Population pharmacokinetics of intramuscular artesunate in African children with severe malaria: implications for a practical dosing regimen.

Parenteral artesunate (ARS) is the drug of choice for the treatment of severe malaria. Pharmacokinetics data on intramuscular ARS are limited with respect to the main treatment group that carries the highest mortality, namely, critically ill children with severe malaria. A population pharmacokinetic study of ARS and dihydroartemisinin (DHA) was conducted from sparse sampling in 70 Tanzanian children of ages 6 months to 11 years. All the children had been admitted with severe falciparum malaria and were treated with intramuscular ARS (2.4 mg/kg at 0, 12, and 24 h). Venous plasma concentration-time profiles were characterized using nonlinear mixed-effects modeling (NONMEM). A one-compartment disposition model accurately described first-dose population pharmacokinetics of ARS and DHA. Body weight significantly affected clearance and apparent volume of distribution (P < 0.001), resulting in lower ARS and DHA exposure levels in smaller children. An adapted dosing regimen including a practical dosing table per weight band is proposed for young children based on the pharmacokinetic model.

Risk factors for low birth-weight in areas with varying malaria transmission in Korogwe, Tanzania: implications for malaria control.

Low birth weight (LBW) is a risk factor for infant mortality, morbidity, growth retardation, poor cognitive development, and chronic diseases. Maternal exposure to diseases such as malaria, HIV, and syphilis has been shown to have a significant impact on birth weight (BW). This study was aimed at determining whether there was a difference in rates of LBW in areas of varying malaria transmission intensity in Korogwe, Tanzania. Retrospective data for one year (June 2004-May 2005) in three maternal and child health (MCH) clinics in the district were analysed. Villages were stratified into three strata: lowlands-semi urban (average altitude of 320m), lowlands-rural (below 600m) and highlands (> or =600m). There was a significant decreasing trend of rate of LBW from rural lowlands to highlands (chi2trend = 7.335, P=0.007). Adjusting for covariates, women in parity-two were at reduced risk of delivering LBW babies compared to first parity women (OR=0.44, 95% CI 0.19-0.98, P=0.045). Similarly, the risk of LBW was higher in women who had delayed MCH gestational booking and in women who conceived during high malaria transmission seasons. There was high degree of preference of digits ending with 0/5 in reporting BW in the studied MCHs. In conclusion, a rate of LWB was high in rural lowlands where malaria is also endemic, and was associated with high malaria transmission seasons.

Biological and haematological safety profile of oral amodiaquine and chloroquine in healthy volunteers with or without Plasmodium falciparum infection in northeast Tanzania.

Amodiaquine (AQ), an effective antimalarial drug for uncomplicated malaria, has been greatly restricted after cases of life-threatening agranulocytosis and hepatic toxicity during prophylactic use. We conducted a hospital based open-label randomised clinical trial in 40 indigenous semi-immune healthy adult male volunteers with and without malaria parasites. The objective was to collect data on biological and haematological safety, tolerability, and parasitological efficacy to serve as baseline in the evaluation of the effectiveness of AQ preventive intermittent treatment against malaria morbidity in infants. Volunteers were stratified according to parasitaemia status and randomly assigned 20 participants each arm to three days treatment with either AQ or chloroquine (CQ). The level of difference of selected haematological and hepatological values pre-and post-trial were marginal and within the normal limits. Clinical adverse effects mostly mild and transient were noticed in 33.3% CQ treated-aparasitaemic, 23.8% of CQ treated-parasitaemic, 28.6% ofAQ-treated parasitaemic and 14.3% of aparasitaemic receiving AQ. Amodiaquine attained 100% parasitological clearance rate versus 70% in CQ-treated volunteers. The findings indicate that there was no agranulocytosis or hepatic toxicity suggesting that AQ may pose no public health risk in its wide therapeutic dosage uses. Larger studies are needed to exclude rare adverse effects.

Paracheck Pf compared with microscopy for diagnosis of Plasmodium falciparum malaria among children in Tanga City, north-eastern Tanzania.

