Giant clouds of dust whipped up by desert storms in Africa can carry infectious organisms to other continents, scientists claim today. Despite being blown more than three miles high and exposed to radiation from the sun, strains of bacteria and fungi survived and were able to grow when they returned to Earth, researchers found.

Among 40 tests of air samples taken in the mid-Atlantic, 24 revealed living microbes, including 26 colonies of bacteria and 83 fungi. They included strains capable of causing disease in humans, animals and plants. A typical gram of Sahara soil contains up to 1bn bacteria, and estimates suggest 2bn tonnes of soil particles are blown around the planet each year.

"Even if the UV kills 90% of the microbes, dust higher up in the cloud will shade those lower down, so you still get a phenomenal number surviving," said lead scientist Dale Griffin of the US Geological Survey. His research will be presented at the American Society for Microbiology meeting in Orlando today.

Dr Griffins team used genetic tests to prove that the micro-organisms collected in the Atlantic were from specific regions in Africa. The microbes included Gordonia terra, which can cause skin disease in humans, Massaria rosatii which infects sycamore trees, and Alternaria dauci, a cause of carrot blight. "If you have an outbreak of crop disease on the west coast of Africa or an outbreak of human disease and then you get an outbreak downwind some time later, we need to ask was it dust or not?" said Dr Griffin.
Ian Sample, science correspondent.
(The Guardian, 25/06/05).
http://www.guardian.co.uk/science/story/0,,1782440,00.html