Rodent control strategies and Lassa virus: some unexpected effects in Guinea, West Africa

ABSTRACT

The Natal multimammate mouse (Mastomys natalensis) is the host of Lassa mammarenavirus, causing Lassa haemorrhagic fever in West Africa. As there is currently no operational vaccine and therapeutic drugs are limited, we explored rodent control as an alternative to prevent Lassa virus spillover in Upper Guinea, where the disease is highly endemic in rural areas. In a seven-year experiment, we distributed rodenticides for 10–30 days once a year and, in the last year, added intensive snap trapping for three months in all the houses of one village. We also captured rodents both before and after the intervention period to assess their effectiveness by examining alterations in trapping success and infection rates (Lassa virus RNA and IgG antibodies). We found that both interventions reduced the rodent population by 74–92% but swiftly rebounded to pre-treatment levels, even already six months after the last snap-trapping control. Furthermore, while we observed that chemical control modestly decreased Lassa virus infection rates annually (a reduction of 5% in seroprevalence per year), the intensive trapping unexpectedly led to a significantly higher infection rate (from a seroprevalence of 28% before to 67% after snap trapping control). After seven years, we conclude that annual chemical control, alone or with intensive trapping, is ineffective and sometimes counterproductive in preventing Lassa virus spillover in rural villages. These unexpected findings may result from density-dependent breeding compensation following culling and the survival of a small percentage of chronically infected rodents that may spread the virus to a new susceptible generation of mice.

KEYWORDS:

• Lassa virus
• anticoagulant rodenticides
• snap trapping
• integrated pest management
• Mastomys natalensis
• Guinea
• West Africa

Acknowledgements

We are particularly grateful to the field assistants of the Projet des Fièvres Hémorragiques en Guinée, who participated in the rodent sampling: Amara Camara, Mamadou Condé, Moussa Fofana, Morlaye Sylla and Mohamed Traoré. We thank Dr Mory Cherif, who facilitated the fieldwork through his constant medical support toward the communities. We also thank Dr Mami Cécé Gowara, Directeur Régional de la Santé, Dr N’Faly Bangoura, Directeur Préfectoral and Sayon Oulare who facilitated our work in the Faranah prefecture.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Author statement

Conceived the study: JM, MS and EFC. Wrote the paper: JM. Performed the experiments: JM, MS, UB, MK, TR, BS, and EFC. Performed the statistical analyses: JM and AL. Supervised field and laboratory work: MS, MD, NM, and EFC. Funding acquisition: NM and EFC. All authors read and approved the final manuscript.

Additional information

Funding

The research was funded by the German Research Foundation (DFG FI 1781/1&2-1, and BO 3790/1&2/1) and by the University of Antwerp and the Antwerp Study Centre for Disease (ASCID) Grant Number GOA BOF FFB3567. During the period of the study, Joachim Mariën was a member of the Outbreak Research Team of the Institute of Tropical Medicine, which is funded by the Department of Economy, Science and Innovation of the Flemish government in Belgium (EE145 4150).