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Airborne Pathogens: New Insights from High Altitude Air Samples

Recent research analyzing air samples collected at altitudes of up to 3,000 meters above Japan has uncovered a remarkable array of viable bacteria and fungi. These microorganisms have been carried by air masses originating more than 2,000 kilometers away, from areas enriched with agricultural fertilizers and pesticides. This significant study, published in Proceedings of the National Academy of Sciences (PNAS), reveals fresh perspectives on how human, animal, and plant pathogens might traverse considerable distances. The research is spearheaded by the Barcelona Institute for Global Health (ISGlobal), with support from “la Caixa” Foundation and the Daniel Bravo Andreu Private Foundation (FPDBA).

While the existence of airborne pathogens is recognized, the diversity and survivability of microbes at elevated altitudes remain largely unexplored. Xavier Rodó, an ICREA researcher at ISGlobal, notes, “We know that beyond a certain altitude in the troposphere, known as the planetary boundary layer, materials can be carried over vast distances. This occurs because the air in this region is largely detached from the surface, minimizing friction. However, the discovery of viable microorganisms at these heights was unexpected.”

Rodó highlights the uniqueness of this study, citing that it involved ten tropospheric flights aimed at capturing microbial diversity at significant altitudes, contrasting with the typical focus of similar studies on ground or ocean-level samples.

The Study Methodology

Airborne Microbes High Above Japan

A Cessna aircraft was used to conduct ten aerial surveys between 1,000 and 3,000 meters above Japan, initiated from Chofu airport near Tokyo. These flights were strategically planned to take advantage of prevailing wind currents from mainland Asia, creating what are referred to as tropospheric bridges. This phenomenon allows air from remote regions to travel vast distances; in this case, from mainland China, where air rises and then descends over Tokyo due to typical winter weather. Additionally, ground samples were collected at Chofu for comparative analysis. The researchers obtained 22 aerosol filter samples over two periods in 2014 (February and April), analyzing their chemical and biological properties.

Through DNA sequencing, the team was able to categorize more than 266 fungal and 305 bacterial genera present in the aerosols, including several species that pose potential health risks to humans and animals. Notably, pathogenic bacteria such as Escherichia coli, Serratia marcescens, Clostridium difficile, Clostridium botulinum, Haemophilus parainfluenzae, Acinetobacter baumannii, and various species of Staphylococcus were identified. Fungal genera linked to diseases in susceptible individuals, such as Candida, Cladosporium, and Malassezia, were also detected.

By culturing certain samples, researchers verified that bacteria isolated from the air remained viable, with resistance to commonly prescribed antibiotics. “One isolate of Micrococcus luteus was notably resistant to multiple drug classes, including carbapenems and glycopeptides. This indicates a possible route for the global spread of antimicrobial resistance,” remarks Sofya Podzniakova, co-first author of the study.

Understanding the Origins and Implications

Travelling Thousands of Kilometres

The presence of aerosols infused with elements like zinc sulfate and potassium—often linked to agricultural use—supports the hypothesis of an agricultural source, aligning with the conditions in intensively farmed areas of northeast China.

Significantly, the similarity in microbial diversity between airborne and ground samples suggests a continuous descent of air and its particles from the upper troposphere to the Earth’s surface. Simulations conducted by Roger Curcoll, a researcher at the Universitat Politècnica de Catalunya — BarcelonaTech (UPC), provide evidence of how these particles could migrate from northeast China, corroborating the observed atmospheric behaviors.

Rodó adds, “The findings present an unprecedented insight into the vast diversity of microbes that can be transported over long distances by intense high-altitude winds. They challenge our understanding of environmental pathogens and their potential impact on human health.”

Although the research does not establish a direct causal relationship between the identified pathogens in aerosols and specific health outcomes, it underscores a compelling need for further investigation into the long-distance dispersal of various microbial threats.

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