Morphology and development of Rift Valley fever virus in Vero cell cultures

Serological Evidence of Antibodies to Rift Valley Fever Virus in Wild and Domestic Animals in Bauchi State, Nigeria

Rift Valley fever (RVF) is an arthropod-borne zoonotic disease responsible for severe outbreaks in livestock and humans with concomitant economic losses in many countries in sub-Saharan Africa. The study, therefore, investigated the seroprevalence of the Rift Valley fever virus (RVFV) among wild and domestic animals. Blood samples were collected between 2013 and 2015 from 106 wild animals, 300 cattle (Bos indicus), and 200 horses (Equus caballus), respectively, in Yankari Game Reserve (YGR) and Sumu Wildlife Park (SWP) in Bauchi state, Nigeria. Harvested sera from blood were evaluated for the presence of anti-RVFV IgM/IgG antibodies. The overall seroprevalence in cattle was 11.3% (p = 0.677; 95% CI: 0.624-0.730) and in wildlife was 8.5% (p = 0.006; 95% CI: 0.00-0.60). The diversity of wildlife species sampled indicated seropositivity of 36.0% in waterbuck (Kobus ellipsiprymus), 25.0% in elephant (Loxodonta africana), 12.5% in eland (Taurotragus oryx), and 8.3% in wildebeest (Connochaetes taurinus). Whereas, samples from zebra (Equus quagga crawshayi), kudu (Tragelaphus strepsiceros), and hartebeest (Alcelaphus buselaphus caama) did not show detectable antibodies to RVFV, and seroprevalence in female (15.0%) wildlife species was higher than in males (4.5%) (p = 0.061). Classification of cattle into breed and sex showed no significant difference in seropositivity. Seropositivity of 12.0% was observed in White Fulani, 12.1% in Red Bororo, and 7.8% in Sokoto Gudali breeds of cattle (p = 0.677). Whereas, seropositivity of 13.6% was observed in females and 6.4% observed in males (p = 0.068). This study indicated the presence of antibodies to RVFV among some wild animals and cattle in the absence of a reported outbreak in the study area. The circulation of RVFV in the study area may pose a significant health risk to livestock, wildlife, and humans. Therefore, surveillance for RVFV should be intensified targeting mosquito vectors and humans in Bauchi state, Nigeria.

A Broad-Spectrum Antiviral Peptide Blocks Infection of Viruses by Binding to Phosphatidylserine in the Viral Envelope

The ongoing threat of viral infections and the emergence of antiviral drug resistance warrants a ceaseless search for new antiviral compounds. Broadly-inhibiting compounds that act on elements shared by many viruses are promising antiviral candidates. Here, we identify a peptide derived from the cowpox virus protein CPXV012 as a broad-spectrum antiviral peptide. We found that CPXV012 peptide hampers infection by a multitude of clinically and economically important enveloped viruses, including poxviruses, herpes simplex virus-1, hepatitis B virus, HIV-1, and Rift Valley fever virus. Infections with non-enveloped viruses such as Coxsackie B3 virus and adenovirus are not affected. The results furthermore suggest that viral particles are neutralized by direct interactions with CPXV012 peptide and that this cationic peptide may specifically bind to and disrupt membranes composed of the anionic phospholipid phosphatidylserine, an important component of many viral membranes. The combined results strongly suggest that CPXV012 peptide inhibits virus infections by direct interactions with phosphatidylserine in the viral envelope. These results reiterate the potential of cationic peptides as broadly-acting virus inhibitors.

Chitosan and chitosan nanoparticles as adjuvant in local Rift Valley Fever inactivated vaccine