Malaria is a major public health problem particularly in rural Sub-Saharan Africa. In most urban areas, malaria transmission intensity is low thus monitoring trends using reliable tools is crucial to provide vital information for future management of the disease. Rapid diagnostic tests (RDT) such as Paracheck Pf are now increasingly adopted for Plasmodium falciparum malaria diagnosis and are advantageous and cost effective alternative to microscopy. This cross sectional survey was carried out during June 2005 to determine the prevalence of malaria in an urban setting and compare microscopy diagnosis versus Paracheck Pf for detecting Plasmodium falciparum. Blood samples from a total of 301 children (< 10 years) attending outpatient clinic at Makorora Health Centre, in Tanga, Tanzania were examined for the presence of malaria. Twenty-nine (9.6%) of the children were positive to malaria by microscopy while 30 (10.0%) were positive by Paracheck test. Three out of 30 positive cases detected by Paracheck were negative by microscopy; thus considered to be false positive results. For the 271 Paracheck Pf negative cases, 2 were positive by microscopy; yielding 2 false negative results. Paracheck Pf sensitivity and specificity were 93.1% and 98.9%, respectively. P. falciparum was the only malarial species observed among the 29 microscopy positive cases. The prevalence of anaemia among the children was 53.16%. These findings indicate a low prevalence of malaria in Tanga City and that Paracheck Pf can be an effective tool for malaria diagnosis.

Prevalence of glucose-6-phosphate dehydrogenase deficiency and haemoglobin S in high and moderate malaria transmission areas of Muheza, north-eastern Tanzania.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency and haemoglobin S (HbS) are very common genetic disorders in sub Saharan Africa, where malaria is endemic. These genetic disorders have been associated with protection against malaria and are therefore under strong selection pressure by the disease. In November-December 2003, we conducted a cross-sectional survey to determine the prevalence of G6PD deficiency and HbS in the population and relate these to malaria infection and haemoglobin levels in lowland and highland areas of differing malaria transmission patterns of Muheza, Tanzania. Blood samples from 1959 individuals aged 6 months to 45 years were collected. A total of 415 (21%) and 1181 (60%) samples were analysed for G6PD deficiency and HbS, respectively. Malarial parasite prevalence was 17.2% (114/1959) in the highlands and 39.6% (49/1959) in the lowlands. Lowlands had higher prevalence of G6PD deficiency and HbS than highlands (G6PD deficiency = 11.32% (24/212) versus 4.43% (9/203), P = 0.01, and HbS = 16.04% (98/611) versus 6.32% (36/570), P = 0.0001). Logistic regression model showed an association between G6PD deficiency and altitude [lowlands] (Odds ratio [OR] 3.4, 95% CI = 1.49; 7.90, P = 0.004). In the lowlands, G6PD deficient individuals had lower mean haemoglobin (10.9g/dl) than normal ones (12.8g/dl), P = 0.01. These findings show that high malaria transmission in the lowlands might have selected for G6PD deficiency and HbS.

Prevalence of Glucose-6-phosphate Dehydrogenase Deficiency and Haemoglobin S in High and Moderate Malaria Transmission Areas of Muheza; North-Eastern Tanzania

Glucose-6-phosphate dehydrogenase (G6PD) deficiency and haemoglobin S (HbS) are very common genetic disorders in sub Saharan Africa; where malaria is endemic. These genetic disorders have been associated with protection against malaria and are therefore under strong selection pressure by the disease. In November-December 2003; we conducted a cross-sectional survey to determine the prevalence of G6PD deficiency and HbS in the population and relate these to malaria infection and haemoglobin levels in lowland and highland areas of differing malaria transmission patterns of Muheza; Tanzania. Blood samples from 1959 individuals aged 6 months to 45 years were collected. A total of 415 (21) and 1181 (60) samples were analysed for G6PD deficiency and HbS; respectively. Malarial parasite prevalence was 17.2(114/1959) in the highlands and 39.6(49/1959) in the lowlands. Lowlands had higher prevalence of G6PD deficiency and HbS than highlands (G6PD deficiency = 11.32(24/212) versus 4.43(9/203); P = 0.01; and HbS = 16.04(98/611) versus 6.32(36/570); P = 0.0001). Logistic regression model showed an association between G6PD deficiency and altitude [lowlands] (Odds ratio [OR] 3.4; 95CI=1.49; 7.90; P=0.004). In the lowlands; G6PD deficient individuals had lower mean haemoglobin (10.9g/dl) than normal ones (12.8g/dl); P = 0.01. These findings show that high malaria transmission in the lowlands might have selected for G6PD deficiency and HbS

Risk Factors for Low Birth-Weight in Areas with Varying Malaria Transmission in Korogwe; Tanzania: Implications for Malaria Control

