EpidemicsAs emerging diseases spread from wildlife to humans, can we predict the next big pandemic?

By Karl Gruber

Published 29 December 2017

Viruses have been moving between organisms for millions of years. And not always in a way that causes harm: Animals and humans alike host millions of different microorganisms, many of which are beneficial. For those that do harm humans, the first step is to come in contact with us. And that’s becoming more and more likely as we invade pristine forests in search of food, building materials, space for commercial developments or land upon which we can create new grassland for our livestock — or catch critters for bushmeat, pets or the “wildlife selfie” trade. Two ambitious projects aim to understand when and how the next human disease will emerge from wildlife, and what we can do to minimize harm when it does.

Earlier this month, the World Health Organization (WHO) reported some troubling news. On September 20, a man from Kween District in eastern Uganda was admitted to a local hospital after developing fever, bleeding, vomiting and diarrhea. According to WHO, the man, a 35-year-old herdsman, frequently hunted near an area known to host bat-inhabited caves. He died five days later, after being transferred to a nearby hospital, but no blood samples were collected at that time and his death was not attributed to a specific disease.

Some three weeks later, his sister, who had cared for him and helped with burial rituals, was hospitalized with similar symptoms and died shortly after. Posthumous samples confirmed the presence of Marburg virus, a microbe that can infect both animals and humans. Shortly afterward, the Ugandan Ministry of Health declared an outbreak of Marburg virus disease (MVD) in Kween District.

But the story didn’t end here. A brother of these two also was diagnosed with MVD — but before he died, the man travelled to Kenya, potentially spreading the virus. Ugandan and Kenyan health authorities, WHO, UNICEF, and the Kenya Red Cross Society are watching for evidence of further dissemination of this virus.

The outbreak, which may have begun when the first man was infected by a bat carrying the virus, is an example of a disease outbreak of zoonotic origin — one that can be transmitted from animals into humans. It appears that this incident has been limited to a local spillover of an animal-borne virus into humans. But the international travel component is a very real reminder that such a course of events can lead to a zoonotic pandemic, a worldwide spread of a pathogen — most often a virus — transmitted from animals to humans. From severe acute respiratory syndrome (SARS) to AIDS and Ebola, zoonotic diseases cause more than a billion cases of illness each year. As humans increasingly encroach on wildlife territory and increasingly travel long distances in short times, the threat of zoonotic pandemics is growing. At the same time, so are efforts to prevent or curtail them.