Geographical heterogeneity of dengue transmission in two villages in southern Vietnam.

This study was performed to test the hypothesis that there are 'hotspots', i.e. geographical heterogeneity, of dengue transmission. Data from two repeat serosurveys in two villages in Vietnam were used to identify incident infections and to relate these to prevalence at baseline and thus assess geographical heterogeneity, i.e. clustering, in dengue transmission. A total of 400 households were surveyed; serological data from 521 children at baseline and from 119 children at follow-up were included in a spatial analysis. Geographical heterogeneity of dengue transmission was explored using a permutation null distribution test. This showed for the first time evidence of clustering of dengue virus transmission at the household level in asymptomatic children. Risk areas could be identified by seroprevalence surveys combined with mapping. Control of dengue virus transmission could be supported by identification and control of hotspots.

Nutritional status following malaria control in a Vietnamese ethnic minority commune.

OBJECTIVE: To study whether control of malaria leads to catch-up growth or an increase of obesity in a marginally nourished population. SETTING: A Vietnamese ethnic minority commune in southern Vietnam. DESIGN: Repeated annual anthropometric surveys were performed from 1995 to 2000. Z-scores for height, weight and BMI for age and weight-for-height were determined by using NCHS 1978 and CDC 2000 reference tables and by the LMS method. INTERVENTION: Active malaria control that reduced the parasite carrier rate from 50% in 1994 to practically nil in 1998. RESULTS: Inhabitants were generally of short stature and very thin. Using the US reference tables, the prevalence of moderate/severe stunting among children was 53/24% and of wasting 27/9% in the first survey in 1995. Physical condition and normal daily activities of most inhabitants were normal. The repeated LMS-Z-scores uncovered a significant recovery of stunting, extending into preadolescence, including the development of a pubertal growth spurt for girls and enhancement of pubertal growth in boys, after control of malaria. The mean (95% CI) annual increase of Z-height-for-age was 0.11 (0.09-0.12) for boys and 0.14 (0.13-0.15) for girls (P<0.001). As a consequence, weight-for-age and BMI Z-scores decreased without indication of developing obesity. CONCLUSION: Catch-up growth, extending into preadolescent age, was observed in a Vietnamese ethnic minority population with a chronic state of low food intake, without indication of developing obesity. The control of malaria was probably the most significant contribution to this catch-up growth.

Mineral homoeostasis in acute renal failure complicating severe falciparum malaria.

Disturbances in calcium metabolism in acute renal failure (ARF) remain incompletely understood. Most data are from patients with rhabdomyolysis. As renal impairment commonly accompanies severe malaria in the absence of rhabdomyolysis, falciparum malaria provides an alternative model of mineral homoeostasis in ARF. We studied 25 Vietnamese subjects, aged 18-63 yr, with severe malaria and 10 controls. Fourteen patients had a serum creatinine level of 250 mumol/L or less during treatment (group 1), five developed ARF but were not dialyzed (group 2a), and six required dialysis (group 2b). Group 1 patients presented with mild hypocalcemia (mean +/- SD serum ionized calcium, 1.18 +/- 0.05 vs. 1.23 +/- 0.02 mmol/L in controls; P = 0.01) that persisted until discharge in the presence of normal serum phosphate, PTH, and vitamin D metabolite levels. Group 2 patients were more hypocalcemic on admission (1.10 +/- 0.08 mmol/L; P < 0.0001 vs. controls), especially those in group 2b whose serum ionized calcium fell to 0.88 +/- 0.13 mmol/L when renal dysfunction was maximal. In group 2 patients, the admission serum PTH level was raised (5.4 +/- 3.8 vs. 2.7 +/- 0.9 pmol/L in controls; P < 0.02) and changed reciprocally with calcemia. Significant rises in serum phosphate occurred only in group 2b patients who had depressed serum free 1,25-dihydroxyvitamin D levels throughout. Hypercalcemia did not accompany the diuretic phase of ARF. These data suggest that parathyroid gland dysfunction is a cause of hypocalcemia in severe malaria without ARF, as seen in group 1 patients; in patients with ARF, the effect of the combination of phosphate retention and altered vitamin D metabolism on skeletal PTH sensitivity is of prime significance.

