Convalescent serum fails to protect monkeys from Ebola virus

Blood serum from rhesus monkeys that had survived Ebola virus (EBOV) infection offered little protection to other rhesus monkeys that were treated with the serum several days after exposure to the virus, according to an Aug 28 report in the Journal of Infectious Diseases.

During West Africa's recent Ebola epidemic, the World Health Organization recommended studying the use of Ebola convalescent serum to treat Ebola patients, with the expectation that antibodies in the serum would be protective. But results from studies so far have been inconclusive.

In the study, nine monkeys were infected with Zaire Ebola virus (ZEBOV). Three days later, 4 of the monkeys were treated with serum from rhesus monkeys that had previously survived ZEBOV infection, 3 received serum from monkeys that had survived Sudan EBOV (SEBOV) disease, and 2 received no treatment. The monkeys that survived long enough received more treatments on days 6 and 9.

All 4 monkeys treated with the ZEBOV convalescent serum died on days 8 and 9, and 2 of the 3 monkeys that received SEBOV serum died on days 7 and 9. The 2 control animals succumbed on day 9.

To further assess the effects of the SEBOV convalescent serum, the researchers did a follow-up study in which three more monkeys were exposed to ZEBOV and then treated with the serum. All the animals died on days 7 and 9 after exposure, which suggests that the survivor in the initial study may not have been protected by the product, the authors said.

They commented that all the monkeys had EBOV in their blood at the time of treatment, which sets a "high bar" for any candidate treatment to clear.

"We conclude that convalescent sera treatment initiated in [monkeys] at the onset of viremia is not an effective therapeutic, particularly when compared to the recent successes of the small interfering RNA and ZMapp therapeutics at advanced stages of disease," the authors concluded.

Aug 28 J Infect Dis abstract

Jan 6 CIDRAP News story on trial of convalescent plasma in Guinea

Report describes simple method for inactivating Ebola in human samples

Researchers reported this week that a protocol involving a little detergent and mild heat can be used in the field to inactivate EBOV in human serum samples while preserving their diagnostic value, thus protecting healthcare workers who handle them.

Writing in the Journal of Infectious Diseases, the authors said the deactivation method consists of treating samples with a 0.5% solution of Tween-20 and heating them to 56°C (133°F) for 1 hour. When this method was used in lab conditions on samples spiked with high levels of EBOV, no surviving virus was found in the samples.

When the protocol was used on 240 samples during Sierra Leone's recent Ebola epidemic, 120 samples tested positive for immunoglobulin G (IgG) and/or IgM antibodies to EBOV. "This demonstrates that the inactivation protocol allows for the safe detection of seropositive samples," the authors wrote.

"Use of this simple inactivation procedure will help strengthen the safety measures in the ﬁeld or in a healthcare setting and conﬁdence of healthcare workers who are performing these diagnostic assays," the researchers said.

Aug 28 J Infect Dis abstract