KeywordsEpidemics Ebola West Africa Hemorrhagic fever
The Ebola virus disease (also known as Ebola hemorrhagic fever) is a potentially lethal infectious disease present mainly on the African continent. It is caused by the Ebolavirus, a genus of viruses that belong to the Filoviridae virus family. In 2015, the World Health Organization (WHO) included it in its list of emerging diseases requiring the most attention in terms of R&D resources (WHO 2015). As of 2017, five different species of the virus have been discovered. These are the Zaire ebolavirus, the Sudan ebolavirus, the Tai Forest ebolavirus (previously called Côte d’Ivoire ebolavirus), the Bundibugyo ebolavirus, and the Reston ebolavirus. All five of them spread to nonhuman primates, but only the first four are known to infect humans.
History and Outbreaks
The first known cases of human infections with ebolaviruses appeared in 1976 in South Sudan and Zaire (presently the Democratic Republic of the Congo [DRC]). Both outbreaks were caused by two different strains of the virus (the Sudan and Zaire ebolaviruses, respectively). The genus is named after the Ebola River, which runs near the village where the Zairian cases emerged. Since then, individual cases and other episodes of disease emergence were regularly registered. Out of the four species of the virus that are able to infect humans, Tai Forest ebolavirus was identified only once in an individual, in 1994, in Côte d’Ivoire, but the case was not fatal. Bundibugyo ebolavirus was responsible for two outbreaks in Uganda and the DRC (in 2007 and 2012, respectively), with the former infecting more than 149 people, though it caused death only in one-fourth of the cases. Sudan ebolavirus spread several times in Sudan and Uganda throughout the years. The biggest epidemic of this type broke out in the latter country in 2000, killing 53% of a total of 425 infected individuals. Finally, by a large margin, the most frequently occurring subtype of ebolaviruses is Zaire, which can be found regularly in West and Central Africa (in the DRC, the Republic of Congo, and Gabon, for instance). The largest epidemic episode so far was the one that unfolded in West Africa between 2014 and 2016 (WHO 2018a) and is described in more detail in a separate section below.
Transmission and Symptoms
Exactly what constitutes the natural reservoir or host of Ebola is one of the questions yet to be answered in connection with the virus. Having said that, based on the knowledge acquired about similar viruses, scientists believe that it is animal-borne, and the primary reservoirs are suspected to be fruit bats. According to the website of the Centers for Disease Control and Prevention (CDC), animal-to-human transmission is a result of direct contact between the individual’s broken skin or mucous membranes (these can be found, for instance, in the eyes, nose, or mouth) and the infected animal, while human-to-human transmission is possible in two ways: either through direct contact with the blood or bodily fluids of an Ebola patient (e.g., saliva, urine, sweat, vomit, breast milk, semen, or feces) or with objects that have previously been contaminated with the blood or bodily fluids of the infected (CDC 2015a).
Scientists believe that contact with the semen of a person who had previously been infected, but successfully recovered might also spread the contagion (CDC 2015a). Consequently, family members, friends, and health workers are threatened the most. Due to its limitation of spreading only through direct contact, the basic reproduction number (R0), that is, the number of new infections caused by one infected individual, is between 1 and 4 in the case of Ebola. This is relatively low, especially if one were to consider other infectious diseases such as measles (12–18) or even HIV (2–5) (Stewart 2014).
Once an individual is infected, the incubation period of the virus, or in other words the period when no symptoms are shown, is on average 8–10 days, but it can last from 2 to 21. During the incubation period, the infected cannot pass it on to other potential hosts. Regarding the symptoms of the virus, as the name “hemorrhagic fever” suggests, infection causes fever with a high propensity to bleed. Further symptoms include severe headache, muscle pain, fatigue, diarrhea, vomiting, abdominal pain, and general weakness (CDC 2014).
Treatment and Recovery
Even though many treatments are being researched, as of 2018 no approved medicine or vaccine was developed against Ebola. An experimental vaccine has shown itself to be highly protective during a large-scale trial conducted in Guinea in 2015 (WHO 2018a). Thus, in accordance with the recommendation of the WHO Strategic Expert Advisory Group on Immunization (SAGE), made in 2017, a total of 7,560 doses of this experimental vaccine have been deployed during the 2018 epidemic in the DRC to protect individuals exposed to high risk (healthcare workers and contacts of Ebola patients) (WHO 2018b). However, as of 2018, it is not yet approved for general vaccination campaigns.
