2 – Environmental Disease Clusters

What is an environmental disease cluster?

An environmental disease cluster is a set of cases in which the illness is generated primarily by the local physical setting.  This physical setting includes some things that many be considered non-physical items, such as solar energy, temperature, ultraviolet and infrared, but is focused on that part of the environment called abiotic.

Example 1.  Altitude Sickness.

One of the simplest examples of this is the medical condition related to elevation change.  People who are at high elevations for a short period of time have not had time to adapt to the new setting, and so begin to develop signs and symptoms of medical conditions possible related to this change in the living setting.

High Altitude sickness is a diagnosis often related to this.  With this disease mapping, we can review the distribution of elevation sickness and determine whether or not its incidence and prevalence behave a certain way spatially in relation to the physiographic features which are its cause.  Is this condition experienced mostly in high altitude areas or areas closely linked to the high altitude human experience?

The following map demonstrates that high altitude or elevation sickness is not a condition that requires care in high altitude living spaces.


The reason for this lack of fit is easy to understand if we spend a minute or two thinking about it.  People who experience this illness do so because they are normally not in the required setting much, and so once exposed to that setting come down with the symptoms.  They do not necessarily experience and/or report that condition however until it becomes problematic and interferes with their daily activities, and the individual experiencing it feels he/she has given their body ample time to either adapt to whatever is causing the problem or making the necessary adjustments to it.

As a consequence, this physiological experience doesn’t become a medical condition until it interferes with normal life processes.  This means that a person experiencing this problem will suffer from interference with normal living expectations back home, or after they have been exposed to the cause for the problem.  For this reason, the high altitude sickness is more often reported as an experience related to a past vacation or travel experience.  The three peaks noted on the map of this diagnosis are possibly linked to three major cities, where international travel to high elevation is at its peak.  The other possible reason for this clustering in the three areas shown is the location of airports, meaning that the trip itself could have been the cause for this event.



Example 2.  Environmentally-induced Lung Diseases

Lung diseases ensue as a consequence of our environment due to the inhalation of a foreign substance, which in turn results in any of a number of reactions to our exposure to this material.  When that material is a solid, taking the form of particulates on up in size to particles, pollen grains, ash, or the like, it cane produce a physical reaction, a chemical reaction and a physiological reaction in a patient.

The physical reaction ensues when the object is imbedded within the patient, usually in the lung mass, and physically interferes with the respiratory process and/or induced physiological changes to ensue that further exacerbate the condition, such as increasing swelling due to inflammation or the developing of scar tissue, either of which in turn reduces the permeability of respiratory surfaces thereby leading to potential anoxic related problems.

The chemical reaction occurs when a material enters the lung and chemically reacts with the materials on or on the respiratory surfaces.  These reactions may also hamper permeability of natural gases thereby reducing oxygenation of blood.  These reactions might also result in secondary reactions that further hamper lung tissue physiology and behaviors, for example the disintegration of alveoli walls or capsules due to a chemical such as an acid or an acidification process.

An example of the biological reaction is the inhalation of materials that result in physiological defense responses of an immunologic nature, such as the inhalation of particulated that result in antihistamine or IgE reactions at the alveolar level, or the inhalation and embedding of materials that result in localized inflammation, followed by swelling, mast cell and fibrocyte reactions and finally escarification, encapsulation of the foreign object, and sometimes carcinogenesis.

The above two items depict coal miner’s lung, the geography of which is dependent almost completely on the geologic natural history.  This natural history defines the place for exposure, which may be passively induced or developed due to living proximal to places rich in this material in the atmosphere, or due to more direct, active exposures induced occupationally, such as the life of a coal miner or related employee of this field.

The second nidus for an exposure related pulmonary disease is linked to one of two causes.  The first is a purely environmental cause, the second an occupational cause with a more ecological aspect of it that needs to be considered.

The first possible cause is exposure to the spores of a fungus as a part of the natural living process.  For the region afflicted, there is history of a very large subterranean Armillaria (Armillariella) mellea colony, purportedly one of the largest ever documented, which may in turn be producing enough spore density to produce this geographical outcome.

The other possibility is that the mushroom grower’s industry is extremely active in this setting, and that this behavior combined with the local environmental features make this setting a perfect places for the disease to develop.  This latter situation perhaps is more fitting as a natural ecological related causality.

