Cryptococcus gattii: Outbreak due to climate change?

National Geographic href="">reports:

A new strain of hypervirulent, deadly Cryptococcus gattii
fungus has been discovered in the United States, a new study says.

The outbreak has already killed six people in Oregon, and it will
likely creep into northern California and possibly farther, experts

Cryptococcus infections in humans are hardly new.  And so
far, the public health impact of the outbreak has been very low
(understanding, of course, that the personal impact has been
dreadful for a few). 

Cryptococcus is a genus of fungus, though, and it is rare for
people to get serious fungal infections unless they are already ill
with something else, or have compromised immunity due to age or some
other factor.  The peculiar thing about Cryptococcus gattii
is that it is causing serious infections in persons who were perfectly

This poses two problems for the clinician.  For one, most
clinicians in North America are unfamiliar with it, as it has not
caused outbreaks here before.  That is, it has not been known to
cause outbreaks here before.  Two, most clinicians would not
suspect a fungal infection as the cause of symptoms in an otherwise
healthy person.  It can be difficult to diagnose a condition, when
the physician is thinking that the true cause is highly unlikely.

Even so, it appears that the diagnosis is not difficult to establish,
once the appropriate tests are done:

presentation, diagnosis and management of Cryptococcus gattii cases:
Lessons learned from British Columbia

Can J Infect Dis Med Microbiol. 2009 Spring; 20(1): 23-28.

The environmental fungus Cryptococcus gattii
emerged on Vancouver Island, British Columbia (BC), in 1999. By the end
of 2006, it led to 176 cases and eight deaths - one of the highest
burdens of C gattii disease worldwide. The present paper
describes three cases, and the BC experience in the diagnosis and
management of this infection. All three cases presented with pulmonary
findings, including cryptococcomas and infiltrates. One also presented
with brain cryptococcomas. Cases were diagnosed by chest and brain
imaging, and laboratory evidence including serum or cerebrospinal fluid
cryptococcal antigen detection and culture of respiratory or
cerebrospinal fluid specimens. Genotyping of fungal isolates confirmed
infection with C gattii VGIIa. Pulmonary cases were treated
with fluconazole. One patient with central nervous system disease was
treated with amphotericin B followed by fluconazole. Although this
infection remains rare, clinicians should be aware of it in patients
with a compatible clinical presentation who are either living in or
returning from a trip to BC.

But here is the rub: this is a very serious illness; see href="">this
brain MRI of a patient, to understand how serious.  Moreover,
the treatment with systemic antifungal medical href="">can be harsh. 
(Full treatment guideline href="">here.)
Therefore, it would be good to establish the diagnosis as quickly as

There is href="">no
need for people to worry about this, in more than a momentary
way.  While it is true that the C. gatti in the Pacific Northwest
is more virulent than it is in other places, it hardly would be
considered "hypervirulent," as characterized in the National Geographic
article.  According to href="">an
article in the Washington Post:

More disturbing, the fungus appeared to be more virulent
than in Australia. There, it infects about four people per million and
is rarely fatal. On Vancouver Island, the rate was 27 per million, and
it was more often killing people.

The Washington State Department of Health has prepared href="">a fact sheet
about the illness, for those who are curious.

What is more of a concern is the possibility that an outbreak of a
tropical disease in Canada and northwestern USA could be linked to
climate change.  As noted in the WaPo article (linked above):

Similar cases have been found elsewhere in British Columbia
and in Washington state and Oregon. 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.

How likely is that?  Unfortunately, there probably is no way to
tell.  Just as you cannot attribute any single hurricane, say, to
climate change, you cannot attribute one disease outbreak to climate
change.  Regardless, it is important for clinicians to be aware of
the possibility that they will be less able to rely on their intuition
when it is time to appraise the likelihood of a particular illness in a
particular patient.  If outbreaks such as this become more common,
diagnostic challenges will become more common.


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