Diseases cause a staggering amount of suffering and death in both people and animals. As a result, human society has committed itself to alleviating the suffering caused by disease. Toward this goal, biomedical research has included the use of animals as one component of research to understand, treat, and cure many human and animal diseases. This publication (1) discusses how animals were and continue to be an important component of biomedical research, (2) presents the role animals play within the whole picture of biomedical research, (3) discusses the regulations and oversight that govern animal research, and (4) discusses continuing efforts to use animals more efficiently and humanely in biomedical research.
Throughout history, people have sought to reduce our vulnerability to the hardships and dangers of life. We have given up the wandering habits of our ancestors to settle in groups and cultivate the land to ensure a regular supply of food. We have built shelters to guard us from the weather and have crafted weapons to defend ourselves against predators. We have also tried to protect ourselves from a threat that is not always visible, but is often deadly—disease.
History is littered with examples of lethal diseases that strike and spread rapidly. Cholera, smallpox, polio, and influenza outbreaks have sickened, disabled, or killed hundreds of millions of people. The outbreak of the bubonic plague (caused by the bacteria Yersinia pestis) during the 14th century killed 25% to 50% of all people in Europe, the Middle East, China, and North Africa.
BUBONIC PLAGUE—A disease caused by the Yersinia pestis bacterium. Characterized by swollen lymph nodes and bleeding beneath the skin, often leading to death. Also called the “Black Death” during the 14th-century outbreak.
PARASITE—An organism that depends upon another organism (host) for its nutrients and protection, usually harming the host in the process.
Infectious diseases and those caused by parasites or malnutrition are not the only challenges to health we have faced. The ancients recognized epilepsy and called it “the sacred disease,” believing that the seizures of epileptics were caused by gods or demons. Babylonian documents describe the symptoms of epilepsy, as do Greek and Roman medical texts. Cancer too was known and feared by our ancestors, who attempted to heal these diseases with remedies both natural and magical. Eventually doctors and scientists turned to the study of animals to help them understand the mysteries of anatomy and the riddles of disease.
So why do scientists study animals to understand human disease? They do so because people are vulnerable to many of the same or similar diseases as animals. Humans have 65 infectious diseases in common with dogs, 50 with cattle, 46 with sheep and goats, 42 with pigs, 35 with horses, and 26 with fowl. We have lived with and among these animals for thousands of years, so it is not surprising that we are susceptible to some of the same parasites, viruses, and bacteria as animals, including some that can be transmitted between animals and people such as rabies and malaria. Nor is it surprising that many chronic, noninfectious diseases such as epilepsy also afflict other species. The parallels between human and animal physiology and pathology were noted long ago, and the practice that we today call “animal research” has roots stretching back to ancient Egypt and Greece.
PHYSIOLOGY—All the functions of a living organism or any of its parts.
PATHOLOGY—The structural or functional manifestations of a disease.
why use animals?
Animals are just one type of model that scientists use in biomedical research to simulate biological functions and organizations:
Molecular models simulate the interactions and functions of molecules and how these molecules form larger structures like proteins and DNA. For example, molecular models help scientists understand how protein structures inside heart cells cause the heart to contract and pump blood.
Cellular models simulate how structures interact inside a cell and how a cell functions. For example, cellular models help scientists understand how cells produce an electrical charge that causes the heart to beat.
Tissue models simulate how cells interact to form tissues and how the tissues function. For example, tissue models help scientists determine how the many electrical cells in the heart synchronize to produce electrical charges at the same time.
Organ models simulate how multiple tissues organize and function as organs. For example, organ models help scientists understand how the four different chambers of the heart work together to pump blood throughout the body.
System models simulate how multiple organs interact and form a system. For example, system models help scientists understand how the heart, arteries, veins, and capillaries (called the cardiovascular system) all work together to move blood from the heart to the body.
Organism models simulate how different systems work together to allow an animal to respond to its environment. For example, organism models help scientists understand how stress causes high blood pressure.
Many questions about molecular, cellular, tissue, and even organ functions can be investigated using test tube, cell culture, and tissue culture models. But some questions, such as how the digestive system interacts with the cardiovascular system or how the environment affects an organism, can only be answered using animal models.
People Often Ask the Questions…
“How can the research be useful when animals are different from people?”
“People and animals suffer from different diseases, so how can scientists justify performing experiments on animals?”
Even though animals differ from people in many ways, they also are very similar to people in many ways. Animals develop many of the same diseases as people, including hemophilia, diabetes, and epilepsy. Animals are also susceptible to many of the same bacteria and viruses as people, such as anthrax, smallpox, and malaria. An animal is chosen as an “animal model” for research only if it shares characteristics with people that are relevant to the research. For example, Louis Pasteur was able to use dogs as an animal model for studying rabies. He was able to develop a rabies vaccine because (1) dogs and people can both develop rabies, and (2) the immune systems of dogs and people react to the rabies virus in the same way. For this research, it did not matter that humans and dogs differ in other ways; for example, dogs cannot develop AIDS or measles, diseases that do affect humans.
ANIMAL MODEL—An animal in which normal biology and behavior or a disease or disability can be studied, and in which the normal or abnormal biology is similar to that in humans
AIDS (acquired immunodeficiency syndrome)—A fatal disease caused by the HIV virus. The HIV virus destroys T cells, which are the cells that fight infection. Eventually, the immune system is weakened enough that common illnesses become life threatening.