Ebola virus is a member of the filovirus group that is clinically significant for causing a syndrome of hemorrhagic fever in humans. The most common symptoms that occur in patients who are infected with Ebola are vomiting and diarrhea but can progress to weakness, internal and external bleeding, as well as organ failure. The mortality rate for patients known to be infected with Ebola is around 40%.
The virus has been in the news sporadically since it was first identified near the Congo River in 1976. There have been 9 outbreaks in the Democratic Republic of the Congo (DRC) since then; the most recent occurring in May 2018.
While there have been a handful of imported cases of Ebola in the United States related to the large outbreak in 2014-2015, the virus is endemic in central and west Africa because it can be found in certain native animal populations, including fruit bats, chimpanzees, and forest antelope. Transmission of Ebola occurs through direct contact with blood or other bodily fluids as well as through consumption of animal meats that may be infected with the virus.
A growing concern about recent infectious disease outbreaks is how they may interface with global transport systems, thereby crossing borders and reaching large cities much faster than ever before. For example, one of the main reasons why the 2014 outbreak in West Africa affected as many people as it did (28,616 cases with 11,310 deaths) was because it reached the densely populated centers of Freetown, Monrovia, and Conakry.
TREATMENT AND VACCINATION
Since the 2014 West Africa outbreak, significant research has been done in identifying novel therapeutic agents and vaccines that may be used against future Ebola outbreaks. At least 8 different vaccines are currently in development, and the most advanced product (rVSV-ZEBOV) was administered to approximately 6000 at-risk individuals during the most recent outbreak in May 2018 in the DRC. This version of the vaccines does not appear to provide long-lasting immunity but is useful in reducing the risk and breaking the chain of transmission during an active outbreak. That being said, there are a number of issues relating to the implementation of the vaccine that need to be addressed:
- Location. Many outbreaks—including the most recent one in the DRC—begin in very remote and rural areas. For a variety of logistical reasons, it is very challenging to identify areas where outbreaks are occurring and reach those areas with the equipment needed to establish vaccine administration centers.
- Cold-chain infrastructure. The rVSV-ZEBOV vaccine in its current form requires constant refrigeration, which limits the distance that the vaccine can be transported away from storage facilities.
- Vaccine acceptance. Certain communities may not necessarily come forward to receive the vaccine because of issues around stigma with Ebola or potential distrust of the government or other health workers, requiring a significant amount of culture exchange and understanding.
- Timing of vaccination. In order for the vaccine to be most efficacious, it should be administered to at-risk people (i.e., individuals with known exposure to patients infected with Ebola) as close to their exposure and before they develop symptoms themselves.
Along with the vaccine, there are a number of experimental therapies for patients who have confirmed Ebola infection that were deployed during the 2018 outbreak. The best studied of these investigational agents is ZMapp, a triple monoclonal antibody cocktail first developed by the Canadian Public Health Agency and the US Army Medical Research Institute of Infectious Diseases. Human trial data collected during its use at the end of the 2014-2015 outbreak was very promising in terms of efficacy. Other agents being evaluated include the RNA polymerase inhibitor favipirivir and the nucleotide analog remdesivir—neither of which would require refrigeration (as would the vaccine and ZMapp).
FUTURE STRATEGIES FOR PREVENTION
Improved surveillance systems are some of the best tools we have for the prevention of future Ebola outbreaks, particularly in terms of identifying cases earlier and being able to activate the infrastructure necessary to provide effective treatment immediately.
Traditional infection surveillance systems have inherent limitations since they are dependent on reporting streams from physicians, clinics, or health care infrastructures. There are a number of newer tools and algorithms available that harness the power of big data to aggregate Google search results or social media posts, for instance. This allows surveillance systems to reach a much wider swath of the population, and therefore hopefully identify signals at earlier time points in an outbreak.
Utilizing novel strategies around social media and syndromic surveillance, identifying cases based on symptoms, and ramping up on the regional and national levels will be important for pillars of the public health response. The 2018 outbreak has demonstrated that Ebola has not gone away; it still affects rural populations, and that is why we will need to have constant vigilance in the future.
Daniel P. Eiras, MD, MPH, is an Assistant Professor in the Department of Medicine at NYU Langone Health, the Director of Infection Control at Bellevue Hospital, and an Associate Director of the Special Pathogens Unit at Bellevue Hospital.
