Temporal trends of dengue fever/dengue hemorrhagic fever in Bangkok, Thailand from 1981 to 2000: an age-period-cohort analysis.

The aim of this study was to examine the effects of age, time period, and birth cohorts with dengue fever/dengue hemorrhagic fever (DF/DHF) in Bangkok, Thailand over the period 1981-2000. The age group at greatest risk for DF/DHF was 5-9 years old. The period effect shows a remittent pattern, with significant increases in 1986-1990 and 1996-2000. The birth cohort group showed a significant decreasing trend from the 1961-1965 group to the 1991-1995 group (R2 = 0.7620) with a decreasing rate of 0.1. We concluded that the temporal trend of DF/DHF is decreasing; especially for DHF.

B cells are the principal circulating mononuclear cells infected by dengue virus.

Although dengue virus infects a variety of cells in vitro, little is known about cell types infected in vivo. Since blood is a readily accessible tissue, we chose to determine which circulating blood cells are infected by dengue viruses. We collected blood mononuclear cells from acutely ill dengue patients and separated the cells by flow cytometry into subsets for virus isolation. Cells were sorted into groups corresponding to the cluster designations CD3, CD14, CD16 and CD20. Virus was isolated from sorted groups by inoculation into Toxorhynchites splendens mosquitos. The majority of the virus was recovered from the CD20 or B cell positive subset. Little virus was isolated from monocytes, NK cells or T cells. Virus was isolated from B cells regardless of the age or sex of the patient, virus serotype isolated, or the patient's history of dengue virus infection. The location of cell associated virus was determined by proteolytic digestion of surface virus. There was an equal distribution of virus between the intracellular compartment and the surface of B cells. The intracellular localization of virus was confirmed by immunocytochemistry. Since this study focused on circulating cells, no inferences were made regarding infection of cells in solid tissues.

Hemorrhagic fever in Cambodia is caused by dengue viruses: evidence for transmission of all four serotypes.

Hemorrhagic fever (HF) has been widespread in Cambodia and thought to be due to dengue virus although laboratory confirmation has been lacking. Between 1980 and 1995, 49,420 cases of HF and 3,032 deaths were reported. Cases increased during this period; large epidemics of HF occurred every two to three years. In 1995 there were 10,208 cases of HF with 424 deaths. Over a two day period in August 1995, 40 consecutive cases were investigated at the National Pediatric Hospital in Phnom Penh, Cambodia. All 40 cases were confirmed as dengue by virus identification and/or serology. Mean age was 6.5 years. Of 39 patients with complete medical records, the diagnoses were: dengue fever (n = 3), dengue hemorrhagic fever (DHF) grade 2 (n = 21), DHF grade 3 (n = 10), and DHF grade 4 (n = 5). The serologic response was secondary in 95%. Dengue virus was identified in 13 of 40 cases. All four dengue serotypes were identified. The high frequency of secondary infections, the low mean age of admission, and identification of all four dengue serotypes support the national statistics to show that DHF is highly endemic in Cambodia.

A field study on Nakayama and Beijing strains of Japanese encephalitis vaccines.

A field study to compare the immune response of children aged 1-6 years to Nakayama and Beijing strains JE vaccines was carried out in Mae Hong Son Province, northwest Thailand, where there was low incidence of JEV infection. The first and second dose of each vaccine was given 1-2 weeks apart and the third dose was 1 year after the second dose. Seroconversion rate was similarly high, about 94% in both groups of vaccinees. At 6 and 12 months after 2 doses of vaccines, the seroconversion rates dropped in both groups of vaccinees, so there were 10-20% of children (50-65% if cross protection was considered) susceptible to JEV infections during this period. After the third dose of vaccine, the seroconversion rate rose to 100% in both groups. The GMT in Bejing strain vaccinees were slightly higher than Nakayama strain JE vaccines. To reduce the number of susceptible children during 6-12 months after the second dose and for longer protection, the primary JE immunization should be 3 doses and the timing for the third dose should be at 6 months after the second dose. Either Nakayama or Beijing strain vaccine could be used in Thailand.

IgM capture ELISA for detection of IgM antibodies to dengue virus: comparison of 2 formats using hemagglutinins and cell culture derived antigens.

The highly sensitive AFRIMS format IgM capture ELISA for the diagnosis of dengue virus infections requires the use of mouse brain derived hemagglutinins and consequently also the use of 20% acetone extracted normal human serum to eliminate high background. These reagents are not always easily available and we have thus compared the AFRIMS format with another published format which uses cell culture derived antigens (culture fluid, CF, format) in order to determine if it is reasonable to use cell culture derived antigens in situations where hemagglutinins and normal human serum are difficult to obtain. The study shows that using AFRIMS results as the reference point, the CF format described here has a sensitivity of 90% and a specificity of 96%.

Human immune responses to dengue viruses.

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)

A study of erythrocyte sedimentation rate in dengue hemorrhagic fever.

