Bunyamwera virus nonstructural protein NSs counteracts interferon regulatory factor 3-mediated induction of early cell death.
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The genome of Bunyamwera virus (BUN; family Bunyaviridae, genus Orthobunyavirus) consists of three segments of negative-sense RNA. The smallest segment, S, encodes two proteins, the nonstructural protein NSs, which is nonessential for viral replication and transcription, and the nucleocapsid protein N. Although a precise role in the replication cycle has yet to be attributed to NSs, it has been shown that NSs inhibits the induction of alpha/beta interferon, suggesting that it plays a part in counteracting the host antiviral defense. A defense mechanism to limit viral spread is programmed cell death by apoptosis. Here we show that a recombinant BUN that does not express NSs (BUNdelNSs) induces apoptotic cell death more rapidly than wild-type virus. Screening for apoptosis pathways revealed that the proapoptotic transcription factor interferon regulatory factor 3 (IRF-3) was activated by both wild-type BUN and BUNdelNSs infection, but only wild-type BUN was able to suppress signaling downstream of IRF-3. Studies with a BUN minireplicon system showed that active replication induced an IRF-3-dependent promoter, which was suppressed by the NSs protein. In a cell line (P2.1) defective in double-stranded RNA signaling due to low levels of IRF-3, induction of apoptosis was similar for wild-type BUN and BUNdelNSs. These data suggest that the BUN NSs protein can delay cell death in the early stages of BUN infection by inhibiting IRF-3-mediated apoptosis. (+info)
Rapid detection of human pathogenic orthobunyaviruses.
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Modern detection and identification tools can help to provide answers to urgent questions about the incidence, prevalence, and epidemiology of currently emerging diseases. We developed highly sensitive one-step TaqMan reverse transcription-PCR assays with sensitivities ranging from 10(4) to 10(1) molecules for 11 human pathogens of the orthobunyaviruses. We compared the performances of these assays on three currently available cyclers (ABI-PRISM 7700, LightCycler, and SmartCycler). The assay for Oropouche virus (OROV) was tested using sera collected from days 1 to 5 after onset of OROV disease and was found to be greatly superior to an established nested PCR system. A mean copy number of 1.31 x 10(7) OROV RNA/ml of serum was detected. Diagnostic RNA detection can be used as early as day 1 after onset of OROV disease. The use of a mobile SmartCycler and a hands-on time of less than 3 h could help to intensify outbreak surveillance and control, especially in field studies. (+info)
Isolation of Kaeng Khoi virus from dead Chaerephon plicata bats in Cambodia.
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A virus isolated from dead Chaerephon plicata bats collected near Kampot, Cambodia, was identified as a member of the family Bunyaviridae by electron microscopy. The only bunyavirus previously isolated from Chaerephon species bats in South-East Asia is Kaeng Khoi (KK) virus (genus Orthobunyavirus), detected in Thailand over 30 years earlier and implicated as a public health problem. Using RT-PCR, nucleotide sequences from the M RNA segment of several virus isolates from the Cambodian C. plicata bats were found to be almost identical and to differ from those of the prototype KK virus by only 2.6-3.2 %, despite the temporal and geographic separation of the viruses. These results identify the Cambodian bat viruses as KK virus, extend the known virus geographic range and document the first KK virus isolation in 30 years. These genetic data, together with earlier serologic data, show that KK viruses represent a distinct group within the genus Orthobunyavirus. (+info)
Induction of severe disease in hamsters by two sandfly fever group viruses, Punta toro and Gabek Forest (Phlebovirus, Bunyaviridae), similar to that caused by Rift Valley fever virus.
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Adult golden hamsters inoculated subcutaneously with either of two sandfly fever group viruses, Punta Toro and Gabek Forest (Phlebovirus, Bunyaviridae), developed a fulminating fatal illness characterized by hepatic and splenic necrosis and interstitial pneumonitis. Most animals died within three days after infection; this was accompanied by high levels of viremia. Necropsy and histopathologic examination of the infected animals revealed pathologic changes involving multiple organs that resembled those described in Rift Valley fever. These two hamster-phlebovirus systems may serve as alternative animal models for Rift Valley fever and should be useful in studying the pathogenesis of severe phlebovirus infection and for testing potential therapeutic agents. (+info)
Ngari virus is a Bunyamwera virus reassortant that can be associated with large outbreaks of hemorrhagic fever in Africa.
