Global Zika-like outbreaks are increasingly inevitable largely due to unprecedented rates of

  • Population mobility and density
  • Rapid global transport
  • Human ecosystem alteration
  • Climate change

existing cheek by jowl with

  • Vast health and wealth disparities
  • Vast global differences in public health infrastructure including sanitation and active disease surveillance capacity
  • Surfeit of neglected and/or little known diseases, many of them tropical, that lack drugs or vaccines to treat or prevent them and whose geographic reach spreads as climate change expands the range of the vectors capable of transmitting them.

Several of these factors also increase human-wildlife interactions, which in turn increase risk of Zoonosis – Wikipedia, diseases transmissible between animals and humans.

Originally discovered in 1947 in the Zika forest adjacent to Lake Victoria in Uganda, for decades Zika was but one of several RNA viruses known only to a handful of aficionados. Its obscurity began changing starting in 2007 when it caused an outbreak on the Micronesian island of Yap (1) followed by a larger 2013-2014 outbreak in French Polynesia (2) culminating of course in the global headlines of the 2015-2016 outbreak in Brazil and beyond (3).

So, clearly a case of a virus that until quite recently remained confined to a remote African forest and yet in less than a decade it’s spread across the globe, not only infecting large swaths of previously unexposed human populations but also expanding its capability in terms of disease outcomes from GBS (Guillain–Barré syndrome – Wikipedia) to fetal abnormalities (Microcephaly – Wikipedia). While less than a decade may sound shocking, not being unprecedented is even more so since Zika’s only following in the footsteps of related viruses, Chikungunya – Wikipedia and Dengue virus – Wikipedia, all zoonoses. Having similarly triumphantly marched across the globe in recent decades, their spread eerily echoes that of their carrier mosquito, Aedes – Wikipedia.

A 2008 study (4) estimated 335 emerging infectious diseases (EID) between 1940 and 2004. Averaging yields a very deceptive ~5 per year, deceptive because frequency between Pandemic – Wikipedia has steadily shrunk in recent years. Consider for example the high-profile global outbreaks of SARS (Severe acute respiratory syndrome – Wikipedia) in 2003, Bird flu (Influenza A virus subtype H5N1 – Wikipedia) in 2007, Swine flu (2009 flu pandemic – Wikipedia) in 2009, MERS (Middle East respiratory syndrome – Wikipedia) in 2012, Ebola virus disease – Wikipedia in 2014 and Zika fever – Wikipedia in 2015.

~60% of EIDs are primarily zoonotic. For e.g., Chikungunya, Dengue Ebola, HIV, Lyme, SARS, West Nile, Zika, to mention just a few.

  • The 2008 analysis (4) concluded majority arose from wildlife and that human population density was the single common predictor for all types of EIDs (zoonotic or not, drug-resistant or not, vector-borne or not).
  • EIDs seem to be a ‘hidden’ cost of human economic development (see below from 4, 5).

Population Mobility & Rapid Global Transport

Practically anywhere in the world is today a mere plane ride away even as these anywheres remain vastly different in basic public health infrastructure and active disease surveillance capacity. One sick person is all it takes for infectious diseases to spread beyond borders, i.e., vastly expanded potential for diseases to rapidly spread globally.

Consider for example how global air travel has exponentially expanded in <100 years. A paltry 1205 total global plane tickets sold in 1914 had increased to a whopping 2,595,448,927 in 2010. Yet large swaths of the world still lack adequate sanitation (see below from 6 and 7).

Human-driven Ecosystem Alterations & Climate Change Tilt The Balance In Favor Of Increased Pandemic Risk

More than ever before, massive human -driven ecosystem alterations have become the norm since the Industrial Revolution – Wikipedia with this process only further globalizing in the current era (8; see below from 9, emphasis mine).

‘With roughly half the temperate and tropical forests cut down, nearly half the icefree, desert-free terrestrial landscape converted to croplands or pasture, and more than 800,000 dams impeding the flow through more than 60% of the world’s rivers, alterations to our planet’s land use and land cover represent some of the most pervasive changes humanity has made to Earth’s natural systems

Human-driven ecological changes increase human encroachments into wildlife habitat. Such human-wildlife interactions increase zoonoses risk.

