Scientists are linking a rise in new and previously suppressed infectious diseases with the dramatic environmental changes now sweeping the planet.
Loss of forests, road and dam building, the spread of cities, the clearing of natural habitats for agriculture, mining and the pollution of coastal waters are promoting conditions under which new and old pathogens can thrive.
Experts cite the case of the highly pathogenic Nipah virus which until recently was found normally in Asian fruit bats.
Its emergence in the late 1990s as an often-fatal disease in humans is being linked with a combination of forest fires in Sumatra and the clearance of natural forests in Malaysia for palm plantations.
Bats, searching for fruit, were forced into closer contact to domestic pigs giving the virus its chance to spread to humans via people handling swine.
Climate change may aggravate the threats of infectious diseases in three ways experts suggest.
Firstly by increasing the temperatures under which many diseases and their carriers flourish, and secondly by further stressing and altering habitats.
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. Also, Neissseria meningitis, a common cause of meningitis, can be spread many miles in the dusty conditions that occur following prolonged drought in the Sahel.
Thirdly, climate change may increase the number of environmental refugees who are forced to migrate to other communities, even countries.
This in turn will also favour the spread of diseases from one location to another where the population may be more susceptible.
These are among the findings from the United Nations Environment Programme (UNEP) in its latest Global Environment Outlook Year Book 2004/2005 under the section Emerging Challenges-New Findings.
The report on the emergence and re-emergence of infectious diseases is based on new research by some of the leading experts in the field.
The issue of environmental degradation and a rise of many new and old infectious diseases is a complex, sometimes subtle, one that is causing increasing concern among scientists and disease specialists.
Overall it seems that intact habitats and landscapes tend to keep infectious agents in check, whereas damaged, altered and degraded ones shift the natural balance thereby triggering the spread to people of new and existing diseases.
Many leading experts are now convinced that ecological disruption, dramatic environmental change and poor handling of human and animal wastes are playing an important part.
Other phenomena also favour the spread of infectious diseases, including international travel, technological change and the globalization of trade in agricultural and other products.
In a paper in the Philosophical Transactions of the Royal Society, Prof McMichael argues that the emergence of many infectious diseases 5,000 to 10,000 years ago was the result of humans coming into increasing contact with animals as people established settlements.
The main cause of long-distance spread of infectious diseases, from around 500 years, ago was through war and conquest during the period of European exploration and imperialism in Latin America, the Caribbean, Africa, Asia and the Pacific. Today the changing pattern of infectious diseases is as much due to environmental change as to trade, travel, migration and social conditions, according to Prof McMichael. — Samina Iqbal
A healthy heart
Aspirin has shown to reduce the risk for a first heart attack (myocardial infarction) in many trials, but the studied subjects had only a small number of women. This was stated in the latest issue of the New England Journal of Medicine.
A large study on nearly 40,000 generally healthy women (mean age, 55) with no history of coronary or cerebrovascular disease were randomized to receive either aspirin (100mg every other day) or placebo (dummy). During an average follow-up of 10 years, aspirin therapy, compared with placebo, was associated with a nonsignificant decrease in nonfatal myocardial infarction, nonfatal stroke, or cardiovascular death, significant decreases in stroke rate and transient ischemic attack rate, no difference in heart attacks (1.0 per cent in both groups) and no difference in all-cause or cardiovascular death rates.
Mortality was significantly lower in the aspirin group among older women (age, >65) but not among younger women. It was also observed that women with multiple cardiovascular risk factors did not derive more benefit than women with few or no risk factors. Gastrointestinal bleeding occurred significantly more in aspirin recipients than in those on placebo.
This study on mainly healthy middle-aged women, showed that aspirin did not significantly reduce the incidence of a cardiovascular mortality or heart attack, but it did lower the risk for stroke and transient ischemic attacks. However, even this low dose caused a slight excess of GI bleeding events. The results suggest a primary preventive role for aspirin in women, especially those older than 65 years, but the benefit is rather small. — Dr Fatema Jawad
