If you've studied malaria, you know Plasmodium is a master of invading the human body by hitchhiking on mosquitoes and then stealthily hiding inside our cells long before the immune system knows what's hit it.

But what if we turned this scenario into a win-win situation by creating our own "good parasites" loaded with cancer-killing drugs or DNA-correcting sequences and then injecting them into the bloodstream'

Science fiction'

No, science fact.

Researchers in the new field of medical nanotechnology are already rushing to build these new weapons in the war against disease.

Engineered nanoparticles are made from one or more materials and are less than about 100 nanometers in diameter, some of which are small enough to pass thru capillaries and enter individual cells. (A nanometer is one-billionth of a meter; a human hair is 60,000 nanometers across.) These nanoparticles come in various chemical compositions, shapes and sizes, depending upon their purpose.

But scientists presenting studies in the "Overview of Application and Implication of Nanotechnology" breakout session at the 2007 Force Health Protection Conference issued a caveat, warning that it is prudent to control exposures to engineered nanoparticles until they are proven safe. They point to asbestos as one of many materials initially thought to be harmless.

Chris Carroll agrees. He's the Army Center for Health Promotion and Preventive Medicine's representative on a DoD working group studying the uses and toxicities of nanomaterials.

"It's important that we work with the other consensus groups to develop guidelines on how to handle these materials safely," he says. Carroll added that there are already more than 400 commercial products using engineered nanomaterials - everything from sunscreens to self-cleaning windows.

Robert Adams of Environ Corporation told conference participants that so far, nanoparticles have not generated any known human or environmental health problems - but he advises exposure control precautions since it's reasonable to expect that some will.

Good advice until we know how our little "friendly parasites" behave in the long run.