Will the world continue to grow healthier, with ever more diseases conquered by scientific advances, and life expectancy extending even longer? Or will new diseases and failing drugs cancel out these gains? If populations live longer, will these extra years be healthy and productive, or merely an extended sentence of suffering?
Will continuing population growth finally stifle the planet's life, depleting finite resources, polluting beyond repair, and making megacities and urban slums the home for more and more? Or will better family planning options, and mounting deaths from AIDS, reverse recent trends?
Will we conquer malnutrition, obesity, drug abuse, poverty, depression and the common cold? Will we eradicate polio, leprosy, measles and other ancient foes? Will deaths from heart disease and cancer finally begin to decline? And when science surely delivers spectacular new therapeutic tools, who will be able to afford them? Will the gaps between the health of the rich and the poor grow ever wider?

As it looks towards the early twenty-first century, the World Health Organization (WHO) predicts that the world - already free of small pox - should also be free of poliomyelitis, measles and neonatal tetanus.

Some other infectious and parasitic diseases will be eliminated, and the burden of many more which currently afflict tropical regions should be further reduced.

Most children should be protected from vaccine-preventable diseases through well-established and sustainable immunization programmes, and deaths among small children would be reduced.

At the same time, however, the world is expected to confront an increase in deaths of adults in the age range of 20 to 64 years, while major health problems by the year 2025 are expected to be diseases of the circulatory system, cancers, infectious and parasitic diseases, and external causes. Available data suggests that in some countries, deaths from circulatory diseases are falling, while cancer deaths are increasing.

WHO estimates that about two thirds of global cancer deaths, cancer incidence during 1997 and cancer prevalence in 1997 can be clustered according to four risk factors: diet-related (stomach, colon-rectum, liver, mouth-pharynx and prostate); tobacco-related (lung); infection-related (lymphoma and cervix); and hormone-related (breast). WHO foresees that the overall global situation in respect of cancers of the stomach, liver, mouth and pharynx, the cervix and the breasts will improve in the early 21st century, while those related to the lung, trachea, bronchus, colon and rectum, and prostate, as well as lymphoma, will worsen.

Other aspects of our current lifestyles will continue to have a negative impact on our health. Sedentary living, excessive or ill-balanced diets, smoking and a deteriorating environment will result in an increase in crippling chronic diseases such as diabetes, rheumatoid arthritis and lower back pain. Many will continue to suffer from mental disorders, from the relatively minor to the incurable and life-threatening.

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Illustration: Computer renderings of Candida albicans, a yeast associated with thrush (top left); Ascaris lumbricoides, worm which leads to Ascariasis, a disease that can cause malnutrition (middle); Histoplasma capsulatum, soil fungus which can lead to pneumonia (upper right); Trypanosoma brucei gambiense, protozoa associated with sleeping sickness (lower left); Giardia lamblia, protozoa that cause gastric disorders (lower right). Courtesy: American Museum of Natural History Exhibition "Epidemic!" (February to September 1999).