The present study aimed to improve the potency of inactivated Rift Valley Fever Virus (RVFV) vaccine using chitosan (CS) or chitosan nanoparticles (CNP) as adjuvants. Chitosan nanoparticles were prepared by ionic gelation method. Rift Valley Fever Virus (RVFV) inactivated antigen was loaded on CS and CNP to form two vaccine formulations, RVFV-chitosan nanoparticles based vaccine (RVFV-CNP) and RVFV chitosan based vaccine (RVFV-CS). Five groups of mice were used in this study, each group was injected with one of the following: phosphate buffer saline (group1 G1), RVFV-CNP (G2), (RVF-CS) (G3), RVFV-Alum based vaccine (RVFV-Alum) (G4) and adjuvant free RVFV inactivated antigen (RVFV-Ag) (G5). The immunization was performed twice with 2 weeks interval. The results showed that, RVFV-CNP vaccine enhanced strongly the phagocytic activity of peritoneal macrophage (PM), neutralization antibodies titer against RVFV and IgG values against RVFV nucleoprotein than other vaccine formulations did. In addition, the RVFV-CNP and RVF-CS vaccines upregulate the gene expression of IL-2, IFN-γ (which promote cell mediated immunity) and IL-4 (which promote humeral immunity), while RVFV-Alum vaccine upregulate the gene expression of IL-4 only. These findings indicated that CS and CNP were comparable to the alum as adjuvant in efficacy but superior to it in inducing cell-mediated immune response and might be a candidate adjuvant for inactivated RVFV vaccine.

Polyamine Depletion Inhibits Bunyavirus Infection via Generation of Noninfectious Interfering Virions

Several host and viral processes contribute to forming infectious virions. Polyamines are small host molecules that play diverse roles in viral replication. We previously demonstrated that polyamines are crucial for RNA viruses; however, the mechanisms by which polyamines function remain unknown. Here, we investigated the role of polyamines in the replication of the bunyaviruses Rift Valley fever virus (vaccine strain MP-12) and La Crosse virus (LACV). We found that polyamine depletion did not impact viral RNA or protein accumulation, despite significant decreases in titer. Viral particles demonstrated no change in morphology, size, or density. Thus, polyamine depletion promotes the formation of noninfectious particles. These particles interfere with virus replication and stimulate innate immune responses. We extended this phenotype to Zika virus; however, coxsackievirus did not similarly produce noninfectious particles. In sum, polyamine depletion results in the accumulation of noninfectious particles that interfere with replication and stimulate immune signaling, with important implications for targeting polyamines therapeutically, as well as for vaccine strategies.IMPORTANCE Bunyaviruses are emerging viral pathogens that cause encephalitis, hemorrhagic fevers, and meningitis. We have uncovered that diverse bunyaviruses require polyamines for productive infection. Polyamines are small, positively charged host-derived molecules that play diverse roles in human cells and in infection. In polyamine-depleted cells, bunyaviruses produce an overabundance of noninfectious particles that are indistinguishable from infectious particles. However, these particles interfere with productive infection and stimulate antiviral signaling pathways. We further find that additional enveloped viruses are similarly sensitive to polyamine depletion but that a nonenveloped enterovirus is not. We posit that polyamines are required to maintain bunyavirus infectivity and that polyamine depletion results in the accumulation of interfering noninfectious particles that limit infectivity. These results highlight a novel means by which bunyaviruses use polyamines for replication and suggest promising means to target host polyamines to reduce virus replication.

In vitro and in vivo efficacy of a Rift Valley fever virus vaccine based on pseudovirus

Rift Valley fever virus (RVFV), a recognized category A priority pathogen, causes large outbreaks of Rift Valley fever with some fatalities in humans in humans and huge economic losses in livestock. As wild-type RVFV must be handled in BSL-3 or BSL-4 laboratories, we constructed a high-titer vesicular stomatitis virus (VSV) pseudotype bearing RVFV envelope glycoproteins to detect neutralizing antibodies in vitro under BSL-2 conditions. The neutralizing properties of 39 amino acid mutant sites that have occurred naturally over time in the RVFV envelope glycoproteins were analyzed with their corresponding pseudoviral mutants separately. Compared with the results in the primary strain, the variants showed no statistically significant differences. We next established a Balb/c mouse pseudovirus infection model for detecting neutralizing antibodies against pseudovirus. Five immunizations with pseudoviral DNA protected the mice from infection with the pseudovirus. Bioluminescence imaging, which we used to evaluate viral dissemination and distribution in the mice, showed a good relationship between the neutralizing antibodies titers in vitro. These pseudovirus methods will allow for the safe determination of neutralizing antibodies in vivo and in vitro, and will assist with studies on vaccines and drugs against RVFV with the long term objective of Rift Valley fever prevention.

