Showing papers on "Dengue fever published in 1990"

The dengue viruses.

Abstract: Dengue, a major public health problem throughout subtropical and tropical regions, is an acute infectious disease characterized by biphasic fever, headache, pain in various parts of the body, prostration, rash, lymphadenopathy, and leukopenia. In more severe or complicated dengue, patients present with a severe febrile illness characterized by abnormalities of hemostasis and increased vascular permeability, which in some instances results in a hypovolemic shock. Four distinct serotypes of the dengue virus (dengue-1, dengue-2, dengue-3, and dengue-4) exist, with numerous virus strains found worldwide. Molecular cloning methods have led to a greater understanding of the structure of the RNA genome and definition of virus-specific structural and nonstructural proteins. Progress towards producing safe, effective dengue virus vaccines, a goal for over 45 years, has been made. Images

Dengue hemorrhagic fever in Cuba, 1981: a retrospective seroepidemiologic study.

Abstract: In Cuba, 2 epidemics of dengue virus occurred: 1 caused by DEN-1 in 1977 and 1 caused by DEN-2 in 1981. The latter was associated with cases of dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS). To study viral risk factors for DHF/DSS, a retrospective seroepidemiological survey was conducted in Cerro, a densely populated district in Havana City. The prevalence of plaque reduction neutralizing antibodies to DEN-1 and DEN-2 viruses was measured in 1,295 individuals (children and adults). Of these, 43.7% were immune to DEN-1 virus and 23.6% to DEN-2 virus. Of those individuals who were immune, 26.1% were immune to DEN-1 virus only, 6% to DEN-2 virus only, and 17.6% to both viruses. The DEN-2 virus infection rate in DEN-1 immune individuals was 3.8 times higher than in non-immune individuals. The 5 DHF/DSS cases in the sample had evidence of DEN-1 virus plus DEN-2 virus infections. Three were children and 2 were young adults. No cases were found in individuals infected with DEN-1 virus or DEN-2 virus only. Children infected by DEN-1 virus followed by DEN-2 virus had a high risk of acquiring DHF/DSS. Blacks and whites were equally infected with DEN-1 and DEN-2 viruses.

Human IgG Fc receptor II mediates antibody-dependent enhancement of dengue virus infection.

Abstract: It is known that anti-dengue virus antibodies at subneutralizing concentrations augment dengue virus infection of IgG FcR (Fc gamma R)-positive cells, and this phenomenon is called antibody-dependent enhancement. This is caused by the uptake of dengue virus-antibody complexes by Fc gamma R. We previously reported that Fc gamma RI can mediate antibody-dependent enhancement. In this study we use an erythroleukemia cell line, K562, which has Fc gamma RII, but does not have Fc gamma RI or Fc gamma RIII, to determine if Fc gamma RII can mediate infection by dengue virus-antibody complexes. Polyclonal mouse anti-dengue virus antibody significantly augments dengue virus infection of K562 cells, whereas normal mouse serum does not. A mAb IV.3, which is specific for Fc gamma RII and is known to inhibit the binding of Ag-antibody complex to Fc gamma RII, inhibits dengue antibody-mediated augmentation of dengue virus infection. It has been reported that Fc gamma RII binds to mouse IgG1, but not to mouse IgG2a. A mouse IgG1 anti-dengue virus mAb (3H5) augments dengue virus infection of K562 cells, but a mouse IgG2a anti-dengue virus mAb (4G2) does not. 4G2 augments dengue virus infection of a human monocytic cell line, U937, which has Fc gamma RI. Based on these results we conclude that Fc gamma RII mediate antibody-dependent enhancement of dengue virus infection in addition to Fc gamma RI.

Immunization of mice with recombinant vaccinia virus expressing authentic dengue virus nonstructural protein NS1 protects against lethal dengue virus encephalitis.

