We studied five fatal cases of dengue haemorrhagic fever (DHF), confirmed using the reverse transcriptase-polymerase chain reaction (RT-PCR) method, in Vietnamese children. The liver seems to be a target for dengue virus, so postmortem examinations were performed to investigate elementary lesions, local recruitment of inflammatory cells and whether the virus was present in target cells of the liver. We detected severe, diffuse hepatitis with midzonal necrosis and steatosis in two patients, focal areas of necrosis in two patients, and normal histology in one patient. Dengue virus antigen was detected using immunohistochemistry in hepatocytes from necrotic areas in four cases. There was no recruitment of polymorphonuclear cells, and no lymphocytes were detected in the liver lesions of patients who died from DHF. Lymphocytic infiltration occurred in only one hepatitis B virus-positive patient, with no signs of chronic hepatitis. Kupffer cells had mostly been destroyed in cases with focal or severe necrosis. TUNEL tests were positive in necrotic areas, with positive cells forming clusters, suggesting that an apoptotic mechanism was involved. Thus, we suggest that the hepatocyte and Kupffer cells may be target cells supporting virus replication and that the councilman body is an apoptotic cell, as in the pathogenesis of yellow fever.

Antigens, Viral↗

PubMed2001

Recent advances in vaccines against viral haemorrhagic fevers.

Development of vaccines against viral haemorrhagic fevers is a public health priority. Recent advances in our knowledge of pathogenesis and of the immune responses elicited by these viruses emphasize the crucial role of the immune system in the control of infection, but also its probable involvement in pathogenesis. Several vaccine candidates against viral haemorrhagic fevers have been evaluated in animals during the past year. Together, these data suggest that a vaccine approach against viral haemorrhagic fevers is feasible, should induce well-balanced immune responses with cellular and humoral components, and should avoid the potential deleterious effects that are associated with such immune responses.

Dengue Virus↗

PubMed2001

West Nile in the Mediterranean basin: 1950-2000.

Recent West Nile virus (WNV) outbreaks have occurred in the Mediterranean basin. In Algeria in 1994, about 50 human cases of WN encephalitis were suspected, including 8 fatal cases. In Morocco in 1996, 94 equines were affected of which 42 died. In Tunisia in 1997, 173 patients were hospitalized for encephalitis or meningoencephalitis. West Nile serology performed on 129 patients was positive in 111 cases (87%) including 5 fatal cases. In Italy in 1998, 14 horses located in Tuscany were laboratory confirmed for WNV infection; 6 animals died. In Israel in 1998, serum samples from horses suffering from encephalomyelitis had WNV antibodies and virus was isolated from the brain of a stork; in 1999 WNV was identified in commercial geese flocks, and in 2000 hundreds of human cases have been reported. In September 2000, WNV infection was detected in horses located in southern France, close to the Camargue National Park where a WNV outbreak occurred in 1962. By November 30, 76 cases were laboratory confirmed among 131 equines presenting with neurological disorders. No human case has been laboratory confirmed among clinically suspect patients. The virus isolated from a brain biopsy is closely related to the Morocco-1996 and Italy-1998 isolates from horses, to the Senegal-1993 and Kenya-1998 isolates from mosquitoes, and to the human isolate from Volgograd-1999. It is distinguishable from the group including the Israel-1998 and New York-1999 isolates, as well as the Tunisia-1997 human isolate.

Animals↗

PubMed2001

Variations in biological features of West Nile viruses.

Pathological findings in humans, horses, and birds with West Nile (WN) encephalitis show neuronal degeneration and necrosis in the central nervous system (CNS), with diffuse inflammation. The mechanisms of WN viral penetration of the CNS and pathophysiology of the encephalitis remain largely unknown. Since 1996, several epizootics involving hundreds of humans, horses, and thousands of wild and domestic bird cases of encephalitis and mortality have been reported in Europe, North Africa, the Middle East, Russia, and the USA (see specific chapters in this issue). However, biological and molecular markers of virus virulence should be characterized to assess whether novel strains with increased virulence are responsible for this recent proliferation of outbreaks.

Aedes↗

PubMed2001

West Nile virus: a newly emergent epidemic disease.

Explore the source record for details and available documents.

Animals↗

PubMed2001

Intercontinental transmission of West Nile virus by migrating white storks.

Explore the source record for details and available documents.

Animals↗

PubMed2000

Determinants in the envelope E protein and viral RNA helicase NS3 that influence the induction of apoptosis in response to infection with dengue type 1 virus.

