Pigeons in south-east Queensland – common in Post Office Square, King George Square and Anzac Square – and the region's river red gums are the two most likely sources of the fungus that causes about six cases of the very rare cryptococcal meningitis in Queensland each year, an infectious diseases expert said.
Fairfax Media this week reported the case study of Camira man Milton Silcock, who said he contracted this rare form of fungal meningitis after sweeping up poo from swallows in a plumbing supplies business in Springfield.
In 2015, Cairns woman Nancy "Lee" Mules received a $6.7 million payout – seven years after she first went to her GP – when the meningitis eventually made her profoundly blind and deaf.
Infectious diseases expert Professor Michael Whitby, from the University of Queensland, said dried dust from pigeon poo kicked up by shoes were the most common carrier of the fungus that caused "about 20" cases of fungal meningitis in Queensland each year.
Pigeons are linked to four diseases including meningitis and salmonella.
Professor Whitby said the cryptococcal meningitis was caught when people breathed in the specific dried fungus from bird poo, or from the fungus that occurs naturally in red river gums.
This usually produces a pneumonia, which can be treated well and "doesn't do too much harm," he said.
"It becomes more common in Queensland as you go further north and you go towards Northern Territory," Professor Whitby said.
"But it is not something that everybody has ever heard of, or that everybody sees," he said.
"I mean the number of fungal meningitis cases that anyone sees in Queensland in a year would be less than 20."
However of those 20 cases, "about six or seven" become cryptococcal meningitis when the disease moves into the brain or the spinal fluids, Dr Whitby explained.
"What does do harm is that the disease has this ability to move from the lung into the brain; the coverings around the brain and to the spinal fluid," he said.
"And cryptococcal meningitis – there would be only six or seven cases a year."
He said the Cairns case study was proof of the awful disabilities that can result, even if patients manage to fight the disease.
"So this variation – where the disease goes to the brain or the spinal fluid – is a disastrous disease," Professor Whitby said.
"Caught early it is eminently treatable, but not always with complete success."
Professor Whitby explained there were two forms of cryptococcal meningitis in Queensland; one linked to pigeon poo (cryptococcal neoformans neoformans) and a second variation linked to red river gums, among other trees, called cryptococcal gattii.
He said most cases happened when the person had a poor immune system.
"It became more common in Queensland during the AIDS epidemic because people's immunity levels were low," he said.
"The other 50 per cent of people were just ordinary, healthy Queenslanders who just got it."
"And given that there may only be five or six cases of this variation a year, it is not something that I would be particularly concerned with."
He said in south-east Queensland about 50 per cent of cryptococcal meningitis cases were linked to pigeon poo and 50 per cent linked to river red gums.
"While it can be isolated from pigeon poo I have never been convinced that this is of particular risk to the community," he said.
"Go and sit in King George Square and look at all the pigeons all over the place.
"And Anzac Square and Post Office squares are exactly the same. It's full of pigeons as well.
"So, if it is such an easily transmitted disease from pigeons to humans we would have expected to have huge numbers in Brisbane," he said.
"But we don't."
Professor Whitby said cryptococcal meningitis was far more common in Papua New Guinea where pigeons roosted inside houses without ceilings.
"The timber structure of the houses are covered with pigeon poo and the people get cryptococcal," he said.
Professor Whitby said it was possible "in theory" that someone clearing river red gums with a chain saw could catch the disease from breathing in the fungus that naturally lived in the river red gum, but the risk was extremely low.
"So does it stop me from walking under gum trees? No," he said.
"Does it stop me from sitting in King George Square? No.
"You are much more likely to be run over by a truck."
