Trials using animals tend to focus on a single question — efficacy or toxicity, for example. But to make something suitable for humans requires the management of side-effects, and this might take years to tackle.
In 2006, Daniel Hackam of the University of Toronto looked at how many animal-based experiments had been later verified by successful human trials. Out of 76 studies published between 1980 and 2000, 28 were successfully replicated in human randomized trials, 14 were contradicted in trials and 34 remained untested.
In a letter published in the Journal of the American Medical Association, Hackam wrote: “Patients and physicians should remain cautious about extrapolating the findings of prominent animal research to the care of human disease ... poor replication of even high-quality animal studies should be expected by those who conduct clinical research.”
There are also physiological limitations.
“We can genetically modify, by a single intramuscular injection, a whole muscle in a mouse,” Wells says. “If we try to do that in a person it just doesn’t work because the spread of the agent we inject is maybe 4 to 5 millimeters — the size of a mouse muscle.”
And in other areas, mice are not sophisticated enough to model humans.
Neurologically, “mice are wired in a different way,” Wells says. “If I showed you a blind mouse and a mouse with perfect eyesight in a cage, you wouldn’t be able to tell the difference because mice rely a lot on smell and touch.”
None of this should put a negative spin, however, on the importance of mice in research. So far, 26 Nobel prizes have gone to discoveries where research on mice has been key, including work on vitamins, the discovery of penicillin, the development of numerous vaccines and understanding the role of viruses.
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