Response to JE vaccine among HIV-infected children, Bangkok, Thailand.

Since 1990, Japanese encephalitis (JE) vaccine has been part of EPI in northern Thailand, where there is a high prevalence of JE and HIV infection. To evaluate the immunogenicity and safety of JE vaccine among HIV-infected children, we conducted a retrospective study of HIV-infected and uninfected children who received 2 doses of JE vaccine at 12 months of age. Pre- and post-immunization plasma specimens were tested by plaque reduction neutralization for antibody levels to JE and dengue(1-4) viruses; titers of > or =10 were considered positive. Excluding 5 children with preimmunization antibodies, 5 of 14 (36%) HIV-infected children and 18 of 27 (67%) uninfected children had positive JE antibody titers after immunization [odds ratio (OR) 0.3, p=0.06]; 31% absolute difference [95% confidence interval (CI) 0-61.7%). The geometric mean titer of HIV-infected children with positive titers was lower than that of control children (15.1 vs, 23.8; p=0.17). No significant vaccine-associated adverse events were noted. We conclude that primary antibody response to JE vaccine was low among HIV-infected children and was approximately half of that seen among uninfected children. In endemic areas, HIV-infected children are likely to be at risk of acquiring JE despite routine immunization with 2 doses.

Cost benefit analysis of Japanese encephalitis vaccination program in Thailand.

Using decision analysis, we estimated benefits, risks, and costs of implementing the Japanese encephalitis (JE) vaccination program in children aged 18 months and 6 years in Thailand. The costs for inclusion of JE vaccine into the routine immunization program at 18 months and 6 years are $2.16 and $3.68 per person, respectively. In the baseline model, the JE vaccination program will prevent 124 JE cases in the program for 18 months old children and 153 JE cases in the program for 6 years old children. The 18 month child program is more cost-effective than the 6 year child program. The cost-effectiveness ratio in the 18 month child program is $15,715 compared with $21,661 in the 6 year child program. The benefits of the JE vaccination program are the savings in treatment cost, disability care, and the future lifetime earnings from JE prevented. The 18 month child program will save $72,922 per one prevented JE compared with $66,197 in the 6 year child program. The JE vaccination program is cost-beneficial under the base-case assumption. Sensitivity analysis which alters various assumptions indicates that the JE vaccination program is worth implementing unless the incidence of JE is less than 3 per 100,000 population. Otherwise, the cost of vaccine has to be reduced.

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.

Storage stability of dengue IgM and IgG antibodies in whole blood and serum dried on filter paper strips detected by ELISA.

Blood specimens from 133 patients clinically diagnosed as dengue virus infection by physicians in Nakhon Phanom Hospital, Thailand, were examined to detect anti-dengue IgM and IgG antibodies by antibody capture ELISA. The blood specimens were divided into 3 types of storage; (1) frozen serum aliquots, (2) whole blood dried on filter paper strips, and (3) sera dried on filter paper strips. These specimens were stored for the periods of 1, 3, 4, and 5 months, at -20 degrees C in the case of frozen serum aliquots, or at room temperature in the case of specimens dried on filter paper strips, before examined in paralleled by the ELISA. Anti-dengue IgG antibodies were stable for at least 5 months of storage as dried whole blood or serum on filter paper strips. So were the anti-dengue IgM antibodies in the dried whole blood from secondary dengue cases. Anti-dengue IgM antibodies from primary dengue cases declined slowly in whole blood and more rapidly in serum, both dried on filter paper strips. In the serum dried on filter paper strips, even anti-dengue IgM antibodies from secondary cases decreased significantly on storage. We suggest that diagnosis on dengue infections by IgM-capture ELISA should be performed within 1 month after the test specimens are collected as whole blood, not as serum, when the filter paper method is used for sample collection.

Comparative nucleotide and deduced amino acid sequence of the envelope glycoprotein gene among three dengue virus type 2 strains isolated from patients with different disease severities in Maha Sarakham, northeast Thailand.

The nucleotide (nt) sequence of the envelope glycoprotein (E) gene of dengue virus type 2 was determined by the primer-extension dideoxy chain-termination method for 3 dengue virus type 2 (D2) strains which had been isolated from patients with dengue fever (DF), dengue hemorrhagic fever (DHF), and dengue shock syndrome (DSS), in Maha Sarakham, Northeast Thailand, in 1986-1987. Their nt sequences were essentially the same except for a single silent nt replacement in each DHF and DSS strain compared with DF strain. Therefore, these 3 strains possessed identical deduced amino acid (AA) sequences in their E protein. The result indicated that the primary structure of the E protein of D2 virus is not related to the clinical severity of the infected patients. Eleven nt replacements which resulted in 4 amino acid replacements were found to be unique to these 3 Northeast Thai strains. Sequence similarity showed that the 3 Northeast Thai strains were closest to the DSS isolate (H) followed by the DHF isolate (D) identified in Bangkok in 1980.

Mapping of functional epitopes of Japanese encephalitis virus using monoclonal antibodies.

Epitopes involved in the important functions, hemagglutination (HA) and neutralization (NT), were mapped on Japanese encephalitis (JE) virus proteins by using monoclonal antibodies (MAbs). Fourteen MAbs raised against Nakayama-Yoken strain of JE virus characterized by hemagglutination inhibition (HI) and plaque reduction neutralization test (PRNT) were used to map the epitopes on the JE proteins by Western blot analysis in which non-reducing conditions were used for sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). With these MAbs, at least 8 functional epitopes were demonstrated comprising (i) epitopes recognized by 5 MAbs which gave strong HI but weak NT activities and were mapped on the envelope (E) 53 kDa protein; (ii) epitopes recognized by 2 MAbs which showed weak HI but strong NT activities and were mapped also on the E protein; (iii) epitopes recognized by 2 MAbs which possessed weak HI but no NT activities and were mapped on the E protein; (iv) an epitope recognized by 1 MAb which gave weak NT and no HI activities and was mapped on the nonstructural protein 5 (NS5); (v) an epitope recognized by 1 MAb which showed activities similar to (i) but was mapped on both E and NS5; (vi) an epitope recognized by 1 MAb which had high activities to both HI and NT and was mapped on E and NS5; (vii and viii) epitopes recognized by 1 MAb which also gave low HI but high NT, and strong HI as well as strong NT activities respectively, but their location could not be demonstrated by SDS-PAGE under non-reducing condition.(ABSTRACT TRUNCATED AT 250 WORDS)

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

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.