For diseases with spatial patterns similar to the Mushroom Grower’s Lung, see Rhinosporidioisis for the biological/ecological aspect of this disease pattern, and the occupational lung disease page.


Example 3.  Rhinosporidiosis–an example of fungus, place and genotype.

On the above image of Rhinosporidiosis cases in the country there are three peaks (in red) that are in need of investigation, two of which are the focus of this review.

What is remarkable about this map of the disease is it tells us that the environmental differences between the Rhode Island and western gulfshore Florida peninsular area are somehow similar, similar enough to make them niduses for Rhinosporidioisis case reporting.

Both settings are maritime shoreline settings, and both slightly detached from the main ocean and its primary streams of flow.  Latitudinally, weather and climate are extremely different.  Topographically, both are similar in that they are fairly planar landforms adjacent to oceanic waters.  It is possible that the two also bear some very unique geochemical or pedochemical (soil chemistry) differences that make the two behave similarly with regard to the Rhinosporidium.

The species linked to this diagnosis is Rhinosporidium seeberi.  It infects both humans and animals cutaneously and subcutaneously.  One theory out there about its existence is it evolved from a fish infecting microorganism (fungal origin) that managed to develop into a form that infects birds and mammals, not necessarily in identical ways by identical strains.  [see Victor Silva, Cristiane N. Pereira, Libero Ajello, and Leonel Mendoza.  Molecular Evidence for Multiple Host-Specific Strains in the Genus Rhinosporidium. J Clin Microbiol. 2005 April; 43(4): 1865–1868.]

This Rhinosporidium problem represent one of a number of human-animal diseases considered possible risks as emerging infectious diseases.  With this in mind, a study of the spatial distribution of the protozoan responsible for it may shed some light onto its ecological behavior and its biological and pathogenic activities. [Link.]

One possibility for the tight clustering of this disease in two places is the geographic-distance feature linked to its ecological patterns.  If the organism subsists primarily in a physiographically defined region or domain, its ability to leave this area becomes increasingly unlikely as genetic changes occur making it more human-pathogenetic.  Associated with this genetic transformation are environmental adaptations that form part of the selection process as well.  With this paradigm, we consider the Florida and Rhode Island case clusters to also bear some genetic and ecological uniqueness when compared to other.

However, the size of the niduses in the two prime sites for infection suggest a combined pathogen-environmental requirement for these endemic patterns.

For more, see also the slideshare on this.


4.  Asbestosis.

Asbestosis was once a condition associated with two settings: the mines from which minerals used to produce asbestos were obtained, and the factory settings where products containing asbestos were manufactured.  This entire focus on the work environment and asbestosis changed beginning some time during the 1960s or early 1970s.  The requirement that asbestos be included in specific interior home building procedures resulting in large amounts of asbestos rich materials being use to produce the walls of buildings.  During the 1970s and early 1980s, it resulted in few problems, but over time was discovered to be related to certain lung conditions prevailing in certain building environments.  In the beginning, just one of the several forms of crystalline asbestos produced naturally was considered to be a problem to an individual’s health.  Since then, the other remaining forms of asbestos have been linked to the various lung conditions this material can cause.

The potential for exposure to asbestos leading to the development of asbestosis is now documented for most living environments, in particular those environments located within urban settings.  Asbestosis is perhaps one of the most diffuse and heavily documented lung conditions produced by particular intrusion down to the bronchioles and possibly alveoli.  The settling of asbestos particularly into respiratory tissue is a permanent process.  It is unusual for the villi and mucosal activities to effectively remove most of this material from the deep respiratory tissues.  As a result, the fibers remain deposited in the lung’s air space, leading to escarification and envelopment of the fiber produced by local fibrocytes, along with related mast cell-linked histamine responses and immunoreactive cell based materials also abundant in this part of the respiratory system.

Asbestosis is the most generic of the external particle-related lung conditions that impact people of all ages.

The following is a video of the distribution of particulate-based pulmonary pathologies: http://youtu.be/jIUOMVRhOs8.

A clustering of asbestosis is still likely to be documented using a GIS or this non-GIS grid mapping routine.  At the small area level, such a use of this tool will be considerably more beneficial at the local public health level.