From Ancient Reservoirs

“The insidious emergence of HIV/AIDS and the lack of due attention by policymakers illustrate how some outbreaks that start subtly can grow to global proportions if they are not aggressively addressed early on.” — Dr Anthony Fauci

The Infectious Diseases Society of America recognizes climate change as a global health emergency and calls for policies responding to the intrinsic links between warming temperatures and rising sea levels and epidemic and pandemic events as well as other infectious disease threats to public and individual health. — IDSA

The climate system of our world envelopes it.

It represents the state of our atmosphere, our oceans, and the frozen regions we rely on. It interacts with and influences all things living here on Earth.

The present changes we now experience due to a climate in crisis are far-reaching. Disruptive to the balance of life itself. Harmful or even demolishing to ecosystems. Driving species of all kinds into new environments after their old safe places have been changed, disrupted, or taken away.

This is a story that we have become sadly familiar with as the burning of fossil fuels keeps dumping heat-trapping carbon into our atmosphere — resulting in rising seas, melting ice, stronger storms, worsening droughts, expanding heat, and far larger and more dangerous wildfires.

Global examples of emerging infectious diseases NIH

Global examples of emerging and re-emerging infectious diseases. Even before COVID-19, they were growing more numerous. Back in the early 1990s, this map showed just one illness — HIV. To humans, quite a few are now rather new. Others are re-emerging. Many are influenced by the climate crisis in various ways. Image source: Three Decades of Responding to Disease Outbreaks — NIH.

But there is one aspect of our changing climate that is often nuanced and overlooked — how the climate crisis can influence the spread of disease itself. How a disrupted global climate can drive sickness up out of the ancient reservoirs that have harbored it throughout the ages. How it can help accelerate the spread of new illness, make us more susceptible to sickness, or cause the re-emergence of previously well-contained diseases. Given the present context of a global pandemic caused by an entirely new illness — COVID-19 — it’s crucial to take a look at generally how harmful interactions with the natural world, particularly through climate crisis, are increasing risks of new and re-emerging diseases.

Reservoirs as Illness Havens

For what we know of as illness is also a kind of life.

Bacteria are micro-organisms. Viruses are pseudo-life and life-altering. And parasites are living things that dwell within or upon other living things. Climate change can generate or worsen such illnesses by directly affecting their environments as well. Creating the conditions that facilitate the transfer of diseases from typical ranges — called reservoirs — to new hosts. Developing pathways for expanded or new (novel) infections.

An illness reservoir is any person, animal, plant, soil or substance in which an infectious agent normally lives and multiplies. A harbor for the bacteria, viruses, or parasites that cause disease.

Human beings are reservoirs for certain diseases. These could be living humans or the dead — long buried and held dormant in ancient frozen tundra for hundreds or even tens of thousands of years. It is possible that the devastating illness smallpox (Variola virus), which was recently considered eradicated, may still be harbored by frozen dead humans entombed in the permafrost. That permafrost is now thawing as the Arctic heats up.

Animals can also be reservoirs — rabies, for example, lives in bats, raccoons, skunks, and foxes. Cholera is a bacteria that lives in water. It can also live in humans and zooplankton. And there is a link between the spread of Cholera and the loss of water security — which the climate crisis risks. Anthrax lives in herd animals like sheep and reindeer. Because it is capable of developing spores, Anthrax can survive for decades in the bodies of dead reindeer and the climate crisis produced thaw of permafrost has already resulted in new outbreaks of this illness in herd animals and, in rarer possible cases, human beings. Dengue fever is a nasty virus harbored by both humans and mosquitoes. And it is worth noting for diseases which cause illness and loss of life in human beings that mosquitoes — whose range can be greatly altered by changes in climate — weigh quite heavily.

Zoonosis — The Transfer of Illness From Animals to Humans

During recent years, human beings have unfortunately seen the emergence of numerous new or novel illnesses. Many of these illnesses have arisen as the result of mistreatment of nature. Our disruption of the natural world and harmful or abusive relationships with animals appears to have done double duty in getting us ill. For a good share of the nastier new ailments have arisen as the result of zoonosis — or the transfer of diseases that previously affected only animals to human beings — involving such harmful acts.

The harmful bushmeat trade in Africa is thought to be the origin of the novel HIV virus transferring from its original reservoir in primates as SIV before mutating into a stronger illness in humans during the 20th Century to become common from the 1980s onward. Though there is little clear and present evidence that the jump from animals to humans for HIV was directly influenced by the climate crisis, the link between harmful industry and disease transfer is a bit close for comfort here. It is also worth noting that those living with HIV are among the most vulnerable to increasing extreme weather events and related disruption of human habitat and support systems driven by the climate crisis.

SARS illnesses (of which COVID-19 is a subset) and Ebola are also novel viruses in humans. As with HIV, they are likely zoonotic illnesses. This means they originated in animal host reservoirs but, through some process of contact, transferred to human beings. These viruses are still rather mysterious in that they presently have unconfirmed reservoirs. But both are reasonably suspected to be harbored by animals — with tropical and subtropical bats relatively high on the list.

