Diseases are distributed by two mechanisms, each playing a unique role in the disease migration-evolution behavior, and each participating in the unique blending of human and physical requirements for a disease to behave the way it does spatially:
- the impact of humans and human populations on their migration and pathogenicity, or
- the impact of natural, environmental and ecological features on their migration and pathogenicity
We are most often taught the human side of disease patterns, but some diseases are purely environmental in nature, with human behaviors dictating where they erupt, how they erupt, and which direction they will go once they are on their course to new regions, to produce new cases.
This very biological view of disease treats a medical problem as if it has its own life, even if it is of some sort of environmental, abiotic origin. This is because the abiotic diseases behave the way they do because of people, and sometimes the other forms of life that bring them to new places to cause further infestation.
1. Leptosporidosis–the Ecological Rule of Survival.
With the purely ecological diseases, we are more a intrusion into the environment than we are a carrier of the disease. This is because the cause for the disease is related mostly to place. The organism responsible for the disease doesn’t need people to survive. These are what defined ecological diseases. In a more modern, environmentalist like sense, we are intruding on the disease related organism and not vice versa. That organism was there before we moved into the region. It will be there once we are gone.
The underlying ecology of these diseases can actually be quite complex. Some of the best work on this ecological relationship was done by Russian ecologist and evolution specialist Voronov. Voronov considered these kinds of diseases to be part of the natural state, self-afflicted consequences ensuing as a part of the natural selection process every environment has when its ecology gets defined, or redefined by man’s changes in the natural ecosystem.
Voronov’s work follows that of the most classic disease or parasite ecologist of the mid-20th century, Pavlovski. During the 1940s, Pavlovski initiated his theory of disease ecology by stating that certain diseases occur where different ecologies and ranges of species distribution come together. What we today refer to as encroachment Pavlovski had already perfected the model for when using it to detail how certain tick-born diseases enter into mankind’s living space and surround land use regions. He defined the endemic region for such a disease as that area where mankind, the hosts and vectors for the pathogen, and the pathogen itself are able to survive alongside each other. Whereas the microcosm of disease causing pathogens was defined by the followers of bacterial theory developer Koch and his numerous microbiologists followers, Pavlovski was still focused on the older environment and ecology interpretation of the same event. To Pavlovski, of course the microcosm was important. After all, it defined the region across which the microorganism could dwell within and between infected people, disease hosts and carriers. But to Pavlovski, the environment played more of an active role in the Russian zoonotic, ecologic based disease theories for the mid to late 20th century.
Ultimately, Pavlovski’s theories, especially as they pertained to parasitology and zoonotic diseases, had to be paid their due attention by the microbiologists of the western world. Today, we look at disease ecology as a fact of science in the various worlds of biology and environmental science that it impacts. But in the end, we have to accept the fact that there are two interpretations of most environmental and ecological disease patterns that have to be paid their due respect. The ecology of microorganisms is just as important as the ecology of the victims they infect and make ill. For a while, the western world seemed to remain so focused on just the internal human ecology of any disease causing pathogen, making us miss some of the important clues to preventing and even treating these parts of the local natural ecology. Whereas the non-Russian way of interpreting this implied the old pastoral traditions inherent to western world Christian thinking, the Russian philosophy, was very much agnostic, atheistic, Leninist, Marxist, Nietzschian, and/or Existentialist in its mindset.
The following is an example of disease that is so limited in its spatial location that it is safe to say that this disease is very much dependent upon the local environmental features in order to remain in this region. Being fungal in its origins, it doesn’t have the limitations produced by having animals included as a part of its local, natural ecology. But it is a parasite of man so to speak, and so adheres to the Russian way of conceptualizing the spatial pattern of this disease in and around the Great Lakes regions, specifically that adjacent to Chicago.
One of the questions that comes to mind looking at this distribution and very specific delineation based on urban setting patterns is what sets of natural features define this spatial pattern? Are these features any of the following, such as latitude, longitude, landform, perilacustrian setting, soil-based hydrological patterns and pedochemistry? How much of a role does the human presence play in its continued persistance? Does the urbanization of the region make it more susceptible to inducing this disease? Is there something about the history of this place that makes it more susceptible to harboring such an organism? Perhaps it was the Great Chicago Fire and the ashes left behind in the soil that made this setting so conducive to growing leptosporidium and other related fungi.
Leptosporidosis is a fungal disease that favors perilacustrine, urban environmental settings to thrive. It has some specific humidity and temperature requirements for its growth and sporulation. For this reason, it exists quite easily in the very densely packed urban setting in Chicago, adjacent to the Great Lakes. In a study I did in Chicago on disease spatial patterns, I produced a video demonstrating the hierarchical, non-hierarchical and environmental ways in which diseases develop and diffuse in an urban setting like Chicago. The winters are very cold there, and the summers very hot. During the summertime, some living settings are so hot and dry that these environments become extremely hazardous to high risk groups, such as low income families, the chronically ill and elders residing in low income high rise building establishments.
This high density of a fungal disease in this region demonstrates the tendency for it to be endemic to this region, and the role that human ecology plays on its spatial pattern. It tends to favor densely packed building settings. Its persistence within this region makes in potentially pandemic. Its ability to impact people provides us with a means to document is spatial distribution, an unfortunate insight into this organism that we get due to its human ecological requirement.
Spatial studies of seeming ecological, biological diseases in which environment plays a major role in its persistence and continue existence without need for human involvement is more an ecological lesson perhaps than anything else we learn from this use of GIS. Some of the major marcoecological aspects of disease patterns defined by Russian parasite ecologists and disease geographers Voronov and Pavlovski provide us with some of the most important insights into disease ecology that today we continue to spend little time with. Their use of geography to better understand disease patterns surpassed some of the methods we developed trying to do the same in the 1960s and 1970s.
