Ebola virus disease (EVD) is a disease caused by Ebolaviruses in the Filoviridae family. There are five known Ebolavirus species (Bundibugyo ebolavirus, Reston ebolavirus, Sudan ebolavirus, Taï Forest ebolavirus, and Zaire ebolavirus (or simply Ebola virus)), four of which cause EVD in humans (Bundibugyo, Sudan, Taï Forest ebolavirus, and Zaire).
The first recorded outbreaks of EVD took place simultaneously in two locations in 1976. One in Nzara, Sudan (caused by Sudan ebolavirus), and the other in Yambuku, Democratic Republic of Congo (caused by Zaire ebolavirus). The disease was named after the Ebola River, which runs close to Yambuku.
Since the 1970s, there have been sporadic outbreaks of EVD in tropical regions of sub-Saharan Africa, however, the 2013-2016 epidemic in West Africa (primarily in the countries of Guinea, Liberia, and Sierra Leone) represents the largest outbreak since the virus was originally identified.
The four Ebolaviruses known to cause disease in humans are Bundibugyo virus, Sudan virus, Taï Forest virus, and Ebola virus (formerly Zaire Ebola virus). The fifth, Reston virus, causes EVD in non-human primates. Scientists believe that fruit bats or primates, such as apes and monkeys, are the natural reservoir host of Ebola viruses, although this theory is yet to be confirmed. Outbreaks of EVD occur when a spillover event occurs from a natural reservoir host to a human. This is followed by human-to-human transmission via direct contact with the blood, or other bodily fluids of infected individuals.
The incubation period, from infection to symptom onset, is 2 to 21 days. The early stage of the disease is usually marked by influenza-like symptoms, such as fever, headache, muscle pain, fatigue, and sore throat. These are followed by vomiting, diarrhea, rash, abdominal pain, and in some cases internal and/or external bleeding. Shortness of breath, chest pain, swelling and confusion may also occur. During its onset, it can be difficult to distinguish EVD from other infectious diseases, such as malaria, typhoid, and meningitis, which increases the risk of transmission. If untreated, the average case fatality rate is ~75%. While no specific treatment options exist for EVD, supportive care with rehydration and symptomatic treatment has proven to be highly effective decreasing the case fatality rate to 20-25%. A number of experimental treatments and vaccine candidates are also currently being evaluated.
Family members and friends caring for loved-ones infected with Ebola virus are at great risk of infections, as are health-care workers treating patients diagnosed with EVD. The risk increases significantly when appropriate personal protective equipment (PPE) is not available or used properly.
Diagnosing EVD patients has historically been hugely challenging, due to the extreme biohazard risk, high level of technical expertise required to run laboratory tests, and the lack of necessary resources and infrastructure in areas where outbreaks have occurred. During the 2013-2016 epidemic, however, VHFC investigators developed a new rapid diagnostic tool for diagnosing EVD patients. Our investigators also developed standard PCR-based tests, that were used to diagnose the first patients in both Sierra Leone and Nigeria by local researchers.
The following methods are currently used to diagnose EVD:
- reverse transcription polymerase chain reaction (RT-PCR) assay (most common)
- rapid diagnostic test (RDTs)
- antibody-capture enzyme-linked immunosorbent assay (ELISA)
- antigen-capture detection tests
- serum neutralization test
- virus isolation by cell culture
Notably in 2105, a new RDT for the presumptive detection of Ebola virus, developed by VHFC partner institution Corgenix Medical Corporation, received FDA authorization for emergency use. The test was also assessed and listed as eligible for procurement by the WHO. The ReEBOV(TM) Antigen Rapid Test uses a drop of blood from a finger prick to deliver a diagnosis in as little as 15 minutes.
Ebola represents a significant public health burden to nations where outbreaks occur, and remains a threat to the global community as a whole. In addition to continuing scientific research in order to develop effective therapeutics and vaccines, successful control and prevention efforts will require support in disease surveillance, community engagement, health-worker training, case management, contact tracing, good laboratory services, infection control, and safe burial practices.
Outbreaks of EVD have occurred in Democratic Republic of Congo, Gabon, Guinea (with later spread to multiple other countries, including Liberia, Sierra Leone, and Nigeria), South Sudan, and Uganda. Additionally, travelers from affected countries have imported the disease to other countries including Italy, Mali, Nigeria, Senegal, Spain, the United Kingdom, and the United States.
Epidemiology and management of the 2013-16 West African Ebola outbreak
Annual Review of Virology, 2016
An outbreak of Ebola virus disease in the Lassa fever zone
J Infect Dis, 2016
Clinical illness and outcomes in patients with Ebola in Sierra Leone
N Engl J Med, 2014
Ebola haemorrhagic fever in Zaire, 1976
Bull World Health Organ, 1978
Emergence of Zaire Ebola virus disease in Guinea.
N Engl J Med, 2014