Members of the scientific community suggest that the threat posed by certain fungi has been underestimated. Existing and emerging infectious diseases caused by fungi threaten plant and animal biodiversity more than other classes of pathogens, according to a study released in the April 11 online issue of Nature. What’s more; that threat is increasing.
Fungi have been “on the radar” and the destructive potential they have towards plants, at least, is well recognized, and has been for decades- a fungus caused the destruction of potato crops in nineteenth century Ireland, which resulted in economic downturn and famine. However, the authors posit that we are just beginning to understand the threat that pathogenic fungi pose to animal health. White-nose syndrome is a disease severely affecting U.S. bat populations, threatening extinction for some species, such as Myotis lucifugus, or the little brown bat. This disease was only discovered in 2007. Researchers suggest that the decrease in bat population caused by WNS could result in a great increase of crop eating pests, and could result in an additional $3.7 billion in agricultural costs per year.
The Americas have also lost over 40% of their amphibian species to a skin infecting fungus, according to the study, which has severely impacted the ecosystem. These trends led Dr. Matthew Fisher and Dr. Sarah Gurr of the Imperial College of London and the University of Oxford respectively, to ask the question: are we witnessing an increased threat from pathogenic fungi, or is an error in reporting causing it to seem as though the threat from fungi is increasing?
To determine an answer, ProMed (the Program for Monitoring Emerging Diseases; promedmail.org) and HealthMap examined disease alerts between 1994 and 2010 to determine the relative proportion of fungal alerts compared to the total number of disease alerts. ProMed uncovered an increase in fungal alerts from 1% to 7% between the years 1995 and 2010. HealthMap found the same upward trend: from 2007 to 2011, alerts for infectious fungi affecting animals increased from 0.1% to 0.3% and alerts for infectious fungi affecting plants increased from 0.1% to 0.2%.
Biological and man made factors contribute to this upward trend. For example, several fungi have high virulence, meaning the pathogen is very capable of producing a disease; fungi reproduce quickly, allowing disease to spread through a host population before it is recognized by the host population; and fungi can live outside of a host as a free living organism. This last characteristic is an important one: being able to live as a free organism means that the fungi have the potential to infect a wider range of hosts.
As the world’s population becomes more mobile, humans also contribute to the spread of emerging infectious diseases caused by fungi. The authors suggest that national and international trade products and food have been infected with fungi in their place of origin, thus introducing new fungi to vulnerable countries and communities.
The impact that fungi can have on vulnerable communities is sobering. Authors suggest that if fungal diseases did not affect crops in 2011, an additional 600 million people could have been fed. The destruction of Canadian Pines by a blue-stain fungus will result in the release of 270 megatons of carbon dioxide between 2000 and 2020 (1).
Dr. Fisher, Dr. Gurr, and corresponding authors including Dr. John Brownstein of HealthMap and Dr. Lawrence Madoff of ProMed, conclude with a call for increased monitoring of fungal diseases, increased biosecurity in trade, and for an increased political and public profile for the “Effects of fungal diseases in natural habitats…outside of the managed agricultural environment.”
(1) Fisher, M. C., Henk, D. A., Briggs, C. J., Brownstein, J. S., Madoff, L. C., McCraw, S. L., & Gurr, S. J. (2012). Emerging fungal threats to animal, plant and ecosystem health. Nature, 484, 186-194. Retrieved from http://www.nature.com/nature/journal/v484/n7393/full/nature10947.html