Recovery from the disease can be helped, but not guaranteed by two things: on the one hand, by the response of the immune system of the infected individual, and on the other, by quality healthcare, which means adequate treatment of the different symptoms. Once recovered, the body of the patient creates antibodies against the virus, but whether it protects them for life or against other species of Ebola has yet to be discovered. They are known to provide protection for at least 10 years against the species that has infected the recovered person (CDC 2014). However, Ebola does not always leave the body without a trace. In some cases it causes long-term vision or joint problems (CDC 2015b). Furthermore the virus might still be present in bodily fluids, such as in the semen and in breast milk after recovery. It takes a different amount of time in every individual for the virus to leave the semen. Even though more research is necessary in order to assess the risk of sexual transmission, particularly in the short and long terms, WHO recommends precaution in sexual practices and the regular testing of the semen of male Ebola survivors (WHO 2018a). Similarly, until more information is available concerning the possibilities of transmission via breastfeeding, in case no laboratory testing is available to make sure that the milk does not contain the virus, the CDC advises substituting it, if possible, with a safer way of feeding the baby (CDC 2016b).
The West African Outbreak of 2014–2016
The largest Ebola epidemic in history originated from a village in Guinea with an animal-to-human transmission. The World Health Organization registered the epidemic in March 2014 and labeled the situation a Public Health Emergency of International Concern (PHEIC) in August of the same year, as even though in late spring the number of cases in Guinea declined, others were registered in neighboring Senegal, Mali, even in Nigeria, and most notably in Sierra Leone and Liberia. Individual cases of returning aid workers were also registered in some European countries and in the United States (US). The total number of cases amounts to approximately 28,652, of which 11,325 died (CDC 2016a), with Guinea, Sierra Leone, and Liberia being the most affected countries that collectively accounted for over 99% of all reported cases (Kalra et al. 2014).
Among the reasons for the large scale of the epidemic, we can list first of all the lack of healthcare workers, equipment, facilities, and resources in general. Since particularly in the last phases of the disease those who care for the sick become more frequently exposed to infected blood or bodily fluids, the possibility of acquiring the disease increases; therefore, adequate measures are crucial to contain the virus for healthcare workers caring for those infected. The circumstances present in the most affected countries combined with the high risk of contact with infected blood or bodily fluids resulted in a lot of health workers getting the disease (Kalra et al. 2014). Inadequate response of governments both on the national and international levels was also a factor contributing to the large scale of the epidemic. The substantial, but slow and disorganized, response of the international community posed a considerable challenge to winning the trust of the local population, which was crucial to successfully implement containment measures (Kalra et al. 2014). Furthermore, cultural factors also played a role in the spread of the disease, as, for example, burial practices usually involved direct contact with the deceased, the body of whom still contained the virus, thus exposing family members and friends to infection (Kalra et al. 2014). The epidemic had a devastating impact on the economies, healthcare systems, and societies of the three most affected countries (Kalra et al. 2014), and therefore it shed light on the need for reforms, both regarding international and local response.
Ebola and Bioterrorism
Contrary to popular belief, fed by the media attention toward the West African outbreak, the Ebola virus is not an ideal biological weapon for two major reasons. Firstly, it requires huge amounts of resources. Even if a person or a group was able to obtain a sample by traveling to Africa, said sample would have to be carried back to a laboratory, which is a challenge in itself, since Ebola is a relatively fragile virus. Outside of its host, it cannot survive for long, and even though under ideal circumstances it can live for several days in bodily fluids, it would be very difficult to create and maintain those circumstances while it is transported from one place to another. Furthermore, as it is a dangerous virus to work with, replication requires a highly safe laboratory which, being very costly, further complicates its application as a weapon (Stewart 2014). This point is perfectly illustrated by the Japanese cult Aum Shinrikyo’s failed attempt to use Ebola as such. In 1993, they tried to obtain Ebola samples in Africa (Olson 1999), and although they had the resources and a laboratory (where other biological weapons projects had already been underway), they were unsuccessful in developing a weapon out of the virus.
Another reason for which it is not an ideal weapon is the way it spreads. As described above, it can take a relatively long time for an infected individual to show symptoms, during which they are not able to infect others. When the incubation period is over, and the person who has acquired the disease starts to show symptoms, and therefore becomes able to spread the disease, those symptoms usually make them bedridden and unable to attempt to do so. Unlike air- or water-borne diseases, Ebola, as mentioned, infects a host via direct contact, which narrows down the number of possible victims. Even if, for example, an infected suicide bomber exploded himself in a crowd, potentially spraying bodily fluids on a large number of people, those would be immediately hospitalized, where the virus may be identified, and containment measures could be applied (Stewart 2014). Consequently, in its present form, Ebola is not an ideal weapon for terrorists.
Even though it can be established that it might not be the most effective biological weapon, the existence of the misbelief regarding its potential utility might reflect the threat Ebola poses as a naturally occurring biological agent. It is a prime example of the dangers emerging infectious diseases pose to humans, most notably because, as a consequence of their nature as emerging threat, the information available about them is scarce. This renders effective response difficult. Nevertheless, since it spreads only through direct contact, containment and the prevention of large-scale epidemics is feasible through education, community engagement, and the use of adequate equipment, the availability and success of which depend on the efficacy of the national and international response.
Therefore, advancements and improvements in the fields of science and policy implementation can considerably mitigate the threat posed by Ebola.
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