Lassa Fever is a zoonotic viral haemorrhagic fever endemic across sub-Saharan western Africa. Zoonotic diseases can be spread from animals to humans. The primary reservoir of Lassa fever is the multimammate mouse, Mastomys natalensis, however new evidence is emerging that other rodents also carry the disease, such as the African wood mouse species Hylomyscus pamfi in Nigeria, and multimammate mouse Mastomys erythroleucus in Guinea. Most infections of Lassa fever occur from direct or indirect contact with infected rodents. Symptoms of Lassa fever in humans include high fever, sore throat and (sometimes) bleeding. Lassa fever can also be spread from human to human through contact with infected fluids, such as blood, although this can be prevented through the use of barrier nursing techniques. As human to human transmission can occur within communities as well as in health-care settings, the level to which appropriate barrier nursing can be used is dependent on local resources, living conditions, and sanitation.
Lassa fever was long considered to be confined to hotspots within Sierra Leone, Liberia, Guinea and Nigeria, forming a so-called ‘Lassa belt’ in the Mano River area. For years, most disease control efforts took place in Sierra Leone. However, over time the disease has spread, and diagnostic capacity has increased. In recent years, cases of Lassa fever have been reported in Benin (2014), Côte d’Ivoire, Ghana, Guinea, Liberia, Mali, Togo (2016), and previously non-endemic areas of Nigeria and Sierra Leone. Recent studies have also found evidence for the growing spread of the disease between the two known Lassa endemic regions indicating that Lassa Fever is more widely distributed throughout the Tropical Wooded Savanna ecozone of West Africa. Epidemiological evidence has estimated that, 10-16% of people in Sierra Leone and Liberia admitted to hospital have Lassa fever. Annual infections of Lassa fever are thought to be in the region of 100,000 – 300,000 with approximately 5,000 deaths. However, this data was collected in the mid 1980s and urgently requires updating. There is no standardised surveillance for Lassa fever across West Africa, and accurate data about current infection rates and disease burden is uncertain.
Further information and ongoing updates on Lassa fever can be found on the Nigeria Centre for disease Control’s Website.