"Biodiversity:
Its Importance
to Human Health"
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BIODIVERSITY & HUMAN HEALTH
by Professor Eric Chivian M.D.
Director, Center for Health and the Global Environment
Harvard Medical SchoolThe relationship of biodiversity to human health has relevance to all eight Millennium Development Goals (MDGs), but it has special and fundamental importance for goals 1, 4, 5, 6, and 7. This brief paper shall attempt to provide a few case studies that illustrate these relationships, focusing on goals 4, 5, and 6. It should be said at the outset that while the need to divide the MDGs into distinct categories so that they may be more easily considered and studied is clear, we must also keep in mind that there are multiple interconnections and synergies between them which tend to be obscured by such distinctions. In particular, this applies to themes involving health, which affect, and are affected by, all the MDGs. When we separate health goals from other environment and development goals, we essentially reinforce the widely held misconception that human beings are separate from the environments in which they live. This misconception, in my view, is at the core of the global environmental crisis, as it leads to a belief that we can disrupt the natural world, altering its physical, chemical, and biological systems, without these alterations having any effect on us whatsoever. People will not do what is necessary to protect the global environment until they begin to understand the risks to themselves and to their children. There is no more effective way to help them achieve this understanding than to frame discussions about development and the environment in the concrete, personal terms of human health.
RELATIONSHIP TO BIODIVERSITY
Human health is dependent on biodiversity and on the natural functioning of healthy ecosystems. As Jeff McNeely has said, “To enhance these linkages [between biodiversity and human health] requires that we consider biodiversity and human health as different aspects of the same issue: that people are an integral part of Nature and must learn to live in balance with its other species and within its ecosystems.” Without a healthy population, a nation cannot hope to develop sustainably or to achieve true prosperity.
Biodiversity supports human life and promotes health by:
1) Providing, at the most basic level, ecosystem services that:
>> Filter toxic substances from air, water, and soil;
>> Protect against flooding, storm surges, and erosion;
>> Break down wastes and recycle nutrients;
>> Pollinate crops and wild plant species;
>> Create and maintain soil fertility;
>> Sequester carbon, thus mitigating global climate change;
>> Help to maintain the water cycle and stabilize local climates;
>> Feed, clothe, and shelter us;
>> Provide a host of other goods and services that support all life, including human life, on Earth.2) Providing medicines from plants, animals, and microbes – on land, in lakes and rivers, and in the oceans.
3) Providing models for medical research that help us understand normal human physiology and disease.
4) Supporting agriculture and the marine food web.
5) Reducing the risk of contracting some human infectious diseases through the "dilution effect"; by controlling populations of vectors, hosts, and parasites; and by other means.
BENEFITS OF BIODIVERSITY TO HUMAN HEALTH
I. MDG 4: Child Morbidity and Mortality
>> Schistosomiasis
“Among human parasitic diseases, schistosomiasis (sometimes called bilharziasis) ranks second behind malaria in terms of socioeconomic and public health importance in tropical and subtropical areas. The disease is endemic in 74 developing countries, infecting more than 200 million people in rural agricultural and peri-urban areas. Of these, 20 million suffer severe consequences from the disease and 120 million are symptomatic. In many areas, schistosomiasis infects a large proportion of children under age 14. An estimated 500-600 million people world-wide are at risk from the disease.” (From: World Health Organization fact sheet on schistosomiasis)
Human schistosomiasis is caused by five species of water-borne flatworms (or flukes) called schistosomes. They infect either the gastrointestinal (including the liver) or the urinary systems and are found in Africa, the Eastern Mediterranean, the Caribbean, South America, South-East Asia, and the Western Pacific Region.
Case Study: Schistosomiasis and Lake Malawi
Before 1992, Lake Malawi was one of the last fresh water lakes in Africa that was considered “schistosomiasis-free,” but in that year, two cases of schistosomiasis from Schistosomiasis haematobium were reported in U.S. Peace Corps volunteers who had been vacationing along the lakes shores. Subsequent investigations found a high prevalence of infection (32 per cent) by S. haematobium among native populations living along the shores of the lake and in the intermediate snail host for S. haematobium, Bulinus globulosus. Based on the work of McKaye, Stauffer et al. (1997), hypothesized that the appearance of schistosomiasis in populations along Lake Malawi was the result of an increase in the numbers of B. globulosus snails, secondary to an overharvesting of their main predator, the fish Trematocranus plachydon. The overfishing may have been the result of larger human populations turning to fish as a source of food after poor corn crop harvests, and of the increased effectiveness from using malarial bed nets for fishing (personal communication. M. Cetron, 2001). This may be the first reported case of an infectious disease outbreak caused by overfishing. Another possible relationship of biodiversity to schistosomiasis may relate to the make up of snail populations themselves. There are suggestions that increased snail species diversity, with some species being incompetent hosts for schistosomiasis, reduces the exposure risk for humans (personal communication, Thomas Kristensen, 2001).