Low birth weight (LBW) is a risk factor for infant mortality; morbidity; growth retardation; poor cognitive development; and chronic diseases. Maternal exposure to diseases such as malaria; HIV; and syphilis has been shown to have a significant impact on birth weight (BW). This study was aimed at determining whether there was a difference in rates of LBW in areas of varying malaria transmission intensity in Korogwe; Tanzania. Retrospective data for one year (June 2004-May 2005) in three maternal and child health (MCH) clinics in the district were analysed. Villages were stratified into three strata: lowlands-semi urban (average altitude of 320m); lowlands-rural (below 600m) and highlands (=600m). There was a significant decreasing trend of rate of LBW from rural lowlands to highlands (X2 trend =7.335; P=0.007). Adjusting for covariates; women in parity-two were at reduced risk of delivering LBW babies compared to first parity women (OR=0.44; 95CI 0.19-0.98; P=0.045). Similarly; the risk of LBW was higher in women who had delayed MCH gestational booking and in women who conceived during high malaria transmission seasons. There was high degree of preference of digits ending with 0/5 in reporting BW in the studied MCHs. In conclusion; a rate of LWB was high in rural lowlands where malaria is also endemic; and was associated with high malaria transmission seasons

Biological and Haematological Safety Profile of Oral Amodiaquine and Chloroquine in Healthy Volunteers with or without Plasmodium falciparum Infection in Northeast Tanzania

Amodiaquine (AQ); an effective antimalarial drug for uncomplicated malaria; has been greatly restricted after cases of life-threatening agranulocytosis and hepatic toxicity during prophylactic use. We conducted a hospital based open-label randomised clinical trial in 40 indigenous semi-immune healthy adult male volunteers with and without malaria parasites. The objective was to collect data on biological and haematological safety; tolerability; and parasitological efficacy to serve as baseline in the evaluation of the effectiveness of AQ preventive intermittent treatment against malaria morbidity in infants. Volunteers were stratified according to parasitaemia status and randomly assigned 20 participants each arm to three days treatment with either AQ or chloroquine (CQ). The level of difference of selected haematological and hepatological values pre-and post-trial were marginal and within the normal limits. Clinical adverse effects mostly mild and transient were noticed in 33.3CQ treated-aparasitaemic; 23.8of CQ treated-parasitaemic; 28.6of AQ-treated parasitaemic and 14.3of aparasitaemic receiving AQ. Amodiaquine attained 100parasitological clearance rate versus 70in CQ-treated volunteers. The findings indicate that there was no agranulocytosis or hepatic toxicity suggesting that AQ may pose no public health risk in its wide therapeutic dosage uses. Larger studies are needed to exclude rare adverse effects

Pattern and spatial distribution of plague in Lushoto, north-eastern Tanzania.

A review of plague records from 1986 to 2002 and household interviews were carried out in the plague endemic villages to establish a pattern and spatial distribution of the disease in Lushoto district, Tanzania. Spatial data of households and village centres were collected and mapped using a hand held Global Positioning System and Geographical Information System. During the 16-year period, there were 6249 cases of plague of which 5302 (84.8%) were bubonic, 391 (6.3%) septicaemic, and 438 (7.0%) pneumonic forms. A total of 118 (1.9%) cases were not categorized. Females and individuals aged 7-18 years old were the most affected groups accounting for 54.4% (95% CI: 52.4-56.0) and 47.0% (95% CI: 45-49) of all reported cases, respectively. Most cases were found in villages at high altitudes (1700-1900m); and there was a decline in case fatality rate (CFR) in areas that experienced frequent outbreaks. Overall, there was a reduction in mean reporting time (from symptoms onset to admission) to an average of 1.35 days (95% CI: 1.30-1.40) over the years, although this remained high among adult patients (>18 years). Despite the decrease in the number of cases and CFR over the years, our findings indicate that Lushoto district experiences human plague epidemic every year; with areas at high altitudes being more prone to outbreaks. The continued presence of plague in this focus warrants further studies. Nonetheless, our findings provide a platform for development of an epidemic preparedness plan to contain future outbreaks.

Malaria specific mortality in lowlands and highlands of Muheza district, north-eastern Tanzania.

