Nigeria Carries 70% of Global Lassa Fever Burden, Review Finds

Nigeria accounts for approximately 70% of the global Lassa fever disease burden, and a new systematic review of 38 studies shows why transmission persists: human behavior, rodent ecology and environmental change reinforce one another faster than any single intervention can break the cycle.

The review, published in BMC Public Health and registered with PROSPERO as CRD420261436085, analyzed studies published from January 2000 through March 2025. Olaiya and colleagues searched five databases — PubMed, Scopus, Web of Science, African Journals Online and Google Scholar — plus grey literature, screened 612 records, and appraised quality with Critical Appraisal Skills Programme and Joanna Briggs Institute checklists before synthesizing findings thematically under PRISMA 2020 guidelines.

The headline for clinicians and public-health teams is consistency. Human behaviors and health-care conditions emerged as the most reliably documented determinants across two decades of evidence.

Which risk factors carried the strongest evidence?

The included studies most consistently reported four human-side exposures:

• open food storage in households;
• occupational exposure;
• poor household hygiene;
• nosocomial transmission in facilities lacking adequate infection prevention and control.

The nosocomial finding deserves attention at the exam table and beyond it. Health-care settings, the evidence shows, can sustain person-to-person transmission when containment is deficient, which makes IPC capacity a frontline variable rather than an administrative afterthought.

What role does the reservoir rodent play?

The animal evidence converged on Mastomys natalensis, the rodent implicated as the reservoir of Lassa virus, and specifically on its peri-domestic ecology. Rodent density correlated strongly with human exposure. The virus moves where the rodents live, and the rodents live near people.

Environmental conditions acted as amplifiers rather than isolated causes. Poor housing, inadequate waste management, deforestation, climate variability and peri-urban expansion each widened contact opportunities between humans, rodents and virus. The review's model is explicitly interconnected: no single determinant explains endemicity, and the synthesis does not claim equal weight for every reported factor.

Where and when does risk concentrate?

Spatial analyses within the reviewed literature identified perennial hotspots in four states: Edo, Ondo, Ebonyi and Plateau. Seasonal peaks arrive at the end of the rainy season. The review also documents thousands of deaths across annual outbreaks, a figure that underscores how little endemic status alone has done to curb transmission.

The authors are candid about limits. The evidence base is heterogeneous, drawn from different locations and domains, so the synthesis cannot quantify a single population-wide effect. What it does establish is that several determinants operate simultaneously across human, animal and environmental systems.

What does the review recommend?

The authors call for an integrated One Health approach rather than reliance on any one intervention. Their recommendations span six areas:

• strengthened infection prevention and control;
• improved diagnostics;
• community-based rodent-proofing and sanitation programs;
• coordinated surveillance across humans, animals and environments;
• culturally tailored risk communication;
• sustained domestic financing.

These measures carry no trial-level backing within the review itself. The authors neither tested the package in a clinical trial nor demonstrated that it will reduce deaths. The contribution is consolidation: the review assembles the available empirical evidence and reframes persistent endemicity as the product of converging determinants.

For veterinary readers, the practical takeaway sits in the surveillance and rodent-ecology findings. Coordinated monitoring that includes reservoir populations, not only human cases, gives practitioners and public-health authorities the shared evidence base that Nigeria's 70% share of global burden now demands.