Disease Ecology

Disease, it turns out, is largely an environmental issue.

Disease, it turns out, is largely an environmental issue. Sixty percent of emerging infectious diseases that affect humans are zoonotic — they originate in animals. And more than two-thirds of those originate in wildlife.

A zoonotic disease is a disease that can be passed between animals and humans. Zoonotic diseases can be caused by viruses, bacteria, parasites, and fungi. These diseases are very common and affect human and non-human great apes alike. Scientists estimate that more than 6 out of every 10 infectious diseases in humans are spread from animals.


Zoonosis, or a zoonotic disease, are responsible for millions of human deaths each year. Since no one treks the world’s undisturbed rainforests and swamp peat forests searching for sick or dead great apes, how many apes are dying of disease is a mystery. The impact on great ape survival is unknown.

What is known, the environment great apes call home—tropical rainforest—is also home to a plethora of zoonotic diseases that have until lately been contained or limited in their devastation. Research suggests the reason is largely because the forests have been undisturbed. Increased clearing of rainforest habitat for industrial logging, agriculture, palm oil plantations, mining, and human expansion has opened up access and contact with disease, accelerating outbreaks.

Ebola and Bushmeat

The hunting and transport of bushmeat has been primary vectors triggering the outbreaks and spread of the deadly hemorrhagic virus Ebola. One of the most difficult challenges is tracing the virus to the exact animal. The recent Ebola epidemic that infected 28,603 and killed 11,301 and spread to 10 countries internationally, began in a bat we believe. Previous outbreaks have been linked to killing of gorillas and chimpanzees for bushmeat.

Disease and Deforestation

Deforestation and human encroachment displaces these species and forces heightened interaction between people and animals indicating a high potential for disease transmission as we have seen from the toll of Nipah virus, Avian Influenza and SARS. EcoHealth Alliances Project Deep Forest seeks identify how and why this is happening.


It generally comes as a shock that non-human great apes—gorillas, bonobos, chimpanzees, orang-utans—contract many of the same diseases inflicting people: Ebola, HIV (SIV), bronchial infections, and more. The full extent of diseases apes are capable of contracting and carrying is unknown.

As often repeated, all great apes share 97% similar DNA. That extends to the diseases we can carry and catch. “In 2002, after human disease outbreaks caused by the Zaire strain of the Ebola virus, the researchers began finding dead gorillas. Over a number of months they found 33, tested 12 for Ebola and found that 9 were infected. And from October 2002 to January 2003, 130 of the 143 gorillas they had been studying — 91 percent — disappeared. The losses continued: 91 of 95 gorillas the researchers were watching died from October 2003 to January 2004. Many chimpanzees in the region have also died.”

Infectious disease has recently joined poaching and habitat loss as a major threat to African apes. Both “naturally” occurring pathogens, such as Ebola and Simian Immunodeficiency Virus (SIV), and respiratory pathogens transmitted from humans, have been confirmed as important sources of mortality in wild gorillas and chimpanzees.

Exploring More About Disease Ecology

PREDICT: is conducting global surveillance to detect and prevent spillover of pathogens of pandemic potential that can move between wildlife and people. The project is part of USAID’s Emerging Pandemic Threats program and is led by the UC Davis One Health Institute, which is part of the UC Davis School of Veterinary Medicine. The implementing partners are USAID, Wildlife Conservation Society, EcoHealth Alliance, Metabiota and Smithsonian Institution.

EcoHealth Alliance: is a global environmental health nonprofit organization dedicated to protecting wildlife and public health from the emergence of disease.

Quote on 2002 gorilla deaths: The New York Times

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