Vital registration of causes of death in Tanzania is incomplete and many deaths occur outside health care settings. Verbal autopsies (VA) are used to determine the underlying cause of death, and the probable diagnosis helps to estimate reasonably cause-specific mortality. In this paper, we report findings of a verbal autopsy survey which involved eight villages in both low and highlands of Muheza district, north-eastern Tanzania. The survey was conducted following a rapid census, which was done to identify households that had lost one or more members within a period of two years from the date of census. Trained research assistants administered VA questionnaires to parents/close relatives. Two physicians reviewed each report independently and a third opinion was sought where there was discordant report between the two. A total of 9,872 households were surveyed and 134 deaths were recorded. A total of 96 (71.6%) deaths were from lowland villages representing high malaria transmission. Majority (72.4%) of the reported deaths occurred at home whilst 32.1% occurred at heath facility settings. Overall, severe malaria was the leading cause accounting for 34.3% of all deaths. Infants were most affected and accounted for 43.5% of the total deaths. Pulmonary tuberculosis ranked second (8.2%) cause of deaths and was exclusively confined to individuals > or = 15 years. Probable cause of death could not be determined in 13.4% of deaths. In conclusion, majority of deaths in rural north-eastern Tanzania occur at home and the immediate causes are usually unknown or not documented. These findings indicate that the verbal autopsy is a useful tool for detecting leading causes of death at community level in the absence of health facility-based data.

Malaria specific mortality in lowlands and highlands of Muheza district; north-eastern Tanzania

Vital registration of causes of death in Tanzania is incomplete and many deaths occur outside health care settings. Verbal autopsies (VA) are used to determine the underlying cause of death, and the probable diagnosis helps to estimate reasonably cause-specific mortality. In this paper, we report findings of a verbal autopsy survey which involved eight villages in both low and highlands of Muheza district, north-eastern Tanzania. The survey was conducted following.a rapid census, which was done to identify households that had lost one or more members within a period of two years from the date of census. Trained research assistants administered VA questionnaires to parents/close relatives. Two physicians reviewed each report independently and a third opinion was sought where there was discordant report between the two. A total of 9,872 households were surveyed and 134 deaths were recorded. A total of 96 (71.6%) deaths were from lowland villages representing high malaria transmission. Majority (72.4%) of the reported deaths occurred at home whilst 32.1% occurred at heath facility settings. Overall, severe malaria was the leading cause accounting for 34.3% of all deaths. Infants were most affected and accounted for 43.5% of the total deaths. Pulmonary tuberculosis ranked second (8.2%) cause of deaths and was exclusively confined to individuals ≥15 years. Probable cause of death could not be determined in 13.4% of deaths. In conclusion, majority of deaths in rural north-eastern Tanzania occur at home and the immediate causes are usually unknown or not documented. These findings indicate that the verbal autopsy is a useful tool for detecting leading causes of death at community level in the absence of health facility-based data

Pattern and spatial distribution of plague in Lushoto; north-eastern Tanzania

A review of plague records from 1986 to 2002 and household interviews were carried out in the plague endemic villages to establish a pattern and spatial distribution of the disease in Lushoto district; Tanzania. Spatial data of households and village centres were collected and mapped using a hand held Global Positioning System and Geographical Information System. During the 16-year period; there were 6249 cases of plague of which 5302 (84.8) were bubonic; 391 (6.3)septicaemic; and 438 (7.0) pneumonic forms. A total of 118 (1.9) cases were not categorized. Females and individuals aged 7-18 years old were the most affected groups accounting for 54.4(95CI: 52.4-56.0) and 47.0(95CI: 45- 49) of all reported cases; respectively. Most cases were found in villages at high altitudes (1700-1900m); and there was a decline in case fatality rate (CFR) in areas that experienced frequent outbreaks. Overall; there was a reduction in mean reporting time (from symptoms onset to admission) to an average of 1.35 days (95CI: 1.30-1.40) over the years; although this remained high among adult patients (18 years). Despite the decrease in the number of cases and CFR over the years; our findings indicate that Lushoto district experiences human plague epidemic every year; with areas at high altitudes being more prone to outbreaks. The continued presence of plague in this focus warrants further studies. Nonetheless; our findings provide a platform for development of an epidemic preparedness plan to contain future outbreaks

A simple technique for the detection of anti-malarial drug formulations and their presence in human urine.