Other examples of the importance of biodiversity to the morbidity and mortality of infants and children include:
>> Broad spectrum antibiotics derived from tropical soil micro-organisms – such as the tetracyclines and erythromycin – that are widely used for treating infections in infants and children. As bacteria are developing widening resistance to currently used antibiotics, the search for new ones becomes ever more urgent.
>> Medicines that treat childhood cancers. The drug vincristine, extracted from the Rosy Periwinkle (Vinca rosea) from Madagascar, has revolutionized the treatment of acute childhood leukemias, increasing the remission rate from 20 to 90 per cent. New chemo-therapeutic agents are in clinical trials from a variety of organisms.
>> The devastating illness, hemolytic disease of the newborn, was conquered by an understanding of the mechanisms of Rh incompatibility between an Rh negative mother and her Rh positive fetus, insights that were learned from experimentation with Rhesus monkeys and other primates.
II. MDG 5: Maternal morbidity and mortality
>> Breast and Ovarian Cancer
Breast cancer is the second leading cause of cancer deaths in women today (after lung cancer) and is the most common cancer among women, after non-melanoma skin cancers. According to the World Health Organization, more than 1.2 million people worldwide will be diagnosed with breast cancer this year. While breast cancer is less common in younger women than in those over 50, it tends to be more aggressive, which may explain why survival rates among younger women are lower.
In the year 2000, there were 59,167 reported cases of breast cancer and 26,616 deaths in Africa; 69,924 cases and 22,735 deaths in South America, and 205,682 cases and 95,632 deaths in Asia. (From: http://www.imaginis.com/breasthealth/statistics.asp)
Cancer of the ovary has a relatively low incidence worldwide, but it is a leading cause of death from gynecologic cancers, as it is often detected only when there is extensive disease and when cures are hard to achieve. While ovarian cancer is primarily a disease of older women in western industrialized countries, it can be found in younger women in developing countries as well.
In both breast and ovarian cancers, genetic factors are prevalent, but environmental factors, perhaps related in part to exposure to some endocrine-disrupting synthetic organic chemicals, are being increasingly implicated in rising cancer rates. Better early detection may also play a role. It may therefore be expected that the incidence of these cancers may rise in the developing world as women in these countries begin to adopt western diets and lifestyles.
Case Study: The story of Taxol
As a result of a massive screening program by the U.S. National Cancer Institute to find new pharmaceuticals, the drug Taxol was discovered in the bark of the Pacific Yew Tree (Taxus brevifolia) in old growth forests of the U.S. Pacific Northwest. In early clinical trials, it was found to be effective for inducing remission in cases of advanced ovarian cancers that were unresponsive to other forms of chemotherapy, and it has since been shown to have significant therapeutic benefit for other advanced malignancies as well, including lung cancer, malignant melanomas, lymphomas, and metastatic breast cancers. The mechanism of action is unlike that of other cancer chemotherapeutic agents. The discovery of Taxol has led to an entire new class of even more effective semi-synthetic “taxoids” for cancer treatment.
>> African Sleeping Sickness
African sleeping sickness is caused by infection with protozoan parasites called trypanosomes which are transmitted to humans through the bite of the tsetse fly. There are two forms, each caused by a different parasite: Trypanosoma brucei gambiense, which causes a chronic infection lasting for years and affecting countries of western and central Africa, and Trypanosoma brucei rhodesiense, which causes an acute illness lasting for several weeks, found in countries of eastern and southern Africa. When a person becomes infected, the trypanosome multiples in the blood and lymph glands, and enters the central nervous system where it results in neurological symptoms – confusion, sensory disturbances, poor coordination, and sleep disturbances, the last often being irreversible, even after successful treatment. A slowing of physical and mental functioning and retardation are frequent among children who have had the disease. Without treatment, the disease is invariably fatal. Sleeping sickness is a daily threat to more than 60 million men, women, and children in 36 countries of sub-Saharan Africa, 22 of which are among the least developed countries in the world. In 1999, only 45,000 cases were reported, but it is estimated by the HO that as many as 500,000 people are thought to have the disease. It is clear from these figures that a majority of people with African Sleeping Sickness will die without ever having been diagnosed. In certain villages in some provinces in Angola, the Democratic Republic of Congo, and southern Sudan, the prevalence rate is between 20 per cent and 50 per cent. Sleeping sickness has become the first or second greatest cause of mortality, even ahead of HIV/AIDS, in those provinces. The infectious trypanosome can also cross the placenta and infect the fetus, causing abortion and perinatal death.
