NPR
How contagious is Ebola, and how worried should you be?
The current outbreak has been characterized as "the perfect storm." This raises questions about how it originated, the features of the strain currently involved, and the implications for global health.
The Ebola case count is escalating substantially each day since the World Health Organization (WHO) designated a public health emergency on Saturday. As of now, there are over 600 suspected cases and 139 suspected deaths attributed to the virus.
Most of these cases are concentrated in a province located in the northeastern region of the Democratic Republic of Congo, an area that has faced significant challenges owing to years of internal conflict. Notably, there are also two reported cases in Uganda's capital. The WHO has identified the outbreak as a rare strain and indicates it may have commenced several months prior to its detection.
"This is an example of a perfect storm," states Dr. Abraar Karan, an infectious disease physician and faculty member at Stanford University.
Given that there has been more than a decade since the last extensive Ebola outbreak in West Africa, it is critical to understand the nature of this virus and the concerns being voiced by experts monitoring the situation.
Where and how do Ebola outbreaks start?
Geographically, the origins of Ebola outbreaks are relatively consistent: they predominantly occur in either East or West Africa, with the Democratic Republic of the Congo being the site of the highest number of occurrences. This outbreak marks the 17th since the virus was first identified in 1976.
The exact mechanisms by which humans contract the virus remain partially understood.
"We cannot definitively say where the virus originates, but we have several hypotheses," explains Karan, who has conducted research on Ebola and similar viruses in Kenya for several years.
Current leading theories suggest that humans may contract Ebola through the consumption of bat meat or exposure to bat guano, which can occur in mining activities that involve cave exploration.
Evidence points to multiple animal species, such as certain deer known as duikers and non-human primates, having tested positive for antibodies, indicating potential involvement.
Typically, the transmission begins with an individual acquiring the virus from an animal—a process referred to as spillover—before it spreads to other humans.
What does the virus do to people?
Dr. Nahid Bhadelia managed more than 500 Ebola patients during the West African outbreak a decade ago.
"One of the essential lessons learned is that Ebola can present in a range of severity. In some instances, symptoms are mild, resembling a flu-like illness, and individuals may recover," says Bhadelia, who is an infectious diseases physician and director at Boston University’s Center on Emerging Infectious Diseases.
In the initial stages of the infection, Ebola often mimics other illnesses such as malaria and typhoid, with symptoms including nausea, diarrhea, and fever.
What is alarming is the progression of the disease. Contrary to sensationalized portrayals in films like "Outbreak," Bhadelia asserts, "I have yet to observe the dramatic symptoms such as bleeding from the eyes."
Instead, the clinical presentation often includes severe diarrhea and vomiting, potentially with blood. Many fatalities occur due to the body entering shock and organs failing, driven by an intensified immune response to the virus.
Survival rates vary significantly based on the promptness and quality of medical intervention, which may include supportive care or the use of monoclonal antibodies—synthetically engineered proteins that mimic the immune system's response.
"In West Africa, we experienced mortality rates ranging from 50 to 70%," she states. In contrast, Americans who were treated after becoming infected had mortality rates below 20%. "This disparity highlights the impact of advanced medical care and available targeted therapies."
What's known about this particular strain of Ebola?
Ebola virus has several strains, each presenting with distinct fatality rates.
The Zaire strain, which was responsible for the large 2014-2016 West African outbreak, carries a mortality rate of up to 90% if left untreated, according to the U.S. Centers for Disease Control and Prevention. However, the Bundibugyo virus—responsible for the current outbreak—exhibits a markedly different profile.
"If there is any positive aspect to note, it is that data from previous Bundibugyo outbreaks indicates a somewhat lower case fatality rate—though still concerning," explains Dr. Daniel Bausch, a visiting professor at the Geneva Graduate Institute.
Historical data suggests the fatality rate for this strain falls between 30 and 50%, as indicated by Bhadelia. However, due to the limited number of past outbreaks recorded, comprehensive data is sparse.
An additional significant hurdle is the absence of vaccines or specific treatments for this strain of the Ebola virus—a stark contrast to the Zaire strain, for which two vaccines are available, in addition to monoclonal antibody options.
The lack of therapeutic resources raises significant concerns among infectious disease experts, but some maintain a degree of optimism. "While the absence of vaccines or treatments is certainly a challenge, we have successfully contained numerous Ebola outbreaks in the past without these tools," notes Bausch. Recently developed interventions have only become accessible for the Zaire strain within the last few years.
In the absence of these options, healthcare professionals depend on alternative containment strategies, including supportive care such as rehydration. Bausch emphasizes that effective control measures encompass rigorous infection control protocols and contact tracing, which involves identifying individuals who have been in contact with infected individuals.
How contagious is Ebola?
On a positive note, "Ebola does not transmit through airborne routes," reports Karan. "Thus, it is not nearly as contagious as diseases like COVID-19 or measles."