Spatial Heterogeneity of Habitat Suitability for Rift Valley Fever Occurrence in Tanzania: An Ecological Niche Modelling Approach

BACKGROUND

Despite the long history of Rift Valley fever (RVF) in Tanzania, extent of its suitable habitat in the country remains unclear. In this study we investigated potential effects of temperature, precipitation, elevation, soil type, livestock density, rainfall pattern, proximity to wild animals, protected areas and forest on the habitat suitability for RVF occurrence in Tanzania.

MATERIALS AND METHODS

Presence-only records of 193 RVF outbreak locations from 1930 to 2007 together with potential predictor variables were used to model and map the suitable habitats for RVF occurrence using ecological niche modelling. Ground-truthing of the model outputs was conducted by comparing the levels of RVF virus specific antibodies in cattle, sheep and goats sampled from locations in Tanzania that presented different predicted habitat suitability values.

PRINCIPAL FINDINGS

Habitat suitability values for RVF occurrence were higher in the northern and central-eastern regions of Tanzania than the rest of the regions in the country. Soil type and precipitation of the wettest quarter contributed equally to habitat suitability (32.4% each), followed by livestock density (25.9%) and rainfall pattern (9.3%). Ground-truthing of model outputs revealed that the odds of an animal being seropositive for RVFV when sampled from areas predicted to be most suitable for RVF occurrence were twice the odds of an animal sampled from areas least suitable for RVF occurrence (95% CI: 1.43, 2.76, p < 0.001).

CONCLUSION/SIGNIFICANCE

The regions in the northern and central-eastern Tanzania were more suitable for RVF occurrence than the rest of the regions in the country. The modelled suitable habitat is characterised by impermeable soils, moderate precipitation in the wettest quarter, high livestock density and a bimodal rainfall pattern. The findings of this study should provide guidance for the design of appropriate RVF surveillance, prevention and control strategies which target areas with these characteristics.

The Rift Valley fever accessory proteins NSm and P78/NSm-GN are distinct determinants of virus propagation in vertebrate and invertebrate hosts

Rift Valley fever virus (RVFV) is an enzootic virus circulating in Africa that is transmitted to its vertebrate host by a mosquito vector and causes severe clinical manifestations in humans and ruminants. RVFV has a tripartite genome of negative or ambisense polarity. The M segment contains five in-frame AUG codons that are alternatively used for the synthesis of two major structural glycoproteins, G_N and G_C, and at least two accessory proteins, NSm, a 14-kDa cytosolic protein, and P78/NSm-G_N, a 78-kDa glycoprotein. To determine the relative contribution of P78 and NSm to RVFV infectivity, AUG codons were knocked out to generate mutant viruses expressing various sets of the M-encoded proteins. We found that, in the absence of the second AUG codon used to express NSm, a 13-kDa protein corresponding to an N-terminally truncated form of NSm, named NSm′, was synthesized from AUG 3. None of the individual accessory proteins had any significant impact on RVFV virulence in mice. However, a mutant virus lacking both NSm and NSm′ was strongly attenuated in mice and grew to reduced titers in murine macrophages, a major target cell type of RVFV. In contrast, P78 was not associated with reduced viral virulence in mice, yet it appeared as a major determinant of virus dissemination in mosquitoes. This study demonstrates how related accessory proteins differentially contribute to RVFV propagation in mammalian and arthropod hosts.

Rift Valley fever risk map model and seroprevalence in selected wild ungulates and camels from Kenya

Since the first isolation of Rift Valley fever virus (RVFV) in the 1930s, there have been multiple epizootics and epidemics in animals and humans in sub-Saharan Africa. Prospective climate-based models have recently been developed that flag areas at risk of RVFV transmission in endemic regions based on key environmental indicators that precede Rift Valley fever (RVF) epizootics and epidemics. Although the timing and locations of human case data from the 2006–2007 RVF outbreak in Kenya have been compared to risk zones flagged by the model, seroprevalence of RVF antibodies in wildlife has not yet been analyzed in light of temporal and spatial predictions of RVF activity. Primarily wild ungulate serum samples from periods before, during, and after the 2006–2007 RVF epizootic were analyzed for the presence of RVFV IgM and/or IgG antibody. Results show an increase in RVF seropositivity from samples collected in 2007 (31.8%), compared to antibody prevalence observed from 2000–2006 (3.3%). After the epizootic, average RVF seropositivity diminished to 5% in samples collected from 2008–2009. Overlaying maps of modeled RVF risk assessments with sampling locations indicated positive RVF serology in several species of wild ungulate in or near areas flagged as being at risk for RVF. Our results establish the need to continue and expand sero-surveillance of wildlife species Kenya and elsewhere in the Horn of Africa to further calibrate and improve the RVF risk model, and better understand the dynamics of RVFV transmission.

