Dramatic environmental changes now sweeping the planet, such as the loss of forests and the spread of cities are promoting conditions for a rise in new and previously suppressed infectious diseases, including malaria and bilharzias, according to the United Nations Environment Programme (UNEP) latest yearbook.

Climate change may aggravate the threats of infectious diseases in three ways, by increasing the temperatures under which many diseases and their carriers flourish, by further stressing and altering habitats, and by causing migrations, experts suggest in UNEP’s Global Environment Outlook Year Book 2004/2005.

For example, the geographic range and seasonality of two of the world’s most serious mosquito-borne infections, malaria and dengue fever, are very sensitive to changes in climate. Neissseria meningitidis, a common cause of meningitis, can also be spread many miles in the dusty conditions that occur following prolonged drought in regions of Africa bordering the Sahara.

Also a rise in the number of environmental refugees forced to migrate to other communities or even countries will favour the spread of diseases from one location to another where the population may be more susceptible.

Noting that one of the Millennium Developments Goals (MDGs) adopted in 2000 by the UN Millennium Summit seeks to reverse the spread of HIV/AIDS, malaria and other diseases, UNEP Executive Director Klaus Toepfer said: “If environmental degradation is not checked then, it is clear from these new findings that this will be harder and tougher to achieve.

“There are implications for many of the other Goals, from poverty eradication to the delivery of universal primary education for all. People who are sick are less able to work and children who are ill find it harder to attend and concentrate at school,” he added of other MDGs seeking to halve extreme poverty and hunger and increase access to education and medical care, all by 2015.

Together with loss of forests and spread of cities the findings also cite road and dam building, the clearing of natural habitats for agriculture, mining and the pollution of coastal waters.

Expansion of mining and other extractive industries can increase the incidence of diseases like malaria. Deforestation and road building often disrupt forest and river systems increasing the habitats for malaria-carrying mosquitoes and migration of workers into previously inaccessible areas is increasing the population at risk.

Meanwhile, water flow changes and changes in water chemistry associated with dams like the Aswan in Egypt and irrigation schemes on the Senegal River are being linked with an increase in snails carrying the parasite that causes schistosomiasis, also known as bilharzia, a disease that leads to chronic ill health.

The Year Book links the emergence of many other old and new diseases with environmental change. Like malaria, Japanese encephalitis and dengue hemorrhagic fever are transmitted to humans by mosquitoes, which also thrive in standing water.

Increasing level of rubbish and solid wastes in developing countries - a result of growing consumerism, poor collection and refuse handling services, fly tipping, lack of recycling schemes and inadequate disposal sites - are aggravating the problem. Discarded plastic bags, old tins and car tyres offer, when filled with rainwater, perfect new breeding opportunities for disease-carrying insects.

Tuberculosis, bubonic plague and Hantavirus pulmonary syndrome, meanwhile, are linked to unplanned urbanization while yellow fever, Kyasanur Forest disease and Ebola are tied to deforestation and its knock-on effects.