Climate Change and the Migration of Infectious Disease

Climate Change and the Migration of Infectious Disease


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Zika is all over the news. Zika is surely dangerous, but it has its limitations and is likely to be well contained. However, its greater significance extends beyond any current spread. Instead, it exemplifies the crucial emerging trend of a novel infectious agent that has swiftly become a global threat.

The common phrase, ‘this time is different’, is almost always wrong. Yet, our modern circumstances are distinctly unlike any previous era. Humans possess a unique ability for rapid travel and we choose to journey with our favorite pets and plants. This unprecedented degree of mobility extends across every planetary habitat. Further yet, it now occurs during a phase of a rapidly shifting climate. Certainly, species migration or global climate change are not new but it is only in this present moment that these factors can amplify through instantaneous global travel in a singular manner.

In fact, the results of this unusual conjunction are already apparent. For example, Zika’s advance across Europe and to the Americas has been extremely rapid. This is such an extraordinary event that at the beginning of this year, the World Health Organization declared Zika a global emergency in recognition of its rapid spread from continent to continent. Its rising incidence mirrors our prior concerns about the global scope of other recent epidemics such as Ebola or SARS.

The World Health Organization notes that infectious diseases are emerging at a greater pace and spreading faster than ever before. There are at least 40 new infectious diseases that have emerged that were unknown only a generation or two ago. For example, Zika was first identified in the 1950s and was initially confined to a narrow band of equatorial Africa and Asia. Monkeys were its primary host. Abruptly, it appeared in humans in Polynesia in 2013. Thereafter, it is suspected to have arrived in the Americas by plane, appearing in Brazil in that same year. Now it demonstrates pandemic spread throughout the Americas and the Caribbean. It is a flexible virus, too. It can be transmitted by mosquito bites, from mother to child, by sexual contact, or blood transfusions.

Chikungunya virus is also a newly emerging threat. Chikungunya is characterized by the sudden onset of fever accompanied by joint pains. It has a low mortality but is associated with a high frequency of chronic medical disabilities, some of which can be devastating. First identified in 1952 and initially confined to small outbreaks in West Africa, it has spread worldwide with millions of cases across Africa, India, and Asia. Only recently, it has appeared in the Caribbean and South America, and recently, there have been hundreds of cases in the US.

Each of these are examples of new enemies. However, there are also consequential old players whose distribution can also be affected by climate and global travel.  For example, dengue fever is a mosquito-borne virus first described in China in about 200 A.D. For centuries, there were only sporadic epidemics. Yet, it surged dramatically after World War II and is now a major factor in childhood mortality in the Pacific and the Americas. Only recently, it achieved a toehold in the US. Worldwide, it affects tens of millions on an annual basis. Even malaria, an old and persistent scourge, is demonstrating an increasing speed of transmission attributed to socioeconomic factors that include land use, population growth and urbanization, migration changes and travel.

The spread of disease through travel is not itself new. For example, in the Middle Ages, bubonic plague originated in China and arrived by trading ships to Europe. That briskly led to a series of devastating epidemics in the 14th Century that is estimated to have killed one-third of the European population.

Yet, even these horrific results are not the limit of epidemic disease. 12,000 years ago, there were abundant giant mammals on the North American continent such as mammoths, saber-tooth tigers, and giant sloths. Suddenly, they all disappeared. The exact cause is not known. However, ‘hyper-disease’ is one prominent theory. It is believed by some scientists that migrating humans or their companion animals inadvertently spread novel diseases from Asia when they crossed to the Americas and the indigenous megafauna had no natural immunity. In fact, extinction on the basis of infectious epidemics may not be rare. For example, the world’s amphibians are threatened by Chytrid fungus and the extinction of several amphibian species has been attributed to this pathogen.

If this is our current reality, what is the appropriate response? Expensive carbon projects are proposed by many climate enthusiasts. Those disputed schemes should be put aside. Instead, our scant resources should be directed towards relatively inexpensive ends with large rewards. That best means would be to concentrate on the remediation of infectious disease. This can be accomplished by mosquito nets, removal of standing water sources in endemic regions, research into improved treatments and vaccines, and a deeper understanding of the reproductive cycle of vector insects or other intermediary hosts. Clearly, our concerns about climate should emphasize coping with and conquering infectious disease as the truest common denominator of human health and welfare and proper planetary stewardship.

Dr. Bill Miller serves as a scientific advisor to OmniBiome Therapeutics, a pioneering company in discovering and developing solutions to problems in human fertility and health through management of the human microbiome. For more information, or

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3 Comments on "Climate Change and the Migration of Infectious Disease"

Apr 17, 2016

This article has been well brought out and put out well. I have never heard of Zika and after reading through this entire article I would have to say that yes, I am a bit worried about it. When the news first started to talk about Ebola many people were stressing out and having anxiety thinking about what would happen if they got ebola. However I feel after reading all the extensive research of Zika that we are in a more of a higher risk. The main concern is if medicine could cure any type of virus like this. Great article!

Apr 14, 2016

“Clearly, our concerns about climate should emphasize coping…

Spoken like a true investor with ROI aspirations. Yes, coping will be our only weapon thanks to the deniers.

One note though is I believe Toronto is considered a tropical infectious disease center in summer given its diverse world population.

Apr 13, 2016

Fascinating article, and well thought-out. In today’s day and age where one can travel from a remote island in Asia, and be in Los Angeles in hours is a testament to the technological wonders humanity has created. As stated, an unwelcome guest could potentially come across as well. The Ebola virus that touched down in the United States led a huge freight on the ten o’clock news, and now this Zika virus. Ebola and Zika were never a part of my vocabulary, nor did I ever heard of them in great detail until they made their way to the United States. The luxury of fast travel today made the spread of the bubonic plague from rats aboard shipping vessel in the middle ages look like child’s play. However, with all that said I am quite shocked that nothing of a huge significant scale came to infect a massive population since the Modern Plague during the turn of the 20th century. Is it better control at ports, better screening, or has medicine advance at a rate to beat back those diseases before they spread. Or is it a mixture of modern medicine in conjunction with proper hygiene and smarter environmental controls to eliminate disease breading grounds.