Glucose metabolism in severe malaria: minimal model analysis of the intravenous glucose tolerance test incorporating a stable glucose label.

Basal plasma glucose is usually increased in uncomplicated malaria, implying insulin resistance. If the infection progresses, the risk of hypoglycemia will increase as host glucose production becomes insufficient for host/parasite demand. To assess the relative contribution of insulin-mediated and non-insulin-mediated glucose disposal to plasma glucose levels in severe malaria, we studied six healthy controls (two males and four females; mean age, 38 years) and eight patients with complicated falciparum malaria (five males and three females; mean age, 31 years) who had a frequently sampled intravenous glucose tolerance test (FSIVGTT) in which 10% of the dextrose bolus was 6,6-D2-glucose. The minimal model was applied to native and labeled plasma glucose and serum insulin profiles over 4 hours postinjection. Basal plasma glucose concentrations in the patients were significantly greater than in the controls (median [range], 6.1 [2.1 to 8.5] v 4.3 [3.9 to 4.7] mmol/L, P = .03). Malaria-associated insulin resistance was confirmed by a lower insulin sensitivity index (SI) in patients (5.6 [2.4 to 17.4] v 16.0 [2.5 to 22.3] x 10(-4).min-1 per microU/mL in controls, P = .026). Glucose effectiveness ([SG] the ability of glucose to reduce its own plasma concentration) was higher in the patients (0.015 [0.006 to 0.024] v 0.008 [0.007 to 0.010] min-1 in controls, p = .019). Glucose disappearance at basal concentration was increased by a median of 42% in severe malaria patients, with the insulin-independent component comprising 81%, versus 67% in controls. Indices of beta-cell function were normal in malaria patients. These data demonstrate that basal plasma glucose utilization is increased approximately 50% in severe malaria, consistent with previously published isotope-turnover studies. Altered SG plays a major role. Prevention and treatment of early hypoglycemia should be based on adequate glucose replacement. Strategies that reduce insulin secretion or effects appear to be of minor importance.

Artemisinin for treatment of uncomplicated falciparum malaria: is there a place for monotherapy?

The efficacy of artemisinin monotherapy was studied in 227 patients with uncomplicated falciparum malaria. They all received artemisinin at t = 0 hr, t = 8 hr, and thereafter once daily; treatment was extended at random until they had taken either 5 days of artemisinin followed by 2 days of placebo (A5), or 7 days (A7) of artemisinin. The adult artemisinin dose was 500 mg; children aged < 15 years received 10 mg/kg per dose. The median (range) parasite clearance time was 39 (8-112) hr for A5 and 43 (38-104) hr for A7 (P = 0.085). The recrudescence rates were similar between the groups. The lowest parasite count achieved during treatment (Pterm) was associated with the occurrence of recrudescence (P = 0.046, Cox regression model); it was lower for patients with a radical cure or late recrudescence than for early recrudescence (P = 0.034, t-test). Artemisinin monotherapy may offer rapid recovery and fast parasite clearance, but recrudescence is frequent. Extending the duration of monotherapy from 5 days to 7 days does not reduce recrudescence.

The metabolism of platelet-activating factor in severe and cerebral malaria.

In order to examine the effects of platelet-activating factor (PAF) in complicated Plasmodium falciparum infections, plasma concentrations of lyso-PAF, stable metabolite and principal precursor of PAF, were measured in 25 Vietnamese adults with severe malaria. The concentration of PAF in the cerebrospinal fluid (CSF) was determined in a sub-group of 23 comatose patients and, together with that of lyso-PAF, in the plasma of 20 patients on recovery of consciousness. The concentration of lyso-PAF in the plasma was depressed on admission to hospital (median [range]; 21 [8-143] vs. 293 [215-410] ng/ml in 10 controls; P < 0.001). There was, however, no change in plasma activity of acetylhydrolase which converts PAF to lyso-PAF (P > 0.01 vs. controls) while simultaneous reduction in the concentration of lipoproteins associated with lyso-PAF were less than those of lyso-PAF per se in the plasma. The plasma concentration of lyso-PAF on admission was associated with parasitaemia and the concentration of serum triglycerides (rs = -0.42, P = 0.04 in each case), the latter being consistent with hepatic effects of PAF reported in previous studies. CSF concentrations of PAF on admission were low (2.3 [0.5-7.7] vs. 0.9 [0-2.5] ng/ml after recovery, P < 0.01) compared with values reported previously in bacterial meningitis. Plasma concentrations of lyso-PAF after recovery lay between admission and control values. While increased availability of PAF may reflect parasite burden and may modulate liver-mediated metabolic disturbances such as hypoglycaemia and lactic acidosis, the role of PAF in cerebral malaria is uncertain.

