Ebola virus disease (EVD) is a severe, often fatal illness in humans caused by orthoebolaviruses. The disease first appeared in 1976 in simultaneous outbreaks in Nzara, South Sudan, and Yambuku, Democratic Republic of Congo, the latter near the Ebola River, which gave the virus its name. The most common species is Zaire ebolavirus, which has caused the largest and deadliest outbreaks. Transmission occurs through direct contact with blood, body fluids, or tissues of infected people or animals, as well as contact with contaminated surfaces and materials. Fruit bats of the Pteropodidae family are considered natural hosts. Symptoms include sudden onset of fever, fatigue, muscle pain, headache, and sore throat, followed by vomiting, diarrhea, rash, impaired kidney and liver function, and in some cases, internal and external bleeding. The average case fatality rate is around 50%, but has varied from 25% to 90% in past outbreaks. The 2014–2016 outbreak in West Africa was the largest Ebola epidemic in history, with 28,646 reported cases and 11,323 deaths, primarily in Guinea, Liberia, and Sierra Leone. This outbreak revealed critical weaknesses in global health security and prompted accelerated development of vaccines and therapeutics. The rVSV-ZEBOV vaccine (Ervebo), developed by Merck, was approved by the FDA in 2019 and has been used in ring vaccination campaigns in the Democratic Republic of Congo and other affected countries. Two monoclonal antibody treatments, Inmazeb and Ebanga, have also been approved. Despite these tools, Ebola remains a persistent threat, with the DRC experiencing 14 outbreaks since 1976, including a 2018–2020 outbreak in North Kivu and Ituri that caused 2,287 deaths. Interest in predicting which countries will report an Ebola case in 2026 stems from several factors. The virus is known to re-emerge from animal reservoirs, particularly in Central and West Africa. Environmental changes, deforestation, and human encroachment into wildlife habitats increase spillover risk. Surveillance systems have improved but remain uneven, and political instability in some regions can hamper response. The World Health Organization maintains a list of priority pathogens for research, and Ebola is classified as a high-consequence infectious disease requiring strict biosafety level 4 containment. The prediction market reflects a bet on where the next confirmed human case will appear, accounting for both endemic regions and potential travel-related importations. The market resolution criteria are specific: only confirmed human cases reported between the market issuance date and January 1, 2027 count. Suspected, probable, or animal cases are excluded. An imported case diagnosed in a country that is not the patient's country of citizenship counts if diagnosed within that country's borders. The date of official confirmation, not symptom onset, determines timing. This narrow definition means that a case detected in a non-endemic country through travel screening or healthcare presentation would count, while a citizen diagnosed abroad would not. The market thus captures both local transmission events and international detection. Historically, imported cases have occurred in countries like Spain, the United Kingdom, Italy, and the United States during major outbreaks.

Historical Context

Ebola virus disease was first identified in 1976 in two simultaneous outbreaks. The first occurred in June in Nzara, South Sudan, with 284 cases and 151 deaths. The second began in August in Yambuku, DRC, with 318 cases and 280 deaths. The virus was named after the Ebola River near Yambuku. Between 1976 and 2012, there were 24 documented outbreaks, all in Central and East Africa, with the largest being the 1995 Kikwit outbreak in DRC (315 cases, 254 deaths) and the 2000–2001 Gulu outbreak in Uganda (425 cases, 224 deaths). These outbreaks were typically contained within rural areas, with case fatality rates ranging from 25% to 90%. The 2014–2016 West Africa outbreak fundamentally changed the global perception of Ebola. It began in December 2013 in Meliandou, Guinea, but was not identified until March 2014. The virus spread to Liberia, Sierra Leone, Nigeria, Senegal, Mali, and the United States. The outbreak caused 28,646 reported cases and 11,323 deaths, though the true number was likely higher. The WHO declared a PHEIC in August 2014, and the UN Security Council declared it a threat to international peace and security in September 2014. The outbreak exposed failures in global health infrastructure, including delayed response, inadequate healthcare systems, and community mistrust. It also led to the rapid development of vaccines and treatments, with the rVSV-ZEBOV vaccine showing 100% efficacy in a Phase 3 trial in Guinea. Since 2018, the DRC has experienced two major outbreaks. The 2018–2020 outbreak in North Kivu and Ituri was the second largest in history, with 3,470 cases and 2,287 deaths. It occurred in an active conflict zone, complicating response efforts. The WHO declared a PHEIC from July 2019 to June 2020. The 2021 outbreak in North Kivu and the 2022 outbreak in Equateur Province were smaller but demonstrated the virus's persistent threat. In 2023, Uganda reported an outbreak of Sudan ebolavirus, for which no licensed vaccine exists. The WHO coordinated a response using candidate vaccines and treatments. These recent events highlight that Ebola remains a serious public health threat in endemic regions, and the risk of international spread through travel is ongoing.