Inhibition of Hazara nairovirus replication by small interfering RNAs
Background
The genus Nairovirus in the family Bunyaviridae contains 34 tick-borne viruses classified into seven serogroups. Hazara virus (HAZV) belongs to the Crimean-Congo hemorrhagic fever (CCHF) serogroup that also includes CCHF virus (CCHFV) a major pathogen for humans. HAZV is an interesting model to study CCHFV due to a close serological and phylogenetical relationship and a classification which allows handling in a BSL2 laboratory. Nairoviruses are characterized by a tripartite negative-sense single stranded RNA genome (named L, M and S segments) that encode the RNA polymerase, the Gn-Gc glycoproteins and the nucleoprotein (NP), respectively. Currently, there are neither vaccines nor effective therapies for the treatment of any bunyavirus infection in humans. In this study we report, for the first time, the use of RNA interference (RNAi) as an approach to inhibit nairovirus replication.
Results
Chemically synthesized siRNAs were designed to target the mRNA produced by the three genomic segments. We first demonstrated that the siRNAs targeting the NP mRNA displayed a stronger antiviral effect than those complementary to the L and M transcripts in A549 cells. We further characterized the two most efficient siRNAs showing, that the induced inhibition is specific and associated with a decrease in NP synthesis during HAZV infection. Furthermore, both siRNAs depicted an antiviral activity when used before and after HAZV infection. We next showed that HAZV was sensitive to ribavirin which is also known to inhibit CCHFV. Finally, we demonstrated the additive or synergistic antiviral effect of siRNAs used in combination with ribavirin.
Conclusions
Our study highlights the interest of using RNAi (alone or in combination with ribavirin) to treat nairovirus infection. This approach has to be considered for the development of future antiviral compounds targeting CCHFV, the most pathogenic nairovirus.
Background
Hazara virus (HAZV) is a member of the genus Nairovirus of the family Bunyaviridae which also includes Orthobunyavirus, Hantavirus, Phlebovirus and Tospovirus. Nairovirus comprises 34 tick-borne viruses classified into seven serogroups. The main representative serogroups are the Nairobi sheep disease group containing Nairobi sheep disease virus (NSDV) and Dugbe virus and the Crimean-Congo hemorrhagic fever (CCHF) group including HAZV and Crimean-Congo hemorrhagic fever virus (CCHFV). While NSDV induces acute hemorrhagic gastroenteritis in sheep and goats, CCHFV is responsible of severe hemorrhagic fever in humans associated with elevated levels of mortality (up to 50%). Due to its high pathogenicity for humans and because of the lack of therapeutics, CCHFV must be handled in BSL4 (biosafety level 4) laboratory. Widely distributed throughout Eastern Europe, Asia and Africa, CCHFV represents a major public health problem and is now considered as an emerging disease. HAZV was isolated for the first time in 1954 from Ixodes ticks collected in Pakistan. Although its natural host is not known, antibodies against HAZV were detected in rodent sera. While non pathogenic for humans, it is lethal in new-born mice and elicits cross-protection against CCHFV challenge in adult mice. HAZV represents an alternative model to study CCHFV due to its close serological and phylogenetical relationship. Furthermore, it can be handled in BSL2 laboratories.