At one point in the 20th century it seemed that transmissible diseases had essentially been defeated, or at least controlled. But today the AIDS pandemic continues, more infectious agents are becoming resistant to antibiotics, increasing numbers of endemic diseases are flaring up in places where they were previously controlled, pathogens are spreading, and new diseases are emerging faster than societies can respond.
As the global health situation becomes more alarming, the relationship between health and biodiversity is receiving greater attention (Chivian and Bernstein, 2008). What are the links between health, climate change and biodiversity? Can we create more effective policy responses by investigating the links? Can alliances among the scientists and policy makers concerned with these respective sectors find common ground that will lead to more effective action?
Urban living and modern technology have diminished general public awareness of the fact that continued good human health depends on a healthy natural environment. Further, modern medical research has tended to focus on individual risk behaviours or unique disease-causing organisms. All too little attention is given to the influences on health that operate at the population level, such as water and soil quality, pollutants that may cause changes in the immune system, organic chemicals that disrupt the endocrine system and enhance the risk of certain kinds of cancer, or changes in climate that may influence the spread of vectors of certain diseases such as mosquitoes carrying malaria or dengue fever. These factors also need to be considered in more comprehensive approaches to human health.
Despite being part of the global economy, many people still think that health is primarily a personal issue, with both prevention and cure centred on the individual. But health is also a characteristic of populations, and looking at the issue from an holistic and larger perspective of society can lead in a very different direction. Of course, it is the individual who finally contracts any particular disease, but the risk of doing so is significantly influenced by the sociological and ecological context within which the population lives.
Emerging infectious diseases resulting from the destruction and fragmentation of tropical forests and other ecosystems (such as the Ebola virus), wildlife-human disease linkages (such as West Nile virus), the many known and yet-undiscovered pharmaceutical products found in nature, the contribution of ecosystems to human health, the increasing recognition of endocrine disrupters on both animal and human health, and the effects of climate change on ecosystems, all confirm the importance of biodiversity in the complex of health-related issues.
Components of biodiversity can be both allies and enemies to our health. Bacteria and viruses can cause disease; large carnivores, poisonous creatures, and plants can kill us; conflict with small herbivores such as rats and large herbivores such as elephants can undermine our food production systems, thereby undermining our nutrition; and non-native species can include some that threaten our health.
Far outweighing the negative impacts of biodiversity on human health are the health benefits of biodiversity, such as medicine from plants and animals, and of ecosystem services that provide clean water and clean air. While many studies focus on health benefits from plant and animal species, other aspects of biodiversity are also important for human health. Nature can be a source of mental as well as physical health, especially for the young (Louv, 2005). Yet some of our actions today threaten our health tomorrow and far into the future. Environmental degradation from habitat loss, overexploitation and climate change can all have implications for human health and well-being.
Our understanding of medicinal biodiversity is based on species. The role of species in support of human health ranges from direct sources for medicines to providing models for research. On the other hand, the way we manage biodiversity (including ourselves) can have implications for human health.
An ally for health
Some 50,000–70,000 plant species are used in medicines, of which 15,000 are threatened (Schippman et al., 2006). The manufacture and production of pharmaceuticals derived from medicinal plants can help human health and conserve plant biodiversity. About 80% of the world's population use remedies and drugs containing natural plant agents, many from within their own countries. The world trade in medicinal plants has increased by 85% since 1991, though the vast majority of trade involves only about a dozen countries.
Medicinal species are part of both traditional medicine and “Western medicine” pharmacopoeias. Treatments for health problems such as obesity are now being addressed through medicinal plants from Africa such as Hoodia sp. A connection with the natural world is an integral part of much traditional indigenous knowledge. Many traditional health practices have been found to have measurable benefits and may continue to help lead to discoveries of medicinal plants or animals.
The traditional knowledge (TK) relating to health held by men and women is often different. An ethno-botanical survey conducted in the Jaú National Park in Brazil found that midwives were knowledgeable about certain plants, while traditional medicine men knew about others. In the Los Guatuzos community in Nicaragua, when asked about the type of medicinal plants found on their plots of land and in the forest, men called upon their spouses to answer the question (Azofeifa, 2003 as cited in Rodriguez, Blanco, & Azofeifa, 2004).
