Zaire ebolavirus

Zaire ebolavirus
Name	Zaire ebolavirus
Taxon	Zaire ebolavirus
Subdivision ranks	Species
Subdivision	Zaire ebolavirus

Zaire ebolavirus. It is the most virulent species within the genus Ebolavirus and the family Filoviridae, responsible for the largest and deadliest outbreaks of Ebola virus disease (EVD). The virus first emerged in 1976 near the Ebola River in the former Zaire, now the Democratic Republic of the Congo (DRC). Its high case fatality rate, which has historically ranged from 25% to 90% in outbreaks, has made it a significant public health threat and a prototype for research into filoviral hemorrhagic fevers.

Taxonomy and classification

Zaire ebolavirus is one of six recognized species within the genus Ebolavirus, which also includes Sudan ebolavirus, Tai Forest ebolavirus, Bundibugyo ebolavirus, Reston ebolavirus, and Bombali ebolavirus. The genus is part of the family Filoviridae, order Mononegavirales. The species name derives from its initial identification in the former Zaire. The International Committee on Taxonomy of Viruses (ICTV) formally classifies it, and its prototype strain is Mayinga, named after a nurse infected during the 1976 outbreak in Kinshasa.

Virology

Zaire ebolavirus is a non-segmented, negative-sense, single-stranded RNA virus with a filamentous, sometimes branched, morphology. Its genome encodes seven structural proteins: nucleoprotein (NP), polymerase cofactor (VP35), matrix proteins (VP40 and VP24), glycoprotein (GP), transcription activator (VP30), and RNA-dependent RNA polymerase (L). The surface glycoprotein GP mediates entry into host cells, primarily targeting cells of the mononuclear phagocyte system. The virus replicates in the cytoplasm of infected cells, and its VP35 protein is a potent inhibitor of the host interferon response, a key factor in its virulence.

Epidemiology

The natural reservoir host of Zaire ebolavirus is believed to be fruit bats of the Pteropodidae family, particularly species within the genera Hypsignathus monstrosus, Epomops franqueti, and Myonycteris torquata. Human outbreaks typically begin with a spillover event from an infected animal, often through contact with blood, secretions, or bushmeat. Subsequent human-to-human transmission occurs via direct contact with bodily fluids of symptomatic individuals or contaminated surfaces, fueling outbreaks often centered in healthcare settings or during funeral rituals. Major outbreaks have occurred primarily in Central and West Africa.

Clinical presentation and pathogenesis

Infection with Zaire ebolavirus causes a severe hemorrhagic fever. After an incubation period of 2 to 21 days, initial symptoms resemble influenza and include sudden onset of fever, fatigue, muscle pain, and headache. This progresses to gastrointestinal symptoms like vomiting and diarrhea, and in severe cases, internal and external bleeding, multi-organ failure, and septic shock. Pathogenesis involves widespread infection of dendritic cells and macrophages, leading to a massive release of pro-inflammatory cytokines, endothelial damage, increased vascular permeability, and disseminated intravascular coagulation.

Diagnosis and treatment

Definitive diagnosis requires laboratory testing, as early symptoms are non-specific. Methods include reverse transcription polymerase chain reaction (RT-PCR), antigen-capture enzyme-linked immunosorbent assay (ELISA), and virus isolation in specialized laboratories like those at the Centers for Disease Control and Prevention (CDC) or the World Health Organization (WHO) network. Treatment is primarily supportive, focusing on fluid and electrolyte balance, oxygen therapy, and treatment of complicating infections. The monoclonal antibody cocktail Inmazeb (atoltivimab, maftivimab, and odesivimab-ebgn) and the single monoclonal antibody Ebanga (ansuvimab-zykl) are approved therapeutics.

Prevention and control

Prevention relies on community engagement, surveillance, and strict infection control practices. Key measures include isolating confirmed cases, tracing and monitoring contacts, ensuring safe burial practices, and promoting hygiene. Personal protective equipment (PPE) is critical for healthcare workers. The rVSV-ZEBOV vaccine, marketed as Ervebo, has proven highly effective in ring vaccination strategies during outbreaks, as demonstrated in the Kivu Ebola epidemic. The Strategic Advisory Group of Experts on Immunization (SAGE) provides guidance on its use.

Outbreak history

The first documented outbreak occurred simultaneously in 1976 in Yambuku, Zaire, and in Nzara, South Sudan (involving a different species). The 2013–2016 epidemic in West Africa, primarily affecting Guinea, Sierra Leone, and Liberia, was the largest in history, with over 28,000 cases. Other significant outbreaks include the 1995 event in Kikwit, DRC, and the 2018–2020 Kivu Ebola epidemic in the eastern DRC, which was complicated by conflict involving groups like the Allied Democratic Forces. The World Health Organization often declares these outbreaks Public Health Emergencies of International Concern (PHEIC).

Category:Virus species Category:Ebola