Molecular typing of dengue virus type 2 in Brazil

Strain typing is a critical tool for molecular epidemiological analysis and can provide important information about the spread of dengue viruses. Here, we performed a molecular characterization of DEN-2 viruses isolated in Brazil during 1990-2000 from geographically and temporally distinct areas in order to investigate the genetic distribution of this serotype circulating in the country. Restriction site-specific polymerase chain reaction (RSS)-PCR presented the same pattern for all 52 Brazilian samples, showing the circulation of just one DEN-2 variant. Phylogenetic analysis using progressive pairwise alignments from 240-nucleotide sequences of the E/NS1 junction in 15 isolates showed that they belong to genotype III (Jamaica genotype).     

B-cell responses during primary and secondary dengue virus infections in humans

Low-avidity serotype-cross-reactive antibodies are hypothesized to play a key role in triggering severe disease in patients with secondary dengue virus (DENV) infection. However, there is little systematic information about the frequency, avidity, and cross-reactivity of DENV-specific B cells in individuals experiencing primary instead of secondary infection. We compared DENV-specific B-cell responses in a cohort of Thai children with primary or secondary DENV infection. B cells specific for DENV precursor membrane protein, envelope (E) protein, and nonstructural protein 1 were detectable in immune peripheral blood mononuclear cells with the highest frequencies of DENV E-specific B cells detected in patients experiencing primary DENV-1 infections. DENV E-specific B cells were highly serotype-specific after primary DENV infections, whereas most E-specific B cells in patients with secondary infection were serotype-cross-reactive and secreted antibodies with higher avidity to heterologous DENV serotypes. Our data suggest that the minor populations of serotype-cross-reactive B cells generated by primary DENV infection are preferentially expanded during secondary DENV infection.     

Epidemiology and control of dengue virus infections in Thai villages in 1987

A severe epidemic of dengue hemorrhagic fever (DHF) in Nakhon Ratchasima, Thailand in August of 1987 prompted a field investigation. DHF rates of 0.4-6.5 cases per 1,000 residents in subdistricts and 2-15 cases per 1,000 residents in 10 villages investigated were reported. Epidemics peaked in neighboring villages at different times; in June and July, and in August before the rainy season began late in the month. In 4 primary schools representing 6 villages, sera from groups of randomly selected children were tested for dengue IgM with the antibody capture ELISA test. Rates of recent dengue infection were 10-65% in the schools and correlated closely with reported rates of DHF. In an effort to control vectors, malathion fog and temephos (1% abate sand granules) were applied. Villagers were educated in prevention and were urged to cover water receptacles. The percentage of houses with larvae dropped from 67 to 20, the percentage of containers with larvae decreased from 30 to 5, and the number of containers with larvae per 100 households decreased from 221 to 33. This was a serious epidemic in which conventional control measures were only moderately effective.     

Seroepidemiological survey on dengue and Japanese encephalitis virus infections in Asian monkeys

To investigate the ecology of dengue and Japanese encephalitis (JE) viruses in the forest in Asia, a seroepidemiological survey was carried out on 358 Southeast Asian cynomolgus (Macaca iris), 33 Indian bonnet (Macaca radiata) and 37 Japanese (Macaca fuscata) monkey sera by a plaque reduction neutralization test. The results indicated that Southeast Asian monkeys were naturally infected with these viruses but the frequency of antibody to them varied considerably according to the geographical origin of the monkeys. The frequency of antibody to one or more types of dengue virus were 87.2, 49.5, 34.3, 34.2 and 14.9% in Malaysian, Vietnamese, Cambodian, Indonesian and Filipino cynomolgus monkey sera, respectively. None of the Indian bonnet monkey sera neutralized type 1 dengue virus which was the only virus type examined with this monkey species. Monkey sera collected in Japan where dengue virus infection had not been known since 1944 did not significantly neutralize dengue viruses. JE virus antibody was detected at 29.7, 9.0, 8.6, 2.7, 1.4 and 0% in Japanese, Cambodian, Vietnamese, Indonesian, Filipino and Malaysian monkey sera respectively.     

Seroprevalence of dengue, chikungunya and sindbis virus infections in German aid workers

Summary Vector-borne virus infections were studied in 670 German overseas aid workers who had spent an average of 37.7 months in tropical areas of Africa and Asia. Antibodies to dengue viruses (DEN) were detected by indirect immunofluorescence assay in 43/670 (6.4%) aid workers. Of these 43, 41 (95.3%) were also positive for antibodies to dengue by haemagglutination inhibition assay. The highest seroprevalence was in aid workers returning from Thailand (19.4%), Benin (14.8%) and Burkina Faso (9.2%). Antibodies to chikungunya virus (CHIK) were detected in 9/670 (1.3%) aid workers, and the highest seroperevalence to anti-CHIK IgG was in aid workers who had resided in Benin (5.7%) and Thailand (5.5%). Antibodies to Sindbis virus were detected only in 1/670 (0.1%) aid worker who had been to Zambia. Vector-borne virus infections, especially DEN, pose a health risk for aid workers.     

