Lassa

Lassa fever is the human disease caused by Lassa virus (LASV), which is identified in the sources as a RNA virus belonging to the Arenaviridae family ^[1]. The condition is characterized in the supplied material as a viral haemorrhagic fever ^[2]. The sources also note that it was recognized as the causative agent of Lassa fever and that the disease remains a continuing public-health concern in West Africa ^[1][2].

The available sources characterize Lassa fever as a viral haemorrhagic fever associated with a high case fatality rate ^[2]. One review notes that the clinical course is discussed in the broader literature, but the provided snippets do not specify the symptom sequence, organ involvement, or timing of complications ^[2]. No source-backed detail on case definitions, distinguishing clinical signs, or sequelae is available in the current payload ^[2][1].

Lassa virus is described as endemic in the rodent populations of Sierra Leone, Nigeria, and other countries in West Africa ^[2]. The disease is said to spill over to humans frequently, and one review estimates that Lassa fever affects some 100,000 people annually ^[2][1]. The supplied sources also note more frequent outbreaks, the potential for geographic expansion of rodent reservoirs, and frequent importation of LASV to North America and Europe ^[2].

The sources support zoonotic spillover from rodent reservoirs to humans as the principal exposure mechanism described here ^[2]. LASV is said to be maintained in rodent populations, including Mastomys natalensis and other rodent reservoirs, with frequent spillover causing human infection ^[2]. No source-backed detail on specific contact routes, person-to-person transmission, or environmental persistence is available in the provided snippets ^[2].

The sources directly identify rodent populations, including reservoirs such as Mastomys natalensis, as the ecological host context for LASV ^[2]. For humans, the snippets only establish that spillover occurs frequently and can lead to severe disease, but they do not specify occupational, age-related, pregnancy-related, or other high-risk groups ^[2][1]. Source-backed detail on vulnerable human subpopulations is not yet available in the provided payload ^[2][1].

The supplied sources indicate that no approved vaccines or therapeutics for human use are available yet ^[2]. They also note active efforts to develop countermeasures, reflecting ongoing prevention research rather than an established public-health package ^[2]. Source-backed detail on specific exposure-control measures, vaccination policy, or community prevention practices is not yet available ^[2].

In surveillance terms, Lassa fever should be interpreted as an endemic West African zoonotic viral haemorrhagic fever with documented spillover into humans and potential for exportation beyond the region ^[2][1]. The available sources emphasize recurrent outbreaks, emergence of novel LASV strains, and the possibility of wider geographic spread of rodent reservoirs, all of which support close monitoring ^[2]. However, the provided material does not supply standardized reporting criteria or case ascertainment guidance ^[2][1].

1. 1 Günther S et al. Lassa virus. Crit Rev Clin Lab Sci. 2004. PMID: 15487592. doi: 10.1080/10408360490497456. PubMed: https://pubmed.ncbi.nlm.nih.gov/15487592/
2. 2 Garry RF et al. Lassa fever - the road ahead. Nat Rev Microbiol. 2023 Feb. PMID: 36097163. doi: 10.1038/s41579-022-00789-8. PubMed: https://pubmed.ncbi.nlm.nih.gov/36097163/
3. 3 Houlihan C et al. Lassa fever. BMJ. 2017 Jul 12. PMID: 28701331. doi: 10.1136/bmj.j2986. PubMed: https://pubmed.ncbi.nlm.nih.gov/28701331/
4. 4 Lassa fever. Definitions. 2020. doi: 10.32388/14rz8j. DOI: https://doi.org/10.32388/14rz8j
5. 5 Lassa fever. Journal of the Japanese Association for Infectious Diseases. 1977. doi: 10.11150/kansenshogakuzasshi1970.51.85. DOI: https://doi.org/10.11150/kansenshogakuzasshi1970.51.85
6. 6 Lassa Fever. Clinical Guide to Bioweapons and Chemical Agents. None. doi: 10.1007/978-1-84628-787-9_24. DOI: https://doi.org/10.1007/978-1-84628-787-9_24

ICD-10

A96.2

ICD-11

1D61

Total cases

1

Peak month

2026-01

Coverage

4 reporting countries · 2026-01-01 → 2023-03-25