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    Why humans are making epidemics worse

    Atlanta—Nearly every year there seems to be some new epidemic that crops up, creating healthcare crises and worldwide panic. Robert Kalayjian, MD, director of infectious diseases at MetroHealth Medical Center in Cleveland, says these epidemics are becoming more common, and he explained the implications for public health during a session at SECO 2016. 

    Dr. Kalayjian says the way humans interact with the environment allows for emerging and reemerging infectious diseases such as Ebola and Zika to play out in similar patterns time and time again.

    Related: How to diagnose Zika in your practice

    How our environmental impact affects disease

    Of the 18 Ebola outbreaks in equatorial Africa since 1975, most occurred in remote areas where extensive transmission from person to person was unlikely, says Dr. Kalayjian. The epidemics were relatively small and quickly contained. In total, fewer than 2,000 people were infected in those epidemics, and 1,296 people died.

    The latest outbreak, however, occurred in densely populated cities in which the virus spread like wildfire. For comparison, the Centers for Disease Control and Prevention (CDC) estimates that more than 28,600 people were infected in Guinea, Sierra Leone, and Liberia during this epidemic, with more than 11,000 deaths. (Other countries, including the United States, experienced a total of 36 infections, including 15 deaths.)

    “The first important principle I’d like to emphasize is that in all cases, we know that these epidemics occurred by interactions with infected animals—bats or primates—and it speaks to environmental degradation and human encroachment into the habitats of these animals that has allowed this to occur,” says Dr. Kalayjian.

    About 60 percent of human infectious diseases are somehow related to wild and domestic animals, he says. Rabies, for example, is passed from a rabid animal to a human, but it is unlikely to be passed to other humans from there. Ebola is passed to humans through some interaction with either great apes or fruit bats, but then it is able to be transmitted from person to person.

    Another factor that makes these epidemics hard to contain is the increasing ease with which humans travel. The most recent Ebola epidemic spread very easily among Guinea, Sierre Leone, and Liberia in part because of the very porous borders among the countries, says Dr. Kalayjian.

    “Importantly, the epidemic could be tracked traveling along the transportation routes between very populous cities,” he says.

    Climate change—not just increasing temperatures, but also changes in precipitation—is also affecting the spread of infectious diseases.

    “Lyme, anaplasma, babesiosis, and ehrlichia are all transmitted by tick vectors,” says Dr. Kalayjain. “Climate change is playing a role in the population of those ticks and their ability to thrive in warm environments.” 

    As such, Dr. Kalayjian says that a “One Health” approach is required to prevent and contain future outbreaks of infectious diseases. This approach requires collaboration among human, animal, and environmental health entities on disease surveillance, outbreak response, and prevention to achieve an optimal human health outcome. The One Health concept is supported by the CDC.

    Next: Ebola

    Colleen E. McCarthy
    Colleen McCarthy is a freelance writer based in the Cleveland area and a former editor of Optometry Times. She is a 2010 graduate of the ...


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