Ebola virus, a member of the filovirus family, is the main cause of Ebola hemorrhagic fever. The virus is named after the river Zaire because of its outbreak in river Zaire in 1976. Filovirus is a family of long filamentous viruses, often enveloped. The Ebola virus has a non-segmented, negative-polarity RNA that is single-stranded, and it also contains RNA-dependent RNA polymerase. A total of five strains of the Ebola virus exist, and all are medically important viruses. The strains are Ebola-Zaire, Ebola-Reston, Ebola-Sudan, Ebola-Ivory Coast, and Ebola-Bundibugyo. Among these, Ebola-Zaire and Ebola-Sudan are pathogenic for humans, and Ebola-Reston is pathogenic for monkeys. The pathogenicity of Ebola-Ivory Coast and Ebola-Bundibugyo is uncertain for humans as cases reported were very low. Ebola-Zaire, Ebola-Sudan, Ebola-Ivory Coast, and Ebola-Bundibugyo are all found in Africa, whereas Ebola-Reston is found in the Philippines.

The natural reservoir of the Ebola virus is unknown to date. Microbiologists have claimed that fruit bats and rodents are suspected of being the reservoir. Transmission from human to human occurs through blood and body fluids; hospital personnel are highly at risk since many cases arise by secondary transmission through contact with patients' blood or secretions. Evidence shows the presence of the Ebola virus in the semen of survivors of the disease. However, there is no evidence of airborne transmission of the disease and no evidence of spreading of the disease through personal contact.

After entering the host body, it starts attacking and killing the hepatocytes, leading to liver failure. It also targets lymphocytes, macrophages, and dendritic cells, thereby inhibiting the active immune response and making the immune system ineffective in the prevention of the disease. Its virulence factor, the glycoprotein, kills endothelial cells, resulting in hemorrhaging, and the other two proteins of the Ebola virus inhibit the induction and action of interferon. This proves that the Ebola virus has evolved to the point where it has become so resistant that neither the immune system nor antiviral drugs are effective in killing and preventing the Ebola virus from reproducing in host cells. The mortality rate of the Ebola virus is 80% to 90%.

Ultimately, after infecting the host body and causing serious damage to organs and cells, the host manifests some symptoms, including fever, headache, sore throat, myalgia, arthralgia, epigastric pain, vomiting, and diarrhea. Subsequently, bleeding occurs into the skin and gastrointestinal tract, followed by shock and disseminated intravascular coagulation, which leads to the failure of many organs. Hemorrhages also occur, and lymphocytopenia develops. In some patients who recover from Ebola hemorrhagic fever, post-Ebola syndrome occurs. It manifests some symptoms, including eye pain, blurred vision, cataracts, hearing loss, headache, joint pain, fatigue, and insomnia. In one patient with uveitis, several months after his recovery, infectious Ebola virus was recovered from fluid aspirate of the interior of his eye.

Ebola virus is the most virulent human virus and is only cultured in monkey cells in Biosafety Containment Type 4. It can only be inactivated by the use of lipid solvents and bleach. Diagnosis is often made using ELISA, PCR, or by detecting IgM antibodies in serum. Electron microscopy is also used.

As of now, there is no specific antiviral therapy for Ebola virus. For supportive treatment, electrolytes and intravenous fluids are given. Immune serum globulin treatment is showing variable results. Experimental drugs are being used, but their effectiveness is uncertain. Prevention includes observing proper safety protocols in hospitals and a 21-day quarantine for patients suspected of having the Ebola virus. Microbiologists are creating different vaccines, but none are approved. In 2018, a recombinant vaccine named rZEBOV, containing the backbone of the vesicular stomatitis virus plus the gene encoding the Ebola virus surface glycoprotein, was put on trial during an outbreak in the Democratic Republic of the Congo.