Ultrastructural study of Rift Valley fever virus in the mouse model

Detailed ultrastructural studies of Rift Valley fever virus (RVFV) in the mouse model are needed to develop and characterize a small animal model of RVF for the evaluation of potential vaccines and therapeutics. In this study, the ultrastructural features of RVFV infection in the mouse model were analyzed. The main changes in the liver included the presence of viral particles in hepatocytes and hepatic stem cells accompanied by hepatocyte apoptosis. However, viral particles were observed rarely in the liver; in contrast, particles were extremely abundant in the CNS. Despite extensive lymphocytolysis, direct evidence of viral replication was not observed in the lymphoid tissue. These results correlate with the acute-onset hepatitis and delayed-onset encephalitis that are dominant features of severe human RVF, but suggest that host immune-mediated mechanisms contribute significantly to pathology. The results of this study expand our knowledge of RVFV-host interactions and further characterize the mouse model of RVF.

Enhanced detection of Rift Valley fever virus using molecular assays on whole blood samples

BACKGROUND

Rift Valley fever (RVF) is an emerging arthropod-borne zoonoses of global agricultural and public health importance. In December 2006, an RVF outbreak was recognized in Kenya which led to the deployment of international response laboratory teams to the area.

OBJECTIVES

A field laboratory was operated in Malindi, Kenya to provide safe sample handling and molecular testing for RVF virus (RVFV) as well as selected other pathogens for differential diagnosis.

STUDY DESIGN

Safe sample handling was carried out using a negative pressure flexible film isolator (glovebox) and commercial reagents to inactivate clinical specimens and purify nucleic acid. Whole blood was routinely used for diagnostic testing although paired plasma samples were also tested in select cases. Subsequently, human macrophages were tested in vitro for their susceptibility to RVFV.

RESULTS

The field laboratory received samples from 33 individuals and a definite laboratory diagnosis was provided in 16 of these cases. Using molecular diagnostic techniques, RVFV was more consistently detected in whole blood than in plasma samples most likely due to association of RVFV with blood cells. Subsequent in vitro studies identified macrophages as a target cell for RVFV replication.

CONCLUSIONS

RVFV appears to replicate in blood cells such as macrophages. Thus, the sensitivity of molecular diagnostic testing is improved if whole blood is used as the clinical specimen rather than plasma or serum.

Rift valley fever virus infection of human cells and insect hosts is promoted by protein kinase C epsilon

As an arthropod-borne human pathogen, Rift Valley fever virus (RVFV) cycles between an insect vector and mammalian hosts. Little is known about the cellular requirements for infection in either host. Here we developed a tissue culture model for RVFV infection of human and insect cells that is amenable to high-throughput screening. Using this approach we screened a library of 1280 small molecules with pharmacologically defined activities and identified 59 drugs that inhibited RVFV infection with 15 inhibiting RVFV replication in both human and insect cells. Amongst the 15 inhibitors that blocked infection in both hosts was a subset that inhibits protein kinase C. Further studies found that infection is dependent upon the novel protein kinase C isozyme epsilon (PKCε) in both human and insect cells as well as in adult flies. Altogether, these data show that inhibition of cellular factors required for early steps in the infection cycle including PKCε can block RVFV infection, and may represent a starting point for the development of anti-RVFV therapeutics.

Restriction of rift valley Fever virus virulence in mosquito cells

Arboviruses are maintained in a natural cycle that requires blood-sucking arthropod and vertebrate hosts. Arboviruses are believed to persistently infect their arthropod host without overt pathology and cause acute infection with viremia in their vertebrate host. We have focused on elucidating how a specific arbovirus, Rift Valley fever (RVF) virus, causes cytopathic effect in cells derived from vertebrates and non-cytopathic infection in cells derived from arthropods. We demonstrate that the vertebrate virulence factor, NSs, is functional in arthropod cells but is expressed at significantly lower levels in infected arthropod versus infected vertebrate cells.

