150 million animals are killed for research worldwide. Do humans really benefit?
Joseph murray, a Nobel laureate and the first person to perform a successful human kidney transplant, said in 1954, “Scientists agree whenever a cure for aids is found, it will be through animal research.” Murray may or may not be right. More than 85 hiv vaccines have shown promise in animal studies but none of them has worked on humans.
Rats and mice account for 90 per cent of all animals in experiments. They are convenient to handle and their genetic constitution is similar to humans. D ogs are suitable for cardiovascular research. The candidates for neurological and behavioural research are monkeys and chimpanzees.
A study led by Malcolm Macleod, head of experimental neuroscience centre at the University of Edinburgh in Scotland, and published on March 30 in PLoS Biology, analyzes what goes wrong with animal studies. The paper cites, among others, the case of stroke experiments. About 500 neuroprotective drugs have shown to improve the condition in animals but most of them failed in human trials. The paper states animals used in stroke research are mostly young and male. This does not represent females and the older animals; besides,s troke occurs mainly in older people.
“Rats and mice are the models of choice due to ease of maintenance and handling,” said T R Raju, dean of basic sciences at the department of neurophysiology at the National Institute of Mental Health and Neurosciences in Bengaluru. “Induction of stroke is also easier under controlled conditions in animal models due to the absence of secondary factors like diabetes, hypertension, stress,” he added. Stroke patients may have a lot of the secondary complications and that is why the success of these studies cannot always translate in humans. Use of monkeys and chimpanzees, animals more anatomically and genetically similar to humans, is often prohibited by ethical regulations, he pointed out.
Animals do not naturally suffer from many of the human illnesses; symptoms are artificially induced. Moreover, variations between animals and humans at the organ level make it impossible to always make valid predictions. Add to that errors in design of experiments. In Parkinson’s disease patients in clinical trials were administered interventions over a period of time because the disease progresses slowly. In animals the interventions took place soon after acute Parkinson’s disease-like lesions were induced. Such discrepancies lead to misleading results.
According to the Food and Drug Administration of usa, 92 per cent of drugs tested safe and effective in animal experiments fail in human trials. This has increased from 86 per cent in 1985. “About half of the eight per cent approved over the past few years are either withdrawn or have received black box labels for severe or lethal adverse effects undetected in animal experiments,” said John Pippin, senior medical and research adviser, Physicians Committee for Responsible Medicine.
The thalidomide disaster is often cited as a case study for animal studies gone wrong (see ‘The thalidomide story explained,’ Down To Earth, April 16-30, 2010). “All animals are not equally susceptible to the ill-effects of a drug. So rats and mice do not show drastic birth defects under thalidomide treatments in specified dose,” said Suvro Chatterjee, thalidomide researcher with Anna University in Chennai. A similar example is Zimeldine. Marketed by Astra AB, a Swedish pharmaceutical, the anti-depressant passed the animal-studies barrier but was eventually withdrawn because it increased risk for the paralyzing Guillain-Barre syndrome.
Around 150 million animals are used for research worldwide. The faulty results give strength to the army of animal protection groups who protest animal testing on ethical grounds. Still, most researchers believe a drug must be tested on a non-human living system before humans.
Computer models and tissue cultures are often touted as better alternatives. “I have seen no convincing evidence in their favour,” said Macleod. “While they can complement animal studies, they cannot substitute them in anything other than a small minority of situations.”
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