Likewise, some of our detail oriented approaches to understanding disease behaviors had their own positive attributes. However, the human geography parts of some of the organismal disease patterns that we seemed to ignore in the past, remained a part of the Russian geography medical geography research programs. With more biota to be involved with such a study, this enabled Russian studies of ecological disease patterns to result in some insights that we can today benefit from, due to the multilayered approach now being used to better understand disease spatial patterns, as a blending of human and natural ecological features, as well as the standard environmental features of the disease environment.
Together, these physical and natural science features along with human geography findings, can used to produce a better GIS for disease mapping and prediction, at both the natural ecological levels and the human population level.
These maps were produced in a very common research setting. The hardware-software accommodations were without GIS or any GIS related tools or sqls. Having produced much the same results in standard GIS work environments over the past 15 years, it seemed to me to be more of an accomplishment to produce a map that says the same as a GIS tool, without the need for all the data manipulation, programming and GIS-related fixes that have to be made here and there for us to receive a good outcome. This method takes 20-30 minutes to map national data on a fast parallel processing system, and produce a map of as many as a couple of thousand maps (takes 10-30 minutes longer) which are immediately presentable, or can be converted into a video presentation.
2. Hanta Virus.
When Hanta virus made its way into Oregon in the mid-1990s it was due to the droughts experienced down south in Arizona and New Mexico, places where the animal ecology for Hanta naturally survived. At first none of us in the GIS labs (then just ArcInfo and the brand new ArcView) could believe that the rodents were able to migrate so far north in just a short period of time. Field work by the State Department of epidemiological teams confirmed this suspicion, but adequate field samples were hard to come by due to the nature of the southeastern parts of the state.
A number of ecological assessments were made and the state’s historical natural history archive data was reviewed in Summer of 2000 to determine if in retrospect certain ecological features made this route possible. It ended up many of the same carriers had a relationship to the lyme disease then developing a hold of the same ecosystems, and ultimately by winter of 2000/2001 it was determined that chrysolithic geology and soil histories in the southwest portion of the state served as a natural barrier to the rodents and/or certain related co-hosts and vectors. This meant the route had to come from the southeast to eastsoutheast, and not from the direct south or southsouthwest. Both the hanta virus and lyme disease study were then stalled by the increase interest in west nile virus, resulting in the first major use of this system I developed for analyzing disease ecology in relation to DEMs, soil, geology, vegetation zones, hydrography and climate-weather.
The following is a result of a much later retrospective Hanta Virus review.
- Hanta Virus (W. US Native American, rodent-spread) — http://youtu.be/DzifZze-cW8
Other unusual ecological disease patterns with animal-host-vector relationships include the following examples:
- Creutzfeld-Jakob (Mad Cow) — http://youtu.be/un1k2oCHBqE
- California Encephalitis — http://youtu.be/1Og5SpTV5yA
- American Leishmaniasis — http://youtu.be/zuJMB618A7c
3. Rhinosporidioisis–two very unmatched ecosystems.
Unlike the Hanta Virus ecology of the western U.S., and a variety of other western and Rocky Mountain diseases noted previously, there are some diseases with very interesting east coast to Great Lake regional ecology. We expect the soil and climate features to prevail in some of these spatial behaviors, but there are possibly some human ecological components to these disease patterns as well yet to be uncovered. The Rhinosporidiosis is unique due to the two niduses noted in the distribution above (center map). The likelihood of purely natural ecological similarities seems hard to imagine, due to the climate differences between Florida and Rhode Island-Long Island Sound niduses, and the probable soil differences (Florida coralline and sediment, versus non-coralline, sandy to glacial moraine and silt in Rhode Island).
So why are the same disease pathogen niduses so far apart?
One possible reason could be genetic differences with the two Rhinosporidia, in turn impacting growth behaviors and growth medium requirements (haven’t looked this up yet.) There could be some other shared pedological feature, related perhaps to chemistry, or a unique mineral or element important to some physiological, biochemical process, etc.
This is an example of a spatial disease pattern with unique hot spots developed due probably to physical environmental features, without much involvement of host, vector animal species ecology. Russian medical geographer and evolutionist Voronov explained this phenomenon about diseases in his environmentalist interpretation of disease from the 1970s, as a follow up to Russian medical geographer Pavlovsky and his “ground breaking” (pardon the pun) disease ecology, parasitology work of the 1950s and 1960s.
Coccidiomycosis also has a very strong western ecological dominance. The more fascinating aspect to this ecology and spatial feature is it is one of the few natural history examples of disease patterns that demonstrates a longitudinal barrier related impact as we.
Longitudinal impacts generally don’t make much scientific sense. Whereas latitudinal impacts are dictated by temperature zones, longitudinal differences have major physiographic features that are usually responsible for their presence. Since the two largest mountain ranges in the U.S., on down into South America for the western Pacific Rim border, are north-south chains, this is probably playing a very large role in how and why a disease like Cryptosporidiosis demonstrates western continent dominance in both the northern and southern hemispheres. In terms of non-telluric, non-terrain related reasons for this effect, aspect (the angle of solar light) at the macrogeographic level could be playing some role in defining this distribution, either directly due to the impact of aspect on surface heating and such, or indirectly due to the obvious effects aspect has on vegetation patterns. Vegetation patterns in turn dictate the chemistry and richness of the soil in these ecological/vegetation domains, making it possible for certain forms of biological richness or diversity to be the cause for this western shoreline to montane region dominance of cryptosporidium.
The following is the link to this video map:
- Coccidiomycosis — http://youtu.be/BFL72mch-yo