One mechanism by which dengue (DEN) virus may cause cell death is apoptosis. In this study, we investigated whether the genetic determinants responsible for acquisition by DEN type 1 (DEN-1) virus of mouse neurovirulence interfere with the induction of apoptosis. Neurovirulent variant FGA/NA d1d was generated during the adaptation of the human isolate of DEN-1 virus strain FGA/89 to grow in newborn mouse brains and mosquito cells in vitro [Desprès, P. Frenkiel, M. -P. Ceccaldi, P.-E. Duarte Dos Santos, C. and Deubel, V. (1998) J. Virol., 72: 823-829]. Genetic determinants possibly responsible for mouse neurovirulence were studied by sequencing the entire genomes of both DEN-1 viruses. Three amino acid differences in the envelope E protein and one in the nonstructural NS3 protein were found. The cytotoxicity of the mouse-neurovirulent DEN-1 variant was studied in different target cells in vitro and compared with the parental strain. FGA/NA d1d was more pathogenic for mouse neuroblastoma cells and attenuated for human hepatoma cells. Changes in virus replicative functions and virus assembly may account, in a large part, for the differences in the induction of apoptosis. Our data suggest that identified amino acid substitutions in the envelope E protein and viral RNA helicase NS3 may influence DEN-1 virus pathogenicity by altering viral growth.

Amino Acid Sequence↗

PubMed2000

Alpha-glucosidase inhibitors reduce dengue virus production by affecting the initial steps of virion morphogenesis in the endoplasmic reticulum.

We report that endoplasmic reticulum alpha-glucosidase inhibitors have antiviral effects on dengue (DEN) virus. We found that glucosidase inhibition strongly affects productive folding pathways of the envelope glycoproteins prM (the intracellular glycosylated precursor of M [membrane protein]) and E (envelope protein): the proper folding of prM bearing unprocessed N-linked oligosaccharide is inefficient, and this causes delayed formation of prME heterodimer. The complexes formed between incompletely folded prM and E appear to be unstable, leading to a nonproductive pathway. Inhibition of alpha-glucosidase-mediated N-linked oligosaccharide trimming may thus prevent the assembly of DEN virus by affecting the early stages of envelope glycoprotein processing.

1-Deoxynojirimycin↗

PubMed2000

[Forest ecosystems and Ebola virus].

Despite data collected since the emergence of the Ebola virus in 1976, its natural transmission cycle and especially the nature of its reservoirs and means of transmission are still an enigma. This means that effective epidemiological surveillance and prevention are difficult to implement. The location of outbreak areas has suggested that the reservoir and the transmission cycle of the Ebola virus are closely linked to the rainforest ecosystem. The fact that outbreaks seldom occur suggests the presence of a rare animal reservoir having few contacts with man. Paradoxically, various serological investigations have shown a high prevalence in human beings, especially in forest areas of the Central African Republic (CAR), with no pathology associated. This would appear to suggest a circulation of both pathogenic and non-pathogenic strains as well as frequent contacts with man. The ecological changes resulting from human activity (agriculture and logging) account for the modification of the fauna (movement of rainforest fauna, introduction of savannah species) and could explain a multiplication of contacts. Likewise, it is interesting to note that the centre of outbreaks has always been in areas bordering on forests (ecotone foreset-savannah in the Democratic Republic of Congo, savannah in Sudan). All these considerations have led us to establish a permanent "watch" in areas bordering on forests in the CAR, involving a multidisciplinary approach to the virological study (strain isolation, molecular biology) of the biodiversity of small terrestrial mammals. The results of a study conducted on 947 small mammals has shown for the first time the presence of the Ebola virus genome in two species of rodents and one species of shrew living in forest border areas. These animals must be considered as intermediary hosts and research should now focus on reservoirs in the ecosystem of forest border areas where contacts with man are likely to be more frequent.

Animals↗

PubMed1999

Origin of the West Nile virus responsible for an outbreak of encephalitis in the northeastern United States.

In late summer 1999, an outbreak of human encephalitis occurred in the northeastern United States that was concurrent with extensive mortality in crows (Corvus species) as well as the deaths of several exotic birds at a zoological park in the same area. Complete genome sequencing of a flavivirus isolated from the brain of a dead Chilean flamingo (Phoenicopterus chilensis), together with partial sequence analysis of envelope glycoprotein (E-glycoprotein) genes amplified from several other species including mosquitoes and two fatal human cases, revealed that West Nile (WN) virus circulated in natural transmission cycles and was responsible for the human disease. Antigenic mapping with E-glycoprotein-specific monoclonal antibodies and E-glycoprotein phylogenetic analysis confirmed these viruses as WN. This North American WN virus was most closely related to a WN virus isolated from a dead goose in Israel in 1998.

