New Bunyavirus Findings for 2004/2005

Attenuation of bunyavirus replication by rearrangement of viral coding and noncoding sequences. J Virol. 2005 Jun; 79(11):6940-6. Lowen AC, Boyd A, Fazakerley JK, Elliott RM.

The research team developed an attenuated version of the bunyavirus Bunyamwera. The researchers created a recombinant virus which was less virulent. This attenuated version shows promise in the development of man-made vaccine viruses to vaccinate against bunyaviruses. Bunyamwera has three RNA segments: small, medium, and large (S, M, and L). The coding segments of the strands are flanked on both sides by complementary untranslated regions (UTRs). To create the recombinant virus, researchers placed the M segment's UTRs on either side of the L open reading frame (ORF). The purpose of the UTR is currently unknown, but the research suggests more research into transforming UTRs to attenuate other viruses.

Production of monoclonal antibodies against Rift Valley fever virus Application for rapid diagnosis tests (virus detection and ELISA) in human sera. J Virol Methods. 2005 Aug 12; Zaki A, Coudrier D, Yousef AI, Fakeeh M, Bouloy M, Billecocq A.

RVF infection can be diagnosed by virus isolation, but this can be dangerous and requires a costly biohazard level 3 setup. It can be diagnosed by RT-PCR, but many labs are not set up for this process. The simplest and cheapest solution is an IgG or IgM capture ELISA test (Enzyme-linked immunosorbent assay). To maximize the efficiency of this process, the authors of this paper created monoclonal antibodies for RVF necessary for this test. In the past, RVF polyclonal mouse antibodies have been used, but their yield is unpredictable. This test will be valuable because rapid and inexpensive diagnosis is necessary to prevent a RVF epizootic. Epizootic prevention will reduce human cases of RVF as well.

Bi-annual surge of Crimean-Congo haemorrhagic fever (CCHF): a five-year experience. Int J Infect Dis. 2005 Jan;9(1):37-42. Sheikh AS, Sheikh AA, Sheikh NS, Rafi-U-Shan, Asif M, Afridi F, Malik MT.

Researchers performed a five year study of cases of CCHF in Pakistan. 83 out of 135 suspected cases were actually CCHF cases. There was a 10% mortality rate in the 83 cases. Four patients were hospital janitors and one was a nurse who had a needle-stick accident with an infected needle, despite post-exposure prophylaxis. Researchers reported a bi-annual surge in cases. Most cases occurred in March-May and August-October, but no reason for these surges was determined. Almost half the cases were slaughterhouse workers, and the rest worked either with livestock or in health care. Researchers noted the need for better exposure control within the hospital and more research into the epidemiology of CCHF. This study highlights many of the issues of a sporadic but dangerous disease confined mostly to rural populations.

California serogroup Gc (G1) glycoprotein is the principal determinant of pH-dependent cell fusion and entry. Virology. 2005 Jul 20;338(1):121-32. Plassmeyer ML, Soldan SS, Stachelek KM, Martin-Garcia J, Gonzalez-Scarano F.

The California serogroup of bunyaviruses has some important disease-causing members, including California encephalitis virus, La Crosse virus, and Tahyna virus. These viruses are known to be highly neurovirulent and invasive, in some cases resulting in severe encephalitis. Investigators worked with recombinant strains of La Crosse, Tahyna, and V22F, trying to identify the gene on the M segment that mediates virus entry. They mapped the gene responsible for virus fusion and cell entry to the specific Gc glycoprotein. This Gc protein is thought to be a type II fusion protein.  

The Bunyamwera virus mRNA transcription signal resides within both the 3' and the 5' terminal regions and allows ambisense transcription from a model RNA segment. J Virol. 2005 Oct;79(19):12602-7. Barr JN, Rodgers JW, Wertz GW.  

Certain members in the bunyavirus family, specifically in the genus Phlebovirus, are capable of performing ambisense transcription. This is not a feature of Bunyamwera virus, but researchers were able to alter a Bunyamwera gene segment to be artificially ambisense. First they identified nontranslated regions thought to regulate the ambisense transcription activity of the viral RNA polymerase. The researchers used those to create a gene segment encoding both negative stranded viral proteins and positive stranded GFP. GFP was expressed, indicating that ambisense segments can be artificially created, and allow for the addition of new proteins into the viral genome.

Complementarity, sequence and structural elements within the 3' and 5' non-coding regions of the Bunyamwera orthobunyavirus S segment determine promoter strength. J Gen Virol. 2004 Nov;85(Pt 11):3269-78. Kohl A, Dunn EF, Lowen AC, Elliott RM.

In this study researchers worked with the 3’ and 5’ regions of the Bunyamwera genome to determine what aspects of them controlled the level of gene expression. The first fifteen nucleotides at each end were found to be complementary to each other, and altering that complementarity resulted in decreased transcription. The complementarity allows the viral genome to form panhandle shapes in the virion, which is possibly an important factor for polymerase activity. In addition, removing more than one nucleotide at each end resulted in decreased transcription, with an especially significant decrease when three nucleotides were excised.

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