Biodiversity and Human Health: Exploring the Linkages

by Candace Nachman
Human health officials and environmentalists, previously two distinct groups, were first brought together by the health effects of breathing in the fumes given off by our vehicles and power plants or drinking toxic water. Based on warnings that high emission levels can lead to diseases such as lung cancer, or that drinking water with high chemical levels can cause deleterious effects on human health, the U.S. Legislature passed both the Clean Air Act of 1970 and the Clean Water Act of 1972, fundamental environmental legislation in the United States.
But now, a new environmental crisis threatens human health worldwide: the loss of biodiversity. Many people do not even know the meaning of this term and therefore have no understanding of how its decline can adversely affect their health. However, this issue is so important that scientists worldwide are studying the link between biodiversity loss and human health, governments are convening conferences, and the United Nations established the Convention on Biological Diversity.
I recently attended a symposium entitled “Biodiversity and Human Health: A Multidisciplinary Approach to Examining the Links” produced by the U.S. Environmental Protection Agency (EPA). The symposium, held at the National Museum of Natural History, was led by the EPA and co-sponsored by a long list of agencies, organizations, and academic institutions: the National Oceanic and Atmospheric Administration, Yale’s Center for EcoEpidemiology, World Health Organization, American Public Health Association, World Federation of Public Health Associations, the World Conservation Union, the Center for Health Applications of Aerospace Related Technologies at NASA Ames Research Center, Smithsonian Institution, Asia-Pacific Institute of Tropical Medicine and Infectious Diseases, Institute of Ecosystem Studies, and the University of Illinois Earth and Society Initiative in Disease Emergence and Ecosystem Health. I felt that what I learnt there was important enough to share with others.
Partly due to the lack of governmental regulation and partly due to the resources and lead-time required to develop effective strategies, few companies have boldly blazed the corporate trail towards addressing climate change. However, it is evident from looking at corporate pioneers such as Dupont, Cinergy, Swiss Re, Whirlpool and The Shell Group, that large corporations not only have the ability to significantly reduce GHG emissions, but they also have the financial motivation. Corporate climate strategies are increasingly viewed as a source of competitive advantage.
I will begin with some definitions and then discuss the importance of plant and animal species for medicinal purposes, the emergence and reemergence of infectious diseases due to biodiversity loss, and current collaborations that are underway to deal with the issue.

Background and Definitions: What is Biodiversity?

Most people understand biodiversity to be merely a count or tally of all plant and animal species on earth. However, the concept is much more complex, incorporating three key interconnected concepts: habitat or ecosystem diversity, genetic diversity, and species diversity.[1]
Habitat or ecosystem diversity refers to the range of places where life exists (e.g. mangroves, coral reefs, forests, etc.). Habitat degradation leads to depletion or extinction of the species that live there.
Genetic diversity refers to another aspect of biodiversity, which is less well known but nonetheless essential for protecting species over the long term. Plant and animal species can have more than one distinct population, living in different regions of the world. Although the defining genetic makeup of an entire species group, regardless of its population grouping, is the same across the board. Each population tends to only mate with individuals from its population, yet the possibility for interbreeding exists. Genetic diversity can be understood as the array of populations that comprise that species group. Maintaining as many different populations as possible is important to stopping biodiversity loss, as each population contains unique information in its genetic makeup for responding to threats. Thus, the fewer populations of a species that remain, the fewer survival tactics available to that species.
The last component of biodiversity is species diversity. This is the element that most think of when trying to define biodiversity as a whole. Simply, it is the variety of plant and animal species on earth. Decreasing or destroying any one of the three components described above has a negative effect on the other two, which in turn cause a loss in overall biodiversity on earth. This loss negatively affects humans in two ways:
1) we lose the potential for finding cures for human diseases
2) we may increase our risk of contracting new or reemerging infectious diseases.
Over the last half century, our actions have caused a severe decline in biodiversity through such actions as habitat destruction and hunting. Current observed rates of species extinction are as much as 100 to 1000 times higher than the average background rate.[2] It is true that species do occasionally go extinct, but humans are killing off plant and animal species at a rate that would be unprecedented if normal extinction patterns were able to run their course.

