Seroprevalence of hepatitis A virus antibody among children and young adults in Bangkok.

OBJECTIVE: To determine the prevalence of hepatitis A virus (HAV) antibodies in various age groups of healthy children and young adults who have not received the hepatitis A vaccine. METHOD: Blood samples were collected from 825 volunteers aged 1-30 years from a well baby clinic and five academic institutions in the Don Mueang area from 1998 to 1999. Serum samples were assayed for specific HAV IgG antibodies using a commercial enzyme-linked immunosorbent assay (ELISA) kit. RESULTS: The seropositivity rate (12.4% overall) in each age group was as follows: 1-3 years, 7.7 per cent; 4-7 years, 6.6 per cent; 8-11 years, 12.4 per cent; 12-15 years, 10.7 per cent and 16-30 years, 25.9 per cent. CONCLUSIONS: In the Don Mueang area of Bangkok, the majority of children (< 16 years) do not have natural immunity against HAV. The use of hepatitis A vaccine for this population should be considered. Pre-vaccination serologic screening for HAV IgG in children may not be worthwhile.

Cell-mediated immunosuppression in mice by street rabies virus not restored by calcium ionophore or PMA.

It is known that rabies virus can suppress the host immune system. In this study we demonstrate a depression of cell-mediated immunity in mice, peripherally infected with Thai street rabies virus. The cell-mediated cytolysis of spleen cells from mice increased transiently on day 5 after infection and declined rapidly thereafter until death. The proliferation of spleen cells stimulated with a T-cell mitogen such as phytohemagglutinin or concanavalin A, was significantly suppressed during the course of infection. There was also a marked suppression of IL-2 secretion in parallel with a decrease of the T-cell proliferative response to mitogen. The suppression of T-cell proliferation was not restored by treatment with a calcium ionophore (A 23187) or phorbol 12-myristate-13 acetate (PMA).

Comparison of separated-lymphocyte and whole-blood lymphocyte proliferation assays for evaluating rabies-induced cellular immunity.

A whole-blood lymphocyte proliferation assay was compared to a standard method requiring the isolation of peripheral blood mononuclear cells (PBMC). Both methods were used to measure the cell-mediated immune responses to rabies in rabies-vaccine recipients. Whole-blood cells gave moderately higher lymphoproliferative responses in terms of stimulation indices than did separated-PBMC. The results obtained from these two methods can be considered equivalent for the purpose of quantitating cellular reactivity to rabies. The use of whole blood has advantages over the standard isolated-PBMC method.

Maternal antibodies against rabies in Thai puppies. A preliminary study.

Serum antibodies to rabies virus were measured in 32 Thai puppies before primary vaccination. Only five showed evidence of rabies antibody by ELISA testing and they had no rabies virus neutralizing activity detectable by RFFIT. Immunologic ignorance of these young dogs leaves a large part of the canine population susceptible to rabies. This could be one reason for the failure of canine rabies control efforts in Thailand.

Radioactive and non-radioactive lymphocyte proliferation assays for measuring rabies-specific cellular immunity.

We compared the radioactive lymphocyte proliferation assay for measuring rabies specific cell-mediated immunity in a group of 42 rabies vaccine recipients with a new technique using rabies-stimulated lymphocytes in a colorimetric test kit (CellTiter 96, Promega Corporation, USA). Results of both tests were good agreement (Kappa = 0.68), however, they did not show good correlation in degree (magnitude) of positivity. In addition, the conventional assay showed a higher degree of sensitivity.