Many animals also provide important models for research into human health, such as the implications for osteoporosis of hibernating bears who lose no bone mass (Chivian and Bernstein, 2008). Animals also have unique physiologies that are providing valuable insights that could improve human health, such as gastric brooding frogs helping to understand peptic ulcers (though these frogs may now be extinct). Numerous animals also provide medicines often from toxins used for offence (for example, by poisonous snakes and cone snails) or defence (amphibians).
A challenge to health
Our species hosts more micro-organisms in and on our bodies than we have human cells. Of this staggering number, over 1,400 species could be pathogenic to humans in at least some conditions. These include at least 217 viruses and prions, 538 bacteria and rickettsia, 307 fungi, 66 protozoa, and 287 helminths (Chivian and Bernstein, 2008). While most of the time our bodies rely on these micro-organisms for healthy functioning, this abundance and diversity also provides the capacity for new diseases to emerge. Humans host such a high diversity of organisms because we are excellent global distribution hosts, travelling far more broadly and occupying far more ecosystem types than any other species.
As more of these micro-organisms come in contact with each other, either through human travel or ecosystem change, new diseases emerge. For instance, nearly 190 new species of arboviruses and other viruses were identified in the Brazilian Amazon from 1954 to 1998 (Vasconcelos et al., 2001). The Brazilian Amazon is very rich in arboviruses, reflecting its rich biodiversity in general. Very little is known about most of these viruses. The kinds of environmental changes that lead to the loss of biodiversity – namely, deforestation, mining, dam and highway construction, human colonization, and urbanization – have been the main environmental changes associated with the emergence and/or re-emergence of relevant arboviruses, including some known pathogens for humans. Other diseases also can be secondary effects of biodiversity loss.
Changing ecological relationships can increase epidemiological risks through the introduction of new pathogens to new populations. For instance, as humans spread into more nesting areas of wild birds, opportunities for genetic exchange may increase. A particularly worrisome mechanism is genetic exchange between viruses infecting people and wild or domestic animals, with the two viruses picking up genes from each other, enabling the virus to produce a new outer coat and so evade the human immune system. This is the main mechanism by which influenza pandemics arise, often involving an influenza virus that infects humans and one that is carried by ducks, including wild ducks, and other species of birds.
Some disease control programmes that target micro-organisms, even if successful, may undermine general health if they disrupt ecological systems. An example of this is the application of DDT, used to kill mosquito vectors for malaria. An unintended result was disrupted interactions among insect pollinators, reduced reproduction in some species of birds, and reduced food production. Agricultural development projects, designed to improve health through better nutrition, can also disrupt ecosystems by altering disease patterns. Promoting sustainable health must consider multiple scales, multiple perspectives, and high degrees of uncertainty, by taking an ecosystem approach to health issues.
The World Health Organization (WHO) (2002) reported that environmental hazards are responsible for an estimated 25% of the total burden of disease worldwide and up to 35% in sub-Saharan Africa. Improving environmental conditions could save up to 13 million lives per year. Better environmental management could prevent 40% of deaths from malaria, 41% of deaths from lower respiratory infections, and 94% of deaths from diarrheal disease – three of the world's biggest childhood killers. Ensuring the health of ecosystems can also help to decrease people's vulnerability to the impacts of extreme natural events.
Biodiversity-related impacts on human health can be compounded by other threats. For example, globalization, with increasing numbers of travellers and globally traded items, is expanding the ranges of many viruses that are potentially dangerous to humans. And climate change has impacts on biodiversity – changing distributions and changing rain patterns have secondary effects on human health including changes in disease vector distribution as well as changes in food and water supply. Patz et al. (2004) report on the links between land-use change and the emergence of infectious disease, emphasizing the need for a broader perspective on land-use management because of the complex relationships among ecosystems in a landscape.
The full gamut of ecosystem services supports human health. This includes provisioning services in the form of medicines and food, supporting services in the form of soils for food and better nutrition, regulating services for suitable water and air quality, and cultural services in support of mental health. Research has shown that interaction with nature has a calming effect on people, and time outside can restore health, give stress relief, and offer life balance. These health values stemming from contact with nature are universal and not limited to “developed” countries. When people are asked to imagine a peaceful place, the vast majority cite a place in nature, such as the beach, a forest, or a lake.