Abstract: The protective immunity conferred by a set of recombinant vaccinia viruses containing the entire coding sequence of dengue virus type 4 nonstructural glycoprotein NS1 plus various flanking sequences was evaluated by using a mouse encephalitis model. Mice immunized with recombinant vNS1-NS2a, which expresses authentic NS1, were solidly protected against intracerebral dengue virus challenge. However, mice immunized with recombinants vNS1-15%NS2a and vRSVG/NS1-15%NS2a, which express aberrant forms of NS1, were only partially protected (63 to 67% survival rate). Serologic analysis showed that mice immunized with vNS1-NS2a developed high titers of antibodies to NS1 as measured by radioimmunoprecipitation, enzyme-linked immunosorbent assay, and complement-mediated cytolytic assays. In addition, a pool of sera from these animals was protective in a passive transfer experiment. Lower titers of NS1-specific antibodies were detected in sera of animals immunized with vNS1-15%NS2a or vRSVG/NS1-15%NS2a by all three assays. These data support the view that protection against dengue virus infection in mice may be mediated at least in part by NS1-specific antibodies through a mechanism of complement-mediated lysis of infected cells. Additionally, immunization with two recombinant viruses expressing authentic NS1 of dengue virus type 2 conferred partial protection (30-50%) against dengue virus type 2 challenge.

Measurement of Antibody-dependent Infection Enhancement of Four Dengue Virus Serotypes by Monoclonal and Polyclonal Antibodies

Abstract: Although its underlying mechanisms are poorly understood, data comparing each of the four dengue virus serotypes suggest that in vitro antibody-dependent infection enhancement is a reproducible and measurable phenomenon related to other serological measures of antibody-virus binding. Information characterizing infection enhancement may provide clues to disease pathogenesis for dengue and other viruses that exhibit antibody-enhanced infection. We propose criteria for the detection and quantification of in vitro antibody-dependent enhancement of flavivirus infection based on observations using all four dengue virus serotypes, macrophage-like cell lines and human peripheral blood monocytes, and various immune sera and monoclonal antibodies. It is proposed that antibody-dependent infection enhancement is defined by the following findings: (i) significantly increased virus production is measured in quantitative assays at different points on the growth curve; (ii) assays of the virus output of cells infected with mixtures of constant amounts of virus and serial dilutions of the pre-existing antibody source produce characteristic 'enhancement profiles' of rising and falling virus output over at least a 10(-3)-fold dilution range; (iii) for each enhancing antibody source the dilution producing maximal infection enhancement is related to other serological measures of binding to the envelope, or another virus component; (iv) infection enhancement is detected with different antibody sources and virus strains (when available) tested over a range of m.o.i.; (v) other causes of enhanced virus production are ruled out.

Egg-laying yellow fever mosquitoes avoid sites containing eggs laid by themselves or by conspecifics

Abstract: Dave D. Chadee, ~ Philip S. Corbet 2 & J. J. D. Greenwood 3 1 Insect Vector Control Division, Ministry of Health, 3 Queen Street, St. Joseph, Trinidad, West lndies; 2 To whom correspondence should be addressed at Department of Zoology, University of Edinburgh, West Mains Road, Edinburgh EH9 3JT, United Kingdom; 3 British Trust for Ornithology, Beech Grove, Station Road, Tring, Hertfordshire HP23 5NR, United Kingdom

Epidemic dengue 1 in Brazil, 1986: evaluation of a clinically based dengue surveillance system.

Abstract: In the last 15 years, dengue fever has emerged as a major health problem in tropical America. Prevention and control of epidemic disease are enhanced by the rapid identification of new or increased dengue activity. Most surveillance systems, however, identify cases by clinical case reports and, therefore, lack the sensitivity needed for early detection. During the 1986 dengue 1 epidemic in Rio de Janeiro, Brazil, the authors evaluated the usefulness of a clinical case definition by comparing it with laboratory-confirmed infection status of residents in two cities. The case definition had a sensitivity of 64% and a false-positive rate of 57%. Thus, for every 100 laboratory-confirmed dengue infections, 230 cases were reported. Both infected and noninfected residents who used medical services and who lived in the city with the highest transmission were more likely to meet the case definition. Thus, factors unrelated to actual infection influenced the sensitivity. With the use of stepwise logistic regression, the authors analyzed combinations of patient symptoms and produced nine new hypothetical case definitions. However, none of the new definitions had a false-positive rate lower than 38%. This study emphasizes the need for laboratory-based dengue surveillance systems.

