Download and share our infographic summarizing outbreaks, occurrences and research on Ebola (Last updated November 11, 2015)
In March 2014, several news outlets shocked the world with reports of an outbreak of the Zaire species of the Ebola virus centered in West Africa, with Liberia, Guinea and Sierra Leone being the most affected countries. Since the discovery of the Ebola virus in 1976, several outbreaks have occurred, but the recent one has been the largest ever recorded. It has claimed the lives of over 11,000 individuals , a toll five times greater than the previous outbreaks combined. In a recent press release announcing advanced development of an experimental Ebola vaccine regimen, Robin Robinson, Ph.D., director of the Biomedical Advanced Research and Development Authority of the U.S. Department of Health and Human Services stated “history has shown that Ebola doesn’t really disappear…”
The current outbreak has definitely shown that the Ebola virus can be persistent, as it has re-emerged in Liberia and Guinea after being dormant for weeks. Liberia and Sierra Leone were recently (September 3 and November 7, respectively) declared Ebola free after experiencing 42 days without any new cases. However, Guinea is still not free of Ebola; being the only country still battling the nearly two year-long epidemic. Although it appears that the current outbreak is mostly under control, scientific research studies paint a less hopeful picture. It has been shown that the virus essentially hides inside the body in sites inaccessible to the immune system. These are known as immune privileged sites and include the eyes, testes, fetus, joint spaces, placenta and the central nervous system.
Deen et al. (2015) demonstrated that Ebola can remain in the semen of survivors for as long as nine months post recovery. One case of sexual transmission of the Ebola virus has been reported; however scientists suggest that this may be a rare occurrence (Mate et al. 2015). Additionally, the Ebola virus was detected at high levels in the amniotic fluid of pregnant women who were declared Ebola free through blood testing (Baggi et al. 2014). Ebola was also found in the eye of a physician five months after he was considered cured of the infection, despite the fact that his tears and the rest his body did not contain the virus (Varkey et al. 2015).
The persistence of the Ebola virus in the body is in stark contrast to previous scientific understanding, since despite its severe course of disease, it is known to be an acute virus that can rapidly be cleared by the immune system of many infected individuals. The small Ebola genome in comparison to other viruses such as herpes, which is known to remain dormant in the body for years, makes its persistence even more puzzling (Jun et al. 2015).
Epidemiological evidence from the recent outbreak indicates that Ebola survivors experience long term effects such as joint pain, vision loss, deafness, palpitations and anorexia (Quereshi et al. 2015; Nanyonga et al. 2015). It is not clear whether these symptoms are directly due to the presence of the Ebola virus in immune privileged sites or are side effects of disease treatment. Most survivors report a reduction in symptoms over time, but how long they persist and exactly what causes them is worth investigation. The evidence points to the existence of a “post-Ebola syndrome” and understanding this is the focus of a recently launched study in Liberia, which is the largest controlled study of Ebola survivors to date.
A concern raised in response to the current findings is the possibility that the Ebola virus could reemerge in the same individual as another related disease. This has been shown in cases of measles and chicken pox, which can recur as subacute sclerosing panencephalits and shingles, respectively. One publicized case of Ebola reemergence as a critical condition is that of a Scottish nurse who nine months after recovery from Ebola virus disease was found to have developed meningitis caused by lingering Ebola virus in the brain, suggesting that survival from initial Ebola infection could be a gateway for other serious diseases.
The insights garnered from the research on the Ebola virus within the context of the current outbreak offers a new perspective on the historical evidence that the Ebola virus “doesn’t really disappear”. However, the findings serve as a platform for further research efforts to better understand the virus and prepare for or prevent future outbreaks.