Atmospheric movement of microorganisms in clouds of desert dust and implications for human health

Abstract

Billions of tons of desert dust move through the atmosphere each year. The primary source regions, which include the Sahara and Sahel regions of North Africa and the Gobi and Takla Makan regions of Asia, are capable of dispersing significant quantities of desert dust across the traditionally viewed oceanic barriers. While a considerable amount of research by scientists has addressed atmospheric pathways and aerosol chemistry, very few studies to determine the numbers and types of microorganisms transported within these desert dust clouds and the roles that they may play in human health have been conducted. This review is a summary of the current state of knowledge of desert dust microbiology and the health impact that desert dust and its microbial constituents may have in downwind environments both close to and far from their sources.

FIG. 1.

African and Asian dust storms. Stars identify dust cloud source regions, and arrows identify dust clouds and the general direction of movement. (A) NASA image, via the moderate-resolution imaging spectroradiometer (MODIS) aboard the Terra satellite, of a dust storm blowing over the Sea of Japan on 1 April 2002. (Image courtesy of Jacques Descloitres, MODIS Land Rapid Response Team, NASA/Goddard Space Flight Center.) (B) NASA image, via MODIS, of a dust storm blowing out of Africa over the Mediterranean Sea in the direction of Turkey. The black spot in the tongue of dust is the Troödos mountain range of Cyprus, which protrudes through the top of the dust cloud. The image was taken on 25 February 2006. (Courtesy of Jeff Schmaltz, MODIS Land Rapid Response Team, NASA/Goddard Space Flight Center.) (C) NASA Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) image of a large dust cloud blowing across the Atlantic. The image was taken on 19 July 2005 and is courtesy of the SeaWiFS Project, NASA/Goddard Space Flight Center, and ORBIMAGE. This dust cloud impacted the air quality in Florida. Airborne particle measurements taken by the author with a handheld laser particle counter south of Tampa Bay, FL, went from 2.6 × 10⁶ m⁻³ on 15 July 2005 (normal clear atmosphere) to 26.1 × 10⁶ m⁻³ on 25 July 2005 (dust conditions). Over 90% of the particles ranged from >0.3 to 0.5 μm in size.

FIG. 2.

Primary sources of desert dust and their atmospheric pathways. (1) During summer in the Northern Hemisphere (approximately June through October), African desert dust is transported across the Atlantic to the northern Caribbean and North America. (2) During winter in the Northern Hemisphere (approximately November through May), African desert dust is transported across the Atlantic to the southern Caribbean and South America. (3) The Asian dust season typically lasts from late February to late April. (4) Large Asian dust events can travel significant distances in the Northern Hemisphere. Yellow lines show Asian desert dust atmospheric routes, orange lines show African dust routes, brown lines show routes of other desert dust sources, and broken black lines depict wind patterns. (Base map image courtesy of NASA's Geospatial Interoperability Office, GSFC [http://viewer.digitalearth.gov/].)