Dengue and dengue hemorrhagic fever

Abstract: Dengue and dengue hemorrhagic fever Scott Halstead; Current Opinion in Infectious Diseases

Preparation of an attenuated dengue 4 (341750 Carib) virus vaccine. I. Pre-clinical studies

Abstract: Dengue 4 (DEN-4) virus strain 341750 Carib was modified by serial passage in primary canine kidney (PCK) cell cultures. By the 15th PCK passage, this virus was less infectious for monkeys and resulted in a significantly reduced viremia as compared to the parent DEN-4 virus. The 30th PCK passage of DEN-4 341750 Carib was non-infectious for monkeys. A vaccine prepared at the 20th PCK passage in DBS-FRhL-2 cells stimulated the production of both neutralizing and hemagglutination inhibition antibodies in monkeys; these animals were also protected against challenge with the homologous strain as well as a heterologous strain of DEN-4. An ID50 titration in monkeys resulted in a titer of greater than 10(4) plaque-forming units (PFU) for the vaccine virus and 0.5 PFU for the parent virus. Reduced monkey infectivity of this magnitude has been correlated with human attenuation in previous dengue vaccine candidates. The DEN-4 strain 341750 Carib PCK-20/FRhL-4 vaccine has been characterized and sufficiently tested to be considered for safety and immunogenicity trials in humans.

An epidemic of dengue haemorrhagic fever and dengue shock syndrome in Delhi: a clinical study.

Abstract: SummaryTwenty-four cases of dengue haemorrhagic fever/dengue shock syndrome were studied in Delhi in the months of September and October, 1988. The majority of these cases were boys aged 6–10 years. Classical symptoms of dengue (fever, headache, aesthesia, myalgia) occurred in all the patients. Digestive symptoms (nausea, vomiting, anorexia, abdominal pain and hepatomegaly) were also common. Haemorrhagic manifestations were present in 41.7% of the cases. Of these, 90% had gastrointestinal haemorrhages. Shock occurred in 17 cases (70.8%). Thrombocytopenia and prolongation of coagulation profile were found in 62.5% of cases. Three patients (12.5%) who presented with encephalopathy died. The other 21 patients recovered after an average period of 2–8 days.

Antibody-enhanced infection of monocytes as the pathogenetic mechanism for severe dengue illness.

Abstract: Antibody-dependent enhancement of certain virus infections can occur in cells expressing Fc receptors. This mechanism plays an important pathogenetic role in the development of complications associated with dengue virus infection, including dengue hemorrhagic infection and dengue shock syndrome. The virulence of the virus, characterized by the ability to infect Fc receptor-bearing monocytes also influences the development of these severe illnesses.

Development of dengue and Japanese encephalitis vaccines.

Abstract: A second scientific meeting was sponsored by the World Health Organization (WHO) to address progress on flavivirus vaccines of importance to developing countries. The meeting was held in Vienna, 24-25 June 1989, in conjunction with the 2nd International Conference on Positive Strand RNA Viruses. A summary of the first meeting held in Canada in 1987 has been reported [1]. The strategic plan for dengue and Japanese encephalitis (JE) virus vaccine development described in that report is essentially on schedule. The importance of the program is underscored by the occurrence of up to 40 million cases of dengue annually [2]. Since JE is primarily an inapparent infection in humans, ~40 million infections result in far fewer cases of JE, ^30,000 cases annually. In the meeting in Austria, Meegan (WHO, Geneva) reported that WHO monitors dengue through regional offices in New Delhi, Manila, and the Pan American Health Organization and supports vaccine development in established laboratories by providing funds for an additional salary or supplies or both. Halstead (USA) pointed out that the global distribution of dengue coincided with the global distribution of Aedes aegypti and Aedes albopictus, that there were tens of millions of cases annually, and that over the past 25 years there were ~2 million cases of dengue hemorrhagic fever resulting in 35,000 deaths. He summarized the information associating severe disease with prior infection to another serotype of dengue: Cross-reactive but nonneutralizing antibodies from a previous dengue infection bind to the newly infecting dengue virus, and the infectious complex then enters susceptible cells via Fc receptors. In infants, the waning of maternal protective antibodies by 6-9 months leaves infants susceptible to hemorrhagic fever because of the greater quantities and hence longer lasting maternal cross-reactive enhancing antibodies. For these reasons, dengue vaccines must induce specific protective antibodies to all four serotypes of dengue virus.