Pituitary-adrenal function in uncomplicated falciparum malaria.

To investigate pituitary-adrenal function in acute uncomplicated falciparum malaria, we performed an overnight dexamethasone suppression test in 13 Vietnamese adults with acute malaria and 6 healthy controls. After blood samples were taken for serum cortisol and plasma ACTH at 23.00 hours on the admission day, 1 mg dexamethasone was given and further samples were taken at 08.00, 16.00 and 23.00 hours the next day. The patients received conventional antimalarial and supportive treatment. Baseline plasma ACTH concentrations in the patients [3.9 (0.2-41.2) pmol/l] and controls [3.4 (1.1-4.3) pmol/l] were similar (p=0.51), and exhibited a similar fall after dexamethasone to 0.6 (0.2-2.5) and 0.9 (0.7-1.6) pmol/l at 08.00 hours respectively (p<0.03 vs 23.00 hour values). Serum cortisol levels before dexamethasone were higher in the patients than in the controls [456 (102-821) vs 145 (64-183) nmol/l respectively; p=0.007] and the overnight fall was less in the patients [208 (26-340) and 23 (15-46) nmol/l at 08.00 hours respectively; p<0.001 vs 23.00 hour values and between groups]. Between 08.00 and 23.00 hours, plasma ACTH and serum cortisol remained suppressed in the controls. In the patients, the serum cortisol continued to fall progressively towards control values. These data suggest that there is a raised set point for cortisol inhibition of ACTH secretion but normal corticotrophin responsiveness to dexamethasone in uncomplicated malaria. A raised serum cortisol after dexamethasone in the patients might reflect the combination of a prolonged cortisol half-life and the stimulatory effects of cytokines on the adrenal cortex, with a consequent protective effect against complications such as hypoglycemia.

Selective high-performance liquid chromatographic determination of artesunate and alpha- and beta-dihydroartemisinin in patients with falciparum malaria.

A novel solid-phase extraction and a robust high-performance liquid chromatographic (HPLC) separation procedure for artesunate and alpha- and beta-dihydroartemisinin, using post-column alkali decomposition and UV detection is described. Extraction was performed with Bond-Elut Phenyl solid-phase extraction cartridges and analysis by HPLC was carried out using a Waters Symmetry C8 5-microns 150 x 3.9 mm I.D. column. The mobile phase was 50% acetonitrile in 0.1 M acetate buffer (pH 4.8) delivered at a flow-rate of 0.7 ml/min. The column eluate was mixed with 1.2 M potassium hydroxide in 90% methanol delivered at 0.3 ml/min, in a 1-ml reaction coil at 69 degrees C, to form UV-absorbing chromophores which were detected at 290 nm. The recovery of all analytes was greater than 80%. There was no significant difference in the peak-area ratio of alpha- and beta-dihydroartemisinin in plasma. Preliminary pharmacokinetic data from six adult Vietnamese patients who received 120 mg of artesunate by intravenous injection for the treatment of acute falciparum malaria are presented. Despite limited data, the mean half-life of artesunate was approximately 3.5 min while that for dihydroartemisinin was 34 min. These data confirm the relatively rapid clearance of both artesunate and its principle active metabolite, dihydroartemisinin.

Serum vitamin A and E concentrations in acute falciparum malaria: modulators or markers of severity?

