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African dust brings germs, fungi across the Atlantic
By RANDOLPH E. SCHMID
WASHINGTON -- Dust from the African deserts is bringing germs and fungi across the Atlantic.
Researchers who tested samples of the dust collected last summer warn that ''pathogenic microbes associated with dust clouds may pose a risk to ecosystem and human health.''
While windborne transport of African dust to North and South America long has been known, scientists thought that few microbes would survive the trip because of exposure to ultraviolet radiation in the atmosphere.
Researchers now believe the dust clouds themselves block enough of the light to protect bacteria and other microbes during the five- to seven-day journey.
The findings of the group, led by Dale W. Griffin of the U.S. Geological Survey, are reported in the June issue of the journal Aerobiologia.
About 10 percent of the microbes identified were ''opportunistic pathogens,'' Griffin said in a telephone interview.
They are organisms that do not cause disease in healthy humans, but could affect someone with a compromised immune system such as AIDS patients, the very old or young and transplant or cancer patients with suppressed immune systems, he said.
''For most healthy individuals, I don't think it's a problem,'' said Griffin, a public health and environmental microbiologist.
In addition, he said, 25 percent of the microbes were known plant pathogens that affect elm trees or such crops as peaches, cotton and rice, he said.
Joseph M. Prospero, director of the Cooperative Institute for Marine and Atmospheric Studies at the University of Miami, said his research in Barbados also has seen fungi and bacteria associated with African dust.
He said there has been a ''very clear association'' of sharply increased incidence of viable fungi and bacteria in African dust arrivals.
''There's no question you can transport a lot of stuff through the atmosphere,'' Prospero said in a telephone interview.
When the trajectories of the dust are traced backward, the dust clouds with the bacteria come only from Africa, while dust arriving from Europe or North America does not include bacteria, said Prospero, who was not associated with Griffin's team.
The movement of African dust across the ocean has been increasing in recent years with the growing drought in Africa. It peaks in June through October. Large dust arrivals have been measured over roughly 30 percent of the United States, with about half the volume settling on Florida.
''The high concentration of dust impacting the Caribbean may pose a significant public health threat, particularly as it pertains to respiratory disease,'' the researchers wrote.
They noted that once a person is sensitized to fungi, exposure to even small amounts can trigger an allergic reaction.
They cited a 17-fold increase in asthma prevalence in Barbados between 1973 and 1996. ''This increase corresponds to the observed increase in African dust flux impacting Barbados.''
The dust also has been implicated in coral reef damage in the Caribbean.
Griffin collected dust samples in St. John, U.S. Virgin Islands, and sent them to Virginia Harrison at the agency's laboratory in St. Petersburg, Fla., for testing.
Using NASA satellites to track the African dust clouds, they were able to take air samples both on clear days and days with dust plumes affecting the region.
On the dusty days there averaged 158 bacteria, 213 viruses and 201 fluorescent bacteria in about a quart of air. By comparison, the same volume of air on a clear day averaged 18 bacteria, 18 viruses and none of the fluorescent bacteria.
Other members of the research team included Jay R. Herman of the National Aeronautics and Space Administration and Eugene A. Shinn of the Geological Survey.
-- Martin Thompson (email@example.com), July 02, 2001