Study of anti-dengue NS1 antibody by western blot.

Abstract: The presence of anti-nonstructural protein (NS1) antibody in natural dengue infections has been suspected to be associated with development of dengue haemorrhagic fever (DHF). The Western blot technique was used to study the dynamics of the immune response to NS1 and to determine the frequency of anti-NS1 antibody among confirmed dengue patients in Indonesia, where DHF is common, and in Puerto Rico, where DHF is less frequently observed. Anti-NS1 antibody was rarely found in those with primary infections in either group. The antibody occurred at a significantly higher frequency in acute-phase serum samples from secondary infections in Indonesia than in those from Puerto Rico. No difference was observed, however, in Indonesian patients with secondary infection who had dengue fever or DHF.

Vertical transmission of dengue viruses by strains of Aedes albopictus recently introduced into Brazil.

Abstract: Three strains of Aedes albopictus from Brazil were examined for their ability to vertically transmit dengue 1 (DEN-1) and dengue 4 (DEN-4) viruses. Parental females were uniformly infected by parenteral inoculation of virus, and 8,121 F1 progeny from DEN-1 and DEN-4 infected mothers were pooled in lots of approximately 50 and tested for virus. Seven of 60 pools were positive for DEN-1 virus, and 1 of 121 pools was positive for DEN-4 virus. In DEN-1 assays, the minimum infection rate (MIR) for larvae (2 pools tested) was 1:84. Among positive cohorts of adults, pooled by sex and by geographic strain of mosquito, the MIR ranged from 1:193 to 1:626 for males and from 1:187 to 1:311 for females. Only a single pool of adult females was positive for DEN-4 virus (MIR 1:1022 for an adult female cohort from Santa Teresa). These results indicate that Brazilian Ae. albopictus have the potential to play a role in the maintenance of dengue viruses in nature.

Variation among strains of Aedes aegypti in susceptibility to oral infection with dengue virus type 2.

Abstract: We compared 18 Aedes aegypti strains for oral susceptibility to dengue virus type 2 (DEN-2) using a feeding protocol in which all parameters remained constant, including the titer of the infectious bloodmeal. For most strains, no significant variation between replicates was observed. Comparisons between pairs of strains showed variation of different degrees, and allowed us to characterize the strains with respect to their oral susceptibility to DEN-2.

Human immune responses to dengue viruses.

Abstract: Dengue fever (DF) and dengue hemorrhagic fever (DHF)/dengue shock syndrome (DSS) are major public health problems in many areas of the world. We are analyzing the human immune responses to dengue viruses, in order to understand the mechanism of recovery from dengue virus infections and the pathogenesis of DHF/DSS. Human natural killer (NK) cells lyse dengue virus-infected cells to a greater degree than uninfected cells. Antibodies to dengue viruses augment the lysis of dengue virus-infected cells by NK cells. Dengue virus-infected monocytes produce high levels of interferon alpha (IFN alpha). DR+ lymphocytes also produce high levels of IFN alpha after contact with dengue virus-infected monocytes. The IFN alpha produced protects uninfected monocytes from dengue virus infection. These results suggest that NK cells and IFN alpha may play an important role in controlling primary dengue virus infection. Dengue virus-specific CD4+CD8(-)T lymphocytes and CD4(-)CD8+T lymphocytes are present in the peripheral blood mononuclear cell population from donors who were infected with dengue virus. Most of CD4+T lymphocytes are dengue serotype-crossreactive. They lyse dengue virus-infected autologous cells in an HLA class II-restricted fashion, and produce interferon gamma (IFN gamma). IFN gamma augments dengue virus infection of monocytic cells in the presence of antidengue virus antibodies by increasing the number of Fc gamma receptors. Dengue virus-specific CD8+T lymphocytes lyse dengue virus-infected autologous cells in an HLA class I-restricted fashion. These CD8+T lymphocytes are also dengue serotype-crossreactive.(ABSTRACT TRUNCATED AT 250 WORDS)

