The link between environment and disease.

"THERE IS A VERY, VERY BIG connection between the emergence of new diseases and environ-mental change", said Nick Nuttall spokesperson for the United Nations Environment Programme (UNEP). "We are only just starting to really fully understand it." Rapid changes to the ecosystems mainly due to deforestation and climate change could create "instability in the web of life, and this seems to favour pests", he told the UN Chronicle.

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In the early 1990s, extensive deforestation in Malaysia, combined with forest fires in Sumatra, destroyed and eradicated large tracks of the natural habitat of fruit bats that carry the highly pathogenic Nipah virus. In search of food, these bats moved closer to human settlements, in backyard fruit trees, where the Nipah virus jumped from bats to pigs and then to people, Mr. Nuttall said.

Deforestation has been shown to affect the prevalence and creation of diseases. Since 1976, the World Health Organization (WHO) has noted the emergance of 30 new human diseases, as well as a resurgence and redistribution of existing ones. A recent study in Latin America found that a 1-percent rise in deforestation resulted in an 8-per-cent increase in malaria-carrying mosquitoes. As forest is cleared, it creates holes that when filled with water become breeding grounds for mosquitoes and other disease-carrying insects, Mr. Nuttall said. Deforestation also contributes towards climate change and creates conditions conducive to the transmission of malaria. This is most evident in mountainous areas in Africa, Asia and Latin America, according to Dr. Paul Epstein, Associate Director of the Center for Health and the Global Environment, at Harvard Medical School, in an interview with the UN Chronicle, adding that it puts an additional 10 per cent of the global population at risk of contracting malaria--"populations that weren't previously exposed".

As scientists look deeper into this phenomenon, they see a strong connection between extreme weather events and mosquito-borne diseases. In 2000, Mozambique was subjected to protracted flooding when it was hit by three cyclones, resulting in a "five-fold increase in malaria", said Dr. Epstein. In Kenya, environmental activist and 2004 Nobel Peace Prize Winner Wangari Mathaai found that the rise in the use of plastic bags could also be linked to incidences of malaria. Mr. Nuttall said that when littered plastic bags are filled with water, they become "a brand new habitat for mosquitoes that carry malaria".

On the flip side, another mosquito-borne disease--the West Nile virus--has been shown to favour drought. Dr. Epstein explained that drought causes small pools of water to form in city drains and, combined with increased temperatures, this creates an environment rich in organic material and perfect for transmission of the disease. In 1999 and 2002, there were significant outbreaks of the West Nile virus in the United States. The Centers for Disease Control and Prevention (CDC) reported in 2003 that about 9,850 persons contracted the virus, resulting in 262 deaths. "This is a pattern that we're seeing globally, that after extreme events we see mosquito-borne disease, water-borne disease and rodent-borne disease", Dr. Epstein said. Cholera is an example of a water-borne disease that favours flooding conditions. It is transmitted to humans through ingesting contaminated food or water, which can happen if flooding causes sewerage reservoirs to overflow and mix with drinking water. In Bangladesh, cholera occurs after every monsoon season, causing widespread illness and death.

The relationship between environment and disease could also be seen in the spread of bilharzia, a chronic disease caused by infestation with blood flukes. The bilharzia parasite is carried by snails that prefer slow-moving water streams. According to Mr. Nuttall, "the damming and straightening of rivers, the creation of paddy fields that flood the land to grow crops like rice", have created conditions that favour bilharzia.

Globalization is also impacting the earth's ecosystem, with diseases being introduced to new regions through trade in plants or animals, including "animals hitching rides on ships", Mr. Nuttall said. This could occur when ships from their originating coastal zone "suck up a lot of water for ballast" and later "dump that ballast into the coastal waters" at their destination port, resulting in the transfer of species that are literally from one part of the world to another. An example is the toxic algae in the North Sea, which are believed to have originated in Asia, "where it was a natural algae and the water was naturally in balance with its environment", Mr. Nuttall said. But when it was transferred to the North Sea, its new environment did not have "any natural checks and balances". The algae can kill or contaminate shellfish, which when ingested can cause illness in humans.

Vehicle emissions, combined with increased levels of carbon dioxide (C[O.sub.2]) in the atmosphere, according to "Inside the Greenhouse", a report co-edited by Dr. Epstein, contribute to the rise in incidences of asthma and other respiratory diseases. The study shows that the rising levels of C[O.sub.2] favour the growth of pollen-producing plants, such as ragweed and poison ivy, and that particles in diesel emission contribute to delivering pollen deep into the lungs, causing increased incidence of asthma. In the United States, self-reported cases of asthma have increased by 75 per cent from 1980 to 1994, with pre-school children registering the largest increase, at 160 per cent, the report says. Lyme disease is also affecting the United States. Due to increased abundance of ticks because of global warming, the bacteria they carry "will move north into Canada", Dr. Epstein said. A scientific study forecasts that areas suitable for tick habitat will increase by 213 per cent by the 2080s.

In March 2005, the Millennium Ecosystem Assessment reported that 60 per cent of the world's ecosystems are in decline or degraded to the point that people are no longer able to rely on the benefits they provide, such as climate regulation, clean air and water, and fertile land, all of which contribute to controlling diseases. Dr. Epstein was not surprised will these findings, saying that "severely disrupted ecological systems are letting loose a barrage of infectious diseases that are infecting us, including wildlife and livestock". Mr. Nuttall said that in order to combat this trend "we have to really start thinking of new and creative economic ways of giving value to nature and not treating it as a freebie", otherwise, he warned, "in the end, we're all going to suffer, because you can only run down the planet's natural resources so far before there's nothing left".

RELATED ARTICLE: The Impact of Climate Change

The world's forests are being cleared at a rate of 250 square kilometres a day. It becomes more worrying when 20 per cent of greenhouse gases are directly attributable to deforestation, according to UNEP estimates.

A study conducted by the Harvard Medical School's Center for Health and the Global Environment, titled "Inside the Greenhouse: The Impact of C[O.sub.2] and Climate Change on Public Health in the Inner City", puts the current atmospheric concentration of carbon dioxide at 379 parts per million (ppm). It points out that the earth has not experienced C[O.sub.2] levels above 280 ppm for at least 420,000 years.

Greenhouse gases are considered to be the cause of climate change--a phenomenon that has seen the average surface temperature increase by approximately 0.6 degrees Celsius during the twentieth century. The Intergovernmental Panel on Climate Change predicts that the temperature will rise by a further 1.4[degrees]C to 5.8[degrees]C in the coming century.

Many scientists credit climate change with the recent spate of extreme weather events, such as hurricanes, droughts and floods. In 2004, Munich Re, one of the biggest reinsurance companies worldwide, reported a record insured losses of $44 billion, associated mainly with extreme weather conditions. According to UNEP, a tract of wetland providing such services as flood protection and water purification has a value of around $6,000 per hectare. This same tract would only be worth about a third of this amount if it was cleared for agricultural purposes. Some sources put the total worth of the earth's ecosystems at about $33 trillion.