Trade winds can transport dust germs, research shows

SCRIPPS HOWARD
New research presented Wednesday adds to evidence that desert dust carried across the Atlantic by trade winds can transport bacteria, viruses and fungi into the Americas.
Scientists in recent years have confirmed that dust plumes from northern Africa, worsened by an extended drought in the region, regularly ride trade winds into the Caribbean and the Gulf of Mexico, with Florida and the islands of the basin bearing the brunt of the microscopic particles. A grain of dust is typically less than 2 microns in size, about a hundred times smaller than the diameter of a human hair.
That means that the tiny particles are easily inhaled, but rarely breathed out, resulting in the chemicals, organic materials and microbes attached to them staying put in the lungs.
While earlier studies have focused on samples taken in the Virgin Islands and Florida, the new study reported before the American Society for Microbiology in Orlando, Fla., involved dust collected aboard a research vessel cruising the mid-Atlantic.
Testing
Microbiologist Dale Griffith and colleagues tested air samples over 40 days in May and June of 2003 to determine the level of microbes and to see if they increased with the presence of airborne desert dust.
"Desert dust storms move an estimated 2.2 billion metric tons [a metric ton is 2,204 pounds] of soil and dried sediments through the Earth's atmosphere each year," said Griffith, who has been studying microbes in dust plumes for the U.S. Geological Survey lab in St. Petersburg, Fla., for the past five years. "Since a gram of desert soil may contain as many as 1 billion bacterial cells, the presence of airborne dust should correspond with increased concentrations of airborne microorganisms."
Viable bacterial and fungal populations were collected on 24 days. The three days when the highest populations of microbes were collected matched up with the two most intense periods of dust activity, as determined by using satellite measurements and a U.S. Navy model that analyzes and predicts dust-storm patterns, Griffith said.
DNA analysis matched two of the microbes exactly to two dust-borne organisms that had been previously collected from air samples in Mali in West Africa, whose Sahel region is known for its dust storms.