A complex adenovirus-vectored vaccine against Rift Valley fever virus protects mice against lethal infection in the presence of preexisting vector immunity

Rift Valley fever virus (RVFV) has been cited as a potential biological-weapon threat due to the serious and fatal disease it causes in humans and animals and the fact that this mosquito-borne virus can be lethal in an aerosolized form. Current human and veterinary vaccines against RVFV, however, are outdated, inefficient, and unsafe. We have incorporated the RVFV glycoprotein genes into a nonreplicating complex adenovirus (CAdVax) vector platform to develop a novel RVFV vaccine. Mice vaccinated with the CAdVax-based vaccine produced potent humoral immune responses and were protected against lethal RVFV infection. Additionally, protection was elicited in mice despite preexisting immunity to the adenovirus vector.

Three-dimensional organization of Rift Valley fever virus revealed by cryoelectron tomography

Rift Valley fever virus (RVFV) is a member of the Bunyaviridae virus family (genus Phlebovirus) and is considered to be one of the most important pathogens in Africa, causing viral zoonoses in livestock and humans. Here, we report the characterization of the three-dimensional structural organization of RVFV vaccine strain MP-12 by cryoelectron tomography. Vitrified-hydrated virions were found to be spherical, with an average diameter of 100 nm. The virus glycoproteins formed cylindrical hollow spikes that clustered into distinct capsomeres. In contrast to previous assertions that RVFV is pleomorphic, the structure of RVFV MP-12 was found to be highly ordered. The three-dimensional map was resolved to a resolution of 6.1 nm, and capsomeres were observed to be arranged on the virus surface in an icosahedral lattice with clear T=12 quasisymmetry. All icosahedral symmetry axes were visible in self-rotation functions calculated using the Fourier transform of the RVFV MP-12 tomogram. To the best of our knowledge, a triangulation number of 12 had previously been reported only for Uukuniemi virus, a bunyavirus also within the Phlebovirus genus. The results presented in this study demonstrate that RVFV MP-12 possesses T=12 icosahedral symmetry and suggest that other members of the Phlebovirus genus, as well as of the Bunyaviridae family, may adopt icosahedral symmetry. Knowledge of the virus architecture may provide a structural template to develop vaccines and diagnostics, since no effective anti-RVFV treatments are available for human use.

Rift Valley fever virus structural proteins: expression, characterization and assembly of recombinant proteins

Background

Studies on Rift Valley Fever Virus (RVFV) infection process and morphogenesis have been hampered due to the biosafety conditions required to handle this virus, making alternative systems such as recombinant virus-like particles, that may facilitate understanding of these processes are highly desirable. In this report we present the expression and characterization of RVFV structural proteins N, Gn and Gc and demonstrate the efficient generation of RVFV virus-like particles (VLPs) using a baculovirus expression system.

Results

A recombinant baculovirus, expressing nucleocapsid (N) protein of RVFV at high level under the control of the polyhedrin promoter was generated. Gel filtration analysis indicated that expressed N protein could form complex multimers. Further, N protein complex when visualized by electron microscopy (EM) exhibited particulate, nucleocapsid like-particles (NLPs). Subsequently, a single recombinant virus was generated that expressed the RVFV glycoproteins (Gn/Gc) together with the N protein using a dual baculovirus vector. Both the Gn and Gc glycoproteins were detected not only in the cytoplasm but also on the cell surface of infected cells. Moreover, expression of the Gn/Gc in insect cells was able to induce cell-cell fusion after a low pH shift indicating the retention of their functional characteristics. In addition, assembly of these three structural proteins into VLPs was identified by purification of cells' supernatant through potassium tartrate-glycerol gradient centrifugation followed by EM analysis. The purified particles exhibited enveloped structures that were similar to the structures of the wild-type RVFV virion particle. In parallel, a second recombinant virus was constructed that expressed only Gc protein together with N protein. This dual recombinant virus also generated VLPs with clear spiky structures, but appeared to be more pleomorphic than the VLPs with both glycoproteins, suggesting that Gc and probably also Gn interacts with N protein complex independent of each other.

Conclusion

Our results suggest that baculovirus expression system has enormous potential to produce large amount of VLPs that may be used both for fundamental and applied research of RVFV.