Supporting this, Bhadelia states, "A single individual with Ebola typically infects about two others, as opposed to measles, which affects approximately 18." While measles is significantly more communicable, the mortality rates for various Ebola strains are considerably higher.
Ebola primarily transmits among individuals through direct contact with bodily fluids, including saliva, blood, semen, and diarrhea.
Individuals infected with Ebola are not considered infectious until they begin to exhibit symptoms. "As the individual's health deteriorates, the viral load in their bodily fluids increases," explains Bhadelia. This underscores the necessity for stringent infection control measures in medical facilities and among caregivers, which should include the use of gloves, gowns, and masks.
The risk of transmission does not cease with death. "Following a patient’s passing, there remains a substantial viral load in bodily fluids," she notes. "Regrettably, at this stage, they harbor the highest concentration of the virus, which underscores the critical need for safe burial practices."
During the 2014-2016 outbreak in West Africa, numerous analyses suggested that funerals and associated burial customs contributed to over 50% of new cases. For instance, in Liberia and Sierra Leone, certain mourning practices involved bathing in water used to clean corpses or sleeping near the body for an extended period.
For individuals who recover from the virus, the risk persists as the virus may remain in certain bodily compartments shielded from the immune system—like the semen. This persistence has previously led to the re-emergence of outbreaks, prompting the importance of long-term monitoring of survivors.
Why have many past Ebola outbreaks "fizzled out"?
"Most Ebola outbreaks tend to diminish over time," asserts Karan of Stanford University, albeit often at a significant toll in human lives.
There are two primary reasons for this phenomenon. First, outbreaks primarily occur in rural regions, where opportunities for widespread transmission are limited. These areas often possess closer interactions with wildlife, facilitating initial transmission.
Second, the virus exhibits high fatality rates, with many patients succumbing to the illness historically before it can spread substantially.
Concerns arise when the virus reaches urban centers. The 2014–2016 outbreak in West Africa serves as a poignant example, leading to over 28,600 reported cases and 11,000 deaths, as recorded by the WHO.
Moreover, Bausch asserts that with contemporary transportation networks facilitating rapid movement and centralized medical facilities, it is no longer feasible to rely on the concept of viruses "burning out," especially when outbreaks begin in isolated settings.
What makes this outbreak worrisome?
The current outbreak has elicited heightened concern from the infectious disease community.
"My level of concern is extremely high," expresses Bhadelia.
Several factors contribute to this heightened alarm.
Firstly, the absence of vaccines or specific treatments for the current strain is alarming.
Secondly, delays in detection have allowed the virus to spread across borders and into major urban areas, including Kampala, the capital of Uganda, and Goma, a regional hub in the DRC.
"The identification of numerous patients across various cities, separated by significant distances, suggests that this outbreak may have been ongoing for some time," warns Bhadelia. Concerns are further amplified by the handling of deceased patients—cultural practices may have exposed more individuals to the virus during burials.
Thirdly, the accelerating case numbers and an increasing proportion of positive test results imply that the outbreak could be substantially more extensive than current figures reflect.
Particularly troubling is the fact that several recent fatalities have involved healthcare workers. "These individuals serve as indicators of a larger problem; it signals the likelihood that many Ebola patients are remaining undiagnosed," she notes. "Current case counts may merely reveal the tip of the iceberg."
Fourthly, the outbreak originated in an area with conditions conducive to disease proliferation. The locality is remote and suffers from inadequate healthcare infrastructure, as well as being home to a migratory workforce and multinational companies that could facilitate cross-border transmission. The region has also been afflicted by conflicts, complicating public health responses.
"It's challenging to conduct contact tracing in an environment with significant insecurity," explains Bausch. He asserts that while standard public health protocols can be effective, their application in such contexts poses considerable challenges.
Experts are wary that this outbreak may not be resolved swiftly. "My expectation is that containment efforts will take several weeks, if not months," predicts Bhadelia.
How concerned should people be outside of the region?
Karan indicates a worry that cases may emerge in other countries, expressing doubt about the preparedness of the United States for potential incoming cases and quarantine procedures.
However, Bausch attempts to alleviate concerns for the general populace.
Since the virus does not spread through airborne means and patients are typically only infectious once they exhibit symptoms, caregivers at home or in medical settings bear the greatest risk. Even then, he observes, "In the U.S., it is uncommon for healthcare workers to face situations where essential supplies like gloves, running water, or soap are unavailable."
While acknowledging the potential for isolated cases, he does not foresee a large-scale Ebola outbreak occurring in high-income nations.
For those reaching out for reassurance regarding the outbreak's risks, he offers a consistent piece of advice: "Get your flu shot and wear your seatbelt while driving," he advises, emphasizing that the risks associated with those activities far exceed the "extremely, extremely small" risk of contracting Ebola.
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