Erythrocyte sedimentation rate (ESR) was determined in 180 DHF patients and 70 patients with various viral and bacterial infections using the Winthrobe method. Seventy-seven percent of DHF patients had normal ESR (less than 20 mm/hour) and 15% had slightly elevated ESR value (between 21-30 mm/hour). The other 8% had ESR in the range of 31-49 mm/hour. Among 7 patients in the latter group, one had definite evidence of complicating urinary tract infection while the other 6 cases had anemia and severe bleeding. The mean ESR in DHF patients (10.71 mm/hour) was significantly lower than the mean values in other groups of patients with viral infection (20.46 mm/hour), bacterial infection (34.81 mm/hour) and miscellaneous illnesses (35.29 mm/hour). The mean ESR in shock cases was 7.63 mm/hour while in non-shock cases it was 13.87 mm/hour and they are statistically different (p less than 0.05). The mean ESR during the time of shock was lower than in the pre-shock and post-shock period. Hemoconcentration, low level of albumin and fibrinogen and the presence of disseminated intravascular clotting (DIC) in a majority of DHF patients are most likely responsible to this observed lower ESR especially during shock period. The determination of ESR, which is simple, is therefore useful in differentiating DHF from bacterial infections and dengue shock syndrome from septic shock.

Platelet function during the acute phase of dengue hemorrhagic fever.

Platelet aggregation, plasma betathromboglobulin (BTG) and platelet factor 4 (PF4) were studied in 35 children with dengue hemorrhagic fever. The suppression of platelet aggregation was demonstrated during acute phase of DHF in both shock and non-shock patients. Simultaneous with abnormal platelet aggregation, there was increased release of BTG and PF4 from platelets into plasma during the acute phase which lasted only 3-4 days after shock or subsidence of fever. Acute phase plasma during DHF infection was also shown to have a stimulatory effect on the aggregation of autologous platelets. In this study we showed that there was an increase in platelet secretory activity of BTG and PF4 along with an impairment of the platelet aggregation during acute phase of DHF.

Protective efficacy of plasma-derived hepatitis beta vaccine in preventing perinatal transmission of HBV infection in infants of HBsAg/HBeAg positive mothers.

Two hundred and four newborn infants of HBsAg/HBeAg carrier mothers were randomly assigned into three groups. Group A (69 infants) received full-dose HB vaccine, group B (70 infants) received half-dose HB vaccine at birth, 1 month, 3 months and group C (65 infants) were untreated control group. After twelve months follow-up the cumulative incidence of HBs antigenemia was 17.2%, 30% in group A, B respectively as compared with 78.4% in group C (p less than 0.001). The protective efficacy rates (PER) of group A and B were 78.1% and 61.7% respectively (p less than 0.05). The vaccine was also effective in preventing persistent HBsAg carriers (HBsAg positive for at least 6 months). The PER of group A and B were at least 74.9% and 49.2% respectively (p less than 0.001) at 1 year follow-up. From the practical point of view and economic reasons administration of full-dose HB vaccine give better protection to high risk infants.

Dengue haemorrhagic fever with unusual manifestations.

A retrospective study on 18 cases of DHF presented with jaundice and neurological signs which were considered unusual manifestation of DHF reveals that the causes or contributing factors are multifactorial. Most commonly found associated conditions were prolonged shock with metabolic acidosis and severe DIC that lead to hypoxia/ischaemia and resulted in both hepatic and brain dysfunction. Gross haemorrhage in the brain was noted in 6 of the 10 fatal cases while brain oedema was noted in 3 cases. Electrolyte disturbance such as hyponatremia could be another cause of brain oedema. It is certain from this study that there is no pathological evidence of encephalitis. Hepatic dysfunction found in associated with jaundice and encephalopathy is possibly caused by toxic substances, drugs and/or associated with underlying liver conditions. Reye's or Reye's-like syndrome was postulated in one case.

Endotoxin and dengue haemorrhagic fever.

Limulus amoebocyte lysate test (LALT) was used to detect endotoxin-like substances in the plasma of 57 patients with dengue haemorrhagic fever and dengue shock syndrome (DHF/DSS), four patients with dengue fever and 20 control patients with other diseases. The LALT positivity rates in DHF/DSS and dengue fever patients were 43.9 and 25 per cent respectively, whereas all control patients were negative (p less than 0.0025). LALT positivity was highest on 5th and 6th days of admission with positive rates of 46 and 50 per cent respectively whereas the positive rates in those admitted on fourth and seventh days of admission were 29 and 33 per cent respectively. A follow-up in LALT positive patients showed a decline in the positive rates after admission. LALT positivity was observed in 48.8 per cent of DHF/DSS patients with shock and in 26.6 per cent of patients without shock.

Japanese encephalitis in Thai children, Bangkok, Thailand.

During a period of 5 years from May 1979 to April 1984, 121 encephalitis patients were admitted to Bangkok Children's Hospital. 79 were proved to be JE. 73.42% of JE patients came from outside Bangkok while the rest came from suburban areas of Bangkok. No distinction could be made between JE and encephalitis caused by other agents by clinical data and cerebrospinal fluid examination. Definite diagnosis of JE could be done by demonstration of specific IgM antibody against JEV in cerebrospinal fluid. Case fatality rate of JE was 25%.

Atypical lymphocyte in dengue hemorrhagic fever: its value in diagnosis.

Simple peripheral and buffy coat smear were studied in 40 serological confirmed dengue hemorrhagic fever patients, and in other patients with viral and bacterial infections. Atypical lymphocytosis was found in majority of dengue hemorrhagic fever both associated with secondary and also in dengue fever with primary infection as compared to other infections. The time course relationship of atypical lymphocytosis, platelet and hematocrit level were discussed, concerning their value as diagnostic and prognostic criteria in dengue hemorrhagic fever.