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. 2021 Jun 11;11(1):12395.
doi: 10.1038/s41598-021-91926-5.

In-vitro and in-vivo study of the interference between Rift Valley fever virus (clone 13) and Sheeppox/Limpy Skin disease viruses

N Safini  1 , Z Bamouh  2 , J Hamdi  2 , M Jazouli  2 , K O Tadlaoui  2 , M El Harrak  2
Affiliations

In-vitro and in-vivo study of the interference between Rift Valley fever virus (clone 13) and Sheeppox/Limpy Skin disease viruses

N Safini et al. Sci Rep. .

Abstract

Viral interference is a common occurrence that has been reported in cell culture in many cases. In the present study, viral interference between two capripox viruses (sheeppox SPPV and lumpy skin disease virus LSDV in cattle) with Rift Valley fever virus (RVFV) was investigated in vitro and in their natural hosts, sheep and cattle. A combination of SPPV/RVFV and LSDV/RVFV was used to co-infect susceptible cells and animals to detect potential competition. In-vitro interference was evaluated by estimating viral infectivity and copies of viral RNA by a qPCR during three serial passages in cell cultures, whereas in-vivo interference was assessed through antibody responses to vaccination. When lamb testis primary cells were infected with the mixture of capripox and RVFV, the replication of both SPPV and LSDV was inhibited by RVFV. In animals, SPPV/RVFV or LSDV/RVFV combinations inhibited the replication SPPV and LSDV and the antibody response following vaccination. The combined SPPV/RVFV did not protect sheep after challenging with the virulent strain of SPPV and the LSDV/RVFV did not induce interferon Gamma to LSDV, while immunological response to RVFV remain unaffected. Our goal was to assess this interference response to RVFV/capripoxviruses' coinfection in order to develop effective combined live-attenuated vaccines as a control strategy for RVF and SPP/LSD diseases. Our findings indicated that this approach was not suitable for developing a combined SPPV/LSDV/RVFV vaccine candidate because of interference of replication and the immune response among these viruses.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Giemsa staining of RVFV, SPPV and LSDV viruses for coinfection of LT cell culture (× 400). (A) Mock cells. (B) RVFV cytopathic effect: RVFV necrotic foci (red arrows). (C) SPPV effect (D) LSDV, (E) SPPV/RVFV 0.01/0.01 coinfection of LT cells and (F) LSDV/RVFV coinfection. Capripoxvirus induced cellular damage. Arrows showing capripox virus-induced vacuoles in cells and intracytoplasmic eosinophilic inclusion bodies (Arrowheads).
Figure 2
Figure 2
Infectivity titers of SPPV and RVFV co-cultured in Vero cells (A) and in LT cells (B) at different MOI 1, 0.1, 0.01 and 0.001. Data shown are means of at least 3 independent experiments.
Figure 3
Figure 3
Infectivity titration (TCID50/ml) and viral genome copies by qPCR (threshold cycles: Ct) of SPPV (A) and RVFV (B) after coinfection in three successive passages (P1, P2 and P3). Infection was performed in (LT cells with different MOIs (RVFV/SPPV: 0.01/0.01; 0.01/0.1; 0.01/0.25; 0.01/0.5; 0.01/1). Data shown are means of at least three independent experiments.
Figure 4
Figure 4
Infectivity titration (TCID50/ml) of LSDV (A) and RVFV (B) alone and after coinfection involving three successive passages (P1, P2 and P3) in LT cells. LSDV and RVFV alone at MOI = 0.01; and coinfection at different MOIs: RVFV/LSDV:0.01/0.01; 0.01/0.1 and 0.01/0.5. Data shown are means of at least three independent experiments (n = 3). NS: not significant. * statistically significant p < 0.05.
Figure 5
Figure 5
Antibody titers response of sheep injected with SPPV alone, RVFV alone, or with combined SPPV/RVFV. The antibody response was determined from from D0 to 3 months pv. (A) Viral neutralizing antibody titers of sheep injected with RVFV and combined SPPV/RVFV (B) Viral neutralizing antibody titers for SPPV Monovalent and SPPV/RVFV co-infected sheep. Data shown are means of at least three neutralization experiments. D: Days M: Months.
Figure 6
Figure 6
Percentage of antibody positive sheep (%) (n = 10) injected with RVFV alone, SPPV alone, or RVFV/SPPV from D0 to 3 months pv. (A) RVFV antibody positive sheep, (B) SPPV antibody positive sheep in n = 10 each of tested groups. D: Days M: Months.
Figure 7
Figure 7
Challenged vaccinated sheep showing hypersensitivity reaction and no local inflammations on site of inoculation with10−1 to 10−6 dilutions (left to right) of virulent SPPV. (A) Figure of challenged unvaccinated sheep showing local inflammation on site of inoculation. (B) Sheep vaccinated with SPPV/RVFV and challenged with SPPV virulent strain (C) sheep vaccinated with SPPV alone and challenged with SPPV virulent strain. Black arrow shows inflammation or hypersensitivity reaction on inoculation site. Red arrow shows absence of the hypersensitivity reaction.
Figure 8
Figure 8
Antibody titers response in cattle vaccinated with LSDV and with combined LSDV/RVFV monitored from D0 to 3 months pv. (A) LSDV neutralization antibody titers in log10. Data shown are means of at least three neutralization experiments. (B) Percentage of cattle positive for LSDV injected with two different doses for LSDV (103.5 and 104.5 TCID50/dose) and RVFV (103.5 and 104.5 TCID50/dose). D: Days M: Months.
Figure 9
Figure 9
Antibody titers response in cattle vaccinated with RVFV alone, and with combined RVFV/LSDV vaccine. Cattle are monitored from D0 to 3 months pv. (A) RVFV neutralization antibody titers. Data shown are means of at least three neutralization experiments. (B) Percentage of cattle thar seroconverted to RVFV injected with a dose of 104.5 TCID50/dose and with a dose of LSDV/RVFV 104.5 TCID50/dose. D: Days M: Months.
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