Analysis of the technical questionnaires revealed variation in
MIT protocols among participating laboratories. Young Swiss albino
mouse strains should be used, preferably baby mice less than
3 days old if possible, as they are more sensitive to the rabies
virus (Koprowski, 1996). Mice transported to the laboratory should
undergo an adaptation stage for a minimum of 3 days so that
mice which die as a result of transport conditions can be eliminated
before the experiment (Koprowski, 1996). Antimicrobial
agents must be added to the brain tissue preparation to avoid
non-specific mortality (streptomycin at 1560 UI/ml and penicillin
at 500 UI/ml) (Koprowski, 1996). To avoid interference phenomena,
it is also preferable to prepare the suspension tissue for
inoculation at 10% (Koprowski, 1996). To avoid animal distress
and suffering, as well as non-specific mortality, any intra-cerebral
injection should be conducted under anaesthesia. It must be
emphasised that half of the laboratories did not anaesthetise mice
before the inoculation step. This contradicts ethical regulations and
efforts made to avoid suffering of animals used for experimental
and scientific purposes (European Council Directive 86/609/EEC,
1986).