discovery of the polio virus in 1908, scientists focussed their main attention on the artificially induced disease in monkeys, believing it to be an exact replica of the human infection. Based on these experiments it was generally thought that polio virus entered the body through the nose and that it only attacked the central nervous system. Yet by 1907, epidemiological studies of human cases had correctly suggested that poliovirus was not entirely or even chiefly a disease of the central nervous system, and that people are infected through the digestive tract. Tragically, animal experiments so dominated research that prior to 1937, most scientists rejected the notion that polio is an intestinal disease.48
Whether the virus entered the body by the mouth or nose was of great practical importance for it determined the kind of remedies that were developed. By 1937, for instance, researchers had produced a nasal spray that prevented infection in monkeys. It was widely promoted for human use but inevitably failed. The only result was to abolish the children’s sense of smell, in some cases permanently.49 Eventually, support for the nasal route of infection began to wane, and it was only when scientists understood that poliovirus enters the mouth and first resides in the intestines that it was possible to develop an orally administered vaccine
In the cases described here, the epidemiological studies have involved observation of human subjects. But epidemiology can also focus on animal diseases and here too vivisection can undermine the results. The cattle disease bovine spongiform encephalopathy (BSE) was first identified in Britain in 1986 and soon reached epidemic proportions. By 1996 over 150,000 animals had died. BSE attacks the brain and is caused by feeding cows with the remains of sheep infected with scrapie. Soon after the first British cases were reported, animal researchers were busy transmitting the disease to other species. It was found, for instance, that BSE could be induced in susceptible strains of mice by injecting infectious material from cows into the brain.50 Mice were therefore used to assess which parts of the cow’s body carried infection. These experiments were to prove misleading.
A wide range of tissues were investigated including spinal cord, liver, kidney and heart. The tissues were ground up in salt water and injected into the mouse’s brain. The animals were then observed to see if they became ill, the amount of infection being calculated from the number of mice dying. If none of the animals became sick, the original tissue was said to be free of disease. The tests suggested that only the brain and spinal cord of cows with BSE were affected. Tissues which a calf would come into contact with, such as placenta, uterus, milk and mammary glands, showed no infection, supporting the belief that BSE was not transmitted from mother to calf.51 This was an important finding for farmers and the British government since any evidence of ‘maternal transmission’ would further undermine confidence in the beef industry by prolonging the epidemic. Not surprisingly, Agriculture ministers vigorously dismissed the idea, one official describing. it as ‘basically rubbish.’52 >>
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