I'm in a village in eastern Sierra Leone staring at a row of dead rats snared in branches, leaves and grass. The contraptions are called funnel traps, or tolei in the local Mende dialect. We're hoping these devices and other easily accessible or producible materials will lower the rodent populations in villages sufficiently to prevent Lassa fever.
With a DfID-funded project called Wash (water, sanitation health), Facility Sierra Leone, Tulane University and Kenema Government Hospital are working in 20 villages introducing Lassa fever education and rodent control training. For the project to be successful, we have to control one of the most ubiquitous rodents in sub-Saharan Africa, Mastomys natalensis — the multimammate rat.
Lassa fever is common in this part of the country where the disease can wipe out entire households and cause panic throughout villages. The disease has a gradual onset of fever, aches and pains that are indistinguishable from malaria or typhoid — diseases as familiar to villagers as the common cold.
For some, Lassa fever will progress from these non-specific symptoms to sore throat, facial oedema, haemorrhaging and death. Although Lassa fever and its severe consequences are well-known by residents in this region, fewer know the rat that commonly infests their homes can spread the disease.
I work with a team based out of KGH. This is the Sierra Leone ministry of health and sanitation's main hub for Lassa fever activities and the only place in the entire country a person can go for laboratory testing and treatment. For the past four years, I've had the privilege of working with five members of the community outreach and disease ecology units based there. We are trying to turn their combined 115-plus years of experience working on Lassa fever into strategies to control the disease.
We think that connecting the dots from rat to Lassa fever in at-risk communities will mobilise residents. With some training and monitoring, maybe we can make a dent in the burden of this disease.
We're using the WHO guidelines for control of Lassa fever which include the use of food storage containers and cats along with other interventions such as house repairs and rodent extermination. Eventually, we hope to integrate these methods into sanitation and hygiene programmes, such as community-led total sanitation campaigns, throughout Sierra Leone.
The reality is we don't yet know what will work to reduce Mastomys to prevent Lassa fever at the community level. The virus was first identified in 1969 and the rodent as harbouring the virus (that is, being its 'reservoir') in 1973. Lassa virus is among the 'viral haemorrhagic fevers' — the terrifying group of viruses that people make movies and write books about. These diseases get attention, not because of the disease burden in endemic countries, but because of the fear they induce in wealthier nations — the fear that a deadly virus will emerge out of Africa (accidentally or intentionally) and cause mass hysteria, morbidity and mortality.
Expenditures for Lassa fever research have reflected this perspective and have concentrated on detection, vaccine development and treatment rather than prevention and control in endemic areas. So here we are, 40 years after the reservoir was identified, without one empirical piece of evidence on how to prevent Lassa fever and very limited information on how the virus is maintained in rodent populations.
Many are sceptical Lassa fever can be prevented with rodent control, maintaining that for sustained reduction we need a vaccine. Yet vaccine development of a neglected disease only endemic in west Africa seems unlikely in the near future. The US Centers for Disease Control and Prevention, an organisation that studied Lassa fever from the early 1970s to 2003, states "the complete control of this rodent is impractical."
In the meantime, more and more cases are reported from Sierra Leone and Nigeria, where the disease is also endemic. The only strategy we now have in our toolbox is good old-fashioned sanitation and hygiene.