How contagious is Ebola? And how worried should you be about the current outbreak?

How contagious is Ebola? And how worried should you be about the current outbreak?

The incidence of Ebola cases has escalated significantly, following the World Health Organization's declaration of a public health emergency on Saturday. The current figures reflect more than 600 suspected cases and 139 suspected deaths attributed to the virus.

The majority of these cases are concentrated in a province located in northeastern Democratic Republic of Congo, a region struggling with the repercussions of prolonged conflict. Additionally, there are reported cases in Uganda's capital, Kampala. The World Health Organization has identified the outbreak as arising from a rare strain of Ebola and suggested that it may have been in circulation for 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.

Considering it has been over a decade since the significant Ebola outbreak in West Africa, it is essential to understand the nature of this virus and the concerns that infectious disease experts are expressing regarding the current outbreak.

Where and how do Ebola outbreaks start?

Geographically, it is well established that Ebola outbreaks typically originate in either East or West Africa. The Democratic Republic of Congo has recorded the highest number of these outbreaks, marking this as its 17th since the disease was first identified in 1976.

The mechanisms by which humans acquire the virus, however, remain less clear.

"We don't know for sure where it comes from but we have suspicions," acknowledges Karan, whose research team has been studying Ebola and related viruses in Kenya for several years.

The prevailing hypothesis, according to Karan, is that Ebola is transmitted to humans through the consumption of bat meat or direct exposure to bat guano, which can occur when individuals access caves for mining purposes.

"Several animal species have also tested positive for antibodies, particularly certain types of deer known as duikers that consume meat. Non-human primates have also shown the presence of antibodies," he adds.

Typically, one person becomes infected through contact with an animal, referred to as a spillover event, and subsequently transmits the virus to others.

What does the virus do to people?

Dr. Nahid Bhadelia has provided care to over 500 Ebola patients during the West African outbreak a decade ago.

"One significant lesson I learned during that time is that Ebola presents a wide array of clinical manifestations. In some instances, it may initially appear relatively mild, resembling a flu-like syndrome, and individuals may recover," explains Bhadelia, an infectious diseases physician and director of the Boston University Center on Emerging Infectious Diseases.

She emphasizes that early symptoms of Ebola can mimic other infectious diseases, such as malaria and typhoid, leading to symptoms like nausea, diarrhea, and fever.

The pressing concern arises when the disease advances; however, it diverges from its dramatic depictions in films such as the 1995 film "Outbreak."

"In many cinematic portrayals, Ebola is depicted as causing bleeding from the eyes. I must say, after caring for hundreds of Ebola patients, I've yet to encounter that symptom," states Bhadelia.

Rather, she describes how patients typically experience "massive amounts of diarrhea and vomiting," often with blood present. Many fatalities occur due to shock and organ failure, "triggered by the patient's immune response to the virus."

Survival rates significantly depend on the promptness and quality of medical intervention, which may include supportive care or the administration of monoclonal antibodies. Monoclonal antibodies are lab-engineered proteins that mimic the body's natural antibodies and can inhibit the virus.

"In West Africa, we faced a mortality rate of 50 to 70%," she recounts. In contrast, Americans infected there and subsequently treated in the U.S. exhibited mortality rates below 20%. "This stark contrast illustrates the impact of quality medical care and targeted treatments."

What's known about this particular strain of Ebola?

Different strains of the Ebola virus exhibit varying fatality rates.

The Zaire strain, which was responsible for the extensive West Africa outbreak from 2014 to 2016, has a fatality rate of up to 90% if left untreated, according to the U.S. Centers for Disease Control and Prevention. This strain accounted for the surge during the West Africa outbreak, but this striking figure is not applicable to the Bundibugyo virus, the strain identified in the current outbreak.

"If there is a silver lining, data from previous Bundibugyo outbreaks indicate a lower case fatality rate—albeit not comfortingly low—compared to some other strains of Ebola," clarifies Dr. Daniel Bausch, visiting professor at the Geneva Graduate Institute.

Past outbreaks reveal that the Bundibugyo strain has a fatality rate ranging from 30% to 50%, as stated by Bhadelia. However, it is essential to note that there are only two recorded Bundibugyo outbreaks, resulting in limited data.

Another significant challenge is the absence of vaccines or specific treatments for this particular Ebola strain. This situation contrasts sharply with the Zaire strain, for which there are two licensed vaccines, in addition to monoclonal antibodies.

The lack of medical countermeasures has raised concern among infectious disease specialists; nonetheless, some remain optimistic. "While the lack of resources is certainly a barrier, we have successfully managed numerous Ebola outbreaks in the past without either a vaccine or therapeutic treatment," Bausch observes. The availability of these resources for the Zaire strain has only emerged in recent years.

In the absence of specific interventions, healthcare providers resort to alternative strategies for virus containment and patient care, including supportive therapies like rehydration. Bausch mentions that control measures encompass effective infection control practices and contact tracing—identifying individuals who have interacted with confirmed Ebola cases.

How contagious is Ebola?

To start with some reassuring news, "Ebola does not transmit through the airborne route," states Karan. "Therefore, it is not nearly as infectious as COVID-19 or measles."