Medicinal Possibilities of Plants and Animals

For thousands of years, humans have used plants for medicinal purposes to alleviate scores of ailments. Few in the Western world understand the importance of these remedies in their everyday lives. Today, there is a push within the scientific community to explore the possibilities of using plants (and in some cases, animals) to discover cures for some of the world’s most prolific and deadliest diseases. At present, an estimated 80% of the world’s population, most of whom live in developing nations, depend upon plant derived sources of medicine. About 75% of the world’s top-selling prescription drugs contain ingredients derived from plant extracts.[3]
Yet this has not stopped large scale deforestation efforts. Once covering 14% of the earth’s land surface, rainforests now cover a mere 6%, and experts estimate that the rainforests could be entirely destroyed in less than 40 years. They estimate that 137 plant, animal and insect species are lost each day due to rainforest deforestation. That equates to 50,000 species a year. As the rainforests disappear, so do many possible cures for life-threatening diseases.
Seventy percent of plants found to have anti-cancer properties are found only in the rainforests. One example is the Madagascar periwinkle plant. Vincristine, a periwinkle extract, is one of the world’s most successful anti-cancer drugs to date. It has increased the survival rates for children with leukemia from 20% to 80%.[4] Of the 265,000 species of flowering plants, it is estimated that less than half of 1% have been screened for their beneficial pharmaceutical properties.[5] If we destroy the rest of the periwinkles’ habitat, then we also destroy the possibility finding other cancer treatments like this one.
Discoveries like those in the 1992 movie “Medicine Man” – in which an eccentric scientist working for a large drug company is seeking to find the cure for cancer in the Amazon jungle – are no longer Hollywood fantasy but on the brink of reality. Researchers at the University of Utah have harvested a substance from the venom of a cone snail that has shown promise in treating pain. Their research indicates that venom-derived compounds may ease pain associated with nerve damage from diseases such as diabetes. According to the American Diabetes Association’s 2005 statistics, approximately 20.8 million Americans (7% of the population) have diabetes. This statistic will most likely continue to rise based on American diets and the increasing cases of obesity seen in this country. Finding a cure for this disease is becoming crucial for more and more people.
The oceans also provide us with a virtually untapped pharmacy. Many more species live in the oceans than on land. However, testing of marine organisms, flora, and fauna has been extremely limited. Recently, researchers affiliated with the National Cancer Institute and other groups have extracted compounds from marine sponges and corals that inhibit the growth of tumor cells, and a group from the Scripps Institution of Oceanography has isolated marine bacteria closely related to the terrestrial organisms from which antimycin antibiotics were originally derived.[6]
Unfortunately, the oceans are under severe stress. Coastal development increases the amount of pollution entering our waterways at a rate never before seen in history. Reefs are being destroyed, and many fish stocks are being driven to near extinction. Since since so few of the organisms in the oceans has been tested for medicinal properties, by destroying the oceans, we are also destroying our chances at curing some of the world’s most devastating diseases.

Infectious Diseases on the Rise

As scientists have begun to study the effects of biodiversity loss, they have noticed that these environmental events are leading to the emergence and reemergence of many infectious diseases. This occurs because disturbances in the ecosystem lead to a loss of species diversity, a population explosion of competitive species, and host switching of pathogens from primary hosts to other hosts, including humans.
A prime example in the U.S. is the increased prevalence of Lyme disease. Lyme disease is a vector-borne or zoonotic infection, which is spread by spirochete-infected Ixodes ticks. This blacklegged-tick vector is a host-generalist, feeding from many different mammal and bird species but only acquires Lyme bacteria efficiently from a few hosts, mainly white-footed mice and eastern chipmunks. The ticks appear to suffer low mortality when feeding from these rodents as compared to other mammalian and avian hosts. The ticks also spend part of their life-cycle on deer. With the elimination of natural predators and recent reforestation of abandoned farmland, there has been an increase in the U.S. deer population. In turn, this has caused a reduced host diversity, and an increased potential for human exposure to the infected ticks.[7]
High host diversity seems to reduce the risk of people contracting Lyme disease in several ways. First, it allows the tick to feed from many hosts that are inefficient in spreading the bacteria. Second, high-diversity communities seem to regulate the abundance of white-footed mice through predation and competition, thus eliminating an effective host for spreading the bacteria. Lastly, high abundance of non-mouse hosts serves to deflect tick meals away from mice, thus reducing tick infestation of mice. Therefore, high diversity of hosts seems to reduce both infection prevalence of ticks and tick density, which in turn reduces human risk of contracting Lyme disease.[8]
Another example is Cholera. Once thought to be transmitted solely via infected humans and contaminated drinking water, the disease can actually remain dormant in phytoplankton and zooplankton. Some researchers now believe that the environmental conditions that cause algal blooms and the subsequent proliferation of zooplankton might act to increase dissemination of cholera into human populations. Current studies of ocean height and sea surface temperatures in Bangladesh and other climatological factors has allowed researchers to better predict when a cholera epidemic is likely to occur, both in its geographic location and its intensity.[9]
The discussion could go on with example after example. Avian influenza, SARS, West Nile Virus, and Hantavirus are just a few of the diseases for which researchers are exploring the link to changes in the world’s ecosystems.

