Animals and Their Importance to Medicine

The increased longevity we see today was not present 150 years ago. In the 1870s, the leading cause of death was tuberculosis and the average human life span was about 30 years (U.S. Census Bureau, 2021). Many of these deaths happened in infancy or early adolescence. Today, the leading cause of death is heart disease, and the average life span has increased to the mid-70s (Ritchie, Spooner, & Roser, 2018). Sanitation and improvement in nutrition have helped reduce the probability of infection and improved overall quality of life, but this is not the only reason. Many diseases could not have been treated or eliminated without animal research. Animal testing significantly contributes to research, especially vaccine and antibiotic development. Animals even allow for the development and testing of  new surgical options. There are many ethical issues revolving around animal research such as animal rights, allocation of resources, and distributive justice. This article keeps these issues in mind but only wishes to be informative on the positive impact animal research has on the field of medicine. 

Many vaccines and antibiotics were found because of animal testing. For example, animal research played a vital role in mRNA COVID-19 vaccine development. The urgency of the COVID-19 pandemic required rapid vaccine development and this was only possible due to the effectiveness of animal research. Before any human testing is done, an initial animal testing is required so any possible side effects can be assessed.  Labs frequently use mice models because of the similarities they share with humans; mice also reproduce quickly which helps limit the time needed to test a gene, antibody, etc. However, there was a challenge that researchers had to face before making an appropriate genetic model. In order for the SARS-CoV-2 to infect cells, it must bind to a human protein called ACE2. As mice do not have this protein, SARS-CoV-2 cannot bind to mouse cells. Consequently, scientists found a way to bypass this by creating a more genetically compatible model capable of expressing ACE2 to effectively test COVID-19 (Wang, 2020). This example demonstrates the great strides made in medicine as current day research is able to use genetic methods to develop transgenic mice to make a model as similar to humans as possible. These mouse models provided important information about COVID-19 symptoms and helped develop vaccine treatments. The models are continually being used to understand disease progression to better understand the COVID-19 disease.

The COVID-19 vaccine is classified as an mRNA-based vaccine, and only transgenic animal models are capable of testing its effectiveness. mRNA vaccines work by introducing a piece of mRNA that corresponds to a viral protein - which is usually a small piece of protein found on the virus's outer membrane - so the individual receiving this vaccine cannot get infected with the virus by the vaccine. Using this mRNA vaccine, cells are able to produce the viral protein which the immune system recognizes and creates antibodies to defend the body with. This method increases the efficiency and likeness of combating the virus as soon as an infection takes place (U.S. National Library of Medicine, n.d.).

mRNA vaccine testing in animals proved that a low dose was enough to effectively boost the immune response once an individual was infected. Moreover, vaccination of non-human primates further confirmed the effectiveness of mRNA vaccine as it induced SARS-CoV-2 neutralizing effects by rapid protection of upper and lower airways as seen in phase 1 of human testing (U.S. Department of Health and Human Services, n.d.). Animal testing was crucial in order to assess the effectiveness of the vaccine and to better understand disease pathology. Without the use of animal testing, these effective genetic therapies would not be possible.

Animal research is a major contributor to many surgical procedures and techniques. This section will specifically focus on heart surgery and how animal research made many procedures possible. 

Effective heart surgery would not be possible without animals. In the 19th century, medicine had little to no solution to treat heart disease as there was no way to repair the heart of a living patient. However, at the beginning of the 20th century, surgeons began to operate on the hearts of dogs and other farm animals to find a surgical method that will work on humans. At the time, these surgeons concentrated on repairing heart valves which were a common consequence of rheumatic fever. By 1923, Dr. Elliot Cutler performed the first successful mitral valve repair. The procedure was done on a young girl with rheumatic mitral valve stenosis who was comatose due to low cardiac output (Cohn, Tchantchaleishvili, & Rajab, 2015). The procedure extended her life by 4 years but she unfortunately passed away from pneumonia. 

Surgical innovation did not stop there. Surgeons continued to use animals to find a way to circulate blood while the heart had to be stopped for more invasive procedures. These continued experiments led to the first operation using a heart-lung machine in 1953, which pathed the way to modern-era open-heart surgeries (Science, Medicine, and Animals, 1991). 

Animals are even used to improve surgical outcomes. In 2004, a study used a sheep model to perform coronary artery bypass surgery in order to develop better surgical procedures to decrease the overall mortality rate (Shofti, 2004). Animal research helps improve existing procedures and does not put human patients at risk. 

