What can a mouse tell us about human health?
Why do so many studies use mice as their primary testing subject, and how much can a mouse really tell us about human health?
Despite our discomfort with them, the Mus musculus (the common house mouse) has been used for decades now to unlock complex medical mysteries and develop new drugs. But why are mice used so often and what can they really tell us about human disease?
Any drug requires years of animal testing before it is tested on humans. It would be hard to convince thousands of humans to voluntarily submit to testing a trial drug with no idea of its safety. Some object to this kind of treatment of mice or any other lab animal, but mice remain the standard testing ground for the vast majority of medical studies.
Between 20 million and 30 million mice are used each year in the United States for biological and medical research. Research institutions have come to rely upon them for their studies. Johns Hopkins, for example, allots millions of dollars of its annual budget to care for its 200,000 mice.
The mouse’s genome is 95 percent similar to ours. The mouse’s immune system is a surprising 98 percent identical to our immune system. These similarities make it very easy to mimic human diseases and responses to therapies in mice without actually testing humans.
Mice also have the advantage of a shorter breeding period and lifespan. This means that mice are easily, quickly and cheaply multiplied, and scientists can see the results of their hypotheses and medications play out in mice much faster than they would in humans or even other mammals.
Since the 1980s, scientists have been able to alter the genetic make up of mice to mimic human diseases and conditions. This allows scientists to give a mouse, or a large quantity of mice, a human disease–such as Alzheimer’s or diabetes–and then test a therapy for that disease on the mouse.
Genetic alterations allow scientists to meticulously control the genetic make-up of mice and therefore pinpoint what therapies work on which diseases. These kind of strict controls are important to determine causality in a study and crucial if the trial is to continue to human testing.
What good are all the similarities between mice and humans if mice cannot communicate with us? In cancer studies it is as simple as testing to see if tumors shrink in response to a therapy on a mouse. Scientists will often train mice to run through mazes to test their memory and cognitive ability.
To determine psychological reactions in mice, scientists must rely on physiological clues. For example, the body often has a chemical response to anxiety or stress that can be measured in blood tests. So to measure these kinds of reactions in mice, scientists can monitor the mouse’s heartbeat and collect blood samples to test for the chemicals that indicate stress.
There will never be one mouse model that will translate perfectly into a human disease. Despite their limitations, mice models do provide a reliable vetting process for drug therapies and ensure that the therapies that do make it to human testing have a better chance of success.
There are certainly other species that are very helpful in studying human responses. The fruit fly, for example, is often used in modern research to study the human genome and is a favorite among scientists to study human sexual behaviors.