Zaire Ebolavirus | Ask Microbiology

Zaire ebolavirus is the ebolavirus species associated with the most severe outbreaks of Ebola virus disease in humans and nonhuman primates.

Explanation

Zaire ebolavirus (species Zaire ebolavirus) belongs to the genus Ebolavirus within the family Filoviridae. Its genome consists of a non‑segmented, negative‑sense single‑stranded RNA of roughly 19 kilobases encoding seven structural proteins: nucleoprotein (NP), virion protein 35 (VP35), VP40, glycoprotein (GP), VP30, VP24 and the RNA‑dependent RNA polymerase (L). The virions are filamentous and enveloped. Zaire ebolavirus was first identified in 1976 during simultaneous outbreaks of hemorrhagic fever in Yambuku, Zaire (now the Democratic Republic of the Congo) and Nzara, Sudan. The virus responsible for the Zaire outbreak exhibited a higher case fatality rate and was subsequently classified as a distinct species. Its natural reservoir is suspected to be fruit bats of the Pteropodidae family, with spillover to humans occurring through contact with infected wildlife or contaminated bodily fluids. After entering a host, the virus targets dendritic cells, macrophages and endothelial cells, leading to systemic viral replication, cytokine dysregulation and vascular leakage. Case fatality rates in past outbreaks have ranged from 60 % to over 80 %, reflecting its high virulence. Genetic analysis shows several lineages, but all belong to the same species and share similar pathogenic properties. Vaccines based on recombinant vesicular stomatitis virus expressing Ebola glycoprotein (rVSV‑ZEBOV) have demonstrated strong protective efficacy and have been deployed in outbreak settings. Therapeutics such as monoclonal antibody cocktails (e.g., REGN‑EB3) and the antiviral remdesivir have improved survival when administered early.

Notable Outbreaks and Control Measures

Zaire ebolavirus has caused multiple outbreaks of Ebola virus disease in Central and West Africa. The 1995 Kikwit outbreak resulted in more than 250 deaths. The largest recorded epidemic occurred in 2014–2016 in Guinea, Liberia and Sierra Leone, resulting in over 28 000 cases and more than 11 000 deaths. More recent outbreaks in the Democratic Republic of the Congo between 2018 and 2021 highlighted the challenges of controlling transmission in conflict zones. Human‑to‑human transmission occurs through direct contact with blood, secretions or tissues of infected individuals and through unsafe burial practices. Healthcare workers are at elevated risk without appropriate personal protective equipment. Ring vaccination with rVSV‑ZEBOV, improved infection control, and community engagement have become central strategies for outbreak containment. Surveillance of wildlife and serological studies support the hypothesis that certain fruit bats maintain the virus asymptomatically. Continued research seeks to clarify reservoir species and mechanisms of spillover.

Zaire ebolavirus remains a major cause of severe Ebola virus disease in humans. Advances in vaccines and therapeutics have improved outcomes, but sustained surveillance, rapid response and public health preparedness are essential to reduce the impact of future outbreaks.