LASSA FEVER - WEST AFRICA (42): NIGERIA

Posted on 20TH OCT 2018
tagged Lassa Fever, West Africa; Nigeria

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Date: Wed 17 Oct 2018
Source: The New England Journal of Medicine [edited]
https://www.nejm.org/doi/full/10.1056/NEJMoa1804498

Siddle KJ, Eromon P, Barnes KG, et al. Genomic analysis of Lassa virus during an increase in cases in Nigeria in 2018.

Summary
During 2018, an unusual increase in Lassa fever cases occurred in Nigeria, raising concern among national and international public health agencies. We analyzed 220 Lassa virus genomes from infected patients, including 129 from the 2017 to 2018 transmission season, to understand the viral populations underpinning the increase. A total of 14 initial genomes from 2018 samples were generated at Redeemer's University in Nigeria, and the findings were shared with the Nigerian Center for Disease Control in real time. We found that the increase in cases was not attributable to a particular Lassa virus strain or sustained by human-to-human transmission. Instead, the data were consistent with ongoing cross-species transmission from local rodent populations. Phylogenetic analysis also revealed extensive viral diversity that was structured according to geography, with major rivers appearing to act as barriers to migration of the rodent reservoir.

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ProMED-mail from HealthMap Alerts

[The 2018 Lassa fever outbreak in Nigeria has been widespread geographically. According to the Nigerian Center for Disease Control, 22 states have recorded at least one confirmed case across 72 local councils. The center reported that 39 healthcare workers have been affected since the onset of the outbreak in 7 states -- Ebonyi (16), Edo (14), Ondo (4), Kogi (2), Nasarawa (1), Taraba (1) and Abia (1), with 10 deaths in Ebonyi (6), Kogi (1), Abia (1), Ondo (1) and Edo (1).

Except for the infected healthcare workers, most affected individuals probably acquired their infections from rodent hosts of the virus. It would be interesting to know whether the prevalence of Lassa fever virus has been increasing in populations of rodent hosts in this wide area. Virus transmission to humans occurs when people are in contact with the reservoir rodent host, the multimammate mouse (_Mastomys natalensis_ and _Mastomys erythroleucus_) and the African wood mouse (_Hylomycus pamfi_) or their excreta, as was likely the situation in these cases. Rodent control must be undertaken at the village level with individual households using preventive measures. This requires an extensive and continuous public education effort.

Images of the 3 rodent reservoir hosts of Lassa fever virus can be seen for _M. natalensis_ mouse at https://www.inaturalist.org/taxa/45326-Mastomys-natalensis and _M. erythroleucus_ and _H. pamfi_ at http://punchng.com/nigerias-large-rat-population-threatens-lassa-fever-war/. - Mod.TY

Maps of Nigeria:
http://www.un.org/Depts/Cartographic/map/profile/nigeria.pdf
http://healthmap.org/promed/p/26098]

See Also
Lassa fever - West Africa (41): Nigeria 20180815.5967485
Lassa fever - West Africa (40): Nigeria (EN) 20180809.5955565
Lassa fever - West Africa (39): Nigeria (ED) 20180727.5931747
Lassa fever - West Africa (38): Nigeria 20180717.5909251
Lassa fever - West Africa (36): Nigeria (ON) 20180701.5884285
Lassa fever - West Africa (34): Nigeria 20180617.5859861
Lassa fever - West Africa (31): Nigeria 20180605.5840563
Lassa fever - West Africa (29): Nigeria 20180530.5829096
Lassa fever - West Africa (26): Nigeria 20180509.5790856
Lassa fever - West Africa (25): WHO Nigeria 20180422.5761965
Lassa fever - West Africa (23): Liberia, WHO 20180417.5753003
Lassa fever - West Africa (22): Nigeria 20180410.5738206
Lassa fever - West Africa (21): Nigeria 20180406.5727850
Lassa fever - West Africa (20): Nigeria 20180327.5714291
Lassa fever - West Africa (19): Nigeria 20180315.5687321
Lassa fever - West Africa (18): Nigeria (BA) 20180313.5683816
Lassa fever - West Africa (16): Nigeria 20180306.5670231
Lassa fever - West Africa (14): Nigeria 20180228.5655382
Lassa fever - West Africa (13): Nigeria 20180222.5645501
Lassa fever - West Africa (12): Nigeria 20180221.5641157
Lassa fever - West Africa (11): Nigeria, WHO 20180215.5629350
Lassa fever - West Africa (10): Nigeria 20180212.5622070
Lassa fever - West Africa (07): Nigeria 20180206.5608967
Lassa fever - West Africa (06): Nigeria (DE, ON) 20180201.5600192
Lassa fever - West Africa (05): Nigeria 20180131.5597457
Lassa fever - West Africa (04): Nigeria 20180125.5585380
Lassa fever - West Africa (03): Benin (AK) ex Nigeria, WHO 20180124.5581805
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