Case Study: Land Use, Vertebrate Diversity, and African Sleeping Sickness
In some cases, it is the change in the elements comprising biodiversity that is more important to disease incidence than biodiversity per se. For example, one vector of animal and human trypanosomiasis, the tsetse fly Glossina fuscipes, multiplied rapidly in breeding sites provided by thickets of the plant Lantana camara, which had invaded cotton and coffee plantations along village edges that had been abandoned during civil unrest in the 1980s under the Amin regime. This chain of events resulted in an epidemic of acute sleeping sickness in Busoga, Uganda, with cattle acting as intermediate reservoirs.
In East and West Africa, the presence of vertebrates that are incompetent reservoirs or hosts for trypanosomiasis may act to reduce the likelihood that humans will become infected. Glossina species are "catholic" feeders, and the infectious trypanosomes they are carrying may become "diluted" in vertebrates that do not support the life cycle of the disease. In West Africa, the two Glossina species, G. palpalis and G. tachinaides, feed preferentially on pigs, the natural reservoir, while in East Africa, G. fuscipes feeds on cattle. Other vertebrates besides pigs and cattle may serve to protect humans from getting trypanosomiasis through what has been called the "dilution effect" by Ostfeld and Keesing in their seminal field work on Lyme Disease. Dilution would occur if wild vertebrates provided blood meals for Glossina flies, but did not infect them with trypanosomes, thus reducing the prevalence of fly infection and the rates at which the flies bit reservoir hosts and people.
III. MDG 6: HIV/AIDS and Malaria
>> HIV/AIDS
The loss of biodiversity resulting from the “bushmeat” trade in chimpanzees, gorillas, and other primates in the West African forests is a stark example of how species may be endangered by human activity and how the loss of our closest relatives may have significant implications for human health. It is believed that a sub-species of chimpanzee (Pan troglodytes troglodytes) may be the original source of the HIV-1 epidemic, caused by the transmission of the chimpanzee simian immunodeficiency virus (SIVcpz) to humans on multiple occasions via blood exposures from the hunting and butchering of chimpanzees for bushmeat (Hahn et al. 2000). Similarly HIV-2 is thought to have its origins from the SIV carried by the sooty mangabey (Cercocebus atys) (SIVsm). New serologic research (Peeters M et al. 2002) has identified 13 other distinct SIVs in other primate species from Cameron that were killed for bushmeat or were kept as pets.
There is also evidence that primates can become infected with Ebola virus and suffer massive die-offs (Formenty et al 1999, ProMED Digest V2003 #41), and that it may be possible for infected primates to transmit the virus to humans (Le Guenno et al, 1999).
The extensive killing of primate species along with loss of their habitat, therefore, not only threatens many of them with extinction, but, in depriving researchers of their most important research model, may also prevent full understanding of the dynamics of HIV/AIDS infections, and success in discovering an effective treatment. Moreover, exposure to new SIVs from the bushmeat trade in other wild primate populations may result in future HIV/AIDS-like epidemics.
Another aspect of biodiversity that relates to HIV/AIDS involves the search for medicines from natural sources to treat the disease. The story of the potential anti-HIV drug Calanolide provides a tragic reminder of what we risk losing with species loss. Chemists from the U.S. National Cancer Institute identified a novel agent (named Calanolide A) from the leaves and twigs of a tree Calophyllum langierum found in Sarawak. It was discovered on a return visit to Sarawak that the original tree was gone and that other C. langierum trees could not be found. It was not clear whether the species was extinct. A close relative C. teymannii was identified and was found to contain a weaker drug, named Calanolide B, which, while having anti-HIV activity and the same mechanism of action (it is a non-nucleoside reverse transcriptase inhibitor), nevertheless was not as potent as Calanolide A. Calanolide B is currently in clinical trials, the result of a successful venture between MediChem Research and the government of Sarawak.
>> Malaria
There are many aspects of biodiversity loss and ecosystem alteration that relate to the risk of acquiring malaria. These include: an increased risk secondary to some urban rice cultivation, creating ideal breeding sites for malarial mosquito vectors, and outbreaks of malaria that can result from poorly designed irrigation systems, such as those which occurred in the 1990s in rural India.