Dengue serologic survey of schoolchildren in Rio de Janeiro, Brazil, in 1986 and 1987.

Abstract: Two major epidemic waves of dengue 1 occurred in Rio de Janeiro, Brazil, in 1986 and 1987. This article reports the results of a survey of Rio schoolchildren who were tested serologically for antibodies to dengue 1 before and after the second major epidemic wave. The highest percentages of positive subjects were found in districts with relatively poor socioeconomic conditions and mosquito control problems. It also appears likely that the estimated number of dengue cases occurring in 1986-1987 was substantially below the number that actually occurred. In addition, because of this exposure to dengue 1, Rio de Janeiro now runs the risk of dengue hemorrhagic fever/dengue shock syndrome occurring should another dengue serotype be introduced within the next few years.

Clinical & virological study of dengue fever outbreak in Jalore city, Rajasthan 1985.

Abstract: An epidemic of acute febrile illness caused by dengue virus occurred in Jalore town, in south-west Rajasthan, in April and May, 1985. Most patients had classical signs and symptoms of dengue fever or had only a mild atypical febrile illness. A few patients had in addition haemorrhagic manifestations/shock or encephalitis. Virological studies (carried out by the National Institute of Virology, Pune) showed that dengue type 3 virus was the main etiological agent. This is the first reported outbreak of dengue in the arid zone in western Rajasthan, that occurred in summer (April-May) in contrast to other parts of India, where such outbreaks are commonly reported after the rains (between August and November).

Passive protection studies in mice with monoclonal antibodies directed against the non-structural protein NS3 of dengue 1 virus.

Abstract: Antibody-mediated enhancement of dengue virus replication is thought to be a mechanism contributing to the pathogenesis of dengue haemorrhagic fever and dengue shock syndrome. Enhancement is associated with antibodies to structural components of the virus. To circumvent the problem of immune enhancement, studies to identify protective antigens of dengue virus have involved non-structural proteins. Passive and active protection against lethal dengue virus infection in mice have been demonstrated with the nonstructural protein NS1. In this study, the dengue virus non-structural protein NS3 was examined in passive protection studies with monoclonal antibodies prepared against NS3 of dengue 1 virus (Hawaiian). Five monoclonal antibodies that were authenticated to be reactive to NS3 were used to immunize 13- to 14-day old mice intraperitoneally. Thereafter, the mice were challenged intracerebrally with 100 LD50 of neurotropic dengue 1 virus and the survival indices of the mice were calculated. Significant decreases in survival indices (P < 0.05), indicating increases in survival times were observed with four of five monoclonal antibodies tested. Monoclonal antibodies to NS3 of dengue 1 virus are able to increase the survival time of mice challenged with a lethal dose of dengue 1 virus, although the mechanism remains to be defined.

Epidemic of fever of unknown origin in rural Thailand, caused by influenza A (H1N1) and dengue fever.

