Gladys Kalema-Zikusoka is a Ugandan veterinarian working on the conservation of the last mountain gorillas in Bwindi Impenetrable National Park. In an interview given to CNN a few days ago, she explains why the last gorillas are threatened by diseases transmitted by humans.

The scientist has worked for more than twenty years to allow humans and gorillas to coexist in one of the African areas with the highest rural population density. In the 1990s, gorilla tourism was still in its infancy. It was at that point that the conservationist wanted to study what its effects might be.

"I was able to see what tourism was doing for the gorillas, both for good and for ill," she said. "And of course I realised how communities have benefited from it, because they are truly poor and gorilla tourism is helping to lift them out of that situation," Kalema-Zikusoka added.

Given the extreme genetic closeness between gorillas and humans, the doctor wanted to study over the years what consequences the increase in contact between the two species has. This demonstrated a rise, in gorilla populations, in parasites and infections present in humans, caused by proximity to local communities, livestock and tourists. One particularly striking example was the scabies outbreak that erupted in 1996 starting from a nearby village, which would have decimated the group had it not been treated in time. Not to mention the deaths caused by the Ebola virus.

For this reason, Kalema-Zikusoka founded Conservation through Public Health (Ctph), an NGO working to prevent the spread of deadly diseases, which also manages a clinic where gorillas can be treated if necessary.

On the other hand, the doctor herself acknowledges that tourism is a fundamental resource for local communities. Each gorilla group brings in 1 million dollars a year in revenue. "We are trying to find a balance between conservation and the economy," explains Kalema-Zikusoka, "and that is why we try to limit the number of people who visit the gorilla groups."

A 2012 census by the Uganda Wildlife Authority identified 400 mountain gorillas now living in Bwindi National Park. The total population stands at around 880 individuals, nearly a hundred more than the 786 estimated in 2010.