For the rich in the western world, human genomics holds the promise of tailoring medical treatment to individuals based on understanding of their specific genetic defects.

In this brave new world, the gap between "haves" and "have-nots" will widen because the resulting sophisticated treatments will, without question, be expensive. The poor will have, at best, limited access.

But there is another side to the story. Although less widely publicised than human genome studies, where scientists seek to identify the function of a gene, similarly important work is going forward in deciphering the genomes of disease-causing organisms. Therse include those of such tropical parasites as malaria and schistosomiasis.

These genome studies reveal exciting new information, on which scientists can base their search for new or improved treatments.

Paradoxically, the most needy in the poorest countries may benefit most from the results of these studies.

Success could sharply narrow the gap between the haves and have nots within these countries and begin to bridge the chasm between the developed and developing countries in public access to healthcare. How might this happen?

The poor in the developing world have far less access to modern medical facilities than do their peers in the industrial countries.

Crucially, too, no effective treatment exists for many of their most common diseases, since these historically have been almost completely ignored by western pharmaceutical companies and academic researchers.

New genomic research into parasites and other organisms aims to produce breakthroughs in the understanding and treatment of these neglected diseases.

Given the rudimentary nature of existing healthcare services, drugs for treatment will inevitably be expensive.

Thus the desired outcome is development of low-cost preventive vaccines, from which the poor would benefit most, such as:

* In August 2000, the full genome sequence of one of the ugliest types of cholera, El Tor, was published. As with many diseases, a variety of mutant forms of cholera exist.

Having the El Tor genome sequence should be of great value to vaccine makers in finding an effective preventive treatment.

* Malaria strikes up to 500m people a year, killing an estimated 23m, most of them young children in tropical countries. Despite years of eradication campaigns, the incidence of malaria continues to rise because drug-resistant strains have emerged and use of insecticides reduced for environmental reasons.

More recently, researchers have learned that malaria parasites can "hide" once they enter the body, morphing into a form that the human immune system cannot detect. That makes design of a traditional vaccine very difficult.

Researchers must gain a more thorough understanding of malaria's biology through genomic approaches. To achieve that, they are working to determine the genome sequence of the malaria parasite.

Effective malaria vaccines would have the same positive effect as cholera vaccines in reducing deaths and improving public health among the poor in developing countries.

* Somewhat longer odds must be placed on the likelihood that genomic research will lead to a short-term breakthrough in developing an HIV vaccine. It is desperately needed by 36m people already infected.

Genomics is different from traditional medical research in that it promises, for the first time, practical preventive measures against many parasitic diseases.

Inexpensive, widely available vaccines would increase life expectancy as well as lead to improved public health. But for any of this to happen, therapies must be developed for long-neglected diseases. That will require large-scale institutional efforts.

As an example, the Scripps Research Institute in La Jolla, California, the US's largest private, not-for-profit biomedical research centre, has recently launched an Institute for Childhood and Neglected Diseases.

The institute is organised to apply the new molecular understanding of biology to address and successfully treat neglected diseases.

In the past, public access to education, healthcare, housing and sanitation has clearly divided haves from have-nots. Efforts such as those at Scripps hold out the hope that genome-based medicines may begin to narrow the yawning gap.