Deforestation in tropical forests has been extensively studied as a contributor to acquiring malaria. The factors include: the creation of stagnant pools for mosquito breeding, particularly from the building of roads; the removal of overhead trees whose falling leaves would have acidified standing water, leading to more neutral pHs; removal of understory plants and litter that would have served to drain standing water; and increased light and temperatures on the forest floor accelerating photosynthesis by algae. The consequence of all of these changes are an improvement in the habitat quality for larval Anopheles mosquitoes, and a higher potential for reproductive success. Some species of mosquitoes, like Anopheles darlingi in Amazonia, benefit more from these changes than others, and tend to outcompete rival species that are less effective vectors for malaria.
Although there does not seem to be documentation for the effects on malarial incidence from a loss of mosquito predators, it would stand to reason that lowered populations of some song birds, bats, dragonflies, amphibians, reptiles, and other species would lead to more outbreaks of disease.
KEY PRIORITIES AND OPPORTUNITIES
There are a large number of key priorities related to biodiversity and human health that need to be discussed (please see Chapter 7 on Policy Options in Biodiversity: Its Importance to Human Health), but for the purposes of this brief background paper, only a few will be mentioned.
These include:
1) The need to improve policy-maker and public understanding of the links between biodiversity and human health so that they are considered comprehensively and together when planning and implementing all development projects.
2) The need to balance the valid concerns of countries and indigenous peoples for the preservation of their natural resources (and of their social and cultural values), with the pressing need for society to be able to use those resources to discover new pharmaceuticals or research models that relieve human suffering.
3) The collection and development of such samples must be scientifically managed and carefully monitored so that the natural functions of the ecosystems from which the samples are taken are maintained and their biodiversity conserved.
4) All internationally traded organisms, whether or not they are currently listed as threatened, should be monitored by CITES, so that there will be baseline records to provide early warning that an organism may be in danger of being over-harvested. By the time some organisms are listed, it may be too late. At the same time, there needs to be more support to enhance the knowledge base about species and their ecosystems so that CITES monitoring and enforcement is based on sound scientific data.
5) Water management projects such as in the construction of dams and irrigation systems should consider the effects of these practices on populations of disease vectors, particularly mosquitoes and snails, and develop adequate means of disease mitigation.
6) Agricultural development should incorporate means of mitigating disease risk by avoiding the overuse of antibiotics in livestock and poultry, preventing close spatial associations between domesticated and wild animals to prevent transmission of infectious agents between them, reducing the potential of livestock and poultry as pathogen reservoirs in the local transmission of human vector-borne diseases, and avoiding the destruction and fragmentation of natural habitat that can increase disease risk.
7) Preserving high levels of biodiversity within vertebrate communities hould be given the highest priority as a means of reducing the risk of some vector-borne diseases.
8) The practice of “bushmeat” using primate species needs to be stopped immediately owing to the great danger of spreading diseases like Ebola, and the prospect of creating new, and potentially even more serious, HIV/AIDS-like epidemics in the future.
9) Consideration should be given to developing a list of species, a so-called “Green List,” that are vitally important to human health, whether or not they are threatened, so that additional levels of attention and protection are in place before they become endangered. These would include, among ountless others, pollinators of food crops, apex predators in terrestrial and marine ecosystems, and predators of vectors that carry human diseases.
KNOWLEDGE GAPS
1) The key knowledge gap is our not knowing how to convince policy-makers and the public of the urgent need to preserve biodiversity and ecosystems. We are doing an extremely poor job at this, and it is critically important that we recognize this situation and address it. We will need the help of social scientists and experts in public opinion to do so. Our scientific reports are often written in language that is too technical for public understanding. Our policy documents are too often vague and written in complex, abstract policy-jargon that does not inspire wakeful attention by readers. As a result, we have not been able to counter the widespread ignorance about how our health and lives depend on biodiversity, which society is inexorably destroying. This is occurring not just in the developing world, but in industrialized countries as well. The U.S. Army Corps of Engineers, for example, under the direction of the Bush Administration, is moving forward with a plan, long promoted by Senator Trent Lott, to drain 200,000 acres of wetlands and hardwood forests in the state of Mississippi, and to remove from protected status hundreds of thousands, and perhaps millions, of acres of other wetlands, allowing them to be drained, filled in, and developed. There are ironic parallels to Saddam Hussein’s deliberate destruction of several thousand square miles of Iraqi marshland, which qualifies as one of the world’s greatest environmental disasters (he has also succeeded in an act of genocide in wiping out the 6000 year old culture of the Marsh Arabs, who, among other things, developed the first known arches, thousands of years before the Romans).
2) We need to acknowledge openly that we have very limited knowledge about what and how many species inhabit our planet and commit ourselves to increasing this knowledge.
