Ten years ago, the haemorrhagic Ebola virus devastated this region, killing over 11,000 people across Guinea, Sierra Leone and Liberia.
In Kenema district, an early Ebola epicentre, scientists are using the lessons learned a decade ago to try to stop new Lassa fever in its tracks.
With an overall fatality rate of one percent, Lassa is nowhere near as deadly as Ebola, which kills on average 50 per cent of sufferers, according to the World Health Organization.
But one in five Lassa infections can result in severe illness with a fatality rate of 15 per cent.
While cases have largely plateaued in Sierra Leone, researchers are seeing a spread beyond traditional Lassa hotspots.
There is no licensed vaccine and only limited treatment, with the scars of Ebola preventing many from seeking early life-saving help.
Monitoring the rodent population is crucial in remote villages like Mapuma, where some 20 houses lie enveloped by dense forest.
Humans usually contract Lassa virus after having contact with the urine, saliva or droppings of infected rats.
Proximity to the forest, rudimentary mud construction, and uncovered grain and water storage make the dwellings 鈥榝ive-star hotels鈥� for rats, said Lansana Kanneh, 58, field supervisor at the region鈥檚 Kenema Government Hospital (KGH).
Trappers can find up to 20 rats per day in some villages.
After identifying if the rodents are the Lassa-carrying Mastomys variety, samples are collected for analysis.
The rats then receive an injection that prevents viral transmission before being released.聽聽
Lassa virus infects between 100,000 and 300,000 people annually in West Africa, killing roughly 5,000, according to the Africa Centres for Disease Control and Prevention.
But the figures likely underestimate the true scale given surveillance challenges.
Admissions to the Lassa unit at KGH -- Sierra Leone鈥檚 only dedicated treatment centre -鈥� have declined in the past decade.
Patients normally arrive in the 14-bed isolation ward during the dry season from November to May, but this once-predictable pattern is increasingly uncertain.