test for assessing neutralization of venom-induced haemorrhagic activity. This is a useful test as in many viperid venoms haemorrhage is considered to be the principal lethal (pathogenic) venom effect in envenomed humans. The main problems with such an assay are, first, the necessity of using large numbers of experimental rodents (rats or mice) in order to obtain statistically significant results and, second, that the test must result in pain for the animals during the 24 hr assay period. The present study compares the rodent assay with an alternative assay using venom, in both the presence and absence of antidote, applied to a filter paper disc and placed on the highly vascularized yolk sac membrane of chickens' eggs at an early developmental stage. This avoids sensitivity to pain as reflex arcs have not yet developed, and haemorrhage or neutralization/inhibition of haemorrhage can be easily recorded. Preliminary results showed a high level of correlation between the results of the two tests when used to assess the efficacy of an antidote. It is hoped that the new assay will reduce the need for pain-sensitive experimental animals in the future.