International Association Against Painful Experiments on Animals

Study of Disease

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The Australian obstetrician William McBride was first alerted to the dangers of thalidomide after seeing just three babies born with birth defects. However, the deformities were so unusual that McBride strongly suspected the drug. Unfortunately, his warnings to the medical profession were delayed because he tried to “confirm” his observations in mice and guinea pigs, both
of whom proved resistant to the drug.1 And it was the dramatic increase in a virtually unknown form of vaginal cancer that warned doctors of the carcinogenic effects of diethylstilbestrol. The cancer appeared in young women whose mothers had taken the drug during pregnancy to prevent miscarriage.6

Initial population studies often provide only circumstantial evidence of the causes of disease but epidemiologists have developed a wide range of techniques to strengthen and verify their conclusions. One of the most ingenious is the study of immigrants. For instance, by observing people who move from Japan, where there is a strikingly low death rate from heart disease, to the United States with its much higher mortality, researchers can decide whether the illness is largely preventable or linked to hereditary factors. It transpires that the Japanese owe their low rates not to their genes but to their way of life, because immigrants quickly acquire America’s higher
death rates.7

Another powerful technique is the discovery of a “dose- response” relationship where the risk of illness rises with increasing exposure to the suspected agent. The link between smoking and lung cancer was confirmed when population studies showed that the chances of becoming ill increased with the number of cigarettes smoked. Proof that 2-naphthylamine caused bladder cancer in the aniline dye industry, came with the discovery that risks depended on the time spent distilling the chemical, so much so that workers exposed for five years were
nearly 100% certain to develop cancer!9



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