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Two isolates of a virus of the genus Orthobunyavirus (family Bunyaviridae) were obtained from hemorrhagic fever cases during a large disease outbreak in East Africa in 1997 and 1998. Sequence analysis of regions of the three genomic RNA segments of the virus (provisionally referred to as Garissa virus) suggested that it was a genetic reassortant virus with S and L segments derived from Bunyamwera virus but an M segment from an unidentified virus of the genus Orthobunyavirus. While high genetic diversity (52%) was revealed by analysis of virus M segment nucleotide sequences obtained from 21 members of the genus Orthobunyavirus, the Garissa and Ngari virus M segments were almost identical. Surprisingly, the Ngari virus L and S segments showed high sequence identity with those of Bunyamwera virus, showing that Garissa virus is an isolate of Ngari virus, which in turn is a Bunyamwera virus reassortant. Ngari virus should be considered when investigating hemorrhagic fever outbreaks throughout sub-Saharan Africa. (+info)
Arthrogryposis, hydranencephaly and cerebellar hypoplasia syndrome in neonatal calves resulting from intrauterine infection with Aino virus.
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To determine the teratogenic potential of Aino virus (AINOV) in cattle, pregnant cows and fetal cattle were infected with a fresh isolate of AINOV. Five pregnant cows were inoculated intravenously with the virus at 122 to 162 days of gestation and allowed to give birth. All of the cows developed neutralizing antibodies to the virus, indicating that the cows had been infected with the virus; however, no clinical abnormalities were seen in their six newborn calves, and no specific antibodies to the virus were detected in the precolostral serum of calves. Five fetuses with fetal ages ranging from 132 to 156 days were inoculated in utero with the virus. One weak newborn and four stillborn calves were delivered at gestation days 256 to 263, i.e., less than the standard gestation term; they had congenital abnormalities including arthrogryposis, hydranencephaly and cerebellar hypoplasia. Antibodies specific to AINOV were detected in their precolostral serum. These results demonstrate that AINOV is a potential etiological agent of congenital malformation of cattle. (+info)
The synthesis of viral RNA species in tomato spotted wilt virus-infected Nicotiana rustica plants was followed in terms of time and relative abundance. Systemic symptoms were visible after 4 days postinoculation (p.i.), but viral (v) and viral-complementary (vc) strands of all three genomic RNA segments [large (L) RNA, medium (M) RNA and small (S) RNA] were detected from 2 days p.i. In addition, two subgenomic mRNAs, derived from S RNA, were detected. For the L RNA segment no subgenomic mRNAs were detected, suggesting that this segment is expressed via the synthesis of a genome-sized vc mRNA. A possible M-specific subgenomic mRNA was detected, showing a similar time course of appearance as the subgenomic mRNAs derived from the S RNA segment. Analysis of cytoplasmic RNA fractions revealed that both v and vc strands of all three genomic segments associate with the nucleocapsid protein into nucleocapsid structures, the vcRNA species being present in lower amounts. Intact, enveloped virus particles contained only the v strand of the L RNA segment and, surprisingly, both v and vc strands of the M and S RNA segment, though in different ratios. (+info)
Competitive enzyme-linked immunosorbent assay for the detection of the antibodies specific to akabane virus.
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A competitive enzyme-linked immunosorbent assay (C-ELISA) using neutralizing monoclonal antibodies (MAbs) against Akabane virus (AKAV) was developed to detect antibodies to AKAV in cattle sera. The performance of the test using 7 different competitor MAbs was evaluated in sequential serum samples and sera from cattle infected with various bovine arboviruses. The dynamics of the antibody response expressed by percentage of inhibition (PI) in C-ELISA coincided with those of neutralizing antibody titers in sequential serum samples from 2 cattle experimentally infected with AKAV. The value of PI in C-ELISA for convalescent sera from cattle infected with arboviruses correlated with the neutralizing antibody titer to AKAV but was unaffected by the antibodies to other arboviruses. In the validation experiment of C-ELISA using 286 bovine sera previously examined for the AKAV antibody by serum neutralization (SN) test, the relative specificity of C-ELISA was more than 98%, whereas the relative sensitivities of individual MAbs ranged from 49% to 82.2%. Overall agreement between C-ELISA and the SN test varied from 72% to 90% depending on the MAb. These results suggest that the C-ELISA is acceptable as a rapid and specific method for detecting antibodies to AKAV and is a potential alternative to the SN test. (+info)