Abstract: In the late summer (rainy season) of 1987, a sharp outbreak of fever of unknown origin (FUO) in rural southern Thailand was investigated by a field epidemiology team. In a random survey of households, 40 percent of the children and 20 percent of adults were reported to have had febrile illnesses within the last month. There was at least one death, possibly from Reye's syndrome. Testing 34 pairs of acute and convalescent sera showed significant HI antibody titer rises to influenza A (Taiwan/(H1N1) (9 cases) and dengue virus (12 cases). Testing 79 single sera with the antibody capture ELISA test for dengue, revealed that 23 percent had high titers in the IgM serum fraction suggesting recent infection. There were also six antibody titer rises to coxsackie B viruses, three from well controls. Dengue has previously been observed as a cause of FUO in rural areas in the tropics, but finding a combined epidemic of dengue and influenza was unexpected. With cooperative villagers, adequate personnel and laboratory support, especially the antigen capture ELISA test for dengue infections, it is feasible to successfully investigate disease outbreaks with serologic methods in remote villages.

Murine typhus identified as a major cause of febrile illness in a camp for displaced Khmers in Thailand.

Abstract: Scrub and murine typhus have been identified as causes of illness among the 238,000 displaced Khmer people residing in temporary settlements on the Thai side of the Thai-Cambodian border. Still, the true extent of the problem and the relative frequency of infection with scrub typhus as compared to murine typhus are unknown. We evaluated consecutive patients with unexplained pyrexia (documented fever, no exclusionary diagnosis, and constitutional symptoms) in 1 temporary settlement over 1 month. Laboratory studies included culture of blood and assay of paired sera for rickettsial IgM and IgG antibody, for dengue IgM and IgG antibody, and for leptospiral IgM and IgG antibody. Among 37 patients (27 adults and 10 children), 28 (75%) had a rickettsiosis (26 cases of murine typhus and 2 cases of scrub typhus). No case of enteric fever, dengue, or leptospirosis was diagnosed. The illnesses of 9 patients were not identified. Signs and symptoms did not distinguish confirmed rickettsial infections from undiagnosed illnesses. The 1 month attack rate of rickettsial infection was 29/100,000 for children and 185/100,000 for adults. Murine typhus was a major cause of febrile illness in this settlement.

Clinical and upper gastroendoscopic features of patients with dengue virus infection.

Abstract: Clinical observation was made on 238 dengue fever cases during an epidemic in Taiwan from September to November 1988. Dengue virus infection type 1 was responsible for all cases. The majority of patients had acute onset of fever with abdominal pain, diarrhoea, and vomiting. Gastrointestinal haemorrhage with manifestation of haematemesis and/or melena was observed in 28 (11.8%) of our patients. The clinical gastrointestinal features in patients with a peptic ulcer history were not different from those in patients without it. There was no significant difference in incidence of gastrointestinal manifestations between premedication and non-premedication patients. Sixty-six non-premedication patients in our series were examined by gastroduodenoscopy. Haemorrhagic gastritis was the most common finding in 27 (40.9%) patients. The incidence of gastric and/or duodenal ulcerations was higher in patients with a peptic ulcer history compared with those without it (P less than 0.01). However, the incidence of upper gastrointestinal bleeding was similar between these two groups (19.2% vs 9.8%). Thrombocytopenia in patients with gastrointestinal haemorrhage was more prominent than in those without it (P less than 0.005). This implied that thrombocytopenia might be one of the predisposing factors for gastrointestinal haemorrhage.

Sequential changes of serum transaminase and abdominal sonography in patients with suspected dengue fever.

Abstract: Southern Taiwan experienced a dengue (type 1) outbreak in the autumn of 1988. One hundred and thirteen febrile patients suspected as having dengue infection were seen in the emergency room of the Kaohsiung Medical College Hospital. These patients were recruited for this study. Two hundred and eighty-six sequential serum aspartate transaminase (AST) and alanine transaminase (ALT) data from these patients were analyzed. Data analysis showed serum AST had increased daily and all data were out of normal range from day 6 of the illness. Compared to the AST level on the first day of the illness, the AST level was noted to elevate to an average of 9.25 folds on day 6. The sequential changes of AST were as follows: AST had elevated since the third ill-day in most cases and reached a peak on the 7th or 8th ill-day. It then declined gradually from the 8th ill-day and became normal about 3 weeks later. The changes of ALT level were about the same as AST but had later onset and lower peak. Abdominal sonographic examinations showed thickening of the gall bladder wall, splenomegaly and ascites in some patients during acute stage of the illness and recovered completely after patients recovered from the dengue attack. The sequential change of serum transaminase levels and sonographic findings were compatible. These findings may be used as a reference for the differential diagnosis among dengue fever, acute hepatitis and acute cholecystitis.