1. To assess the association between vitamin A, vitamin E and the clinical course of severe malaria, serial morning blood samples were taken from 24 Vietnamese patients, aged 18-62 years, receiving intensive treatment for complicated Plasmodium falciparum infections. A single fasting blood sample was also taken from 10 control subjects aged 22-45 years. Serum retinol, carotene and vitamin E concentrations were measured by h.p.l.c. 2. Admission serum retinol concentration was depressed relative to that of the control subjects (0.69 +/- 0.35 versus 1.86 +/- 0.41 mumol/l mean +/- SD, P < 0.001) and correlated inversely with indices of hepatic function, but positively with the simultaneous serum creatinine concentration (P < 0.05). During the first week of treatment, serum retinol concentration increased in parallel with improving liver function, whereas serum creatinine concentration remained elevated in the majority of patients. Serum alpha- and beta-carotene concentrations remained depressed throughout. 3. Serum vitamin E concentration, corrected for total serum cholesterol concentration in the form of a ratio, was also depressed at presentation (3.1 +/- 1.8 x 10(3) versus 4.2 +/- 0.8 x 10(3) in control subjects; P < 0.05), but tended to be higher than the control value at the time of discharge (0.1 > P > 0.05); there was a significant correlation between admission ratio and parasite clearance time (P = 0.04). 4. On the basis of this and previous studies, vitamin A replacement could be considered in selected severely ill patients without renal impairment. As found previously in animal models, depressed vitamin E levels may have a beneficial effect on the course of malarial infection.

Atovaquone-proguanil for recrudescent Plasmodium falciparum in Vietnam.

Malarone, a fixed combination of atovaquone with proguanil (AP), has recently been recognized as a promising treatment against multidrug-resistant Plasmodium falciparum. In Vietnam, the first-line treatment for P. falciparum malaria is currently a combination of mefloquine and an artemisinin derivative, and the use of AP has not been explored. The aim of the present study, based in Vietnam, was to assess the efficacy of AP when used to treat P. falciparum recrudescences that had occurred after primary treatment with mefloquine-artesunate. All but two of the 39 patients investigated completed follow-up. The mean parasite- and fever-clearance times [and 95% confidence intervals (CI)] after AP treatment were 36 (30-42) and 21 (18-24) h, respectively. Most (32) of the 37 infections that were followed adequately appeared to be eradicated by the AP, the other five recrudescing once more. The overall cure 'rate' and (CI) was 86% (76%-98%). All of the patients tolerated the AP well. Atovaquone-proguanil appears to be a safe and promising alternative treatment for P. falciparum infections in South-east Asia, although the combination is relatively expensive and may not clear some infections with multidrug-resistant parasites.

Rapid serological assays for leptospirosis are of limited value in southern Vietnam.

Leptospirosis, although ubiquitous and potentially lethal, is often not diagnosed. The seroprevalence of anti-Leptospira antibodies and the utility of two rapid tests for the serodiagnosis of the disease were studied in Binh Thuan, an area in southern Vietnam with favourable conditions for Leptospira. In an initial survey, blood samples from 44 patients with undifferentiated fever and 83 healthy subjects were each examined for anti- Leptospira antibodies using three tests: an ELISA; a latex card-agglutination test (Dri Dot); and a lateral-flow assay (LeptoTek Lateral Flow). In the ELISA, samples from 35% of the healthy subjects and 40% of the febrile patients were found to have titres of anti- Leptospira IgM of at least 1:80. Only one of the 13 patients checked again, in ELISA, 3 weeks later, showed the marked increase in IgM titre that is indicative of acute leptospirosis. In the initial survey, although the positive results of the lateral-flow assay, applied to whole blood and serum, showed a good agreement with those of the ELISA (kappa = 0.743), the results of the lateral-flow assay were often indeterminate. The card-agglutination test was more specific. The overall agreement between the results of the rapid tests and those of the ELISA was generally poor. When the samples classified as 'indeterminate' in the lateral-flow assay were considered positive, the maximum kappa-value for this assay applied to whole blood was only 0.512. In conclusion, it appears that high seroprevalences of anti- Leptospira IgM and low incidences of acute leptospirosis limit the diagnostic value of the rapid tests that were investigated. The lateral-flow assay is not specific enough. The card-agglutination test is possibly better but, because of the low incidence, its sensitivity could not be evaluated adequately in the present study.

