感染症：エボラ出血熱生存者では抗体レベルが上下する

39 out of 51 healthy survivors of Ebola experienced a resurgence in antibody levels nearly a year after recovery, a Nature study reveals. The finding, which hints that hidden reservoirs of virus could exist long after symptoms ease, has implications for monitoring programmes and vaccination strategies.

When a person is infected with Ebola virus, their body produces antibodies to fight the disease. Antibody concentrations peak and then decline over time, providing the body with some degree of immune memory to the infection, but little is known about the antibody response over prolonged time periods. Georgios Pollakis and colleagues tracked antibodies in a cohort of 115 survivors of Ebola from the 2013–2016 Sierra Leone outbreak for up to 500 days after infection. As expected, antibody concentrations dropped during the acute phase of recovery, but then unexpectedly increased around 200 days later, only to decline thereafter. This particular pattern was observed in 39 out of the 51 study participants with available longitudinal follow up.

Although there was no detectable Ebola virus in the participants’ plasma during the resurgence, the study hints that sometimes, the Ebola virus may be able to persist inside the bodies of recovered patients for long periods of time. ‘Hiding’ inside immunologically privileged sites, such as the eyes, central nervous system or testes, the virus may then start to replicate, prompting the renewed antibody response. With this in mind, the authors suggest that long-term monitoring of survivors is warranted, and that repeat vaccination may be needed to boost protective antibody responses in survivors.