Epidemic Rift Valley fever in Saudi Arabia: a clinical study of severe illness in humans

We describe the clinical patterns and case-fatality rate associated with severe Rift Valley fever (RVF) in patients who were admitted to the Gizan regional referral hospital during an outbreak of RVF in Saudi Arabia from September through November 2000. A total of 165 consecutive patients (136 men and 29 women) were prospectively studied; all were identified according to a strict case definition, were confirmed to have RVF by serologic testing, and were treated according to a predetermined protocol. The major clinical characteristics of RVF included a high frequency of hepatocellular failure in 124 patients (75.2%), acute renal failure in 68 patients (41.2%), and hemorrhagic manifestations in 32 patients (19.4%). Sixteen patients had retinitis and 7 patients had meningoencephalitis as late complications in the course of the disease. A total of 56 patients (33.9%) died. Hepatorenal failure, shock, and severe anemia were major factors associated with patient death.

The carboxy-terminal acidic domain of Rift Valley Fever virus NSs protein is essential for the formation of filamentous structures but not for the nuclear localization of the protein

The ambisense S segment of Rift Valley fever (RVF) virus (a phlebovirus in the Bunyaviridae family) codes for two proteins: the viral complementary-sense RNA for the N nucleoprotein and the genomic-sense RNA for the nonstructural protein NSs. Except for the fact that the NSs protein is phosphorylated and forms filamentous structures in the nuclei of infected cells (R. Swanepoel and N. K. Blackburn, J. Gen. Virol. 34:557-561, 1977), its role is poorly understood, especially since the replication cycle of all these viruses takes place in the cytoplasm. To investigate the mechanisms involved in filament formation, we expressed NSs in mammalian cells via a recombinant Semliki Forest virus and demonstrated that the protein alone was able to form structures similar to those observed in RVF virus-infected cells, indicating that the presence of other RVF virus proteins is not required for filament formation. The yeast two-hybrid system was used to show that the protein interacts with itself and to map the interacting domains. Various deletion and substitution mutants were constructed, and the mutant proteins were analyzed by immunoprecipitation, Western blotting and immunofluorescence. These experiments indicated that the 10 to 17 amino acids of the carboxy-terminal domain were involved in self-association of the protein and that deletion of this acidic carboxy-terminal domain prevents the protein from forming filaments but does not affect its nuclear localization. The role of two phosphorylation sites present in this domain was also investigated, but they were not found to have a major influence on the formation of the nuclear filament.

Ultrastructural studies on the replication and morphogenesis of Nairobi sheep disease virus, a Nairovirus

The Nairovirus Nairobi sheep disease virus (NSDV) affects sheep and goats causing severe hemorrhagic gastroenteritis and high mortality. Replication and morphogenesis of NSDV was determined by electron microscopic examination of ultra-thin sections of 143B and BHK-21 cells at varying times after infection. By 4 h post-infection (p.i.) of 143B cells, virions budding from the luminal side of the bilayer membrane of smooth membrane vesicles were observed. Morphologically mature virus particles were electron-dense, spherical and of uniform size (100 nm diameter) and accumulated in smooth membrane vesicles associated with the Golgi complex. In BHK-21 clone 13 cells, mature virus particles in smooth membrane vesicles were present by 8 h p.i. The morphogenesis of NSDV was restricted to the smooth membrane vesicles of Golgi complex, and budding of virus from other sites was not detected. Extracellular virus particles were observed by 10 h p.i., before expression of cytopathic effects. The cytopathic effects were observed at 24 h p.i. in 143B cells and at 36 h p.i. in BHK-21 cells. The morphology and morphogenesis of NSDV in BHK-21 cells and in 143B cells resembles that of other members of the family Bunyaviridae.

Toga virus-like particles in acute liver failure attributed to sporadic non-A, non-B hepatitis and recurrence after liver transplantation

Toga virus-like particles (typically 60-70 nm: enveloped with small surface spikes) were detected in the native hepatectomy specimens in 7 of 18 patients grafted for acute liver failure attributed to sporadic non-A, non-B hepatitis and in 2 patients grafted for fulminant hepatitis attributed to anti-epileptic drug hepatotoxicity. These particles were not detected in the hepatectomies from 12 other patients grafted for other causes of acute liver failure, 12 for various chronic liver diseases, and 2 histologically normal livers. Acute hepatic failure, characterized histologically by severe haemorrhagic necrosis, developed 7 days after grafting in 5 patients, all in the non-A, non-B group with toga virus-like particles in native liver. Similar virus-like particles were detected in all grafts and were in greater abundance than in the native livers. The agent may be novel because pre- and post-grafting sera were negative for antibodies against representative panels of arboviruses and in first and second generation antibody tests for hepatitis C virus.