Isolation and partial characterization of dengue virus type 2 and 4 strains from dengue fever and dengue haemorrhagic fever patients from Mindanao, Republic of the Philippines

OBJECTIVE: Isolation of dengue virus from dengue fever and dengue haemorrhagic fever cases from Mindanao, Republic of the Philippines. METHODS: 12 patients with clinically suspected dengue fever (DF) or dengue haemorrhagic fever (DHF) presenting in four regional hospitals between August and September 1995 on Minadano were enrolled in the study. Dengue virus was isolated by inoculation of Vero/E6 or C6/36 cells with patient serum. IgM antibodies were measured using a commercial test system. Up to 454 bp of the capsid region and 240 bp of the E/NS1 gene junction of different viral isolates were sequenced and phylogenetically analyzed. RESULTS: Virus could be isolated from seven patients, five isolates were typed as dengue virus type 2 and two as dengue virus type 4 by immunostaining with monoclonal antibodies or by RT/PCR. Phylogenetic analysis confirmed a close relationship of the dengue virus type 2 isolates with viruses isolated in the Philippines in 1983 and 1988. CONCLUSION: As observed in studies from other parts of South East Asia, dengue virus type 2 was readily isolated from dengue haemorrhagic fever cases. Dengue virus type 2 and 4 circulate in Mindanao, Philippines, with dengue type 2 being responsible for most of our severe DF or DHF cases.     

Anti-dengue virus envelope protein domain III IgG ELISA among infants with primary dengue virus infections

Dengue is the most prevalent arthropod-borne viral illness in humans. The current gold standard serologic test for dengue virus (DENV) infection is a neutralizing antibody assay. We examined a DENV recombinant (r)E protein domain III IgG ELISA among infants with primary DENV infections. Infants experience a primary DENV infection in the presence of maternally derived anti-DENV IgG. The estimated DENV rE protein domain III IgG levels to the infecting serotype at the time of infant primary symptomatic DENV2 and DENV3 infections correlated with the 50% plaque reduction neutralization reciprocal antibody titers (PRNT₅₀). Anti-DENVs 1–4 rE protein domain III IgG levels all correlated with each other, and the estimated rE protein domain III IgG level to the infecting serotype at the time of infection inversely correlated with dengue disease severity. The anti-DENV rE protein domain III IgG ELISA may be a useful and potentially high-throughput alternative to traditional DENV neutralizing antibody assays.     

Cellular immune activation in children with acute dengue virus infections is modulated by apoptosis

Apoptosis is an important modulator of cellular immune responses during systemic viral infections. Peripheral-blood mononuclear cell (PBMC) apoptosis and plasma soluble levels of CD95, a mediator of apoptosis, were determined in sequential samples from children participating in a prospective study of dengue virus (DV) infections. During the period of defervescence, levels of PBMC apoptosis were higher in children developing dengue hemorrhagic fever (DHF), the most severe form of illness, than in those with dengue fever (DF) and other, nondengue, febrile illnesses. CD8(+) T lymphocytes made up approximately half of the peak circulating apoptotic PBMCs in DHF and DF. Maximum plasma levels of soluble CD95 were also higher in children with DHF than in those with DF. The level of PBMC apoptosis correlated with dengue disease severity. Apoptosis appears to be involved in modulation of the innate and adaptive immune responses to DV infection and is likely involved in the evolution of immune responses in other viral hemorrhagic fevers.     

Natural history of dengue virus (DENV)-1 and DENV-4 infections: reanalysis of classic studies

BACKGROUND: The natural history of wild-type dengue virus (DENV) infections of humans, including incubation and infectious periods, requires further study. METHODS: Two experimental studies in the Philippines of DENV-4 (1924-1925) and DENV-1 (1929-1930) were reexamined. The intrinsic incubation periods were fitted to log-normal distribution using the maximum likelihood method, and the infectious and extrinsic incubation periods were assessed by proportions of successful transmissions causing clinically apparent dengue. Correlations between the intrinsic incubation period and other variables and univariate associations between clinical severity and serotype were also examined. RESULTS: Mean+/-SD incubation periods were 6.0+/-1.4 and 5.7+/-1.5 days for DENV-4 and DENV-1, respectively. Significant negative correlations were observed between the incubation period and duration of fever (r=-0.43 and -0.33). Even 1 and 2 days before the onset of fever, 80.0% (95% confidence interval [CI], 44.9%-100%) and 25.0% (CI, 0%-67.4%) of biting experiments caused clinically apparent dengue. DENV-1 infections resulted in a significantly longer duration of fever than DENV-4 infections (P<.01). CONCLUSIONS: Incubation period was negatively correlated with disease severity, potentially reflecting a dose-response mechanism. The historical data provided useful details concerning serotype differences in the natural history of primary DENV infections.     

Liver involvement associated with dengue infection in adults in Vietnam

Globally, the number of adults hospitalized with dengue has increased markedly in recent years. It has been suggested that hepatic dysfunction is more significant in this group than among children. We describe the spectrum and evolution of disease manifestations among 644 adults with dengue who were prospectively recruited on admission to a major infectious disease hospital in southern Vietnam and compare them with a group of patients with similar illnesses not caused by dengue. Transaminase levels increased in virtually all dengue patients and correlated with other markers of disease severity. However, peak enzyme values usually occurred later than other complications. Clinically severe liver involvement was infrequent and idiosyncratic, but usually resulted in severe bleeding. Chronic co-infection with hepatitis B was associated with modestly but significantly increased levels of alanine aminotransferase, but did not otherwise impact the clinical picture.