Infection and Transmission of Rift Valley Fever Viruses Lacking the NSs and/or NSm Genes in Mosquitoes: Potential Role for NSm in Mosquito Infection

Division of Vector-Borne Diseases, Centers for Disease Control and Prevention, Fort Collins, Colorado, United States of America.
PLoS Neglected Tropical Diseases (Impact Factor: 4.45). 05/2012; 6(5):e1639. DOI: 10.1371/journal.pntd.0001639
Source: PubMed


Rift Valley fever virus is an arthropod-borne human and animal pathogen responsible for large outbreaks of acute and febrile illness throughout Africa and the Arabian Peninsula. Reverse genetics technology has been used to develop deletion mutants of the virus that lack the NSs and/or NSm virulence genes and have been shown to be stable, immunogenic and protective against Rift Valley fever virus infection in animals. We assessed the potential for these deletion mutant viruses to infect and be transmitted by Aedes mosquitoes, which are the principal vectors for maintenance of the virus in nature and emergence of virus initiating disease outbreaks, and by Culex mosquitoes which are important amplification vectors.
Aedes aegypti and Culex quinquefasciatus mosquitoes were fed bloodmeals containing the deletion mutant viruses. Two weeks post-exposure mosquitoes were assayed for infection, dissemination, and transmission. In Ae. aegypti, infection and transmission rates of the NSs deletion virus were similar to wild type virus while dissemination rates were significantly reduced. Infection and dissemination rates for the NSm deletion virus were lower compared to wild type. Virus lacking both NSs and NSm failed to infect Ae. aegypti. In Cx. quinquefasciatus, infection rates for viruses lacking NSm or both NSs and NSm were lower than for wild type virus.
In both species, deletion of NSm or both NSs and NSm reduced the infection and transmission potential of the virus. Deletion of both NSs and NSm resulted in the highest level of attenuation of virus replication. Deletion of NSm alone was sufficient to nearly abolish infection in Aedes aegypti mosquitoes, indicating an important role for this protein. The double deleted viruses represent an ideal vaccine profile in terms of environmental containment due to lack of ability to efficiently infect and be transmitted by mosquitoes.

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Available from: Brian H Bird, Jun 05, 2014
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    • "The minor virulence factor, NSm, inhibits the apoptosis of infected cells, yet the lack of NSm expression only moderately affects the RVFV mortality in mice (Won et al., 2006; Terasaki et al., 2013; Kreher et al., 2014). The 78-kD protein and NSm contribute to an efficient dissemination of RVFV in mosquitoes (Crabtree et al., 2012; Kading et al., 2014; Kreher et al., 2014). "
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    ABSTRACT: Rift Valley fever (RVF) is a mosquito-borne zoonotic disease endemic to the African continent. RVF is characterized by high rate of abortions in ruminants and hemorrhagic fever, encephalitis, or blindness in humans. RVF is caused by the Rift Valley fever virus (RVFV: genus Phlebovirus, family Bunyaviridae). Vaccination is the only known effective strategy to prevent the disease, but there are no licensed RVF vaccines available for humans. A live-attenuated vaccine candidate derived from the wild-type pathogenic Egyptian ZH548 strain, MP-12, has been conditionally licensed for veterinary use in the U.S. MP-12 displays a temperature-sensitive (ts) phenotype and does not replicate at 41°C. The ts mutation limits viral replication at a specific body temperature and may lead to an attenuation of the virus. Here we will review well-characterized ts mutations for RNA viruses, and further discuss the potential in designing novel live-attenuated vaccines for RVF.
    Frontiers in Microbiology 08/2015; 6:787. DOI:10.3389/fmicb.2015.00787 · 3.99 Impact Factor
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    • "Using a recombinant Rift Valley fever system (Bird et al., 2008; Bird, Albarino, & Nichol, 2007; Gerrard, Bird, Albarino, & Nichol, 2007), Crabtree et al. were able to demonstrate that deletions of the individual nonstructural proteins from the small and medium segments (NSs and NSm) had a deleterious effect on virus infection and dissemination within Ae. aegypti and Culex quinquefasciatus. The combination of deletions resulted in the highest attenuation phenotype and ablated infection in Ae. aegypti (Crabtree et al., 2012). "
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    ABSTRACT: Arthropod-borne viruses (arboviruses) are transmitted between vertebrate hosts and arthropod vectors. An inherently complex interaction among virus, vector, and the environment determines successful transmission of the virus. Once believed to be "flying syringes," recent advances in the field have demonstrated that mosquito genetics, microbiota, salivary components, and mosquito innate immune responses all play important roles in modulating arbovirus transmissibility. The literature on the interaction among virus, mosquito, and environment has expanded dramatically in the preceding decade and the utilization of next-generation sequencing and transgenic vector methodologies assuredly will increase the pace of knowledge acquisition in this field. This chapter outlines the interplay among the three factors in both direct physical and biochemical manners as well as indirectly through superinfection barriers and altered induction of innate immune responses in mosquito vectors. The culmination of the aforementioned interactions and the arms race between the mosquito innate immune response and the capacity of arboviruses to antagonize such a response ultimately results in the subjugation of mosquito cells for viral replication and subsequent transmission.
    Advances in Virus Research 04/2014; 89:39-83. DOI:10.1016/B978-0-12-800172-1.00002-1 · 4.57 Impact Factor
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    • "However, LGp may be important for replication in the mosquito host. Crabtree et al., [26] who studied replication of recombinant virus lacking the NSm protein coding sequence in Aedes aegypti and Culex quinquefasciatus mosquitoes, observed a significantly decreased infection rate and transmission of the recombinant virus compared to the recombinant wild type RVFV. Since deletion of the NSm coding sequence also abolishes expression of the LGp, this observation can be a composite effect of the virus lacking expression of both proteins. "
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    ABSTRACT: Rift Valley fever virus (RVFV), genus Phlebovirus, family Bunyaviridae is a zoonotic arthropod-borne virus able to transition between distant host species, causing potentially severe disease in humans and ruminants. Viral proteins are encoded by three genomic segments, with the medium M segment coding for four proteins: nonstructural NSm protein, two glycoproteins Gn and Gc and large 78 kDa glycoprotein (LGp) of unknown function. Goat anti-RVFV polyclonal antibody and mouse monoclonal antibody, generated against a polypeptide unique to the LGp within the RVFV proteome, detected this protein in gradient purified RVFV ZH501 virions harvested from mosquito C6/36 cells but not in virions harvested from the mammalian Vero E6 cells. The incorporation of LGp into the mosquito cell line - matured virions was confirmed by immune-electron microscopy. The LGp was incorporated into the virions immediately during the first passage in C6/36 cells of Vero E6 derived virus. Our data indicate that LGp is a structural protein in C6/36 mosquito cell generated virions. The protein may aid the transmission from the mosquitoes to the ruminant host, with a possible role in replication of RVFV in the mosquito host. To our knowledge, this is a first report of different protein composition between virions formed in insect C6/36 versus mammalian Vero E6 cells.
    PLoS ONE 01/2014; 9(1):e87385. DOI:10.1371/journal.pone.0087385 · 3.23 Impact Factor
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