Climate Change I: the Mesoamerican Biologic Corridor
The Mesoamerican Biologic Corridor. The GABI and Paracoccidioides cetii and P. loboi. Dolphins, humans and mosquitos. Dengue, Zika, Deep time and the future.
By way of a prologue
Paracoccidioides is a vile fungus with horrific effects on the body. It is able to infect many species including humans, marine mammals and has been reported in California sea lions, Amazonian river dolphins, West Indian manatees, pinnipeds (5 species), and marine cetaceans (18 species). This yeast originates in warm tropical regions. It is versatile- capable of making zoonotic transfers among both land and sea mammal
The fungus could have increased population due to climate change and this has conservation implications for already endangered aquatic mammals.
A history
It all begins in a very old event. Roughly three million years ago, the formerly separate northern and southern continents of the western hemisphere linked together via the volcanic formation of a connector, what we call the Panamanian isthmus. What we call the Mesoamerican Biologic Corridor (MBC) is the comparatively narrow central American regional connector between the South America and North American continents. It has both land and offshore elements. It is the main highway of propagation for life in either direction. As movement became easier via the MBC, what we call the Great American Biological Interchange (GABI) rapidly picked up pace. The early period of the connection's diffusion was fairly balanced as one would expect, in both directions, but the effects on the biota of each continent were asymmetric- the unique fauna of the southern continent suffered more extinctions as a result of the influx of northern immigrants than what happened to the northern continent’s biota. Eventually this diffusion stabilized and extinctions slowed. In recent times climate changes have driven increased northward propagation, especially of microbial life. That life is primarily hitchhiking on host animals, both marine and land, to move north. Some of it has the capability of jumping to hosts of different species- this is termed zoonotic transfer. Zoonotic transfers can be land-land, sea-sea or sea-land and land-sea. Building physical or immunologic barriers to such northward spread of pathogens is accordingly very difficult. Continental geographic barriers are very porous. Political barriers even more so or nonexistent.
It is a very complex picture with a tremendous number of anthropogenic, climatalogic, geographic, atmospheric, oceanic, and plant and animal diffusion variables to calculate over short, medium and long term time scales for the northern hemisphere.
Life has been circulating around the planet for a couple billions of years. Generally many life forms tend to diffuse unless they self-limit via some adaptation that requires a very special geographic or biological region for sustenance and they lack the transport mechanisms to spread to other such regions. In the general case the major limits to diffusions are significant geographic barriers such as high mountain ranges and wide oceans or inhospitable climatic regions such as ones with very low temperatures or high aridity. In the case of the northern American continent, desert regions have resisted encroachment and lower winter temperatures have held in check many of the host vectors that pathogens hitchhike on- limiting them to the warmer, more humid parts of the country. These are generalizations only as pathogens have traditionally crossed all these barriers by hitchhiking on hosts that could transit through.
Warming trends are accelerating the northward spread of invasive species and pathogens such as Lacazia, Dengue and Zika, up the Mesoamerican Biologic Corridor and close-in coastal waters. Politicians talk about northward human migration and the health risks involved, but that's a fairly minor piece in a far larger puzzle. The problem is our whole country is quickly becoming more hospitable for pathogens, the bulk of which do not come via human carriers. Birds, bats, mosquitos, rodents, fish, can all carry viruses, fungi, parasites, bacteria harmful to human life and to other species who lack immunologic resistance.
By way of a forecast
Lacazia was chosen to be the poster child for this essay but although horrific, it is by no means the worst of what's moving north- very few contract it, fewer die from it. The same can't be said of the rest of the host, countless pathogens and invasives moving into the nearctic formerly temperate zones. As where we live yearly becomes warmer and thus more hospitable to life forms that thrive in the warmth and greater humidity, so too we will find ourselves ever more subject to their modes of expression. That is the future we face and we should prepare ourselves for it lest we face the fate of the ancient South American fauna of the Pleistocene . War is coming and it may be a lasting one.
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The interdisciplinary literature is enormous. Selected references showing some of the variety:
Vilela R, de Hoog S, Bensch K, Bagagli E, Mendoza L. A taxonomic review of the genus Paracoccidioides, with focus on the uncultivable species. PLoS Negl Trop Dis. 2023;17:e0011220.
Marine Mammal Zoonoses: A Review of Disease Manifestations
T. B. Waltzek, G. Cortés‐Hinojosa, J. F. X. Wellehan Jr., and Gregory C. Gray. Zoonoses Public Health 2012 Dec; 59(8): 521–535.
Zoonotic protozoa: from land to sea. Ronald Fayer, Jitender P. Dubey, David S. Lindsay Trends in Parisitology, volume 20 issue 11 November 2004, Pages 531-5
The impact of deforestation, urbanization, and changing land use patterns on the ecology of mosquito and tick-borne diseases in Central America
Diana I Ortiz, Marta Piche-Ovares, Luis M Romero-Vega, Joseph Wagman, Adriana Troyo
Insects 13 (1), 20, 202
Interesting piece Michael. I remember some years ago a professor Thomas Homer-Dixon providing some lectures and papers on the changing climate effects on resources and resulting conflicts. Interesting times.
Climate warming in action:
https://www.cdc.gov/mmwr/volumes/73/wr/mm7307a2.htm