Electron microscopic identification of Zinga virus as a strain of Rift Valley fever virus

Electron microscopic examination of a negatively stained suspension of Zinga virus showed particles 90-100 nm in diameter, enveloped with spikes 12-20 nm in length and 5 nm in diameter. Further identification of the virus by immune electron microscopy showed the reactivity of human Rift Valley fever virus-positive serum with Zinga virus. Results of this study are in agreement with earlier reports that Zinga virus is a strain of Rift Valley fever virus.

Toga-like virus as a cause of fulminant hepatitis attributed to sporadic non-A, non-B

Virus-like particles (60-70 nm) with spiked surfaces budding into cell vacuoles and rod-shaped inclusions were detected in nuclei of hepatocytes from a British patient transplanted for sporadic non-A, non-B fulminant hepatitis (NANB-FHF), probably contracted in Kenya. Identical particles were seen in two successive grafts (days 2 and 10) at regrafting for recurrent FHF. Ultrastructural features resembled those of the RNA-containing arbovirus, Rift Valley fever virus, but serological markers against a representative panel for arboviruses (Togaviruses) and transmission in mice proved negative. The particles shared features with the different arboviruses seen in the hepatectomy specimen of a second patient with NANB-FHF, and in both patients an insect vector was implicated in the clinical history. The particles were identical in size to those of a third patient with NANB-FHF, who had remained in the United Kingdom. These findings, together with the recent report of isolation of an RNA-containing virus resembling the Togaviridae, in parenteral NANB, suggest that several exotic virus-like agents resembling the arboviruses may be involved in the aetiology of NANB, including in the sporadic forms of FHF in the United Kingdom.

Isolation of the Rift Valley fever virus by inoculation into Aedes pseudoscutellaris cells: comparison with other diagnostic methods

The Rift Valley fever epidemic, which arose in the south of Mauritania beginning on October 15, 1987, enabled a comparative study of different diagnostic methods among humans. During the first two weeks of the epidemic, four parallel methods were used: inoculation into Aedes pseudoscutellaris cells, inoculation intracerebrally into suckling mice, tests by immunocapture of the circulating antigen and detection of type IgM gammaglobulins. Of 370 examined sera, 181 showed at least one marker of recent infection. Inoculation into A. pseudoscutellaris cells was by far the most sensitive and easiest method to use. Detection of the antigen by immunocapture was also a useful technique, since it allowed quick aetiological diagnosis or examination of sera conserved under poor conditions. However, its sensitivity was weak, as it could only detect 26% of positive cases. Vero cells used on a limited scale, in this particular case seemed less sensitive than A. pseudoscutellaris cells. Of a total of 991 sera, 221 diagnoses were reported by discovery of the virus and 271 by detection of specific IgM. In every case, A. pseudoscutellaris cells seemed most appropriate as the system of reference.

Viruslike particles in liver in sporadic non-A, non-B fulminant hepatitis

In a patient who followed the typical clinical course of fulminant hepatitis attributable to "sporadic" non-A,non-B (NANB) hepatitis and who finally received treatment by orthotopic liver grafting, three, apparently separate, virus-like agents (26, 45, and 80 nm) and cytoplasmic, reticular tubular structures (CTS) were identified in collapsed and regenerating areas of liver using electron microscopy. The 80-nm particles present within vacuoles, together with the finding of intranuclear rods in association with the smaller particles (26 nm), are similar to those found in the nuclei of cells infected with several different arboviruses. The third type of particle, existing as 45-nm spheres and rods, is similar in morphology only to some form of polyoma virus, which, hitherto, has not been reported as affecting the liver. Unlike typical polyoma virus, replication of the virus "cores" (25-26 nm) was extranuclear and appeared to be occurring in vacuoles. Although analysis for serological markers against a representative panel for arboviruses, flaviviruses, phleboviruses, arenavirus, and nairovirus was negative, an insect vector was implicated in the clinical history.