Pharmacokinetics of retinyl palmitate and retinol after intramuscular retinyl palmitate administration in severe malaria.

Retinol (vitamin A alcohol) is an accepted adjunctive treatment in infections such as measles. There is also indirect evidence from in vitro, animal and human studies that retinol supplementation may be beneficial in severe malaria. There have, however, been no studies that have examined the pharmacokinetics of acute retinol supplementation in severe illness. To establish whether mobilization of intramuscular retinyl palmitate (RP) and its availability as retinol are adequate in complicated falciparum malaria, we administered a single dose of 400000 i.u. of RP to six Vietnamese adults with severe malaria. Another 28 patients were not given RP. All patients had blood samples taken over 96 h for RP and retinol assay using HPLC, and received conventional anti-malarial and supportive therapy. Admission serum retinol concentrations were below the lower limit of the reference range (<1.0 micromol/l) in 74% of the 34 patients. In supplemented patients, analysis of serum RP between 0 and 96 h using a multi-compartmental model revealed a median (range) delay in mobilization of 6.9 h (0.7-15.1 h), a bioavailability of 55% (19-100%) and an elimination half-life of 13.5 h (4.2-23.7 h). The area under the serum retinol curve expressed as an absolute or percentage change from baseline was greater in supplemented than in unsupplemented patients (P<0.05). The separation in median serum retinol concentrations in the two groups was maximal at 48 h. The model-derived retinol half-life [1.5 (0.7-15.8) h] suggested rapid uptake, metabolism and/or excretion. In conclusion, there is variable RP bioavailability in severe malaria, but a significant if delayed increase in serum retinol over that associated with recovery from the infection. In severe infections, RP supplementation appears simple, well tolerated and of potential benefit once anti-microbial and supportive therapy have been established.

Oral bioavailability of dihydroartemisinin in Vietnamese volunteers and in patients with falciparum malaria.

AIMS: To obtain comprehensive bioavailability data for artesunate (ARTS) and its active metabolite dihydroartemisinin (DHA) following their separate oral administration to Vietnamese volunteers and to patients with acute, uncomplicated falciparum malaria. METHODS: Volunteers were randomized to receive either i.v. ARTS (120 mg) followed by oral ARTS (150 mg) 8 h later (Group 1, n = 10), or i.v. ARTS (120 mg) followed by oral DHA (120 mg) 8 h later. Patients, also received oral ARTS (150 mg; Group 3, n = 8) or DHA (120 mg; Group 2, n = 7), in a randomized cross-over study design. Multiple blood samples were collected after each administration and plasma ARTS and/or DHA concentrations were determined by h.p.l.c. Pharmacokinetic descriptors were obtained from noncompartmental analysis and bioavailability was calculated from AUC data. In the patients, the time to 50% parasite clearance (PCT50) and fever clearance time (FCT) also were measured. RESULTS: In Group 1 (volunteers), the mean (95% CI) absolute bioavailability of oral ARTS was 80% (62,98%), while in Group 2 (volunteers), the bioavailability of oral DHA was 45% (34,56%). In the patients (Group 3), the bioavailability of oral DHA relative to oral ARTS was 88% (49,127%). The median PCT50 and FCT were 2.3 and 28 h, respectively. CONCLUSIONS: The study shows that the absolute bioavailability of DHA was significantly lower than that for ARTS in healthy volunteers. The bioavailability of ARTS in volunteers was consistent with previous studies in patients with uncomplicated falciparum malaria. The dose-normalized Cmax and AUC(0,infinity) for DHA were significantly greater in patients with falciparum malaria than in healthy volunteers. The high relative bioavailability of DHA in the patients may have been due to lower first-pass clearance. We conclude that, for the treatment of malaria, DHA is likely to be a suitable oral substitute for ARTS. Based on our mean AUC measurements, it appears that equal doses of DHA and ARTS (mg basis) should give equivalent systemic exposure to bioactive DHA in uncomplicated falciparum malaria.

