IS CLIMATE CHANGE BEHIND THE RISING INCIDENCE OF CRYPTOCOCCOSIS CASES IN THE PACIFIC NORTHWEST?
C. gatti case distribution
Emerging and reemerging infectious diseases are increasing worldwide and represent a major public health concern with fungi an ever emerging class of human and animal diseases.
In a report published in the Public Library of Science journal PLoS Pathogens ( http://dx.plos.org/10.1371/journal.ppat.1000850), an emerging strain of airborne fungus is spreading among animals and people in the northwestern United States and British Columbia which is likely to expand into neighboring regions. This outbreak is caused predominantly by Cryptococcus gattii molecular type VGII, (specifically VGIIa/major). In addition, another novel genotype (VGIIc) has emerged in Oregon and is now a major source of illness in the region. Cryptococcus gattii is distinct from its sibling species Cryptococcus neoformans, which more commonly infects immuno-suppressed hosts. Cryptococcus gattii can cause life-threatening disease in otherwise healthy hosts.
Previously considered a tropical fungus, C. gatti emerged to cause an outbreak in the temperate climate of Vancouver Island in 1999 and is now causing disease in humans and animals in the region. This illustrates two hallmarks of emerging outbreaks: high clonality and the emergence of novel genotypes via recombination where virulence evolution has been characterized in bacterial, viral, fungal, and parasitic human diseases.
Newly emerging and reemerging diseases have become a major focus of infectious disease research in the 21st century. Reemerging diseases are classified as those that have been previously documented, but are now rapidly increasing in incidence, geographic range, or both. Emerging disease events have been occurring at higher than average rates in the United States due to several factors such as wildlife diversity, environmental change, international travel, and increases in host susceptibility.
Over the past decade, Cryptococcus gattii has emerged as a primary pathogen in northwestern North America, and its appearance in North America is alarming because this is the first major emergence in a temperate climate, indicating a possible expansion in the endemic ecology of this pathogen. Isolates from the recent Pacific NW outbreak exhibit high virulence and that enhanced virulence, when compared with those from other regions, suggests that the genotypes circulating in the Pacific NW are inherently increased in their predilection to cause disease in mammalian hosts.
The continued expansion of C. gattii in the United States is ongoing, and the diversity of hosts increasing. Cases have been observed in urban and rural areas, and have occurred in a range of mammals. On Vancouver Island and the mainland of British Columbia, cases have been documented in marine and terrestrial mammals including cats, dogs, porpoises, ferrets, and llamas. This trend has continued in the United States, with several cases in agrarian, domestic, and wild terrestrial mammals, as well as marine mammals, adding elk, alpacas, and sheep to the list.
The co-expansion of the outbreak among mammals and humans is significant for several reasons. Non-migratory mammals serve as sentinels for disease expansion, particularly given that isolation of C. gattii from the environment is difficult, and not yet successful at all in Oregon. Additionally, the threat to agricultural and domestic animals is significant and thus the need for cooperation among health officials is critical. Finally, the widespread spectrum of disease illustrates that the organism is likely to be pervasive in the environment.
While rare, little is currently known about how or why specific humans and animals become infected. The potential dangers of travel-associated risks should be noted, as a growing number of cases attributable to travel within the Pacific NW region have been documented. Northern California has similar temperate climates to endemic regions within Oregon, leading to speculation that the emergence of C. gattii may spread there, while expansion eastward may be limited by the below freezing average temperature winters.
FROM: Emergence and Pathogenicity of Highly Virulent Cryptococcus gattii Genotypes in the Northwest United States – April 22, 2010
Byrnes EJ III, Li W, Lewit Y, Ma H, Voelz K, et al. 2010 Emergence and Pathogenicity of Highly Virulent Cryptococcus gattii Genotypes in the Northwest United States. PLoS Pathog 6(4): e1000850. doi:10.1371/journal.ppat.1000850
http://www.plospathogens.org/article/info%3Adoi%2F10.1371%2Fjournal.ppat.1000850
………………………………………………………………………………
There are questions that arise from this report which revolve around the effects of climate change on the emergence of new genetic variants and the spread of this novel stain throughout the Pacific Northwest. What might those relationships be?
For example, what influences does climate change offer for novel shuffling of genetic material and in what way?
Will climatic boundaries be a factor in the expansion of these individual strains?
If a particular strain is pervasive in the environment, will the disease evolve differently in the wild versus domesticated livestock versus humans and what role will mobility play in its development?
If the spread eastward of a strain may be limited by below freezing average temperatures, then what is the role of geography in combination with climate in its potential spread?
Editors Note: the above post contains edited excerpts from the original paper.
