It’s 6am on a warm May morning and I am waiting for the sunrise and a truck to take me to Missira, a village on the Guinean coast. I’m travelling with a team from the national programme fighting sleeping sickness – they’ve been visiting villages in the area for the past two weeks and this is their last day in the field.

We bounce along rust-red roads, stopping only to pick up some bread along the way. Since gaining independence in 1958, Guinea has retained some French culture, not least its official language and a love of freshly baked baguettes. We pass many bikes and motorbikes on the early-morning roads with loaves sprouting out of their panniers. These, along with a cup of instant coffee and a bit of cheese, are the basis of our breakfast when we finally reach Missira around 8am.

I learn later that another name for sleeping sickness here translates as “the sickness at the end of the track” – and Missira is literally at the end of the track, for the road leads straight to the edge of the Atlantic Ocean. We’re close to the mangroves where people hunt, fish and grow crops. Mangroves are also home to tsetse flies, which carry the sleeping sickness parasite and whose bites are the source of all human infections. And that’s why we’re here today – to test everyone in Missira for signs of the parasites in their blood.

The team – 10 or 12 scientists, health workers and local representatives, all but one from Guinea – get smoothly on with setting up for the day. Tables form stations for every stage of the process: registration, then a finger-prick to take blood, the test itself, and somewhere more private for a consultation with the nurse if the test is positive. Here, the nurse will check for swollen lymph nodes in the neck, before they take more blood to try and spot parasites wriggling about under the microscope.

These field tests aren’t perfect, although they are relatively accurate considering they can be done anywhere there’s a power source (a car battery is enough). But not everyone who tests positive will actually be infected. Some will be false positives, while others may have antibodies to the parasites – which are what the test detects – but not any actual parasites in their blood. So anyone who tests positive today will be invited to the clinic in Forécariah for more tests and only then – if required – receive treatment.

© Antoine Nogueira

This approach, which is how Camara was diagnosed a few days ago, is called active surveillance. Unlike passive surveillance, which relies on having the capacity to diagnose and treat people who come to a health centre with symptoms, active surveillance means regularly testing everyone in specific areas. In other countries, when cases of sleeping sickness have fallen to similarly low levels, the World Health Organization (WHO) has recommended that passive surveillance is enough. But the man in charge of fighting sleeping sickness in Guinea wants to keep throwing everything he can at the disease because he knows what will happen if they step back before it has been eliminated.

Mamadou Camara, no relation to Ibrahima, is a biologist and director of Guinea’s programme against sleeping sickness. He tells me that the disease has been recognised as a major problem for decades.

It killed millions of people in the 20th century, in a series of devastating epidemics as well as the slower, persistent death tolls of endemic disease. In the 1940s, the number of reported cases across Africa was around 50,000 a year, with the real number likely to have been much higher. By the end of the 1960s, after sustained internationally supported efforts dropping insecticide from aircraft to kill the flies, and culling wild animals suspected of harbouring the disease, cases of sleeping sickness fell to just 5,000 a year.

But leaving that small foothold for the disease proved a disastrous mistake. By the 1990s, cases of sleeping sickness had soared back almost to the levels of 50 years earlier. Was there something we hadn’t understood about this infection? And will that same gap in our knowledge stop us eliminating sleeping sickness this time around, too? A 2017 Lancet article says that neglecting sleeping sickness, “either because of social or political instability or the tyranny of success, will inevitably lead to resurgence”.

Active surveillance has been enough to get rid of the infection in many countries and regions since the 1990s. But in three small areas of Guinea, including the villages around Forécariah, the disease just won’t die out. The national programme here now includes vector control – targeted ways to trap and kill tsetse flies – which has helped, but there always seem to be a few more cases cropping up. Since 2004, there have been between 50 and 100 reported cases a year in Guinea. There was a dip to 33 in 2014 and just 29 in 2015, but this was due to under-reporting during the Ebola epidemic. In 2016, after the end of Ebola, 107 cases were reported – the highest for 13 years.

Camara says the disease is back under control now, thanks to the actions of his team, the ministry of health, and the international partners who provide resources for surveillance and vector control as well as funding research to better understand the parasite and how it spreads.

Jose Franco is the WHO’s Medical Officer for the Department of Control of Neglected Tropical Diseases. He says that, although it can be hard to keep pushing when cases fall so low, it is not the number of cases being treated that should be counted but “the number of cases you are avoiding”.

“You are always working,” he explains. “Detecting cases, treating them, and complementing in some areas with vector control… In some countries, they are not detecting cases for some time, they have a good health system, then in these cases we are now working more in setting up a surveillance system, mainly based on passive screening.

“We have to adapt these strategies according to the evolution of the disease and the evolution of the country.”

The WHO’s current aim is to eliminate the disease in 80 per cent of endemic areas by 2020. In this instance, “elimination” is a technical term, meaning transmission is so low that it is no longer a public health problem in the country. It doesn’t mean there are zero cases – and this worries Camara, because he knows that history shows it can always come roaring back.

So as well as active surveillance and vector control, Camara is a big supporter of more scientific research into sleeping sickness, to figure out why it is clinging on in Guinea, and whether a change in approach could help them make further progress – and, maybe one day, eradicate it altogether.

Somewhat surprisingly, there are no positive results in Missira today, meaning no one has to come back to the clinic for more tests. Over the fortnight that the team have been testing villages around Forécariah, around 25 people have been invited to go to the treatment centre in town. They will all arrive there tomorrow for further tests, and treatment if they need it. While they are there, if they are willing, they can also take part in research to test a new hypothesis about sleeping sickness and just why it is proving so stubborn in Guinea.