Unprecedented Upsurge of Lassa fever cases in Nigeria, January to March 2018: a glimpse of hope

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Lassa fever is an acute viral hemorrhagic fever (VHF) endemic in Nigeria. The 2018 massive wave of confirmed cases of Lassa fever in Nigeria raised the important question, whether the “outbreak” was due to a new virus variant, improved case detection/ diagnosis or a combination of these factors. We therefore described the likely causes of the 2018 upsurge of Lassa fever cases in Nigeria.
The national Lassa fever 2017 and 2018 data was extracted from the VHF case-investigation-form database and analysed. Genomic sequencing was carried out on positive Lassa fever samples. Key informant interviews were conducted for national Lassa fever multisectoral multi-partner Emergency Operation Centre (EOC) leads and stake- holders. One-health approach was used to ensure implementation of human, animal and environmental interventions.
A total of 394 confirmed cases were recorded in the first 12 weeks of 2018 compared to 107 reported in the same period in 2017. The case-fatality-rate decline from 44% in 2017 to 26% in 2018. Majority (81%) of all confirmed cases were reported from three historical hotspot states. Age-group 21-40(44%) were mostly affected with a male to female ratio of 2:1. Results: from viral sequencing yielded no indication of new circulating viruses. Phylogeny points to multiple zoonotic infections not extended person-to-person transmission. Key informant interview Results: revealed improved case detection, increased diagnosis, heightened awareness due to increased risk communication activities and enhanced one health response coordination by Nigeria Centre for Disease Control (NCDC).
The 2018 upsurge of Lassa fever cases in Nigeria was certainly multifactorial, however, not due to new virus strain. A coordinated one health EOC response approach ensured robust reporting of case and less severe outcome of disease giving a glimpse of hope in the outbreak control .We therefore recommended to NCDC to conduct Lassa fever modeling and research to identify the possible role of increased rodent population and ecological factors in the large outbreak.

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