A simple, sensitive, specific assay technique for the detection and semi-quantification of chloroquine, amodiaquine, quinine, primaquine, sulfadoxine and pyrimethamine in formulations and in human urine by using thin layer chromatography (TLC) was developed and tested in the laboratory. The method involved developing test samples spotted on TLC chromatogram by diethylamine-toluene-isopropanol (1:4:5 v/v/v) as the eluting solvent. The solvent system diethylamine-toluene-isopropanol (1:4:5 v/v/v) enabled the elution and detection of all the tested antimalarial drugs in solution and those spiked in human urine. Detection limits for chloroquine, amodiaquine, quinine and primaquine were the lowest at 0.00025 mg/ml. Sulfadoxine exhibited a detection limit of 0.0005 mg/ml whereas that of pyrimethamine was 0.001 mg/ml. The results indicate the suitability of this technique in antimalarial drug quality and bioavailability studies. It is envisaged that this technique will adequately address the role of drug absorption and excretion in the chemotherapy of malaria as well as to detect types of antimalarial drugs commonly used in the community.

Estimating medium- and long-term trends in malaria transmission by using serological markers of malaria exposure.

The implementation and evaluation of malaria control programs would be greatly facilitated by new tools for the rapid assessment of malaria transmission intensity. Because acquisition and maintenance of antimalarial antibodies depend on exposure to malaria infection, such antibodies might be used as proxy measures of transmission intensity. We have compared the prevalence of IgG antibodies with three Plasmodium falciparum asexual stage antigens in individuals of all ages living at varying altitudes encompassing a range of transmission intensities from hyper- to hypoendemic in northeastern Tanzania, with alternative measures of transmission intensity. The prevalence of antibodies to merozoite surface protein-1(19) was significantly more closely correlated with altitude than either point-prevalence malaria parasitemia or single measures of hemoglobin concentration. Analysis of age-specific seroprevalence rates enabled differentiation of recent (seasonal) changes in transmission intensity from longer-term transmission trends and, using a mathematical model of the annual rate of seroconversion, estimation of the longevity of the antibody response. Thus, serological tools allow us to detect variations in malaria transmission over time. Such tools will be invaluable for monitoring trends in malaria endemicity and the effectiveness of malaria control programs.

A randomized, double-blind, placebo-controlled study with diethylcarbamazine for the treatment of hydrocoele in an area of Tanzania endemic for lymphatic filariasis.

Hydrocoele is common in men in Wuchereria bancrofti-endemic areas, the treatment for which is currently surgical intervention. Two community studies have recently suggested that the antifilarial drug diethylcarbamazine (DEC) may have a beneficial effect of reducing the size of hydrocoeles of filarial origin. To test this hypothesis, a double-blind, placebo-controlled study was carried out in 1998 and 1999 in an area of north-eastern Tanzania where microfilaria (mf) carrier rates and hydrocoele prevalence rates were known to be high. Ninety-eight adult male volunteers (aged > or = 15 years) with chronic hydrocoele received DEC 300 mg per day for 12 days (49 patients), or placebo (49 patients). Circumferential and ultrasonographic measurements of the scrotum, and a serum sample for measuring W. bancrofti antigen, were obtained at the onset and after 3, 6 and 12 months. Scrotal size and hydrocoele fluid volume indices were calculated. No statistically significant differences in volumetric measurements between the DEC and placebo groups were found at any of the follow-ups. Separate analyses dividing patients by antigen status, hydrocoele size or presence of thickening of the scrotal skins gave similar results. Geometric mean intensity of W. bancrofti antigen was significantly lower in the DEC group than in the placebo group (P = 0.008), indicating that lack of compliance was not a significant factor. Two months into the treatment trial, mass treatment with monthly low-dose DEC was given to the rest of the community. We conclude that DEC is not effective in reducing the size of hydrocoele of filarial origin. Interventions to replace or supplement hydrocoelectomy should be investigated.

Genital manifestations and reproductive health in female residents of a Wuchereria bancrofti-endemic area in Tanzania.

To assess the significance of lymphatic filariasis for the development of chronic genital manifestations and for reproductive health in women, we conducted a cross-sectional study of 2 villages in north-eastern Tanzania including interview and gynaecological examination of adult women, focusing primarily on reproductive history and genital health. In a population of 2165 residents, prevalence of Wuchereria bancrofti microfilaraemia was 28%, and geometric mean intensity of microfilariae (mf) was 722 mf/mL. Leg lymphoedema (elephantiasis) was present in 4.2% of adults aged > or = 15 years, and hydrocoele in 26.5% of adult males. Five hundred and thirty women completed an interview, and 404 of these completed a gynaecological examination. Most women were Muslims (72%), polygamy was common (29%), and 49% of women had undergone circumcision (clitoridectomy). Presence of microfilaraemia did not influence fertility or fertility-related variables including age at menarche, parity, spontaneous abortion, stillbirth, Caesarean section and premature labour, nor presence of primary or secondary infertility. Mf status was strongly correlated with abnormal menstruation pattern in the 30+ years age-group (P = 0.001), but not in the < 30 years age-group. Cervical, vaginal and vulval pathology was unrelated to mf status. Two women, aged 46 and 77 years, had vulval oedema of probable filarial origin, both were mf negative. Overall, microfilaraemia appeared to have no influence on genital disease or reproductive health, and chronic manifestations of lymphatic filariasis of the genitals does not appear to be a substantial problem in women.

