The Full Picture

[

] 182

Human health and

biodiversity: making the connection

Gary Foley, Montira Pongsiri and Aaron Ferster, US Environmental Protection Agency

or centuries, people have been able to alter landscapes and

natural systems with seemingly little consequence, tapping a

variety of ‘ecosystem services’ unabated. In the last 50 years,

however, things have changed. We have altered the environment to

such a degree that entire ecosystems are at risk, and the loss to

biological diversity is mounting at an alarming rate. In addition to

pollution, increased erosion, and flooding, studies strongly suggest

that another consequence of land use is the emergence and re-

emergence of disease.

The Global EarthObservation Systemof Systems (GEOSS) is being devel-

oped to allow people to access and provide the right information, in the

right format, at the right time, to the right people, tomake the right deci-

sions. The US Environmental Protection Agency (EPA) is contributing

to this effort in the health societal benefit area with a focus on emerging

disease, by conducting research on the use of earth observations on biodi-

versity and ecosystems to reduce the incidence of vector-borne diseases.

The United Nations, through the Millennium Development Goals,

recognizes the fundamental links between biodiversity conservation and

health and well-being. However, there is a lack of available tools that

decision makers can use to better understand how changes we make to

the environment can affect our health. If we can better understand how

environmental factors and peoples’ behaviour contributes to infectious

diseases, we may be able tomake better decisions to reduce, and perhaps,

prevent disease.

There are new tools, both remote and in situ, that provide informa-

tion on earth systems, or ‘earth observations’. These tools include

instruments aboard space satellites that orbit the earth, collecting infor-

mation over the entire earth’s surface, on weather and such features as

land cover and vegetation.

What if we could use information from these new tools to better under-

stand how man made changes to the environment, along with natural

factors, are related to disease emergence? Imagine a world in which we

can predict where the next outbreak of malaria, SARS or West Nile virus

is likely to hit. Imagine a world in which we can also understand how to

manage the biodiversity, specifically the diversity or numbers of animal

hosts or disease-carrying vectors, in ecosystems so that the services they

provide can prevent or minimize the extent of disease outbreaks.

Making the link: biodiversity and disease

The World Health Organization (WHO)’s estimates of the global envi-

ronmental disease (see figure opposite) burden do not include how

changed or damaged ecosystems are associated with disease. Senior scien-

tist Richard Ostfeld of the Institute of Ecosystem Studies is working on

a regional scale to show thatWHO estimates may be low. His cutting-edge

research is illuminating the link between biodiversity, specif-

ically the diversity of animal hosts, and the risk of Lyme

disease.

Through field experiments and modelling, Ostfeld has

suggested that a greater diversity of mammalian hosts native

to healthy forests could help decrease the risk of people

getting Lyme disease. People acquire the Lyme disease agent

through tick bites, but ticks acquire the Lyme disease agent

by feeding on mammals such as mice and squirrels. Not all

mammals are equally effective or efficient in transmitting

the disease agent to ticks when fed upon. For example, mice

are better, more efficient “hosts” of the Lyme disease agent

than squirrels. So, it’s thought that a greater diversity of

mammalian species, with varying degrees of transmission

efficiency, could ‘dilute’ the rates that ticks get infected with

the Lyme disease agent. With lower rates of tick infection,

there would be lower rates of human infection. The ‘dilu-

tion effect’ may apply to other infectious diseases as well.

There is also a connection between diversity of animal

hosts and the landscape in which they live. Studies suggest

that the makeup of these host communities is largely deter-

mined by how intact the forest habitat is. Forest

fragmentation and destruction in the US have been shown

to reduce mammalian species diversity and to increase

populations of the white-footed mouse, the most efficient

host of Lyme disease. Greater numbers of efficient hosts and

greater numbers of ticks that become infected from feeding

on them couldmean higher risk of Lyme disease for people.

In the tropics, malaria is a major problem. Changes in

biodiversity through deforestation can have adverse effects

on the risk of malaria. This was demonstrated for the first

time by Amy Vittor and her colleagues in the Peruvian

Amazon. Her group found that not only the numbers, but

also the human biting rates, of the most effective malaria-

transmitting mosquito species were higher in deforested

areas compared to forested areas. This was unrelated to

human population density.

The links between changes in ecosystems, biodiversity

and infectious diseases are complex. Such links may involve

other social and global environmental changes, such as

climate change, which occur over different scales of space

and time. This means that there could be many ways in

which these factors interact to affect human disease. A better

understanding of the role that changes in biodiversity plays

in human health, particularly for diseases that continue to

OCIETAL

ENEFIT

REAS

– H

EALTH