Researchers who found previously unreported cases of “minimally symptomatic” Ebola virus infection in Sierra Leone say the discovery means the largest Ebola outbreak in history may have been even bigger.
The researchers tested inhabitants of a Sierra Leonean village and found that some had signs of previous Ebola infection without ever having been diagnosed with the disease.
Most, in fact, never had any symptoms, and those who did reported only mild symptoms.
“The findings provide further evidence that Ebola, like many other viral infections, presents with a spectrum of clinical manifestations, including minimally symptomatic infection,” Eugene T. Richardson, MD, clinical fellow in the department of infectious diseases and geographic medicine and PhD student in anthropology at Stanford University, and colleagues wrote in PLoS Neglected Tropical Diseases.
Beginning in 2013, the West African Ebola outbreak infected more than 28,000 people in Guinea, Liberia and Sierra Leone, killing more than 11,300, according to WHO. But Richardson and colleagues say their findings suggest “a significant portion” of cases may have gone undetected in minimally symptomatic patients who were not considered part of the outbreak.
To investigate the occurrence of such patients, they blood tested inhabitants of Sukudu, a small village of approximately 900 people in the diamond-rich district of Kono. The village is in eastern Sierra Leone near the borders of both Guinea and Liberia and was considered an Ebola hotspot during the outbreak, with 301 reported cases between August 2014 and February 2015.
Richardson and colleagues conducted their study in two parts between October 2015 and January 2016, testing 187 people from the village who had been quarantined during the outbreak and who were not known to have been infected with Ebola. They used 132 individuals with a self-reported low likelihood of Ebola exposure as negative controls and 30 Ebola survivors as positive controls.
Ebola virus particles
Source: National Institute of Allergy and Infectious Diseases
Of the 187 study participants, 14 showed immunoglobin G responses to Zaire ebolavirus 1 year after the peak of the outbreak in Sierra Leone. Twelve of the 14 said they had no symptoms of Ebola virus infection during quarantine, while the other two reported only fever.
Richardson and colleagues said it was possible that study participants who tested positive for previous Ebola infection had symptoms, but denied them. There were other limitations, as well.
“Our study focused on the quarantined population of one village,” they advised. “Extrapolation of our findings to other villages and generalizability to the epidemic should be approached with caution.” – by Gerard Gallagher
Disclosures: The researchers report no relevant financial disclosures.