Bhadelia supports this assertion, stating, "The average number of individuals infected by one person with Ebola is about two, in stark contrast to measles, where one infected person can transmit the virus to about 18 others." While measles is considerably more transmissible, the mortality rates for many Ebola species are significantly higher.

Generally, Ebola spreads between individuals through contact with bodily fluids, including saliva, blood, semen, and diarrhea.

Individuals infected with Ebola are not considered contagious until they begin to exhibit symptoms. "As the illness progresses, the viral load in their bodily fluids increases," Bhadelia notes. This underscores the critical importance of stringent infection control protocols for healthcare workers and caregivers—utilizing gloves, gowns, and masks.

Importantly, even after death, the risk of transmission persists. "Post-mortem, patients' bodily fluids contain a substantial viral load," she explains. "Regrettably, that is often when the concentration of virus within their bodies is at its peak, which is why safe burial practices are so vital."

During the 2014-2016 West Africa outbreak, numerous analyses indicated that traditional funeral customs and burial practices were associated with over 50% of new cases. For instance, in Liberia and Sierra Leone, some mourners would bathe in water used to cleanse corpses, while other traditions involved sleeping near the deceased for several nights, according to the World Health Organization.

Moreover, survivors of the virus can harbor the virus in certain body compartments that are shielded from the immune system, such as in semen. This phenomenon has previously triggered renewed outbreaks and is a compelling reason for monitoring survivors in the months and years after infection.

Why have many past Ebola outbreaks "fizzled out"?

"Most Ebola outbreaks tend to fizzle out," remarks Dr. Karan from Stanford—albeit not without a profound human cost.

Two principal factors contribute to this pattern. First, such outbreaks typically transpire in rural locales where the opportunities for broad transmission are limited. The propensity for outbreaks to initiate in remote areas is largely due to significant interaction between local populations and wildlife.

Second, the high fatality rate associated with Ebola means that affected individuals often succumb quickly, reducing the potential for extensive spread.

Karan’s concern escalates when the virus infiltrates larger urban settings. This was the case during the unprecedented 2014–2016 outbreak in West Africa, which resulted in more than 28,600 reported cases and 11,000 fatalities, as documented by the World Health Organization.

Bausch adds that globalization has altered the dynamics, emphasizing that contemporary transport networks and centralized healthcare facilities complicate containment. "You can no longer rely on the assumption that the outbreak will fizzle out simply because it begins in a remote location."

What makes this outbreak worrisome?

There is mounting apprehension among infectious disease experts regarding the current outbreak.

"My anxiety levels are quite elevated," states Bhadelia.

What factors contribute to this heightened concern?

Firstly, the absence of vaccines or targeted treatments for this strain of the virus raises alarms.

Secondly, this outbreak was slow to detect and has already extended beyond borders, affecting major cities such as Kampala, the capital of Uganda, and Goma, a regional hub in the DRC.

"The discovery of numerous patients across various cities and towns that are geographically distant indicates that this situation has likely been unfolding for some time," warns Bhadelia. "In many instances, when individuals who succumbed to the virus were repatriated for burial in their home communities, the handling of their remains raises questions regarding potential additional exposures."

Thirdly, the rapid increase in case numbers—coupled with a significant percentage of positive test results for Ebola—suggests that the outbreak may be far more extensive than the numbers indicate.

Bhadelia expresses particular concern about the fatalities among healthcare professionals. "These individuals serve as early indicators of the situation; their infections signal that many Ebola patients are not being diagnosed," she explains. "I believe the current reported cases represent merely the tip of the iceberg."

Additionally, the outbreak's origin in a region characterized by poor healthcare infrastructure, migrant labor, and external corporate involvement, compounded by ongoing conflict, presents unique challenges for containment.

"It's challenging to implement contact tracing amidst ongoing conflict," states Bausch. He insists that while standard public health measures are effective, "applying these strategies in such complex environments is not straightforward."

The consensus among experts is that controlling this outbreak may take considerable time: "I anticipate that we will not be able to bring this outbreak to an end for several weeks, if not months," cautions Bhadelia.

How concerned should people be outside of the region?

Karan expresses concern that cases may arise in other countries, stating, "I genuinely doubt that the United States is adequately prepared for a scenario in which multiple individuals require quarantine here," noting that a specialized quarantine facility in Nebraska is currently occupied with individuals potentially exposed to hantavirus aboard a cruise.

However, Bausch conveys a more measured perspective.

Given that the virus is not transmitted via airborne particles and that infected individuals are only contagious once symptomatic, he assesses that caregivers—whether in domestic or clinical settings—bear the greatest risk. Even under those conditions, "you never find a situation [in the U.S.] where healthcare workers report an absence of gloves, running water, or soap," he affirms.

While acknowledging the potential for isolated cases, he remains optimistic that "we are unlikely to witness a significant Ebola outbreak in a high-income country."

Thus, for friends and family members inquiring about the risks associated with the outbreak, he provides a consistent reassurance: "Get your flu shot and remember to wear your seatbelt while driving," as these dangers far outweigh the "extremely, extremely small" risk of contracting Ebola.