Ebola virus disease is an acute viral disease endemic to Sub-Saharan Africa that can cause severe and hemorrhagic disease [1]. Ebola virus disease outbreaks in people have been caused by three of the six ebolavirus species: Zaire ebolavirus, Sudan ebolavirus, and Bundibugyo ebolavirus [2,3]. Additionally, both asymptomatic seroconversion for Reston ebolavirus and a single human case of infection with Taï Forest ebolavirus have been reported in patients [3]. While most of these viruses are endemic in Africa, Reston ebolavirus variants have been identified in pigs and primates from the Philippines [3]. The average case fatality rate across all reported outbreaks is roughly 45%, with rates exceeding 80% in some outbreaks [2]. African countries of concern include: the Congo, Democratic Republic of Congo, Gabon, Guinea, Ivory Coast, Liberia, Sierra Leone, South Sudan, and Uganda. Cases have also been exported to nearby countries, such as Mali and Nigeria, as well as internationally, including to Europe and the United States [3].
Ebolavirus transmission is thought to occur initially from animal sources followed by person-to-person transmission. Potential animal sources include fruit bats and primates [4]. Ebolaviruses are spread through contact with blood, body fluids (urine, saliva, sweat, feces, vomit, breast milk, amniotic fluid, and semen), and contaminated objects (clothes, bedding, needles, medical equipment). Routes of transmission include the mucous membranes (eyes, nose, mouth) and broken skin. Sexual transmission from men to women has also been documented. Ebolaviruses remain in semen, among other body fluids, even after a patient no longer has symptoms of disease [5].
The incubation period following initial exposure to the virus ranges between 2-21 days (8-10 days on average). Initial symptoms include fever, aches and pains, and fatigue, followed by the development of vomiting and diarrhea. Other symptoms can include sore throat, loss of appetite, abdominal pain, red eyes, skin rash, or hiccups [6]. In severe cases, patients can develop sepsis and organ failure, including renal failure. The liver is a common site of tissue injury during acute infection. Following recovery from infection, some patients still experience symptoms, including fatigue, joint pain, and inflammation of the eye (uveitis) [7].
Treatment for Ebola virus disease includes supportive care and antibody therapy. Supportive therapies include oral or intravenous fluids, blood pressure supporting medications, medications for reducing diarrhea/vomiting, fever/pain management, and treatment of other infections. There are two antibody therapies approved by the U.S. Food and Drug Administration (FDA) for the treatment of Ebola virus disease caused by Zaire ebolavirus: InmazebTM and EbangaTM. These biologic therapies bind to the ebolavirus glycoprotein, preventing virus entry into host cells. These drugs have not been evaluated for efficacy against the other ebolavirus species [8].
Two vaccines have been developed for the prevention of ebolavirus infection. Ervebo® is a replication-competent, live-attenuated recombinant vesicular stomatitis virus vaccine that expresses the glycoprotein from a member of the Zaire ebolavirus species. This vaccine was approved by the U.S. FDA [9]. In Europe, an additional vaccine regimen was approved for use under exceptional circumstances. This vaccine regimen includes the Zabdeno® (Adenovirus 26-vectored vaccine expressing a Zaire ebolavirus glycoprotein) and Mvabea® (modified Vaccinia Ankara Bavarian Nordic virus-vectored vaccine expressing Zaire ebolavirus, Sudan ebolavirus, and Marburg marburgvirus glycoproteins, as well as a Taï Forest ebolavirus nucleoprotein) vaccines, which are given as a series eight weeks apart [10,11].
Timothy Wanninger is an MD/PhD student at the University of Texas Medical Branch interested in tropical and emerging infectious diseases.
References
1. Malvy D, McElroy AK, de Clerck H, Günther S, van Griensven J. Ebola virus disease. Lancet. 2019;393: 936–948. doi:10.1016/S0140-6736(18)33132-5
2. Kuhn JH, Amarasinghe GK, Perry DL. Filoviridae. 7th ed. In: Howley PM, Knipe DM, editors. Fields Virology: Emerging Viruses - Volume 1. 7th ed. Philadelphia: Lippincott Williams & Wilkins; 2021. pp. 449–503.
3. Centers for Disease Control and Prevention. History of Ebola Outbreaks. 2022. Available: https://www.cdc.gov/vhf/ebola/history/chronology.html
4. Centers for Disease Control and Prevention. Ebola Disease. 23 Mar 2023 [cited 23 May 2023]. Available: https://www.cdc.gov/vhf/ebola/index.html
5. Centers for Disease Control and Prevention. Ebola Disease: Transmission. 14 Apr 2023 [cited 23 May 2023]. Available: https://www.cdc.gov/vhf/ebola/transmission/index.html
6. Centers for Disease Control and Prevention. Ebola Disease: Signs and Symptoms. 23 Mar 2023 [cited 23 May 2023]. Available: https://www.cdc.gov/vhf/ebola/symptoms/index.html
7. Jacob ST, Crozier I, Fischer WA, Hewlett A, Kraft CS, Vega MA, et al. Ebola virus disease. Nat Rev Dis Primers. 2020;6: 13. doi:10.1038/s41572-020-0147-3
8. Centers for Disease Control and Prevention. Ebola Disease: Treatment. 26 Feb 2021 [cited 23 May 2023]. Available: https://www.cdc.gov/vhf/ebola/treatment/index.html
9. Centers for Disease Control and Prevention. Ebola Vaccine: Information about ERVEBO®. 2023 [cited 23 May 2023]. Available: https://www.cdc.gov/vhf/ebola/clinicians/vaccine/index.html
10. European Medicines Agency. Zabdeno. In: European Medicines Agency [Internet]. [cited 13 Dec 2022]. Available: https://www.ema.europa.eu/en/medicines/human/EPAR/zabdeno#authorisation-details-section
11. European Medicines Agency. Mvabea. In: European Medicines Agency [Internet]. [cited 13 Dec 2022]. Available: https://www.ema.europa.eu/en/medicines/human/EPAR/mvabea#authorisation-details-section