Lassa Fever in Guinea and Sierra Leone: rodent-human cohabitation and disease control (LAROCS 2)

• Applicants: Matthias Borchert, Ph.D.; Dr. Elisabeth Fichet-Calvet
• Subject Area: Virology ; Epidemiology and Medical Biometry/Statistics ; Ecology and Biodiversity of Animals and Ecosystems, Organismic Interactions ; Public Health, Healthcare Research, Social and Occupational Medicine
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 299194041

Lassa fever is a viral haemorrhagic fever endemic in the Mano River region (Guinea, Sierra Leone and Liberia) and Nigeria, affecting 200,000-300,000 persons with 5,000-10,000 fatalities per year. Its case-fatality is low (1 2%) in communities of endemic areas, but reaches 50% in hospitalised patients during outbreaks. Lassa virus has a rodent reservoir, Mastomys natalensis, and is transmitted to humans through contact with Mastomys, their body fluids or droppings and possibly by aerosol. Human to human transmission occurs in the community and in health care settings. Treatment options are limited. Intravenous ribavirin improves survival in Lassa patients and is available in Sierra Leone, but not in Guinea. There is no vaccine, so that prevention of primary transmission has to be based on reducing the contact between humans and infectious Mastomys. From earlier studies in Guinea we know that Mastomys probably aggregates in houses during the dry season, thus presumably increasing the risk for transmission to humans. The investigation whether the same seasonal pattern exists in Eastern Sierra Leone is ongoing. In Guinea we test the hypothesis that reducing Mastomys abundance decreases the chance of transmission between adult Mastomys and thus the prevalence of Lassa virus in the Mastomys population, so that rodent elimination reduces the primary transmission of Lassa virus to humans by reducing contact with Mastomys and by decreasing the probability that the Mastomys is infected. We have found that villagers in Guinea view rodent elimination favourably for health reasons, for avoiding damage to stored food and for reducing nocturnal disturbances; they anticipate that poisoning will not be sufficient to eliminate rodents, and are willing to make behavioural changes to enhance the effectiveness of rodent elimination. The role of rodents as food source requires further investigation in the second phase. Furthermore, in Guinea we have found a very high Lassa IgG seroprevalence. During LAROCS 2 we suggest for Guinea to continue the investigation of the effectiveness of rodent elimination, and to explore options for complementary behavioural interventions. Rodent dispersal between houses and their surroundings will be examined. Given the high seroprevalence in humans we plan to investigate the Lassa disease burden among health facility users. In Sierra Leone we plan to estimate Lassa seroprevalence by age and sex, and to explore whether rodent elimination is promising, feasible and acceptable. In both countries we suggest to study Lassa virus migration, environmental including airborne transmission, household determinants of rodent-to-human transmission of Lassa virus, perceptions and attitudes towards various ways of rodent elimination and how the Ebola outbreak has shaped people attitudes towards zoonotic disease risk.

• DFG Programme: Research Grants
• International Connection: Belgium, Guinea, Sierra Leone, United Kingdom
• Cooperation Partners: Schadrac Agbla; Professor Steven Belmain, Ph.D.; Pepe Bilivogui; Professorin Hannah Brown; Professor Simon Cousens; Roger Hewson, Ph.D.; Ann H. Kelly, Ph.D.; Professor Dr. Herwig Leirs; Dr. Lisa Oestereich
• Co-Investigator: Professor Dr. Stephan Günther
• International Co-Applicants: NFaly Magassouba; Professor Foday Sahr, Ph.D.