Pathogenesis of dengue: an alternative hypothesis.

Abstract: This paper presents a novel but entirely hypothetical concept on the pathogenesis of the shock syndrome (DSS) associated with dengue hemorrhagic fever (DHF). Antibody-dependent enhancement (ADE) is widely thought to be central to the development of these clinical entities. Current views on the mechanisms underlying ADE centre on two major lines of thought: 1) Non-neutralizing antibodies to dengue virus (DV) can enhance viral uptake and replication in target cells (monocytes). 2) DHF/DSS are the consequences of enhanced viral replication, paired with immunopathological processes that are evoked by monocyte dysfunction and detrimental reactions caused by activated T-lymphocytes. The present hypothesis proposes, by contrast, a central role for the following processes: 1) Secondary infection of an individual who has sub or non-neutralizing antibody titers against DV leads to a booster antibody response and a steep rise in antibody levels. 2) Antibodies against DV bind to and direct a selective attack of the complement system onto cells expressing viral antigens on their surface. DHF/DSS are the direct and indirect consequences of complement activation on these cells. The advanced hypothesis, which departs from the mainstream of "immune enhancement" concepts, can easily be tested by experimentation.

Identification of monoclonal antibodies that distinguish between 17D-204 and other strains of yellow fever virus

Abstract: Eight monoclonal antibodies (MAbs) prepared against the flaviviruses Saint Louis encephalitis, dengue 2 and dengue 3 viruses all recognized epitopes on the envelope protein of the prototype flavivirus, yellow fever (YF) virus. Three of these MAbs with flavivirus group-common specificity and two MAbs with a flavivirus-subgroup specificity were found to distinguish wild-type YF viruses from YF 17D-204 vaccine virus, but not from the closely related 17DD vaccine virus, nor from the French neurotropic vaccine virus. This pattern of reactivity was seen only with viruses grown in Aedes albopictus C6/36 cells and not with viruses grown in vertebrate cells (SW13 and Vero cells), where all five MAbs recognized epitopes on both wild-type and 17D-204 viruses. Examination of adult A. aegypti mosquitoes infected with the same YF viruses as above gave a different pattern of results to those in C6/36 cells. Thus, epitope expression differs between mammalian and arthropod cells and between arthropod cells in vitro and in vivo. Neutralization tests showed that all five MAbs would neutralize wild-type Asibi virus grown in SW13 cells, but not Asibi virus grown in C6/36 cells, nor 17D-204 vaccine virus grown in either cell type. Therefore, it is concluded that when YF virus is grown in mosquito cells, wild-type virus is antigenically and biologically distinct from the 17D-204 vaccine virus.

Expression of the structural proteins of dengue 2 virus and yellow fever virus by recombinant vaccinia viruses.

Abstract: Vaccinia virus recombinants were constructed which contained cDNA sequences encoding the structural region of dengue 2 virus (PR159/S1 strain) or yellow fever virus (17D strain). The flavivirus cDNA sequences were expressed under the control of the vaccinia 7.5k early/late promotor. Cultured cells infected with these recombinants expressed immunologically reactive flavivirus structural proteins, precursor prM and E. These proteins appeared to be cleaved and glycosylated properly since they comigrated with the authentic proteins from dengue 2 virus- and yellow fever virus-infected cells. Mice immunized with the dengue/vaccinia recombinant showed a dengue-specific immune response that included low levels of neutralizing antibodies. Immunization of mice with the yellow fever/vaccinia recombinant was less effective at inducing an immune response to yellow fever virus and in only some of the mice were low titers of neutralizing antibodies produced.