Francesca Tomasi received her B.A. from the University of Chicago and is now a microbiologist.
Last week, the CDC published a perspective on the recent Ebola outbreak that ravaged parts of West Africa over the past 3 years. The exposé discusses different factors responsible for the delayed detection of the outbreak and the staccato responses that made it difficult to control the epidemic.
Among the many risk factors associated with poor outbreak responses, the authors of the article focus on three specific categories: social factors, educational factors, and medical factors.
Socially, West Africa was facing regional instability from recent civil wars. Furthermore, traveling populations and extensive urban spread of the virus contributed to the scale of the Ebola outbreak. In terms of educational factors, a lack of community knowledge of the disease resulted in exacerbation of the outbreak: improper containment practices and unfamiliarity with Ebola allowed the virus to persist rather than burning out. Lastly, medical factors contributing to the breadth of the epidemic include inadequate disease surveillance, unsatisfactory case detection, and insufficient resources for patient care.
Ebola: A History
Ebola virus disease (EVD) was discovered during two separate outbreaks of hemorrhagic fever in 1976. The first occurred in Nzara, Sudan, which is now part of South Sudan. The second occurred in a small village called Yambuku, Zaire, which is now part of the Democratic Republic of Congo.
Hemorrhagic fever was by no means a new pathology; at the time, it was already known to be caused by 3 different virus families (Lassa, Marburg, and yellow fever). Ebolavirus, which is most similar to Marburg, was added as a fourth family upon its discovery by CDC and Belgian scientists. Hemorrhagic fever is characterized by damaged blood vessels spanning multiple organs that ultimately impair the body’s ability to regulate itself. This is the most serious – and dramatic – possible symptom of Lassa, Marburg, Yellow Fever, and Ebola.
During the outbreak in Sudan, 284 people were infected and 151 succumbed to the disease. A few months later, in Zaire, there were 318 cases and 280 deaths. Upon epidemiological and microbiological analyses, it turned out that there were two different strains circulating in Zaire – one was the same as the one in Sudan, and was named Sudan virus. The other was unique to Yambuku, and named Zaire Ebolavirus (now simply Ebola Virus Disease). Ebola’s namesake is the Ebola River, located in Zaire near where the latter outbreak occurred. The first known patient in the Zaire outbreak, a local school headmaster, had recently returned from a trip there. Sudan virus and the Zaire strain are 2 of five different Ebolaviruses isolated to this date.
The next recorded Ebola outbreak took place once again in Zaire, but this time it flared up in 1995. Out of 315 infected individuals who developed the disease, 254 died. Five years later, in Uganda, an outbreak affected 425 people and killed 224. The strain in Uganda was found to be the Sudan virus that caused an outbreak in Sudan in 1976. In 2003, another Republic of the Congo outbreak killed 128 infected individuals out of 143. This is the highest death rate of an Ebola virus to date. For the next decade, a handful of small outbreaks affecting under 200 people each would flare up in Uganda and Democratic Republic of the Congo.
In March 2014, the WHO reported a new major Ebola outbreak unfolding. This time, however, the disease was in Guinea, a nation in West Africa, a region that had not previously seen the virus before. South Sudan, Democratic Republic of the Congo, and Uganda are located in Central/East Africa. Epidemiologists traced the outbreak to an infant who died in December 2013. Within a few months, the disease spread to Liberia and Sierra Leone, which border Guinea and each other. In August, the WHO declared the epidemic an international public health emergency and called for international aid in the affected regions.
"The Ebola epidemic ravaging parts of West Africa is the most severe acute public health emergency seen in modern times,” read a statement by the WHO media center. “Never before in recorded history has a biosafety [level] four pathogen infected so many people so quickly, over such a broad geographical area, for so long."
For the first time, Ebola was on the global radar as forces were mobilized to the front lines of the epidemic. According to the WHO, about ten percent of the individuals who died from Ebola were health care workers, both local and international. This should not come as surprising, since the disease is spread via bodily fluids.
Which strain was in West Africa?
As you can see, the case counts for previous Ebola outbreaks pale in comparison to the West African epidemic that erupted almost 40 years after Ebola first emerged. The recent Ebola outbreak spread through three countries – Guinea, Liberia, and Sierra Leone – where there were at least 28,603 cases and 11,301 deaths. The fatality rate of this outbreak comes to about 39%, which is lower than the 52% and 88% fatality rates in 1976 then-Sudan and then-Zaire, respectively.
