Global warming will bring new fungal diseases for mammals

Abstract

Fungi are major pathogens of plants, other fungi, rotifers, insects, and amphibians, but relatively few cause disease in mammals. Fungi became important human pathogens only in the late 20th century, primarily in hosts with impaired immunity as a consequence of medical interventions or HIV infection. The relatively high resistance of mammals has been attributed to a combination of a complex immune system and endothermy. Mammals maintain high body temperatures relative to environmental temperatures, creating a thermally restrictive ambient for the majority of fungi. According to this view, protection given by endothermy requires a temperature gradient between those of mammals and the environment. We hypothesize that global warming will increase the prevalence of fungal diseases in mammals by two mechanisms: (i) increasing the geographic range of currently pathogenic species and (ii) selecting for adaptive thermotolerance for species with significant pathogenic potential but currently not pathogenic by virtue of being restricted by mammalian temperatures.

FIG 1

Earth’s mean global temperature during the past 20,000 years (; Goddard Institute for Space Studies, 2010) in relation to human body temperature. The difference between the mean global temperature (black line) and the human body temperature (red line) is ~22°C, but as shown in the inset, the increment in global warming is occurring very rapidly (17 times as fast from 1941 to 2009 AD than from 20,000 to 6,500 years before the present [BP]), making the mammalian-environment gradient smaller. Recent climatic events that have impacted human history are the end of the last glacial period about 12,500 years ago (double asterisks), the medieval warm period (800 to 1300 AD, diamond), the little ice age (1650 to 1850 AD, asterisk), and the current global warming (arrowhead). KYears, Years in thousands.