Circulation of Lassa virus across the endemic Edo-Ondo axis, Nigeria, with cross-species transmission between multimammate mice

ABSTRACT

We phylogenetically compared sequences of the zoonotic Lassa virus (LASV) obtained from Mastomys rodents in seven localities across the highly endemic Edo and Ondo States within Nigeria. Sequencing 1641 nt from the S segment of the virus genome, we resolved clades within lineage II that were either limited to Ebudin and Okhuesan in Edo state (2g-beta) or along Owo-Okeluse-Ifon in Ondo state (2g-gamma). We also found clades within Ekpoma, a relatively large cosmopolitan town in Edo state, that extended into other localities within Edo (2g-alpha) and Ondo (2g-delta). LASV variants from M. natalensis within Ebudin and Ekpoma in Edo State (dated approximately 1961) were more ancient compared to those from Ondo state (approximately 1977), suggesting a broadly east-west virus migration across south-western Nigeria; a pattern not always consistent with LASV sequences derived from humans in the same localities. Additionally, in Ebudin and Ekpoma, LASV sequences between M. natalensis and M. erythroleucus were interspersed on the phylogenetic tree, but those from M. erythroleucus were estimated to emerge more recently (approximately 2005). Overall, our results show that LASV amplification in certain localities (reaching a prevalence as high as 76% in Okeluse), anthropogenically-aided spread of rodent-borne variants amidst the larger towns (involving communal accommodation such as student hostels), and virus-exchange between syntopic M. natalensis and M. erythroleucus rodents (as the latter, a savanna species, encroaches southward into the degraded forest) pose perpetual zoonotic hazard across the Edo-Ondo Lassa fever belt, threatening to accelerate the dissemination of the virus into non endemic areas.

KEYWORDS:

• Lassa virus
• Mastomys
• host-switching
• emergence and spreading
• Nigeria

Acknowledgements

We thank the entire staff of the Lassa Fever Research Institute, Irrua Specialist Teaching Hospital, Irrua, Edo State (ISTH). Among them are Yemisi Ighodalo, Dr Deborah Ehichioya and Godwin Ehielu. Destiny Aigbomian from Edo state also greatly assisted our fieldwork. Within Ondo State, our work was immensely facilitated by Dr Adelabu of Adelabu Hospital, Ifon; the Akogun of Okeluse; and Mrs R. Adeleye and Mrs E. Abejegah of the Federal Medical Centre, Owo. Oleksandra Bondarenko provided excellent technical assistance and Lisa Oestereich helped with Biosafety Level-4 work. Hugo Soubrier graciously lent his expertise to our map creation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was funded by the Deutsche Forschungsgemainschaft (DFG; grants FI 1781/1-1, FI 1781/6-1, GU 883/4-1, GU883/4-2, and OL 419/1-1) and the European Foundation Initiative for African Research into Neglected Tropical Diseases (EFINTD; grants 1/85/022 & 89 540). Sampling in Owo was supported by the Pan-African Network for Rapid Research, Response, Relief and Preparedness for Infectious Disease Epidemics (PANDORA-NET). Award of a Georg-Forster Alexander von Humboldt fellowship to A.O. facilitated aspects of the final analyses and manuscript preparation. ET and CD were supported by the Medical Research Council [grant MC UU 1201412].