More than 100 enteric (gut) viruses can move from human feces to wastewater. Viruses are much smaller than bacteria, and that "allows rapid transmission through soil and water," Rose says. The seaside villains include hepatitis A, a cause of serious liver disease; and coxsackie B, which is thought to attack the heart.

Don't touch that fork!
Coastal populations are soaring. Beaches are a favorite vacation destination. And shellfish is popular food. Adding it up, scientists warn about more disease from water-borne viruses.

Why do they pick on shellfish when discussing diseases associated with the ocean? Because those poor oysters or clams resting on the ocean floor make a living by patiently extracting nutrients from seawater. That filtering mechanism makes shellfish beds targets for invading toxins and viruses, and excellent indicators of water pollution.

It also makes them questionable food.

How are human viruses entering near-shore waters? A major culprit is antiquated -- or non-existent -- sewage treatment. In Florida, where Rose works, septic tanks, designed to degrade sewage a bit before it seeps into the subsurface soil and rock, quickly leak into groundwater.

At least in Florida, septic tanks -- not to mention the even more primitive "cesspits" don't work. If you flush something down a toilet today, you can find it tomorrow in the nearby ocean.

Don't touch that plunger!
Rose's scientific technique was simplicity itself. Her research group grew a harmless virus, then flushed it down toilets in homes with septic tanks or cesspits. Over the next week or so, they sampled the nearby ocean for the virus, using a test able to detect one viral particle in 10 liters of water.

In some studies in the Florida Keys, the marker viruses were found within 24 hours in shellfish beds a mile offshore. The movement was propelled by heavy rain and "tidal pumping," the motion of the groundwater caused by tides. In another study, open shellfish beds in Charlotte Harbor, Fla., were contaminated with infectious human waste. That's according to Erin Lipp, a graduate student in marine sciences at the University of South Florida.

As evidence gathers about the presence of viruses in the near-shore waters, the dispute is shifting from science to politics. The best way to clean up is to build sewers and a modern sewage treatment plant, which kills most pathogens in sewage. Since that's expensive -- one Florida estimate came to $10,000 per household -- scientists are trying to pin down the risk and help regulators focus on the worst sources first.

Costly cleanup
The "worst go first" approach focuses on older homes with rudimentary sewage "treatment." The U.S. has already banned cesspits, says Rose.

Still unknown is how much cleanup will make a difference. Would, for example, cleaning up half the sewage reduce viral contamination enough to matter, or is a much greater reduction required?

Scientists trying to prevent ocean-borne disease are running up against antiquated regulations. D. Jay Grimes, director of the Institute of Marine Sciences at the University of Southern Mississippi, says the present approach to assuring clean water -- counting harmless bacteria that originate in the human intestines -- misses the point. "We have predicted the risk based on fecal coliforms," he says. "But they don't correlate with viruses, most bacteria, fungi, protozoa or helminths," all known causes of human disease.

Rather than rely on indirect indications, Grimes says regulators should identify pathogens directly with molecular biological techniques.

Can scientists assess ocean-borne diseases without flushing a toilet?

©1999, University of Wisconsin, Board of Regents.