Modelling filovirus maintenance in nature by experimental transmission of Marburg virus between Egyptian rousette bats

Abstract

The Egyptian rousette bat (ERB) is a natural reservoir host for Marburg virus (MARV); however, the mechanisms by which MARV is transmitted bat-to-bat and to other animals are unclear. Here we co-house MARV-inoculated donor ERBs with naive contact ERBs. MARV shedding is detected in oral, rectal and urine specimens from inoculated bats from 5-19 days post infection. Simultaneously, MARV is detected in oral specimens from contact bats, indicating oral exposure to the virus. In the late study phase, we provide evidence that MARV can be horizontally transmitted from inoculated to contact ERBs by finding MARV RNA in blood and oral specimens from contact bats, followed by MARV IgG antibodies in these same bats. This study demonstrates that MARV can be horizontally transmitted from inoculated to contact ERBs, thereby providing a model for filovirus maintenance in its natural reservoir host and a potential mechanism for virus spillover to other animals.

Figure 1. Housing configurations throughout the study.

Bats were transferred to different housing configurations at the time indicated above each caging diagram.

Figure 2. MARV IgG antibody responses in inoculated donor and naive contact bats.

MARV IgG antibody responses in (a) inoculated and (b) contact bats, as detected by ELISA with purified recombinant nucleoprotein of the Angola strain of MARV expressed in Escherichia coli. The dashed lines represent the cutoff value of the assay (MARV seropositive ≥0.95). The legends indicate the housing unit (1–6) and group (inoculated donor-ID and naive contact-NC) of each bat during the early study phase. Open symbols in b at 8 MPI represent the three contact bats which were viremic at 7 MPI.

Figure 3. MARV loads in specimens obtained from inoculated donor bats.

MARV loads (Q-RT–PCR-derived log₁₀TCID₅₀eq ml⁻¹) in (a) blood, (b) oral swabs, (c) rectal swabs and (d) urine. The orange dotted lines in a–d represent the overall mean MARV load in blood specimens and the black dotted line in b represents the overall mean viral load in oral swabs. The legend indicates the housing unit (1, 3 or 5) and group (inoculated donor-ID) of each bat during the early study phase. Open symbols in b represent oral swabs from which infectious MARV was isolated. The lower limit of detection was 0.4, 0.7, −0.3 and −0.3 log₁₀TCID₅₀eq ml⁻¹ for blood, oral swabs, rectal swabs and urine, respectively.

Figure 4. Cumulative oral MARV shedding from inoculated bats and contact bat exposures.

(a) Cumulative oral MARV shedding in log₁₀TCID₅₀eq ml⁻¹ from each of the inoculated bats (symbols at the top of each unit) and the number of exposures in the contact bats (symbols at the bottom of each unit; exposure defined as a Q-RT–PCR-positive oral or rectal swab) according to unit and bat, and (b) Lorenz curve of cumulative percentage of the inoculated bat population versus cumulative percentage of oral MARV shedding ranked in descending order (that is, first circle on the curve represents bat 685734, which had the highest cumulative percentage of oral MARV shedding). The legends indicate the housing unit (1–6) and group (inoculated donor-ID and naive contact-NC) of each bat during the early study phase.

Figure 5. MARV loads in biological specimens obtained from naive contact bats.

MARV loads (Q-RT–PCR-derived log₁₀TCID₅₀eq ml⁻¹) in oral swabs, rectal swabs and blood obtained during the early and late study phases (that is, 7 MPI). The legend indicates the housing unit (1–6) and group (naive contact-NC) of each bat during the early study phase. The lower limit of detection was 0.4, 0.7 and −0.3 log₁₀TCID₅₀eq ml⁻¹ for blood, oral swabs and rectal swabs, respectively.

Figure 6. Bat identification numbers according to group and unit.

Inoculated donor bats are coloured orange and naive contact bats are coloured blue.