Washington, Oct 16: A suspected case of sexual transmission of Ebola virus disease in Liberia has been confirmed using genomic analysis, scientists say.
Scientists working with the Liberian Institute for Biomedical Research (LIBR) earlier this year analysed blood samples from a female patient who tested positive for Ebola virus (EBOV) in March 2015 when there had been no new documented cases for 30 days.
The patient was reported to have had recent sexual intercourse with a male partner who had survived Ebola virus disease (EVD) and had been declared EBOV negative in early October 2014.
Following the patient's death in March, public health officials were able to secure the consent of the male survivor to obtain and test a semen sample from him, said Suzanne Mate of the US Army Medical Research Institute of Infectious Diseases (USAMRIID).
The semen sample tested EBOV positive by quantitative reverse transcription polymerase chain reaction (RT-PCR) but the assay indicated that the level of viral RNA was low and required a different sample preparation method than the one originally deployed to sequence EBOV RNA from acute samples.
"We implemented a new enrichment strategy in collaboration with scientists from Illumina, Inc that was pivotal in obtaining the required coverage to complete downstream genomic analysis," said Michael Wiley of USAMRIID.
Next-generation sequencing of the enriched EBOV RNA extracted from the male survivor's semen was used to compare the genome for similarity to the virus RNA extracted from the female patient's blood sample.
"Ebola virus genomes assembled from the patient's blood and the survivor's semen were consistent with direct transmission," said Jason Ladner of USAMRIID.
"The samples shared three genetic substitutions that have not been found in any other Ebola virus sequences in Western Africa," Ladner said.
In addition, said Ladner, these three genetic changes were distinct from the last documented transmission chain in Liberia prior to this case. Combined with epidemiologic data, the genomic analysis provides support for sexual transmission of Ebola virus and for the persistence of infective EBOV in semen for more than 179 days after disease onset, researchers said.
This caused both the Centers for Disease Control and Prevention and the World Health Organisation to change their recommendations for convalescent patients regarding sexual contact until more definitive information is obtained about how long Ebola virus can persist in semen, researchers said.
The study was published in the New England Journal of Medicine.