However, new research published Thursday in the journal Science suggests that the virus is undergoing only limited mutational changes, and is no more virulent than when the outbreak began.
"Despite the extensive and prolonged human-to-human transmission in this outbreak, the virus is not mutating at a rate beyond what is expected," wrote lead study author Thomas Hoenen, a virologist at the National Institute of Allergy and Infectious Diseases, and colleagues.
The conclusion comes as a bit of a relief. Early reports had suggested that the Ebola virus was mutating twice as fast as it had in other outbreaks. If in fact it were changing that quickly, it could possibly evolve ways of evading diagnostic tests or develop protections against experimental vaccines and treatments such as ZMapp or TKM-Ebola.
"Our data indicate that Ebola virus is not undergoing rapid evolution in humans during the current outbreak," the authors wrote.
Researchers arrived at this conclusion after genetically sequencing samples of Ebola taken from patients in Mali. The samples were taken from a toddler who died from the virus in October and from three other patients who were infected in November.
The researchers said they were surprised to find that the virus sample from the toddler showed only nine nucleotide differences from another sample obtained in Sierra Leone almost six months earlier. (The Ebola genome consists of a single strand of RNA made up of almost 19,000 nucleotides.)
To date, the Ebola epidemic has sickened 24,907 people and killed 10,326, according to the World Health Organization. Most of the infections have occurred in Guinea, Sierra Leone and Liberia.
"In the past, Ebola viruses have been reported to undergo only limited genetic changes during outbreaks, a phenomenon that also seems to be true in the current outbreak," the study authors wrote.
"Whereas from a public health perspective the current Ebola virus outbreak in West Africa continues to be an extremely pressing emergency, it is doubtful that either virulence or transmissibility has increased in the circulating Ebola virus strains."