2022-02-07-世界卫生组织-Zika_epidemiology_update_-_February_2022_8页_253kb

Zika Virus Epidemiology Update Summary

Global Overview

• As of Dec 2021, 89 countries/territories documented autochthonous (local, mosquito-borne) Zika virus (ZIKV) transmission across 5 WHO regions.
• Bangladesh and Cuba added to list since 2019 update.
• Indian states Kerala and Maharashtra experienced ZIKV outbreaks in 2021, indicating wider circulation within Southeast Asia.
• Pre-existing immunity, particularly to Dengue virus (DENV), likely limits re-emergence potential in previously infected areas.
• Areas with past transmission remain at risk.
• Global spread of ZIKV, characterized by two main lineages (African and Asian, with numerous sub-lineages), shows varied epidemic potential and pathogenicity.

Regional Assessment (Focus Areas)

• Americas: Highest region by number of annual cases. Brazil is the main country reporting cases (suspected vs confirmed), with very low cumulative incidence but heterogeneity. Surveillance inconsistent.
• East Mediterranean: No autochthonous transmission reported, but vector potential exists and preparedness plans in place.
• Europe: No autochthonous transmission since 2019 (France cluster); relies on surveillance and control.
• South-East Asia: Widespread vector presence. India saw a significant 2021 outbreak beyond prior cases. Need better surveillance.
• Africa: Limited current incidence data. Kenya had new serological evidence of autochthonous transmission recently. Similar to other regions, complications like congenital Zika syndrome (CZS) remain a concern.
• Western Pacific: Limited data; one probable case of ZIKV-associated microcephaly reported from Laos. No sustained local transmission sustained.

Virus Biology

• Phylodynamics tracks ZIKV spread from Africa/Asia to American outbreak in 2015-16.
• Genetic lineage (African vs. Asian/American) is linked to different surveillance characteristics (cross-reactivity) but epidemiology and pathogenicity impact unclear for some strains.

Monitoring, Challenges, and Recommendations

• Most infections are asymptomatic or mild, hindering case detection.
• Surveillance systems are often weak or absent.
• Incidence during normal times based on clinical cases, travelers, and research.
• Laboratory assays are challenging due to limitations in testing availability, interpretation difficulties (especially cross-reactivity with DENV), and resource constraints.
• The COVID-19 pandemic significantly hampered ZIKV control efforts due to diverted resources and reduced healthcare-seeking behavior.
• Decisions regarding travel and family planning should be based on updated national public health department information.

WHO Actions

WHO remains committed to strengthening public health systems, surveillance (including CZS/Guillain-Barré), laboratory capacity, and response capabilities for ZIKV and other Aedes-borne arboviruses worldwide.

Summary: Updated epidemiological data indicates ongoing risk for Zika virus transmission in several countries across global regions that previously experienced or still experience outbreaks. While the intensity of transmission is generally low outside affected areas, weaknesses in surveillance and diagnostic capacity, exacerbated by the COVID-19 pandemic, may mean activity goes undetected. Some regions, particularly India and parts of the Americas, saw increased transmission or outbreaks recently. Genetic information indicates the virus continues to spread globally with potentially varying clinical impact depending on the specific strain and context. Consistent control relies on continuous surveillance, improved diagnostic capabilities, understanding different lineages, and maintaining vector control activities.