In vivo and in vitro studies of quinine sensitivity of Plasmodium falciparum in Thailand.

Forty-four patients with falciparum malaria were studied. Nine patients were given quinine orally at a daily dose of 1.5 gm base for a period of 14 days. The mean parasite clearance in all 9 patients was 3.3 days, and none had recrudescence in follow-up examinations for 31 days. The in vivo study of these 9 patients showed sensitivity to quinine which correlated with the in vitro test, with concentration of quinine base 2.5-5.8 microgram/ml of blood that inhibited the maturation of Plasmodium falciparum parasites. The results of the in vitro test of 35 patients showed concentrations of quinine base 2.1-5.4 microgram/ml of blood were able to inhibit the maturation of P. falciparum parasites. Therefore, these studies indicate that Plasmodium falciparum are still sensitive to quinine and quinine remains to be the drug of choice for the treatment of falciparum malaria in Thailand.     

Preliminary field trial of a radioimmunoassay for the diagnosis of malaria

A radioimmunoassay (RIA) has been developed for the detection of Plasmodium falciparum in infected blood. The assay is based on the ability of solubilized, infected red blood cells (RBC) (P. falciparum "antigen") to combine with anti-P. falciparum antibodies and thus prevent the subsequent interaction of the latter with "antigen"-coated microtiter plates. A preliminary trial was carried out in Thailand to determine the usefulness of the RIA for the immunodiagnosis of malaria. Blood samples from malarious and non-malarious patients were examined both by standard microscopy and by RIA. Efficient solubilization of the parasites proved to be a major requirement for the successful performance of the RIA. Sonication or freezing and thawing, which were perfectly satisfactory for the solubilization of cultured, infected RBC, were found to be totally inadequate when applied to RBC taken from patients. However, parasites in RBC from patients could be solubilized efficiently by treatment with detergents (e.g., NP40, Triton X-100, etc.). Of the 108 blood samples tested, 23 were found positive for falciparum parasitemia by microscopy and 39 by RIA. One sample from a patient with patent falciparum parasitemia and three with patent vivax parasitemia were negative by RIA. Ten of the samples positive only by RIA belonged to patients with recent malarial infection, as shown by microscopy. Thus, the RIA detected almost all of the patients with microscopic evidence of falciparum malaria. The proportion of false positives in the RIA test was low.     

Immune responses following killed whole vibrio-B subunit oral cholera vaccine in human volunteers

Immunogenicity of killed whole vibrio and B subunit oral cholera vaccines in American and Thai volunteers were analysed in terms of significant rise of antibody titre. Three doses of 2 x 10(11) killed vibrios and 5 mg of cholera toxin B subunit were given at two-week intervals. There were no differences in the percent of volunteers with significant rise of serum immunoglobulin G and secretory immunoglobulin A (sIgA) to cholera toxin. However, the percent with significant rises of serum antibody to whole cell V. cholerae Inaba measured by vibriocidal titre and serum immunoglobulin G, and secretory immunoglobulin A to lipopolysaccharide (LPS) measured by ELISA in American volunteers were significantly different from those in Thai volunteers (89% VS 45%, 68% VS 9% and 53% VS 0%, respectively) (p less than 0.05).     

Clinical and bacteriological studies of El Tor cholera after ingestion of known inocula in Thai volunteers.

Twenty-six healthy adult Thai volunteers were recruited for clinical and bacteriological studies of cholera induced by oral inoculation with Vibrio cholerae El Tor Inaba strain N16961. Vibrio dosages of 0.3 x 10(4), 1.6 x 10(5) and 1.9 x 10(6) c.f.u. were given to three groups of five volunteers, and 2.0 x 10(7) c.f.u. to 11 volunteers. Diarrhoeal attack rates correlated positively with the size of the inocula (p less than 0.01). It was estimated that a diarrhoeal attack rate of 90% (ED90) would be achievable by inoculation of 1.3 x 10(7) c.f.u. of the organisms. There were no significant differences between the groups in the latent period to positive stool culture, maximum vibrio count per gram of stool and duration of stool positivity. The ED90 of V. cholerae obtained may be used as a challenge dose in subsequent studies on protective efficacy of cholera vaccines in Thai adult volunteers.     

