A mycologist’s view on the fungi in The Last of Us

The blockbuster TV show The Last of Us has raised the prospect of a devastating fungal pandemic, where humans are infected by a brain controlling Cordyceps fungus. We ask one of our mycologists what fungi we should be worried about.

A brain con­trol­ling fun­gus that has adapt­ed to cli­mate change to infect humans, plung­ing the world into a ter­ri­fy­ing fun­gal pandemic.

The HBO dra­ma The Last of Us is gain­ing a huge audi­ence of fans and presents us with a future where human­i­ty is all but wiped out by a Cordy­ceps fun­gal infection.
Cordy­ceps fun­gi are real. But, rather than humans, they infect insects and manip­u­late the behav­iour of their host to mul­ti­ply and spread.

So, could they mutate and infect humans?

We asked our very own fun­gal expert here at NSW Health Pathol­o­gy, Dr Catri­ona Hal­l­i­day, whose work involves iden­ti­fy­ing fun­gi and devel­op­ing diag­nos­tic tests for fun­gal infections.

Catri­ona, have you seen The Last of Us and what do you think of the sci­ence behind it?

“I haven’t watched it yet, but I have had a lot of peo­ple send­ing me links to arti­cles about it, so I am aware of it. I don’t come across Cordy­ceps fun­gi in the lab­o­ra­to­ry because it’s not some­thing which actu­al­ly does cause infec­tions in humans. 
“There are many dif­fer­ent Cordy­ceps species and they cause infec­tions in dif­fer­ent insects. Each species caus­es an infec­tion in a spe­cif­ic host insect. 
“I’ve looked at some amaz­ing footage on YouTube where David Attenborough’s Plan­et Earth shows a Cordy­ceps infect­ing an ant in that colony. I can tell you I won’t be show­ing it to my 10-year-old because he will have nightmares!”

There’s an omi­nous line in that video where Atten­bor­ough explains that the Cordy­ceps fun­gus works to keep each insect species in check, pre­vent­ing any one ani­mal from over­pop­u­lat­ing an area. So, is it far-fetched that we might be next?

“Yes, it is unlike­ly, because that par­tic­u­lar fun­gus just does­n’t cause infec­tions in humans, but it’s an inter­est­ing concept.”

So, what fun­gi do pose a risk and how wor­ried should we be about fun­gal infections?

“The World Health Organ­i­sa­tion (WHO) recent­ly released a Fun­gal Pri­or­i­ty Pathogen List to draw atten­tion to the fun­gus threat and guide research into new fun­gal diag­nos­tics and anti­fun­gal agents. It high­lights 19 fun­gal species that pose the largest threat. The “big four” are:

1. Cryp­to­coc­cus neoformans
2. Can­di­da auris (a fun­gal ‘super­bug’)
3. Aspergillus fumigatus
4. Can­di­da albi­cans (a yeast that is part of our skin, mouth and guts micro­bio­me that is usu­al­ly harm­less but can dis­sem­i­nate and cause life threat­en­ing ill­ness dur­ing immunosuppression)

“Most fun­gi cause infec­tions in humans with com­pro­mised immune sys­tems although there are some that infect healthy hosts. 
“Fun­gi are every­where, and peo­ple breathe and come into con­tact with them every day with­out get­ting sick thanks to a healthy immune sys­tem. Your body tem­per­a­ture of 37 degrees, your body’s abil­i­ty to get rid of things that you might breathe in – they all help you to avoid get­ting a fun­gal infec­tion. It’s usu­al­ly only peo­ple who’ve got a com­pro­mised immune sys­tem, whether that’s because they’re under­go­ing treat­ment for can­cer, or if they’ve had immuno­sup­pres­sive treat­ment for trans­plants or they may have HIV. Those par­tic­u­lar peo­ple are more like­ly to devel­op a nasty fun­gal infection.
“The most com­mon mould that caus­es infec­tions is Aspergillus fumi­ga­tus. Aspergillus lives very hap­pi­ly in soil, com­posts, and plant debris. Its role is actu­al­ly for degra­da­tion of mate­r­i­al in the envi­ron­ment. They’re very good for the envi­ron­ment and we real­ly need them. But it’s when peo­ple have a com­pro­mised immune sys­tem that fun­gus can cause real­ly hor­ri­ble, nasty infec­tions that are quite life threatening.”

Are these infec­tions hard to diag­nose? Are doc­tors look­ing out for the symptoms?

“I think prob­a­bly fun­gal infec­tions are not the first thing that’s nec­es­sar­i­ly thought of and it might be when a patien­t’s not respond­ing to antibi­otics that then they might do some fur­ther tests and dis­cov­er a fun­gal infection.

“Fun­ni­ly enough, fun­gi weren’t even on anyone’s radar for caus­ing infec­tions till the 1980s. It was only when we had HIV and lots of peo­ple with immuno-com­pro­mis­ing con­di­tions that they were even acknowl­edged as an issue. 
“Fun­gi have only real­ly been rec­og­nized as caus­ing a prob­lem in the last 40 to 50 years, so we’re a long way behind oth­er infec­tious dis­eases, like virus­es, because we’re start­ing a lot later.”

What got you start­ed with Mycol­o­gy – have you always been inter­est­ed in fungi?

“Not at all! In fact, I don’t even eat mush­rooms, I nev­er have. I did a basic sci­ence degree with a major in micro­bi­ol­o­gy, and I think we prob­a­bly had one lec­ture on fun­gi. I went on to do a PhD look­ing at a par­tic­u­lar fun­gus and it was then that a role came up at West­mead. So, I’ve devel­oped PCR tests to diag­nose fun­gal infec­tions. I’ve gone from learn­ing about one par­tic­u­lar fun­gus to learn­ing about a lot more of them and there’s about 200 of them that cause infec­tions in humans.”

*Dr Hal­l­i­day has recent­ly pub­lished the 4th Edi­tion of Descrip­tions of Med­ical Fun­gi, a 350 page book detail­ing updat­ed species, images and tips for identification.