The strain that tore through Guinea, Liberia, and Sierra Leone and trickled into a couple of other nations is called the Makona strain, and it is part of the Zaire ebolavirus species. In animal studies, Makona showed a decreased ability to cause disease compared to the 1976 Zaire strain, which is underscored by the starkly different fatality rates. Another contributing factor to the lower fatality rate, of course, is the level of supportive care available for patients infected in 2014 versus 1976. Though there is currently no antiviral treatment for Ebola, supportive care including fluid replenishment, rest, and fever reduction can go a long way in treating someone with Ebola, especially a milder form of the disease.
An Ebola of Epidemic Proportions
When the outbreak in Guinea spread so rapidly, many hypothesized that the culprit strain was rapidly mutating into an epically virulent pathogen. However, anecdotal evidence mentioned above and genetic analysis of viral isolates show that this was not the case: viral mutation rates were no greater than those observed in previous Ebola outbreaks, and the virus was still only spread through fluid contact as opposed to even more contagious routes like airborne transmission. As a result, the scale of this Ebola outbreak had to be due to factors extrinsic to the virus itself.
The 2013-2016 Ebola outbreak is the first Ebola outbreak to reach epidemic proportions: the aforementioned outbreaks over the last few decades were all quelled within a couple of weeks. Several factors contributed to the size and scale of West Africa’s Ebola epidemic. Extreme poverty in the regions coupled with a dysfunctional healthcare system made it impossible to provide adequate surveillance, case detection, and proper containment practices every time somebody became ill. Furthermore, the outbreak came at the heels of civil war; distrust of government officials halted the already delayed official local response to news of the outbreak.
Local burial customs consist of washing a body after death. Ebola is spread by bodily fluids, and a deceased patient is particularly hot (teeming with virus). As a result, cases climbed up even more. As the outbreak spread, the few existing hospitals in affected regions became overwhelmed. Already short on staff and medical supplies, they were soon forced to close. Thus, in addition to Ebola-related fatalities, an additional death toll was tacked on to the epidemic from people who needed urgent care for other medical needs.
So why here? Why now? As the CDC report says, we do not have exact answers to these questions. Many outbreaks tend to occur as the result of a spillover, an event wherein an animal harboring a pathogen comes into contact with another species (in this case, humans). In the right conditions, the infection is transmitted from the animal reservoir to the new host. In addition to Ebola, other popular spillover microbes include the related Marburg virus, Hendra virus, Nipah virus, malaria, Q fever, HIV, and Legionnaire’s disease.
“In the right conditions” is the operative phrase here. Spillover events are exceedingly rare, and require highly specific environmental and genetic factors that allow a pathogen to survive and eventually propagate within a new host. Nonetheless, due to the massive quantities of microbes and increased human-wild animal interactions, such a one in a million-type event should not come to complete surprise.
Sure enough, genetic analysis of Ebola viruses has put forth nonhuman primates (such chimpanzees, gorillas, and monkeys) and bats as potential primary reservoirs of Ebola. Humans who hunt and eat nonhuman primates, especially when dealing with raw meat, are at risk of hosting a spillover. Contact with bats either directly or indirectly (such as by fecal contact) can also lead to such an event. We will never know the specific interaction that led to a one-year-old baby contracting the first case of Ebola virus in West Africa that led to this epidemic, but the widespread consensus is that it was some sort of spillover.
Organizations from all over the world have helped put a stop to the Ebola epidemic. When the WHO declared the outbreak an international emergency in August 2014, it published a roadmap to help guide and coordinate international response. The goal was to stop Ebola transmission within 6 to 9 months. In September 2014, the UN Security Council declared the epidemic a threat to international peace and security: it quickly resolved that United Nations member states ought to bring forth resources in efforts to raise at least $1 billion to fight the outbreak.
TIME magazine named the healthcare workers on the front lines against Ebola its “Person of the Year” in 2014. Local doctors and nurses, and healthcare workers from many different organizations such as Doctors Without Borders and Samaritan’s Purse were commended heavily for their early response efforts and dedicated workers who put their lives on the line to put a stop to this terrible disease.
The large-scale Ebola epidemic was finally over by the end of 2015. On January 14, 2016, the WHO declared that all known chains of transmission were stopped in West Africa. They cautioned, however, that small outbreaks were still possible in the future and that steadfast attention is essential. On January 15, Sierra Leone confirmed its first new case in 4 months. Sporadic cases have been trickling in, but so far they have been contained and no new outbreak has flared up.
Lessons learned during the outbreak and lessons still to be learned over the next several years will be pivotal in honing future outbreak responses. This is especially important now as the Zika pandemic unfolds in North and South America. While Ebola and Zika are massively different diseases (a point I cannot emphasize more), the broad themes of global infection control from one outbreak can always be applied to another. After all, emerging and re-emerging infectious diseases have been and always will be a perpetual challenge to human survival.