Recognizing how the changes in today's world can affect biodiversity and health is crucial to recognizing where threats may originate, and how to respond to these threats. Conservationists can contribute through valuing medicinal plants and promoting research and sustainable use of native species that are relevant to the health industry, recognizing nature's impact on all aspects of health, and focusing on biodiversity-related policy.
The protection of medicinal plants involves many types of stakeholders. Those concerned with nature conservation are focused primarily on habitat protection, sustainable collection from the wild, appropriate controls on trade, and so forth. Those with social interests seek acknowledgement of traditional knowledge, and reliable and sufficient income to enable harvesters and farmers to make a viable income. Those with primarily commercial interests are concerned with quality standards, a prosperous trade, and a profitable processing industry leading to a lucrative trade.
The WHO, together with IUCN, WWF and TRAFFIC has developed guidelines for conservation of medicinal species (1993). In addition, the recently completed International Standard for Sustainable Wild Collection of Medicinal and Aromatic Plants (ISSC-MAP) (IUCN SSC Medicinal Plant Specialist Group, 2007), created by an industry-conservation-communitygovernment partnership, building on the 1993 guidelines as well as the WHO Guidelines on Good Agricultural and Collection Practices (GACP) for Medicinal Plants (WHO, 2003), is a key vehicle for a future collaborative approach to the sustainable use and trade of medicinal and aromatic plants from the wild.
The linkages between human and animal health are also being explored by conservationists. A Programme entitled Animal & Human Health for the Environment and Development (AHEAD) was launched by the Wildlife Conservation Society, IUCN and partners at the Vth IUCN World Parks Congress in 2003. Since then, AHEAD has brought together diverse stakeholders across southern Africa to examine the landscape-level nexus represented by the triangle of wildlife health, domestic animal health, and human health and livelihoods as underpinned by environmental stewardship.
“When people are asked to imagine a peaceful place, the vast majority cite a place in nature.”
One particular focus has been the Great Limpopo Transfrontier Conservation Area (TFCA), where AHEAD has been supporting multidisciplinary dialogue and planning on the management of wildlife and livestock diseases (including zoonoses – those diseases transmissible between animals and people) within the developing transboundary landscape. Corridors in transboundary conservation areas serve not only to connect animals and people but also provide a “biological bridge” for vectors and the pathogens they carry. The need for a holistic approach to such large scale land-use planning activities could not be more urgent. In TFCAs like the Great Limpopo, fences are already coming down, allowing wildlife and livestock access to areas and to each other for the first time in decades. While this represents a potential milestone for conservation and the nature-based tourism (photographic, hunting, etc.) revenues it supports, it also demands a closer look at some of the implications. What effects might these transfrontier areas have on the health and sustainability of wildlife, domestic animals and human communities? AHEAD, a convening and facilitating mechanism, is actively working to create enabling environments that allow different and often competing sectors to literally come to the same table and find collaborative ways forward to address such challenges and look at health and disease not in isolation but within a given region's socio-economic and environmental context (Osofsky et al., 2005).
Human population growth, globalization and international trade, and climate change are accelerating habitat loss, introducing new strains of diseases, and changing the way natural systems regulate themselves. A greater diversity of species performing similar functions within an ecosystem is likely to enhance the probability of ecosystem processes being maintained in the face of environmental change. From a human health perspective, the greater the diversity in an ecosystem, the more likely that the ecosystem services upon which our health depends will continue to be delivered.
Looking at biodiversity through the lens of human health can help provide new perspectives on policy and practice of biodiversity conservation with a view to supporting human health. Equally, conserving biodiversity for human health can help bring larger constituencies to conservation practices. Demonstrating biodiversity's links to human health puts conservation at the centre of humanitarian concerns.
Considering the obvious importance of all components of biodiversity to human health, in the coming decade, delivering biodiversity conservation that supports maintenance or improvement of human health will require improved knowledge sharing, expanding partnerships and management of biodiversity resources at a landscape-scale and implementing policies and guidelines, such as the ISSC-MAP, directed at conservation of medicinal biodiversity.
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