The Way Forward

The increasing awareness of the links between biodiversity loss and human health effects has caught the attention of academia, national governments, and even the UN. The Convention on Biological Diversity (CBD) was created as a result of the 1992 Earth Summit in Rio de Janeiro. The Convention established three primary goals: the conservation of biological diversity, the sustainable use of its components, and the fair and equitable sharing of the benefits from the use of genetic resources. The seven biodiversity thematic program areas to be addressed by the Conference of the Parties include: agriculture, dry and sub-humid lands, forests, inland waters, islands, marine and coastal habitats, and mountains.
The CBD calls for efforts at both the national and international levels. On a national scale, countries should conduct surveys to inventory their biodiversity and to work with those members of society who have the greatest potential to cause ecosystem change (e.g. private companies, landowners, fisherman, and farmers). Additionally, these countries need to come together as global citizens to halt the severe decline in biodiversity.
As you can see, this is a problem that is being taken seriously by many groups. However, this long list can be deceiving. The global population far outweighs the efforts that are currently being made by a handful of the world’s population. This is a problem that affects each and every one of us, and we need learn more and take action to reverse these trends.
Candace Nachman has a MA in Marine Affairs and Policy from the University of Miami’s Rosenstiel School of Marine and Atmospheric Science. She currently works at the National Oceanic and Atmospheric Administration’s Office of Coast Survey. She is also very active with the “Green Group” at Kesher Israel Congregation in Georgetown, Washington, DC.


[1]    Harte, John. 1996. “Defining the ‘B’ Word.” Defenders Spring Issue.
[2]    Pimm, S.L., G.J. Russell, J.L. Gittleman, and T.M. Brooks. 1995. “The future of biodiversity.” Science 269:347-350.
[3]    Masood, E. 2005. “Biodiversity loss ‘poses grave threat to human health.'” SciDevNet,
[4]    Taylor, Leslie. 2004. The Healing Power of Rainforest Herbs. Square One Publishers, Inc.: Garden City, N.Y.
[5]    Cox P.A. Biodiversity and human health conference. Session III: Biodiversity and traditional health systems. Washington, D.C.: Smithsonian Institution, 1995.
[6]    Freeman, Kris. 2004. “New Centers for Oceans and Human Health.” Environmental Health Perspectives 112 (8): A468-A470.
[7]    Rapport, D.J., R. Costanza, and A.J. McMichael. 1998. “Assessing ecosystem health.” TREE 13 (10): 397-402.
[8]    Ostfeld, R.S. 2006. “Biodiversity and the Dilution Effect: The Case of Lyme Disease.” Abstract presented at the Biodiversity and Human Health: A Multidisciplinary Approach to Examining the Links Symposium, 14 Sept 2006, Washington, DC.
[9]    Colwell, R.R. 2006. “Disease Emergence in Terrestrial and Marine Environments.” Abstract presented at the Biodiversity and Human Health: A Multidisciplinary Approach to Examining the Links Symposium, 14 Sept 2006, Washington, DC

Originally posted in “On Eagles’  Wings” January 10th 2007 

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