Climate Disruption and Changes in Infectious Disease Patterns: The Worst is Yet to Come.


humanhealth-copy-cdcMost scientists will tell you that evolution does not favor the fastest, the strongest, or even the cleverest. Evolution favors the most adaptable. Humans, as a species (race is an antiquated and dishonest ideology), are highly adaptable, having populated, at least to some degree, every continent on planet earth regardless of how inhospitable. While there are few areas that remain completely unexplored on our planet, there are some areas that are so remote that few Westerners, or even natives, have visited.

The New Kids on the Block

In our comparatively short tenure, amounting to perhaps 1000,000 years or so, we are a relatively young species, especially when compared to bacteria and viruses that have existed for hundreds of millions of years. Nevertheless, we have established dominance over the planet, at least the drier parts. Certainly, in time we will master the aquatic domains as well. Perhaps this is the reason that the disruption in climate cycles does not alarm everyone, as many believe that humans will thrive regardless of what the weather does. And I tend to agree that humanity will persevere, although it may not be so easy as many think. One area that is of great interest is the migration of different species that have been isolated by either geography or climate into new areas, bringing them into contact with native species.

Even a tertiary review of the scientific literature demonstrates a clear migration of plants and animals away from historical domains, and we see certain tree species slowly moving northward as the overall climate in North America warms. Along with this slow progression of plants into these new domains come the animals, birds, and insects that feed or live upon them. And while this northward movement may not be rapid, it is steady.

Over time, species never seen in northern locales are beginning to push into new areas where they often out-compete native species. And while native species evolved over thousands of years along with insects or animals that feed upon them, many invasive plants and insects (and arachnids) have no natural agents to keep them from overwhelming existing species.

Climate Disruption

Scientists are in agreement that the disruption of the climate is the primary driving force behind this migration. It doesn’t matter if you believe that climate change is spurred on by human civilization or by the solar maximum, or a combination, denying that the Earth’s climates are undergoing rapid change is simply refusing to see the obvious.

The appearance of non-native plants and trees may be a nuisance; the animals, particularly the insects and arachnids, pose a far more serious threat. This is because some are vectors for disease.

Expanding Vectors and Pathogens

A vector in epidemiology refers to an animal or plant on which (or in which) pathogens of disease live. While these vectors do not suffer from the disease itself, they can spread it to other species, and while there are some infections diseases that are carried by larger animals, for example rabies, the primary threats come from insects and arachnids. Research has established that the geographical locations and populations of insects and arachnids change along with disrupted patterns in weather. This was first identified in sub-Saharan Africa. As temperatures increased, insect species began to move into higher elevations, spreading infectious diseases like malaria and trypanosomiasis. This has now been observed in North America with tick-borne diseases including Lyme disease, Tick-borne encephalitis, Human granulocytic, Monocytic Ehrlichiosis, Babesiosis, and Tularemia. Virtually every week we receive updates from the Centers for Disease Control and Prevention (CDC) in our northern states warning of Tick-born disease.

Life is opportunistic.

Parasites, viruses (more or less), and bacteria are all life forms, and like other species will take every advantage to survive. This is often at the expense of other life forms that, for any number of reasons, have some exploitable weakness in their defenses. This weakness may have resulted in the failure to vaccinate against a known virus (Mumps or Measles), consuming unclean vegetables (Giardia lamblia) or improperly cooked meats (Salmonella, E. Coli, and any host of parasites found in beef, pork, poultry, or fish). Another example of this opportunistic reality is when two species, separated by geography (a mountain range or deep forest), are brought into contact, as in the case of Ebola. Certainly the farmers had no interest in traveling deeper into the jungles; however, the charcoal trade that supports most of the poor in areas of sub-Saharan Africa has used up the forest immediately surrounding the villages. As Western societies move into these areas to capitalize on forestry and heavy-metal mining, the charcoal makers are forced deeper and deeper into the forest, bringing them into contact with species that have been historically separated. If an area in habited by humans becomes significantly wetter, waterborne disease will become endemic. If an area becomes dryer, other viruses may increase.

Natural Borders

Infectious disease agents can be separated by geography including oceans, deep jungles, or mountain ranges that can effectively isolate species. Time can also separate infectious agents from vulnerable populations; one example is the widespread vaccination against polio in the United States starting in 1954, and in just 25 years, polio was effectively eliminated from the United States. Thus time, in this case, a quarter century separates polio from American populations. However, failure to maintain vigilance against a virus greatly reduces this separation, making an outbreak more likely, particularly if the virus is introduced from another location where it has not been eradicated. Oceans may have separated populations at one time, but with the advent of world travel, this no longer limits the spread of infections. Dozens of new cases of polio are reported from African nations, including Chad and Nigeria, and many are diagnosed annually in Afghanistan and Pakistan. Not surprisingly, these areas are marked with abject poverty and religious suppression of science and medicine. When ignorance and poverty are combined, disease is often the result.

Other aspects of shifting climates include floods, droughts, severe storms, and ocean changes including salinity, temperature, and level, which may further affect the migration of species into new areas. Moreover, climate disruption has been positively associated with increases in diseases, particularly vector-borne disease. El Niño has been linked to increasing in emerging disease, in particular malaria, and other waterborne disease, particularly diarrheal diseases in areas prone to coastal flooding. La Niña has been linked to outbreaks of Chikungunya, and increases in West Nile Virus and Japanese encephalitis, and in areas of drought increases have been seen in Hantavirus pulmonary syndrome, and increases in West Nile Virus. Globally, these climate-driven weather patterns such as increases in hurricane or typhoons have been associated with increases in waterborne disease, increases in viruses, and increases in bacteriological infections including leptospirosis.

Displaced Populations

As extreme weather and climate change affect human populations as well as their domesticated livestock, areas lost to flooding or drought force populations closer together in habitable areas and along with them, and their animals come they are infectious disease. Displaced populations, either from conflict or extreme weather are often in precarious situations. They are universally underfed, often have difficulty obtaining clean water, and are forced to live in less than sanitary conditions, all of which combined to make these populations extremely susceptible to infections disease. Combined with the stress of forced relocation, and the impact of that stress on the immune response, it is not surprising that these populations experience significantly shorter lifespans and poor health.

In the end, it doesn’t matter if you understand climate change as a natural process, one that is man-made, or a combination, to deny that climate disruption is occurring is denying the obvious and measurable environmental changes linked to increasing infectious diseases.


One thought on “Climate Disruption and Changes in Infectious Disease Patterns: The Worst is Yet to Come.

  1. Ana Mendoza

    Great read! Interesting to know how climate can increase disease. Since you told me about Ebola I now know how it became a bigger issue recently, elaborating about this in the article would have been interesting for others to know. I had to look of about Chikungunya virus, I was not familiar .


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