A fungus is a eukaryotic organism that belongs to the kingdom Fungi. Fungi include yeasts, moulds, mildews and mushrooms. Recently, the fungus Ophiocordyceps unilateralis has become a popular topic of discussion. This so-called “zombie fungus” infects and controls the behaviour of ants. The “zombie” ants carry out behaviours that aid in spreading the spores of the fungus to other ants.
The Ophiocordyceps zombie fungus cannot infiltrate humans. In order for a fungus to infect humans, four main conditions must be met. First, the fungus must be able to grow and thrive at human body temperature. Fungi like Ophiocordyceps cannot withstand temperatures as high as human body temperature, and therefore infect ectotherms like ants instead. Secondly, the fungus must be able to penetrate surface barriers in order to access internal tissues. Thirdly, the fungus must be able to digest and absorb human tissue. Fourthly, the fungus must be able to withstand the immune response in humans. If these four criteria are met, then the fungus can infect humans. In fact, there are four lineages of fungi that meet these conditions. These include Zygomycota, Entomophthorales, Ascomycota, and Basidiomycota.
Although there are no fungi that have a zombie-like effect on humans, there are some examples of fungi from these lineages that have behaviour-altering effects in humans. For instance, there is ergot fungi, such as Calviceps purpurea, which grow on rye and related plants. Ingesting ergot-contaminated foods can lead to ergot poisoning or ergotism. Symptoms of ergotism are caused by the alkaloids ingested and include convulsions, hallucinations and confusion. Historically, it is thought that women displaying symptoms of ergotism were accused of witchcraft in the Salem witch trials.
There is another well-known fungus that can cause hallucinations. Psilocybin mushrooms, commonly known as magic mushrooms, cause their effects when they are ingested. The psilocybin in the mushrooms is converted into psilocin once in the body. Psilocin is thought to affect serotonin levels in the brain, leading to euphoria, hallucinations, paranoia and a distorted sense of time and reality.
The relationship between humans and fungi is an interesting one. Although there are currently no fungi that turn us into zombies, there are many fungi that can affect us and our behaviours.