Résumé
The West African Ebola virus disease (EVD) outbreak has resulted in 28,616 confirmed or suspected cases. Contact tracing and quarantine for 21 days were key actions. However, data on exposure to EVD cases, the proportion of antibodies to EBOV and of a- or pauci-symptomatic infection, as well as the presence of virus in body fluids of seropositive contact persons, remain scarce. The study aimed:
–to quantify individual risk of exposure of contact persons to EVD cases;
–to measure the presence of antibodies to EBOV;
–to look for EBOV RNA in semen of adult seropositive men.
Persons living in the same compounds than patients enrolled in a survivors’ cohort in Guinea in Conakry, Forecariah, Nzérékoré and Macenta (Postebogui) were invited to participate. After consent, a questionnaire detailing exposure to EVD cases was passed to establish a score of exposure and a history of vaccination with rVSV-ZEBOV vaccine was recalled. Antibodies to GP, NP and VP40 proteins were assessed using Luminex® and EBOV RNA in semen was analysed by PCR.
As of September 30, 2017, 1721 individuals were enrolled (51% males, median age 22 years [17–32]) and have accumulated 3074 exposures. Overall, 18.5% declared to have been vaccinated and 80% were exposed to less than 3 EVD cases (median=1 [1–2]). Zero to moderate risk exposure, one high-risk exposure and 2+ high-risk exposures per contacts person were estimated at 3%, 67% and 30%, respectively. Serology was available for 1716 contact persons: 53/1716 (3.1%) had antibodies to GP+NP, 32/1579 (2.0%) to GP+NP+VP40 and are strongly suspected to have been infected with EBV. In addition, 35/1579 (2.2%) patients had antibodies to NP+VP40, 78/1579 (4.9%) to GP+VP40 and 364 (23.0%) to a single antigen, GP (n=267, 15.6%), NP (n=79, 4.6%) or VP40 (n=157/1579, 9.9%). A history of vaccination was associated with antibodies to GP (23.3% vs. 13.8%, P<10−3). There was a trend with the number of high-risk exposures in GP+NP+VP40 (P=0.003), GP+NP (P=0.03), GP+VP40 (0.09) and NP+VP40 (P=0.003). EBOV RT-PCR was negative in semen of the tested men.
Among the contact persons, 3.3% had an antibody profile (GP+NP or GP+NP+VP) corresponding to an EVD infection suggesting a-/pauci-symptomatic infection but various other antibodies profiles were observed. A trend of the antibodies profiles with the number of high-risk exposures was observed. Among the individuals vaccinated with the GP vaccine, antibodies to GP were observed in 23%.