Fungi produce a variety of metabolites that impact other organisms. Many antibiotics, such as penicillin, are fungal metabolites that are toxic to bacteria. We have learned to use these antibacterial compounds to treat bacterial infections in humans and other animals.
When these fungal metabolites are toxic to humans or other vertebrate animals, they are called mycotoxins. While the number of mycotoxins that impacts humans is relatively small (compared to the great deal of damage done to plants and insects by fungi) those that do cause disease in humans are significant.
Some disease-causing fungi are mostly annoying – such as the fungi that cause athlete’s foot (there are a number of different fungal species that cause this condition). Others, such as aflatoxin, are responsible for significant human disease.
Aflatoxins are metabolites produced by several species of Aspergillus, particularly those that grow on grain crops. Human exposure to aflatoxins is primarily through food – either by eating contaminated grains or consuming animals that have eaten contaminated grains. In the US there are food safety regulations to ensure that consumers are not exposed to unsafe levels of aflatoxins. Countries with less developed food safety systems, however, do not have these protections. Liver cancer rates are up to 10 times higher in some developing countries than in developed countries – a situation that is linked to aflatoxin exposure.
Ochratoxins are another important disease-causing fungal metabolite (also produced by several species of Aspergillus) that grow on grain crops. Exposure to ochratoxin can result in kidney disease and may cause spontaneous abortions in pregnant women. It has been hypothesized that high levels of ochratoxin in the environment were a selective pressure in Irish and Scottish populations that resulted in a heterozygote advantage for the allele that causes the genetic disease phenylketonuria (PKU). This will be discussed more when we talk about genetics.