After the West African epidemic, Ebola disappeared. But having hidden somewhere – maybe in forest animals, maybe closer to home – it’s now re-emerged in the Democratic Republic of the Congo. Leigh Cowart joins the hunt for its hiding place.
There was a certain kind of quiet hopefulness when, in late April 2016, the last Ebola patient of the West African epidemic – a two-year-old boy – walked out of a treatment facility in Monrovia, Liberia. With the smouldering embers of the outbreak fading, there was cause for celebration. But there remained the impotent fear of the unseen: Ebola was still out there, lurking. We just didn’t know where it was hiding or when it would be back.
It’s now resurfaced in the Democratic Republic of the Congo, emerging in the country’s rural north-west before spreading to Mbandaka, a city of nearly 350,000. The threat of a new epidemic looms.
Ebola is a zoonotic disease, meaning that it can spread between animals and humans. It burns hot and fast through people. Its ruthless nature means that we are often the end of the line for the virus: a host like us that gets too sick too fast, that dies too quickly, cuts down the virus’s ability to jump into a fresh body. To remain a threat, Ebola needs a safe house in which to lie low and hide.
Such a long-term host, the quiet refuge of a pathogen, is known as a reservoir species. If a reservoir species is Ebola’s safe house, we are its luxury retirement property, a place for it to live out its last days with a bang. The trouble is that we aren’t sure where the safe house is. If we are going to be vigilant against Ebola’s re-emergence, we need to find it.
Searches so far have focused on forested parts of Africa, the home of a number of possible reservoirs. Classically, bats have been considered the most likely culprits, given that they overlap with humans geographically and can carry Ebola infection without symptoms. Based on research that has tested a wide variety of small mammals, bats, primates, insects and amphibians, several species of fruit bat have emerged as possible candidates.
A 2005 study published in Nature and helmed by Eric Leroy tested over 1,000 small vertebrates in central Africa and found evidence of symptomless Ebola infection in three species of fruit bat, suggesting that these animals – which are sometimes hunted for bushmeat – might be Ebola’s reservoir. An editor’s summary ran alongside the paper, titled simply: ‘Ebola virus: don’t eat the bats’.