Animals are also used to act as transplant donors when an appropriate donor is unavailable. This kind of transplantation is called xenotransplantation. Xenotransplantation can be traced back to the early 1960s when scientists used donor organs of chimpanzees to treat kidney disease in humans (“Xenotransplantation: Animal to human transplants”, 2022). Transplant organs are a scarce resource and people are desperately trying to find other suitable options such as organ regeneration or artificial organs that can imitate the physiological function. The idea that certain animal organs are very similar to humans in anatomy and size led many scientists to believe that xenotransplantation would be successful. In March 2022, David Bennett received a genetically modified heart on an emergency authorization from the Food and Drug Administration. Before his transplant, Bennett had been suffering from a life-threatening arrhythmia and was connected to a heart-lung bypass machine. Physicians were forced to transplant a pig’s heart into David which prolonged his life. Unfortunately, David died 2 months after the operation. However, this example of xenotransplantation has given hope to future transplantation procedures, and that an animal organ can be used as a temporary substitute until a viable organ can be obtained (Fieldstadt, 2022). 

It should be noted that in each instance animal research was used, proper ethics and health guidelines were enforced to make the experiments as humane as possible. There are still many ethical concerns revolving around animal testing, but society has tried its best to limit the number of animal casualties and respect animal rights. 

Heart surgery continues to expand and improves the lives of many people. About 3 million people undergo various kinds of cardiovascular operations in the United States each year (U.S. Department of Health and Human Services, 2022). Without animal research, the consequence of these surgical tests would have been much costlier. 

Animal research is essential in vaccine development and the creation of surgical methods and protocols. Continued animal testing will be performed in the future to better understand disease pathology and to safely access surgical protocols. The contribution of animals to medicine is vast and this article has only showed a few examples to demonstrate their significance. Animal testing is one of the main reasons that the field of medicine has gone as far as it did, especially in the last 200 years. We have continually found ways to make procedures more efficient and create medication to combat disease. 

References

Cohn, L. H., Tchantchaleishvili, V., & Rajab, T. K. (2015, July 1). Evolution of the concept and practice of mitral valve repair. Annals of cardiothoracic surgery. Retrieved January 21, 2023, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4526492/#:~:text=In%201923%2C%20Dr.,comatose%20from%20low%20cardiac%20output

Fieldstadt, E. (2022, July 7). First man to receive a transplanted pig heart died of heart failure, not rejection, encouraging doctors. NBCNews.com. Retrieved January 21, 2023, from https://www.nbcnews.com/health/heart-health/first-man-receive-transplanted-pig-heart-died-heart-failure-not-reject-rcna37078

Read "Science, medicine, and animals" at nap.edu. How Have Animals Contributed to Improving Human Health? | Science, Medicine, and Animals |The National Academies Press. (1991). Retrieved January 21, 2023, from https://nap.nationalacademies.org/read/10089/chapter/4

Ritchie, H., Spooner, F., & Roser, M. (2018, February 14). Causes of death. Our World in Data. Retrieved January 21, 2023, from https://ourworldindata.org/causes-of-death

Shofti, R., Zaretzki, A., Cohen, E., Engel, A., & Bar-El, Y. (2004). The sheep as a model for coronary artery bypass surgery. Laboratory Animals, 38(2), 149–157. https://doi.org/10.1258/002367704322968821

U.S. Census Bureau (2021, December 16). 1850 census: Mortality statistics of the seventh census of the United States, 1850. Census.gov. Retrieved January 21, 2023, from https://www.census.gov/library/publications/1855/dec/1850b.html

U.S. Department of Health and Human Services. (n.d.). The important role of animal research in mrna COVID-19 vaccine development. National Institute of Allergy and Infectious Diseases. Retrieved January 21, 2023, from https://www.niaid.nih.gov/news-events/role-animal-research-mrna-covid-19-vaccine-development#:~:text=Animal%20studies%20contributed%20to%20the,in%20mice%20and%20nonhuman%20primates

U.S. Department of Health and Human Services. (2022, June 1). What is heart surgery? National Heart Lung and Blood Institute. Retrieved January 21, 2023, from https://www.nhlbi.nih.gov/health/heart-surgery#:~:text=Each%20year%2C%20more%20than%202,to%20treat%20various%20heart%20problems

U.S. National Library of Medicine. (n.d.). What are mrna vaccines and how do they work?: Medlineplus Genetics. MedlinePlus. Retrieved January 21, 2023, from https://medlineplus.gov/genetics/understanding/therapy/mrnavaccines/

Wang, Q. (2020, February 25). Hace2 transgenic mouse model for Coronavirus (COVID-19) research. The Jackson Laboratory. Retrieved January 21, 2023, from https://www.jax.org/news-and-insights/2020/february/introducing-mouse-model-for-corona-virus

Xenotransplantation: Animal to human transplants. PKD Foundation. (2022, May 16). Retrieved January 21, 2023, from https://pkdcure.org/xenotransplantation-animal-to-human-transplants/#:~:text=Since%20the%201990's%2C%20pigs%20have,to%20human%20kidneys%20and%20hearts.