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Arenaviridae

RNA virus family including Lassa and Junin; WHO Blueprint roadmap published 12 March 2026, relevant to Argentina's Pampas.

Last refreshed: 7 May 2026

Key Question

With Argentina facing both Andes hantavirus and Junin arenavirus, is the Pampas the world's densest zoonotic spillover zone?

Timeline for Arenaviridae

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Common Questions
What is Lassa fever and how is it related to other haemorrhagic viruses?
Lassa fever is caused by Lassa virus, an arenavirus endemic in West Africa, estimated to cause 100,000-300,000 infections and 5,000 deaths per year. Arenaviruses also include Junin in Argentina and Machupo in Bolivia.
Why is Argentina particularly exposed to two types of haemorrhagic virus?
Argentina faces Andes hantavirus in Patagonia and Junin arenavirus in the Pampas grain belt, both rodent-borne and both on the WHO R&D Blueprint priority list, making it one of the world's denser zoonotic spillover environments.Source: WHO R&D Blueprint
What did the WHO publish on Lassa and Junin fever in 2026?
The WHO R&D Blueprint published an Arenaviridae medical countermeasure roadmap on 12 March 2026, covering Lassa, Junin and other pathogenic family members. Consultation remains open through late May.Source: WHO R&D Blueprint

Background

Arenaviridae (arenaviruses) are a family of negative-sense, ambisense RNA viruses that include several significant haemorrhagic fever pathogens. The family divides into Old World arenaviruses (including Lassa virus, endemic in West Africa, with an estimated 100,000 to 300,000 cases and 5,000 deaths per year) and New World arenaviruses (including Junin virus in Argentina, Machupo in Bolivia, and Sabia in Brazil). Rodents are the primary reservoir host for all known pathogenic arenaviruses; human infections typically result from contact with infected rodent excreta. Arenaviruses are on the WHO R&D Blueprint priority list due to the high mortality of severe Lassa disease, the geographic spread of New World variants, and the absence of licensed therapeutics beyond the off-label use of ribavirin.

The WHO R&D Blueprint published its Arenaviridae medical countermeasure roadmap on 12 March 2026, covering Lassa, Junin, and other pathogenic family members. The roadmap is geographically pertinent to the MV Hondius briefing: Argentina faces both Andes virus (a hantavirus) in Patagonia and Junin virus (an arenavirus) in the Pampas grain belt, making it one of the world's denser zoonotic spillover environments. Public consultation on the Arenaviridae roadmap remains open through late May 2026. For Lowdown's pandemics coverage, the Arenaviridae roadmap connects the Southern Cone hantavirus signal documented in the PAHO December 2025 alert with a broader landscape in which Argentina sits at the intersection of two WHO Blueprint priority pathogen families.

Source Material
WHO R&D Blueprint — Arenaviridae RoadmapArenaviridae