A small group of scientists studying the movement of dust from Africa to the United States and Caribbean nations has found living bacteria, fungi and what appear to be viruses in the very first, small samples of African dust taken from the air over the U.S. Virgin Islands.

The finding strongly demonstrates a need for further study, they say, because it shows that African dust is a potential transport for a variety of disease-causing organisms.

Among other things, the dust could play a role in triggering asthma in the United States and in Caribbean nations, where the rate of respiratory illness is high. And the dust has the potential to cause other health problems, too, although they are not yet proved.

Mercury, lead and a radioactive isotope called beryllium-7 have been found in African dust, said Eugene Shinn, a marine geologist with the U.S. Geological Survey in St. Petersburg.

Shinn says the dust is linked to the demise of certain Caribbean corals and might be linked to the presence of mercury in the Everglades, Red Tide and disease in some amphibians.

The more pressing matter, though, is the possibility that African dust threatens human health.

"I'd like to see the USGS create a program to study dust," said Shinn, an affable, plain-speaking scientist now approaching his 67th birthday. "What's present in the dust? What is surviving the trip across the Atlantic? And in what quantities?"

"The oceans have always been thought of as a barrier to disease, and to an extent they are," said Dale Griffin, a microbiologist working with Shinn at the USGS Center for Coastal Geology in St. Petersburg. "But perhaps they are not the barrier we thought."

Nancy Maynard, associate director for environment and health at NASA's Goddard Space Flight Center in Greenbelt, Md., last week called Shinn's discovery of living bacteria and fungi in African dust "potentially very important to human health." It "absolutely needs to be studied further," she said, adding that NASA already funds part of Shinn's work.

There is nothing new about clouds of dust blowing westward across the Atlantic. Mariners -- among them Charles Darwin in 1832 -- have noted the phenomenon in their ships' logs for hundreds of years. The prevailing easterlies that guide the dust clouds are the same "trade winds" that drive hurricanes toward U.S. and Caribbean shorelines every year.

So much dirt makes the journey that air plants in the Amazon have come to depend on nutrients derived from the airborne soil.

But a couple of things have changed in recent years.

A long-term, continuing drought in the Sahel grasslands near the Sahara in Northern Africa has caused huge and more frequent dust storms in recent years. Hundreds of millions of tons of soil are being blown away every year, scientists estimate.

And coincidentally, thanks to a new generation of Earth-observing satellites, the dust clouds can be seen and tracked as never before.

On Feb. 26 of this year a NASA satellite photographed one of the largest dust storms ever observed. About as big as Spain, the brown cloud was seen leaving Africa, heading west across the Atlantic toward the Caribbean and the United States. Smaller clouds make the trip more frequently.

But there's more than just dirt in the dust.

Hitchhiking along are bacteria, fungi, probably viruses and pesticides, even radiation.

Thus far, said microbiologist Griffin, 130 colonies of bacteria and fungi taken from four air samples in the U.S. Virgin Islands in May, June and July are growing rapidly.

"About 80 percent of those are bacteria," he said, "and about 20 percent is fungi."

Only four of the bacteria samples have been identified, he said, through genetic profiling of the organism's DNA. "They are bacteria typically found in soil," Griffin said. "We will do more as we can afford it."

Griffin is nearly certain the samples contain viruses, too, but said that has not been proved.

"I've seen viruslike particles in the samples," he said, "but I can't be absolutely sure yet." New equipment he has on order will determine one way or the other, he said.

The presence of some viruses seems likely, however, since they are known to hitch a ride on the wind from time to time.

In March 1999, 26 people in central Senegal died from a lethal outbreak of meningitis, blamed by health officials on infected dust spread throughout the area by the Sahara's wind. Senegal and other countries in the Sahel region on the outskirts of the Sahara are plagued by outbreaks of the disease every year.

"It doesn't really matter what these particular bacteria are," Shinn said. "What does matter is that bacteria, fungi and probably viruses are surviving the trip."

NASA's Maynard agrees.

"We're at the front end of things because of (Shinn's) discovery of viable microbes and pollutants in that dust. No one realized that microbes could survive such a journey.

"It's very important to know, for example, if the dust is sufficient to set off asthma. We need to know what's there, and in what amounts. Now it's important that we take the next step."

For now, more questions than answers

USGS marine biologist Virginia Garrison rises every morning to the sound of waves slapping against the hull of her 42-foot Grand Banks trawler, at anchor in the clear waters of Virgin Islands National Park near St. John.

Among the day's first chores is a scan of the horizon to the east, toward Africa, looking for dust -- a fine, reddish powder that five or six days earlier was soil on the dry plains of North Africa.

"You can see it," she says. "On really heavy days it will be so hazy you won't be able to see an island 5 miles away. This is a very dusty year."

From her boat and from a nearby hilltop she gathers air samples for analysis by Shinn and Griffin at USGS labs in Florida.

More than a thousand miles to the west, on the roof of the Knight Oceanographic Research Building at USF's St. Petersburg campus, graduate student Lisa Merman is doing the same. She removes dust collecting filters from an air collection machine, cuts the filter into marked segments and sends them down for analysis.

Shinn and Griffin are looking for a number of things: bacteria, fungi, viruses, mercury, lead and a radioactive element that occurs naturally in the atmosphere, beryllium-7. They say they have found them all in African dust samples, though the presence of viruses has yet to be confirmed.

Shinn acknowledges that the health significance of these discoveries is unknown.

Caribbean nations have long had a high rate of asthma, for example, and African dust seems a logical culprit. But there are other probable causes of respiratory problems in the Caribbean, including pollution and dust mites.

Beryllium-7 is present in African dust, apparently in large amounts. But there have been few if any studies of what might be harmful levels of exposure.

Chuck Holmes, a USGS geologist who studies radioisotopes, calls the levels of beryllium-7 and lead-210 found in the dust "awfully high, higher than what is found in local soil."

But the levels "can't be characterized as dangerous," he said, "because we don't know enough about how much would constitute a danger. But I think we should be looking at this."

Shinn's concern about the health effects of African dust began with his work on coral reefs. Shinn, and others, believe that an organism called aspergillus sydowii in African dust causes the widespread death of seafans on Caribbean coral reefs. He makes the case in the cover story of the Oct. 1 issue of Geophysical Research Letters, the international publication of the American Geophysical Union.

Shinn says his attention was drawn to the potential human health effects of African dust when it was pointed out to him that a species of aspergillus is a major killer of people with AIDS. "I looked into it and found another species produces a powerful natural carcinogen."

The more he looked, he said, the more he found other scientists who had their own suspicions and questions about dust.

Sarasota physician Mary Jelks is a member of the American Academy of Allergy, Asthma and Immunology and serves on the academy's aerobiology committee. She pointed out that the USGS scientists ultimately will have to prove that the organisms they found came from African dust and not some local source.

"I'm somewhat skeptical," she said, "that they (bacteria and fungi) could have survived the journey, the effects of ultraviolet light and even the salt in the air. I don't quite see how you can be sure of where these things are coming from."

Nevertheless, she said, "We're not on an island; the whole planet is intermixing. It is certainly something that ought to be looked at."

"The evidence of health effects of dust is circumstantial at this point," Shinn said, "but there are many potential implications.

"The bottom line is not only do we have fine particles that contain bacteria, viruses, and fungi . . . but the dust also contains elevated mercury, beryllium-7 and lead-210. And then there may be pesticides, too.

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