Many health care workers in the Democratic Republic of Congo showed reactivity to Ebola virus proteins despite never having reported symptoms, suggesting that more Ebola exposure and infection is occurring than previously reported, according to a new study, published in The Journal of Infectious Diseases.
The study found that 41.4% of 565 enrolled health care workers were reactive to at least 1 Ebola virus protein.
The study was conducted in the Boende Health Zone in the aftermath of a 2014 Ebola outbreak in that area. It found that 28.1% of those tested were seroreactive for anti-glycoprotein immunoglobulin G (IgG), 15.8% were seroreactive for anti-nucleoprotein IgG, 9.5% were VP40 positive, and sera from 2.8% of health care workers demonstrated neutralization capacity.
"Starting to find individuals who are able to have broad neutralizing effects may give some indication of how to develop a better vaccine," Nicole Hoff, PhD, MPH, assistant adjunct professor at the University of California, Los Angeles, Fielding School of Public Health, and lead author of the study, told Contagion®
The highest GP and NP seroprevalence was seen among those who had direct contact with patients during the 2014 outbreak, including traditional healers, pastors, and midwives, the study said. VP40 seroprevalence and neutralizing capacity were highest among Red Cross workers.
High GP seroprevalence among all workers, including guards and administrators, suggest wide exposure risks that could reflect the general population and may indicate endemic exposure to Ebola virus in the area.
The strain of Ebola from the 2014 outbreak was phylogenetically similar to that of Ebola outbreaks in the mid-1990s in Middle Africa, Robert Garry, PhD, of the Department of Microbiology and Immunology at Tulane University School of Medicine, pointed out in an associated commentary
, calling the similarities "inexplicable" and much greater than expected.
"Some people with no known history of Ebola or who live in areas where no Ebola outbreak has occurred produce antibodies that react, often strongly, with [Ebola virus] proteins," Dr. Garry wrote. "Proven explanations for the presence of these markers are lacking, but it is not for lack of trying."
The majority of participants were reactive to only 1 Ebola protein, with only 6 reacting to all 3, suggesting that most individuals may have been exposed to cross-reactive epitopes rather than intact Ebola virus, Dr. Garry noted.
"We started this research to answer questions, but in fact, the results just generated a huge number of additional questions," Dr. Hoff said in the interview.
These questions include: Why were the results so high? What does reactivity mean to immunity? Is there an overarching antibody that could be reacting similarly to various tests? What are the best testing procedures?
The study noted that serological testing varies with no gold standard applied across studies. More research to examine the roles each protein plays in immune response is needed.
"Answers to the questions of whether the serological responses are due to a subclinical infection, exposure to inactivated or disrupted virus, cross-reactivity to a nonpathogenic filovirus, or other spurious cross-reactivities will not be answered by more-precisely calibrated tests," Garry wrote. "To answer these questions, new techniques will need to be applied to the problem."
Identifying Ebola virus reservoirs could provide some answers. Investigators in Liberia recently reported evidence of a strain of Ebola virus in Greater Long-fingered bats
The study underscores the importance of adequate training and access to equipment to reduce exposure among health care workers, who are at elevated risk.
Investigators at the Medical University of South Carolina recently conducted a pilot trial of online software program to train health care workers on techniques to reduce infection when treating patients infected with Ebola. The study was published in the journal Health Security.
Concerns about the spread of Ebola led some investigators to consider preemptive screening
of those who have traveled to outbreak zones, particularly for health care workers and others at high risk.
Hoff emphasized that seroreactivity is not the same as seropositivity and does not necessarily mean that those whose blood was reactive to Ebola proteins had ever had the infection.
"We know for sure they’re reactive," Dr. Hoff explained. "There is something that is making their blood reactive to our tests, but the exact cause of it is uncertain."
Answering the questions surrounding Ebola virus will require a multidisciplinary approach, Dr. Hoff concluded.
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