Disease 'superspreaders' were driving cause of 2014 Ebola epidemic

February 13, 2017, Oregon State University
The Ebola virus, isolated in November 2014 from patient blood samples obtained in Mali. The virus was isolated on Vero cells in a BSL-4 suite at Rocky Mountain Laboratories. Credit: NIAID

A new study about the overwhelming importance of "superspreaders" in some infectious disease epidemics has shown that in the catastrophic 2014-15 Ebola epidemic in West Africa, about 3 percent of the people infected were ultimately responsible for infecting 61 percent of all cases.

The issue of superspreaders is so significant, scientists say, that it's important to put a better face on just who these people are. It might then be possible to better reach them with public health measures designed to control the spread of infectious disease during epidemics.

Findings were reported this week in Proceedings of the National Academy of Sciences.

The researchers concluded that Ebola superspreaders often fit into certain age groups and were based more in the community than in . They also continued to spread the disease after many of the people first infected had been placed in care facilities, where transmission was much better controlled.

If superspreading had been completely controlled, almost two thirds of the infections might have been prevented, scientists said in the study. The researchers also noted that their findings were conservative, since they only focused on people who had been buried safely.

This suggests that the role of superspreaders may have been even more profound than this research indicates.

The research was led by Princeton University, in collaboration with scientists from Oregon State University, the London School of Hygiene and Tropical Medicine, the International Federation of Red Cross and Red Crescent Societies, the Imperial College London, and the National Institutes of Health.

The concept of superspreaders is not new, researchers say, and it has evolved during the 2000s as scientists increasingly appreciate that not all individuals play an equal role in spreading an infectious disease.

Superspreaders, for instance, have also been implicated in the spread of severe acute respiratory syndrome, or SARS, in 2003; and the more recent Middle East respiratory syndrome in 2012.

But there's less understanding of who and how important these superspreaders are.

"In the recent Ebola outbreak it's now clear that superspreaders were an important component in driving the epidemic," said Benjamin Dalziel, an assistant professor of population biology in the College of Science at Oregon State University, and co-author of the study.

"We now see the role of superspreaders as larger than initially suspected. There wasn't a lot of transmission once people reached hospitals and care centers. Because case counts during the epidemic relied heavily on hospital data, those hospitalized cases tended to be the cases we 'saw.'

"However, it was the cases you didn't see that really drove the epidemic, particularly people who died at home, without making it to a care center. In our analysis we were able to see a web of transmission that would often track back to a community-based superspreader."

Superspreading has already been cited in many first-hand narratives of Ebola transmission. This study, however, created a new statistical framework that allowed scientists to measure how important the phenomenon was in driving the epidemic. It also allowed them to measure how superspreading changed over time, as the epidemic progressed, and as control measures were implemented.

The outbreak size of the 2014 Ebola epidemic in Africa was unprecedented, and early control measures failed. Scientists believe that a better understanding of superspreading might allow more targeted, and effective interventions, instead of focusing on whole populations.

"As we can learn more about these infection pathways, we should be better able to focus on the types of individual behavior and demographics that are at highest risk for becoming infected, and transmitting infection," Dalziel said.

Researchers pointed out, for instance, that millions of dollars were spent implementing message strategies about Ebola prevention and control across entire countries. They suggest that messages tailored to individuals with higher risk and certain types of behavior may have been more successful, and prevented the from being so persistent.

Explore further: Control of emerging Ebola infections could be aided by new monitoring method

More information: Spatial and temporal dynamics of superspreading events in the 2014–2015 West Africa Ebola epidemic, PNAS, www.pnas.org/cgi/doi/10.1073/pnas.1614595114

Related Stories

Control of emerging Ebola infections could be aided by new monitoring method

December 8, 2016
New research on the 2014 Ebola epidemic tracks the rate at which infections move from one district to another and how often infections cross the borders between countries. This study, published in PLOS Computational Biology, ...

Study uses social media, internet to forecast disease outbreaks

January 19, 2017
When epidemiological data are scarce, social media and Internet reports can be reliable tools for forecasting infectious disease outbreaks, according to a study led by an expert in the School of Public Health at Georgia State ...

Areas of increased poverty associated with higher rates of Ebola transmission

December 31, 2015
Since October 2014 the Ebola epidemic in West Africa has been diminishing and efforts have shifted from emergency response to prevention and mitigation of future outbreaks. Researchers from the Liberian Ministry of Health ...

UN: Latest Ebola outbreak in Guinea is now over

June 1, 2016
The World Health Organization says the latest Ebola outbreak in Guinea has ended and the country is now entering a 90-day heightened surveillance period to monitor for any unexpected cases.

Postmortem on Ebola outbreak in Sierra Leone offers new insights into effective intervention strategies

March 29, 2016
(Medical Xpress)—A team of researchers from China, the U.S. and Sierra Leone has performed a postmortem on the Ebola outbreak that occurred during 2014/15 infecting approximately 8,700 people in Sierra Leone and killing ...

Recommended for you

Research finds new mechanism that can cause the spread of deadly infection

April 20, 2018
Scientists at the University of Birmingham have discovered a unique mechanism that drives the spread of a deadly infection.

Selection of a pyrethroid metabolic enzyme CYP9K1 by malaria control activities

April 20, 2018
Researchers from LSTM, with partners from a number of international institutions, have shown the rapid selection of a novel P450 enzyme leading to insecticide resistance in a major malaria vector.

Study predicts 2018 flu vaccine will have 20 percent efficacy

April 19, 2018
A Rice University study predicts that this fall's flu vaccine—a new H3N2 formulation for the first time since 2015—will likely have the same reduced efficacy against the dominant circulating strain of influenza A as the ...

Low-cost anti-hookworm drug boosts female farmers' physical fitness

April 19, 2018
Impoverished female farm workers infected with intestinal parasites known as hookworms saw significant improvements in physical fitness when they were treated with a low-cost deworming drug. The benefits were seen even in ...

Zika presents hot spots in brains of chicken embryos

April 19, 2018
Zika prefers certain "hot spots" in the brains of chicken embryos, offering insight into how brain development is affected by the virus.

Super-superbug clones invade Gulf States

April 18, 2018
A new wave of highly antibiotic resistant superbugs has been found in the Middle East Gulf States, discovered by University of Queensland researchers.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.