世界卫生组织快速风险评估——尼帕病毒——全球——第1版

Dateandversionof current assessment:Date(s)and version(s)of previous assessment(s): Overall Global risk and confidence Risk Statement This Rapid Risk Assessment (RRA) evaluates the global public health risk posed by Nipah virus (NiV),consideringthe distinctepidemiological profiles of i) enzootic countries, where recurrent zoonotic spillover and limited human‑to‑human transmissioncontinue to occur, and ii) non‑enzootic regions, where the risk remains primarily associated with infected travellers or importationof infected livestock. The assessment considers the ecological and seasonal drivers of spillover, the constrained efficiency ofhuman‑to‑human transmission, and the capacity of health and community systems to detect, confirm, and rapidly containoutbreaks. Given that NiV has not demonstrated sustained transmission beyond outbreak settings and no human cases have everbeen reported outside Asia, the global risk is largely determined by localized outbreaks in endemic areas and the very lowlikelihood of onward transmission following importation. NiV activity remains geographically limited, with human cases occurring primarily in the South-East Asia Region with limitedoutbreaks in the Western Pacific Region. The epidemiological profile of NiV is characterized by low frequency, localized outbreaks,occurring predominantly in Bangladesh and India, with additional historical events reported in Malaysia, Singapore, and thePhilippines. Bangladesh has reported sporadic cases almost annually since 2001, largely associated with consumption of raw datepalm sap, following a well‑defined seasonal pattern between December and April. India reported its first outbreak in 2001 andhas documented near-annual cases in Kerala since 2018 with sporadic cases reported in West Bengal. In 2025, eightlaboratory‑confirmed cases were detected across Bangladesh (four) and India (four). As of March 2026, three sporadic cases havebeen reported in the two countries, two in India and one in Bangladesh. Malaysia (1998–1999), Singapore (1999), and thePhilippines (2014) experienced outbreaks previously but have not reported any additional NiV events recently. Although NiV has a high case‑fatality ratio (40–75%), transmission remains limited in scale, typically arising from isolated spilloverevents linked to fruit bats, contaminated fruits or fruit products, or occasionally infected livestock. Human‑to‑human transmissionhas been documented, particularly in Bangladesh and India. However, sustained community transmission or multi‑country spreadhas never been observed. KEY RISK FACTORS 1. Risk to Enzootic Countries•Sporadic zoonotic spillover events occur due to contact with infected bats or consumption of contaminated fruits or fruit products.•Serological evidence of NiV circulation beyond affected areas in Bangladesh and India (Kerala and West Bengal), suggestthat spillover could potentially occur in other areas where infected bats are present.•Human‑to‑human transmission, although documented, is limited to close contacts and has not resulted in widespreadcommunity transmission.•The case‑fatality ratio is high; however, the total number of reported cases remains low.•Health care settings may amplify transmission when infection prevention and control (IPC) measures are insufficient.•Spillover from other susceptible animal hosts (pigs, horses) cannot be ruled out, nor the risk of importation throughinfected livestock, though probably very low. 2. Risk to Non‑Enzootic Regions (reservoirs may be present; no human cases to date)•Risk is primarily associated with an infected traveller. •No human NiV transmission has ever been reported outside affected Asian countries.•In settings without established animal reservoirs or intermediate hosts, onward transmission following importation isunlikely and would require close, prolonged contact. •Historical spread via movement of infected animals (e.g., pigs exported from Malaysia to Singapore in 1999)demonstrates that animal trade–related spillover is possible, however current evidence suggests that the risk underpresent animal‑health and trade practices is likely very low. 3. Risk to Countries Without Known Bat Reservoirs (reservoirs absent; no human cases) •Importation via travellers (and, exceptionally, livestock) may occur and while secondary transmission is possible it isunlikely, given the absence of established animal reservoirs and the need for close contact for human‑to‑human spread.4. Risk to Travellers •Travellers to affected areas face a very low but non‑zero risk, particularly if they have direct exposure to fruit bats,consume contaminated food products, or come into contact with other infected animals, including pigs or horses.•Returning infected travellers pose a limited risk of onward transmission due to low NiV transmissibility.5. Risk Determinants •Ecological presence ofPteropodidaebats in enzootic countries.•Presence of potential intermediary hosts that could transmit to humans (