Lack of increased HIV risk behavior among injection drug users participating in the AIDSVAX B/E HIV vaccine trial in Bangkok, Thailand

OBJECTIVE: To determine whether HIV vaccine trial participation leads to increased risk behavior through beliefs about vaccine protection against infection. METHODS: Changes in risk behavior were evaluated among 2545 injection drug users participating in the AIDSVAX B/E vaccine trial in Bangkok, enrolled from March 1999 to August 2000. Demographic characteristics, beliefs and risk behavior were assessed at baseline and every 6 months thereafter. Risk-reduction counseling was provided at every study visit. Generalized estimation-equation logistic regression analysis was used to study trends in risk behavior and associated factors. RESULTS: Participants were 93.4% male, their median age was 26 years, and 67.2% had at least secondary education. At baseline, 61.3% were receiving methadone detoxification and 20.9% were receiving methadone maintenance. From baseline to the 12-month follow-up visit, injection drug use decreased from 93.8% to 66.5% (P < 0.001) and needle sharing from 33.0% to 17.5% (P < 0.001). Multivariate analyses showed earlier follow-up time (at baseline and 6 months) and believing the vaccine to be efficacious associated with more-frequent injecting; younger age and lower education associated with less-frequent injecting. Earlier follow-up time (at baseline), younger age, and injection of methamphetamine and midazolam were associated with more-frequent needle sharing; methadone treatment and injecting less than weekly were associated with less-frequent needle sharing. CONCLUSIONS: Injection drug use and needle sharing decreased during the first 12 months of the trial. No increases in risk behavior in relation to beliefs about vaccine protection against HIV infection could be identified.     

Cytoadherence and ultrastructure of Plasmodium falciparum-infected erythrocytes from a splenectomized patient.

In malarial infections of primates, the spleen has been shown to modulate parasite antigen expression on the surfaces of infected erythrocytes. The processes affected include cytoadherence, which is central to the pathophysiology of severe falciparum malaria, and the related phenomenon of rosette formation. In this study, the cytoadherence and rosette formation behaviors of Plasmodium falciparum-infected erythrocytes from a splenectomized patient were examined during the first erythrocytic cycle in vitro. Ultrastructural studies were also performed. Infected erythrocytes were found to cytoadhere to C32 melanoma cells via leukocyte differentiation antigen CD36 but not intercellular adhesion molecule 1. They also displayed on their surfaces electron-dense knobs similar in structure and density to those on infected erythrocytes from intact hosts. These findings may reflect a stable cytoadherent phenotype of the parasite isolate that is unaffected by the absence of the spleen. Alternatively, the modulating role of the spleen may have been assumed by other organs of the mononuclear phagocytic system in a previously infected individual. No rosette formation was observed, but as not all natural isolates form rosettes, this observation may or may not be related to the asplenic status of the patient. Parasite and host factors appear to be important in determining the effect of splenectomy on cytoadherence and rosette formation in human falciparum malaria.     

Enzyme immunoassay using BCG in serodiagnosis of pulmonary tuberculosis.

Amounts of Mycobacterium tuberculosis antibodies were determined in sera from patients with either active or inactive tuberculosis and in healthy subjects by an immunoenzymatic assay in which whole BCG cells attached covalently to polystyrene disks were used as antigen. Statistically significant differences (P less than 0.005) were found both between the active and inactive tuberculosis groups and between the active group and healthy controls. No significant differences were found between the inactive group and controls. Since this procedure is efficient (91%) and can be used in areas which lack laboratory equipment, it appears promising for individual serodiagnosis and for epidemiological surveys.     

Effect of inosiplex on the humoral and cell-mediated immune responses to intradermal human diploid cell rabies vaccine

Antigen-stimulated lymphocyte transformation was studied in recipients of intradermal human diploid cell rabies vaccine (HDCV). HDCV was administered intradermally at 8 different anatomical sites, 0.1 ml each, on day 0; followed by another 4-site injection on day 7. Rabies antigen-stimulated in vitro proliferative response was evident as early as 7 days after starting immunization. It reached a peak on day 14 and had declined by day 28. The cellular proliferative response preceded and roughly correlated with the antirabies antibody response. Simultaneous administration of inosiplex, an antiviral and immunopotentiating drug, during the first 10 days of intradermal HDCV immunization did not result in heightened antibody titres or cell-mediated immune response to the vaccine. The number of T cells and the lymphocyte proliferative response to phytohaemagglutinin in inosiplex-treated vaccinees were similarly not significantly different from untreated controls. Our results confirm other previous findings that a specific cell-mediated immune response can be consistently and rapidly induced by an intradermal regimen of HDCV immunization. The addition of inosiplex to this regimen did not enhance the humoral or cell-mediated immune responses to the vaccine. The apparent lack of immunostimulating effect of inosiplex in this setting may be the result of several factors such as the immunization schedule and the immunologic parameters examined.