  • For example, studies suggest such processes may have kick-started the initial Ebola and HIV outbreaks (10).
  • No surprise then that ~75% of EIDs are zoonoses (4, 5, 11).
  • New disease outbreaks become more inevitable when previously unimaginable mobility and enormous human-driven ecological changes exist alongside crippling poverty consisting of acute food scarcity and no sanitation, hygiene or running water since the more malnourished are weaker and likelier to get sick, especially with new EIDs.
  • A corollary is increased hunting and consumption of wild meat, Bushmeat – Wikipedia (12).
    • For example, ‘ground zero’ for the 2013-2016 West African Ebola outbreak is suspected to be hungry children living in the remote Meliandou – Wikipedia village in southern Guinea – Wikipedia who killed and ate infected fruit bats (13, 14).
    • Something so seemingly inconsequential and yet it triggered a global public health emergency with a total of 28616 cases and 11310 fatalities from 10 countries according to West African Ebola virus epidemic – Wikipedia.
  • Mapping such outbreaks only emphasizes that infectious disease transmissions have become that much easier given how fluidly, rapidly and easily humans can traverse the globe these days, and the increasingly porous divides between previously more strongly demarcated divisions such as affluence and poverty, sanitation and filth.

Thus, since lack of hygiene, sanitation and running water are today only a plane ride away so is pandemic risk.

The rapid, global expansion of mosquito species such as Aedes aegypti – Wikipedia and Aedes albopictus – Wikipedia is but one example of how climate change effects place greater selection pressures on vast numbers of species to adapt to these rapid changes, many of which end up increasing infectious disease risk not just in humans but for all types of life forms (see some other examples below from 15).

A 2009 analysis (16) concluded climate change may influence different arthropod-transmitted Arbovirus – Wikipedia diseases differently.

  • Chikungunya: A single mutation in the Chikungunya virus facilitated its adaptation to the fast expanding mosquito species, A. albopictus, i.e., Chikungunya’s spreading by latching on to this mosquito’s coat-tails, whose spread is facilitated by climate change. Human travel simply augments spread even more.
  • Rift Valley fever – Wikipedia, Bluetongue disease – Wikipedia: According to these authors, climate change helps mosquitoes spread in newly flooded areas while human activities such as irrigation projects, movements of herded animals and animal imports to feed large numbers of humans, for example during Mecca pilgrimages, also contribute to Rift Valley virus outbreaks.


1. Duffy, Mark R., et al. “Zika virus outbreak on Yap Island, federated states of Micronesia.” New England Journal of Medicine 360.24 (2009): 2536-2543. http://www.nejm.org/doi/pdf/10.1…

2. Cao-Lormeau, V. M., et al. “Zika virus, French polynesia, South pacific, 2013.” Emerging infectious diseases 20.6 (2014): 1085-1086. http://wwwnc.cdc.gov/eid/article…

3. Campos, Gubio S., Antonio C. Bandeira, and Silvia I. Sardi. “Zika virus outbreak, Bahia, Brazil.” Emerging infectious diseases 21.10 (2015): 1885. https://www.ncbi.nlm.nih.gov/pmc…

4. Jones, Kate E., et al. “Global trends in emerging infectious diseases.” Nature 451.7181 (2008): 990-993.

5. World Organisation for Animal Health

6. In flight

7. Total population: access to sanitation

8. Foley, Jonathan A., et al. “Global consequences of land use.” science 309.5734 (2005): 570-574. https://www.researchgate.net/pro…

9. Myers, Samuel S., et al. “Human health impacts of ecosystem alteration.” Proceedings of the National Academy of Sciences 110.47 (2013): 18753-18760. https://www.researchgate.net/pro…

10. Hahn, Beatrice H., et al. “AIDS as a zoonosis: scientific and public health implications.” Science 287.5453 (2000): 607-614. https://www.researchgate.net/pro…

11. Taylor, Louise H., Sophia M. Latham, and E. J. Mark. “Risk factors for human disease emergence.” Philosophical Transactions of the Royal Society of London B: Biological Sciences 356.1411 (2001): 983-989. http://rstb.royalsocietypublishi…

12. Wolfe, Nathan D., et al. “Naturally acquired simian retrovirus infections in central African hunters.” The Lancet 363.9413 (2004): 932-937. http://www.jhsph.edu/research/af…

13. Vogel, Gretchen. “Bat-filled tree source of Ebola epidemic?.” Science 347.6218 (2015): 142-143. Bat-filled tree may have been ground zero for the Ebola epidemic

14. Bausch, Daniel G., and Lara Schwarz. “Outbreak of Ebola virus disease in Guinea: where ecology meets economy.” PLoS Negl Trop Dis 8.7 (2014): e3056. http://journals.plos.org/plosntd…

15. Altizer, Sonia, et al. “Climate change and infectious diseases: from evidence to a predictive framework.” science 341.6145 (2013): 514-519. http://www.colorado.edu/eeb/facu…

16. Gould, Ernest A., and Stephen Higgs. “Impact of climate change and other factors on emerging arbovirus diseases.” Transactions of the Royal Society of Tropical Medicine and Hygiene 103.2 (2009): 109-121. http://www.idpublications.com/jo…