With Ebola in particular (we’ll talk about some similarities between Ebola and SARS due to suspect reservoirs in the next chapter), there is a bit of an ominous interaction with the climate crisis. New modeling produced in Nature Communications suggests that under the present pathway of global heating, Ebola epidemics in Africa could occur once every 10 years — or almost twice as often as they do at present. This is because the bats and other animals that are thought to harbor the virus are expected to be driven by warming temperatures into new areas — expanding the epidemic-prone region by 20 percent.

Expanding Heat

The heating function of the climate crisis is very well understood. And, early-on, scientific research from world health and climate agencies identified the risk that more global heat posed to expanding illness. In particular, mosquitoes which are both reservoirs and vectors (agents of disease transfer) for numerous harmful illnesses are seeing their ranges greatly expand as the world heats up.

Mosquito-borne infection is an ancient and well-known threat to humankind. But it has thankfully been relegated to warmer climates. Despite knowing little about mosquito-borne Malaria, the Roman aristocrats of antiquity did know they could avoid infection by retreating to villas in the cooler hills. Away from where mosquitoes were plentiful. Unfortunately, the climate crisis is driving heat, and the mosquitoes that come with it, both uphill and into higher latitudes.

A single populous species of mosquito — Aedes aegypti — can spread four serious illnesses. They include Dengue Fever, Zika virus, Chikunyunga and Yellow Fever. As global heating continues to be driven by fossil fuel burning, the range of this mosquito is expected to greatly expand. How much depends on how rapidly we halt fossil fuel burning and transition to clean energy (or not). But a business as usual (worst case) fossil fuel burning scenario in which the clean energy transition continues to be hobbled will bring this so-called jungle fever carrier to the Arctic by the 2080s (see image above).

There are over 3,500 species of mosquito. Most are relegated to warmer climates. In addition to the illnesses mentioned above, these insects also carry Malaria and West Nile virus among many others. And as the climate heats up, their range and their ability to transfer diseases among humans will expand.

But mosquitoes are not the only disease reservoir and disease vector species now on the move as a result of the disruption caused by climate crisis. There are many. Some which we probably don’t yet know about.

Receding Cold

If tropical heat spreading northward bringing with it flights of mosquitoes and displacing other disease carriers presents one illness expansion problem, the ongoing thaw of cold regions presents another. In particular, there is evidence that the Arctic has locked away numerous ancient illnesses that could be released in the thaw produced by climate crisis.

The Variola virus which causes Smallpox may well be sequestered in the various graves and burial mounds scattered throughout the Asian and European north. A study conducted in the 1990s detected fragments of smallpox DNA in the remains of Stone Age humans as well as people who were known to have died from smallpox during the 19th Century. Though smallpox was considered eradicated from human beings, long deceased humans frozen in the Arctic may serve as a reservoir that results in potential new infections. If such a reservoir exists, the Arctic thaw produced by the climate crisis will disturb it.

Other pathogens that may still be harbored by dead humans frozen the Arctic includes the 1918 Spanish flu (H1N1) which was found in frozen regions of Alaska. In 2007, scientists discovered Spanish flu RNA in the body of an Inuit woman who’d been buried for 75 years in the permafrost.

Anthrax is a bacteria-caused infectious disease that typically afflicts herd animals such as sheep and reindeer. But Anthrax can pass to humans that are exposed to the bacteria. In 2016, 2,000 reindeer became infected with Anthrax in the Yamal Peninsula region of Siberia. Nearby, it is thought that a reindeer killed by anthrax decades before thawed out, spreading the bacteria into the lands where the reindeer grazed. These reindeer then spread the illness to a number of human beings, including a 12 year old boy who died.

The potential for the release of both known and other as-yet unknown infectious agents from the thawing regions of our world have generated concern among top researchers. Jean-Michel Claverie a professor of microbiology at Aix-Marseilles University recently noted to BBC:

“Following our work and that of others, there is now a non-zero probability that pathogenic microbes could be revived, and infect us. How likely that is is not known, but it’s a possibility. It could be bacteria that are curable with antibiotics, or resistant bacteria, or a virus. If the pathogen hasn’t been in contact with humans for a long time, then our immune system would not be prepared. So yes, that could be dangerous.”

A Context of General Disturbance

Overall, it is likely that there are more numerous climate influences to disease transfer than mere heating and thawing. The general disturbance to the natural world generated by more extreme fires and floods, by instances of flash drought, and even by the mechanism of rising seas is likely to displace more disease reservoirs, creating previously unknown illness transmission potentials.

As far as our general scientific knowledge of illness related to or influenced by the climate crisis at this time, what we see now is likely the tip of the proverbial iceberg. And, as with all things climate crisis related, we require more research, more knowledge-sharing, more general public support of scientific discovery to pull back the veil on this particular new threat. So in conclusion of this chapter on the climate crisis relationship to human illness, we’ll depart with a statement from the World Health Organization:

Changes in infectious disease transmission patterns are a likely major consequence of climate change. We need to learn more about the underlying complex causal  relationships, and apply this information to the prediction of future impacts, using more complete, better validated, integrated, models.

Up Next — Harmful Contacts with our Living Earth and Redounding Shots Across the Bow

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