Bubbling: Man has long cultivated favored strains of yeasts, using them to produce baked goods, alcoholic beverages, root beers, some pickled items, etc. The handy thing about these particular yeasts is that they ferment carbohydrates (like sugars and starches), producing carbon dioxide and alcohol (ethanol). In a way, these single-cell fungi are one of the first things that man domesticated.
There are tens of thousands of species of yeast, only a fraction of which have been described. They're found just about everywhere, including the oceans, soil, air, in our guts and on our skin, etc. Some spoil foods, break down hydrocarbons, serve as nutritional supplements, help with specialized composting, on and on.
There is disagreement over which fungi to call yeasts, but I'm not going to dive into that morass. Instead, I'll skip to the fact that a few of them cause us health problems. That's definitely not news to the women (and some men) who've suffered yeast infections...which by the way are caused by members of genus Candida, same as that Tony Orlando and Dawn song. But, there are other pathogenic yeasts as well, like the ones that caused by members of genus Cryptococcus.
Opportunistic Infection: One member of the genus has gained notoriety for taking advantage of compromised immune systems. Here in the U.S.
Approximately 7-15% of patients with AIDS develop cryptococcal infections. ...patients with AIDS-associated cryptococcal infections now account for 80-90% of all patients with cryptococcosis.
...
In sub-Saharan Africa, 15-30% of all patients with AIDS develop cryptococcal disease. However, in some areas, such as Zimbabwe, 88% of patients with AIDS have cryptococcal infection as their AIDS-defining illness.
C. neoformans is commonly found in soils around the world and things like bird droppings--notably those of pigeons and chickens. We're regularly exposed to this and other yeasts through breathing. Our immune system easily dispatches the vast majority of them, but the ones which are "encapsulated" can provide more difficulty. Crypto means hidden, a reference to it having a coating that gives immune systems more of a battle. There are multiple strains of C. neoformans, whose coatings can vary.
Cryptococcal infections in AIDS patients usually begin as a lung ailment that acts like a pneumonia and then progresses to other organs, including the brain (as a type of meningitis). If not treated with antifungal medications, the infections are usually fatal.
Nuke 'Em 'Til They...: Remember the story earlier this year about fungi that were found feeding upon radiation at the Chernobyl Nuclear Power Plant? One of the three fungi was the yeast mentioned above, C. neoformans. It's growing faster in the presence of ionizing radiation that is 500 times the normal background amount. The scientists suspect that it's the melanin in these organisms that makes this possible.
Exposure of melanin to ionizing radiation, and possibly other forms of electromagnetic radiation, changes its electronic properties. Melanized fungal cells manifested increased growth relative to non-melanized cells after exposure to ionizing radiation, raising intriguing questions about a potential role for melanin in energy capture and utilization.
There are a number of types of melanin. In people, it's responsible for most of our skin color--our natural sunscreen. In the eyes, it protects against high frequency light, both visible and UV. Et cetera.
International Traveler: In recent years, a Cryptococcus not native to the Northwest has been causing a stir.
An alien fungus took root on Vancouver Island eight years ago and has since killed eight people and infected at least 163 others, as well as many animals.
Similar cases have been found elsewhere in British Columbia and in Washington state and Oregon.
C. gattii causes similar type of cryptococcosis to the one mentioned above, but this one more readily strikes healthy people. The victims aren't contagious. Reservoirs of the yeast were first discovered in South Australia, associated with a particular species of eucalyptus (yes, koalas can suffer from cryptococcosis). Over time, C. gattii has been found in a number of nations in tropical through temperate latitudes around the globe. However...
By comparing select gene sequences that spanned the genomes of the Vancouver Island fungi to samples collected from around the world, the team traced the rarer type to identical isolates in Australia. The major form matched a sample taken from an infected person in Seattle 30 years ago and another collected from a Eucalyptus tree in San Francisco in 1992.
And from more recent research...
All clinical and environmental isolates found in BC were genotypically consistent with Vancouver Island strains. In addition, local acquisition was detected in 3 cats in Washington and 2 persons in Oregon. The molecular profiles of Oregon isolates differed from those found in BC and Washington.
On Vancouver Island, C. gattii doesn't need certain types of eucalyptus to spread. Over ten species of trees native to the forests there have tested positive for the yeast, but none of the introduced eucalyptus trees have. Plus...
Systematic sampling showed C. gattii was associated with high-traffic locations. In addition, C. gattii was isolated from the wheel wells of vehicles on Vancouver Island and the mainland and on footwear, consistent with anthropogenic dispersal of the organism. Increased levels of airborne C. gattii were detected during forestry and municipal activities such as wood chipping, the byproducts of which are frequently used in park landscaping.
That offers possible explanations for why people who've never traveled to where C. gattii is found have come down with the disease. And the yeast can clearly stay airborne for awhile...over 25 porpoises have washed ashore on the island, dead from cryptococcosis.
Scientific Activism: Some are speculating that C. gattii may be spreading because of climate change. For example...
Scientists say the fungus may be thriving because of a string of unusually warm summers here. They say it is a sign of things to come.
"As climate change happens, new ecological niches will become available to organisms, and we will see this kind of thing happen again," said Karen Bartlett, a scientist at the University of British Columbia who played a central role in the search for the disease's cause.
...
"With global warming, it may have finally been able to emerge to a level [at which] it is infectious," Fyfe said. Humans and animals living in the area, having had no exposure, had developed no immunities to it. Some people reacted to exposure by developing the disease.
They may be right regarding C. gattii and climate change, but they're guessing. Other articles on the pathogen (example here) selectively note that the yeast is typically found in tropical and semitropical locales. Yet as I alluded to above, it also thrives in some more temperate regions, such as where it was originally discovered in South Australia (a Mediterranean climate), parts of Italy (same), Mexico City (elevation over 7,000 feet), etc. The yeast clearly tolerates cool, damp winters, which is what the lower elevations on Vancouver Island offer. Scientists ought to be doing some research on the cold tolerance of the yeast in nature.
In Australia, airborne C. gattii appears in late spring. The same isn't true on Vancouver Island. I converted the metric units in the following.
The concentration of airborne cryptococci during the northern hemisphere spring and summer months peaked in August, when the weather in southwest British Columbia is the warmest (average temperature, 52 to 75°F) and driest (mean monthly rainfall, 1.24"). In cooler, wetter months, e.g., December (average temperature, 30 to 43°F; mean monthly rainfall, 6.55"), the concentrations of airborne cryptococci declined, presumably because all of the propagules were washed out of the air. None of the air samples taken during periods of rain or shortly thereafter were positive.
Summer in that part of BC is rather similar to the springtime in Mediterranean climates.
Let's just hope that in promoting concern about climate change, these scientists don't blind themselves to other possibilities regarding this pathogen. There are far too many scientists who can't keep their science and politics separate.
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