Amino Acid Sequence↗

PubMed1999

A recombinant Fab neutralizes dengue virus in vitro.

A recombinant Fab that recognizes a neutralizing epitope located in the (296-400) region of protein E of dengue virus was obtained from cloned hybridoma cells secreting the mouse monoclonal antibody (mAb) 4E11. The Fd and light chain antibody genes were amplified by polymerase chain reaction, cloned into the phagemid vector pMad, expressed in bacteria to produce Fab fragments and sequenced. The mAb 4E11, in particular its light chain complementary-determining regions, shared homologies with two other anti-viral mAbs. The affinity of the parental mAb and the cloned Fab to the MalE-E(296-400) fusion protein were shown to be of the same magnitude, i.e. nanomolar. Fab 4E11 neutralization capacity was found between 8 and 4-times or less lower than that of mAb 4E11, depending on serotypes, thus the Fab could have a smaller antiviral activity than the mAb in vitro.

Animals↗

PubMed1999

Induction of protective immunity against Dengue virus type 2: comparison of candidate live attenuated and recombinant vaccines.

Dengue (DEN) viruses (serotypes 1 to 4) are mosquito-borne flaviviruses which cause about fifty million human infections annually and represent an expanding public health problem in the tropics. At present, there are no safe and effective vaccines which induce protective immunity to all four serotypes of DEN. Natural infection or vaccination with native and recombinant proteins may induce an immune response to the surface envelope E-protein which was shown to be protective to super-infection with homologous serotype of the virus. Purified recombinant E-protein was made in the baculovirus-Spodoptera frugiperda expression system. This protein induced neutralizing antibodies in mice. These results prompted us to immunize cynomolgus monkeys (Macaca fascicularis) with either a live attenuated DEN-2 vaccine or the recombinant E-protein complexed to aluminum hydroxide. After immunization, the monkeys were challenged with the homologous DEN virus. Serum was collected at several time points and a virus-specific antibody response including a virus neutralizing antibody response was measured. Antibody kinetics and levels were similar to those recorded in humans with a natural DEN-virus infection. Virus isolation and type specific RT-PCR were performed on the serum samples. The virus was isolated from sham vaccinated control monkeys but not from monkeys vaccinated with the live attenuated vaccine. One of the two monkeys immunized with the recombinant E-protein was also protected. Taken together these data indicate the potential of both candidate vaccines and stress the need for evaluation of different antigen presentation systems for the development of a subunit vaccine approach for DEN.

Aedes↗

PubMed1999

Complete nucleotide sequence and phylogeny of an American strain of yellow fever virus, TRINID79A.

Yellow fever was presumably imported to the Americas from West-Africa from the 16th to the 19th century. American and African genotypes of the virus are distinguishable, indicating separate evolution in different vector/host cycles. The complete nucleotide sequence of the yellow fever virus strain TRINID79A, isolated in Trinidad in 1979, has been established. It exhibits extensive homology with those of current West-African strains and attenuated strain FNV. However, a unique deletion of the 3' non-coding region (NCR) of the viral RNA has been identified. It indicates that RYF1 and RYF2 repeated sequences of the 3' NCR are not necessary to the replication of the virus.

3' Untranslated Regions↗

PubMed1999

Report of a fatal case of dengue infection with hepatitis: demonstration of dengue antigens in hepatocytes and liver apoptosis.

A fatal case of dengue (DEN) infection associated with a spleen rupture and with hepatitis is reported here. Microscopic studies showed numerous areas of spleen rupture with hematomas and revealed necrotic foci in liver samples obtained at autopsy. Although hepatitis was reported in several cases of DEN fever, the mechanism of liver injury remains poorly understood. In this case, immunohistochemistry showed that DEN viral antigens were mostly detected in hepatocytes surrounding the necrotic foci. By in situ detection of DNA fragmentation, apoptotic hepatocytes were found to be colocated with DEN virus-infected hepatocytes. These findings suggest that hepatocytes are the major sites of DEN virus replication in the liver and that DEN virus induces apoptosis of hepatocytes in vivo.

Adult↗