3) There needs to be much more research on ecosystem services, clearly the most important and perhaps one of the most taken-for-granted and neglected areas of biology. What species are essential for some life-supporting services? How do pollution, climate change, ozone depletion, invasive species, etc. affect these services? Under what circumstances could some services collapse? These are areas of research and understanding that we neglect at our peril.
4) We need to challenge the belief (held very widely, for example, by environmental foundations in the US) that putting a fence around a forest or a marine reserve is enough to protect it. While such preservation is essential in the short run, global environmental changes respect no boundaries, and we must address these as well if we are to have any success in saving habitat and species.
5) We must devote much, much more attention to the problem of global climate change, as it is becoming increasingly clear that we are seeing major impacts on biological systems with only 1 degree Farenheit in mean global surface temperature warming – what will occur with warming that is several times that number, changes that we are already seeing in boreal regions? Many biologists believe that threats to biodiversity from climate change will rival those from loss of habitat and all other factors in the near future.
6) We need to study the synergistic effects of global environmental changes on biological systems as David Schindler and others have begun to do.
7) We should broaden our almost exclusive focus on terrestrial, charismatic, macroscopic species (not surprisingly the areas of expertise of most ecologists) and consider marine, non-charismatic, and microscopic species. Clearly, most of the world’s biodiversity is microbial, and marine biologists believe there is much greater biodiversity in the oceans than current estimates reveal.
STRATEGIC PARTNERSHIPS
In order to promote wider understanding of the relationship between biodiversity and human health and to encourage effective action to protect them, we need to:
1) "Enhance collaboration between health and environment sectors, organizations, and ministries […] conservation and environmental groups and major international agencies, including the WHO, UNEP, CBD, FAO, UNDP, the World Bank, and regional development banks;
2) “Enhance the channels of communication and collaboration between grass-roots environmental and health organizations;
3) “Ensure that biodiversity and human health issues are considered comprehensively and together when planning and implementing development projects.”
(Items # 1, 2, and 3 are taken from Chapter 7 of Biodiversity: Its Importance to Human Health)4) It is of major importance that the private sector be heavily engaged in achieving MDG targets, such as Target 17 of MDG 8 (“providing access to affordable, essential drugs in developing countries”).
Of key importance is the need to develop closer ties in general between UNEP and the WHO on the issue of biodiversity and human health, and in particular between the WHO and the CBD. On August 23, 1999, Drs. Gro Brundtland and Klaus Toepfer signed a Memorandum of Understanding between the WHO and UNEP on “Enhancement of Cooperation in the field of Environmental Health” which included the clause “the Parties will endeavour to explore new areas of cooperation, particularly on critical and emerging issues in the field of environmental health.” One of the areas mentioned was item d. “Biological diversity and human health, including the issues of genetically modified organisms and genetically modified foods.” This MOU was of great importance, but it is not clear what initiatives, other than the WHO/UNEP joint project organized by the Center for Health and the Global Environment at Harvard Medical School (Biodiversity: Its Importance to Human Health) have derived from it. Major efforts of cooperation need to be encouraged.
In this regard, Article 6a of the CBD calls on each party to prepare a National Biodiversity Strategy and Action Plan. Efforts should be made by the parties to incorporate human health issues into these plans. By the same token, biodiversity considerations should be included in National Environmental Health Action Plans called for by the WHO to help countries achieve environmental health and sustainable development for their citizens.
INDICATORS
I am confused by the exclusive focus on mortality and believe the MDGs should be broadened to include morbidity as well for children and mothers. I am also confused by the absence of women who are not bearing children, including older women, and the lack of specific mention of men in the MDGs, as if their suffering were somehow of lesser importance. I believe this is a medical, ethical, and political mistake.
Further information:
Biodiversity: Its Importance to Human Health (PDF) [Harvard]
Biodiversity Brief 7: Health and Biodiversity (PDF) [IUCN / DFID / EC]
Online resources:
Center for Health and the Global Environment, Harvard Medical SchoolMedBioWorld
Links to journals, research sites and references on the topic of biodiversity and human healthBiodiversity and Human Health
Hosted by the Wilderness Medical CentreMedPlant
Medicinal Plants NetworkWHO fact sheet: African Sleeping Sickness
http://www.med.harvard.edu/chge/biobrief.html
Complete videotaped congressional briefing with Jane Goodall, Beatrice Hahn, Stuart Pimm, Robert Engelman, and Eric Chivian held by the Center for Health and the Global Environment on Feb. 19, 2002 “Bushmeat and the Origin of HIV/AIDS – A Case Study of Biodiversity, Population Pressures, and Human Health.”
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Top photo by Galen R Frysinger (www.galenfrysinger.com)