A pharmacokinetic and pharmacodynamic study of intravenous vs oral artesunate in uncomplicated falciparum malaria.

AIMS: To obtain comprehensive pharmacokinetic and pharmacodynamic data for artesunate (ARTS) and its active metabolite dihydroartemisinin (DHA) following i.v. and oral administration of ARTS to patients with acute, uncomplicated falciparum malaria. METHODS: Twenty-six Vietnamese patients with falciparum malaria were randomized to receive either i.v. ARTS (120 mg; group 1) or oral ARTS (100 mg; group 2), with the alternative preparation given 8 h later in an open crossover design. Mefloquine (750 mg) was administered at 24 h. Plasma concentrations of ARTS and DHA were determined by h.p.l.c. assay. Pharmacokinetic parameters were calculated by non-compartmental methods. The time to 50% parasite clearance (PCT50) was calculated by linear interpolation of parasite density determinations. Linear least squares and multiple linear regression analyses were used to evaluate pharmacokinetic-pharmacodynamic relationships. RESULTS: Following i.v. bolus, ARTS had a peak concentration of 29.5 microM (11 mg l[-1]), elimination t1/2 = 2.7 min, CL = 2.33 l h(-1) kg(-1) and V = 0.14 l kg(-1). The Cmax for DHA was 9.3 microM (2.64 mg l[-1]), t1/2 = 40 min, CL =0.75 l h(-1) kg(-1) and V = 0.76 l kg(-1). Following oral ARTS, relative bioavailability of DHA was 82%, Cmax was 2.6 microM (0.74 mg l[-1]), t1/2 = 39 min, and MAT = 67 min. Overall, the PCT50 and fever clearance time (FCT) were 6.5 h and 24 h, respectively. There was no correlation between PCT50 or FCT and AUC, Cmax or MRT for DHA. CONCLUSIONS: Despite rapid clearance of ARTS and DHA in patients with uncomplicated falciparum malaria, prompt parasite and fever clearance were achieved. High relative bioavailability of DHA following oral ARTS administration, and clinical outcomes comparable with those after i.v. ARTS, support the use of the oral formulation in the primary care setting.

Pharmacokinetics and pharmacodynamics of intravenous artesunate in severe falciparum malaria.

To provide novel data relating to the dispositions, effects, and toxicities of the artemisinin derivatives in severe malaria, we studied 30 Vietnamese adults with slide-positive falciparum malaria treated with intravenous artesunate. Twelve patients with complications (severe; group 1) and 8 patients without complications but requiring parenteral therapy (moderately severe; group 2) received 120 mg of artesunate by injection, and 10 patients with moderately severe complications (group 3) were given 240 mg by infusion. Serial concentrations of artesunate and its active metabolite dihydroartemisinin in plasma were measured by high-performance liquid chromatography. The time to 50% parasite clearance (PCT(50)) was determined from serial parasite densities. Full clinical (including neurological) assessments were performed at least daily. In noncompartmental pharmacokinetic analyses, group mean artesunate half-lives (t(1/2)) were short (range, 2.3 to 4.3 min). The dihydroartemisinin t(1/2) (range, 40 to 64 min), clearance (range, 0.73 to 1.01 liters/h/kg), and volume of distribution (range, 0.77 to 1.01 liters/kg) were also similar both across the three patient groups (P > 0.1) and to previously reported values for patients with uncomplicated malaria. Parasite clearance was prompt (group median PCT(50) range 6 to 9 h) and clinical recovery was complete under all three regimens. These data indicate that the pharmacokinetics of artesunate and dihydroartemisinin are not influenced by the severity of malaria. Since the pharmacokinetic parameters for both artesunate and dihydroartemisinin were similar regardless of whether injection or infusion was used, artesunate can be considered a prodrug that is converted stoichiometrically to dhydroartemisinin. Conventional doses of artesunate are safe and effective when given to patients with complications of falciparum malaria.