IgG reactivities against recombinant Rhoptry-Associated Protein-1 (rRAP-1) are associated with mixed Plasmodium infections and protection against disease in Tanzanian children.

A cross-sectional sero-epidemiological study was performed in Magoda, Tanzania, an area where malaria is holoendemic. Blood samples were collected from children (1-4 years) and tested for IgG antibody reactivity against 2 recombinant protein fragments of Plasmodium falciparum Rhoptry-Associated Protein-1 (rRAP-1). The data were related to the prevalence of malarial disease and single P. falciparum or mixed Plasmodium infections. Fever (> or = 37.5 degrees C) in combination with parasite densities > 5000/microliter were used to distinguish between children with asymptomatic malaria infections and those with acute clinical disease. Furthermore, C-reactive protein (CRP) was applied as a surrogate marker of malaria morbidity. The prevalence of Plasmodium infections was 96.0%. Eleven children were defined as clinical malaria cases, all with single P. falciparum infections. The density of P. falciparum was significantly lower in children with mixed Plasmodium infections compared to those with single P. falciparum infections. Children with asymptomatic P. falciparum infections had higher IgG reactivities to rRAP-1, compared to IgG reactivities of children with malarial disease. Children with mixed Plasmodium infections generally showed elevated IgG reactivity to rRAP-1, when compared to children with single P. falciparum infections. The possible relationship between mixed species infections, clinical outcome of the disease and antibody responses to RAP-1 is discussed.

Polymorphisms in the dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS) genes of Plasmodium falciparum and in vivo resistance to sulphadoxine/pyrimethamine in isolates from Tanzania.

The efficacy of sulphadoxine/pyrimethamine (S/P) in treatment of uncomplicated falciparum malaria in Africa is increasingly compromised by development of resistance. The occurrence of mutations associated with the active site sequence in the Plasmodium falciparum genes coding for dihydrofolate reductase (DHFR) and dihydropteroate synthetase (DHPS) is associated with in vitro resistance to pyrimethamine and sulphadoxine. This study investigates the occurrence of these mutations in infected blood samples taken from Tanzanian children before treatment with S/P and their relationship to parasite breakthrough by day 7. The results show that alleles of DHPS (436-alanine, 437-alanine and 540-lysine) were significantly reduced in prevalence on day 7 after S/P treatment. In this area, a DHPS with 436-serine, 437-glycine and 540-glutamate appears to play a major role in resistance to S/P in vivo. Evidence for the influence of mutations in the DHFR gene in this investigation is not clear, probably because of the high prevalence of 'resistance-related' mutations at day 0 in the local parasite population. For apparently the same reason, it was not possible to show a statistical association between S/P resistance and the presence of particular polymorphisms in the DHFR and DHPS genes before treatment.

Identification of an erythrocyte binding peptide from the erythrocyte binding antigen, EBA-175, which blocks parasite multiplication and induces peptide-blocking antibodies.

A biotinylated peptide covering a sequence of 21 amino acids (aa) from the erythrocyte binding antigen (EBA-175) of Plasmodium falciparum bound to human glycophorin A, an erythrocyte receptor for merozoites, as demonstrated by enzyme-linked immunosorbent assay (ELISA) and to erythrocytes as demonstrated by flow cytometry analysis. The peptide, EBA(aa1076-96), also bound to desialylated glycophorin A and glycophorin B when tested by ELISA. The peptide blocked parasite multiplication in vitro. The glycophorin A binding sequence was further delineated to a 12-aa sequence, EBA(aa1085-96), by testing the binding of a range of truncated peptides to immobilized glycophorin A. Our data indicate that EBA(aa1085-96) is part of a ligand on the merozoite for binding to erythrocyte receptors. This binding suggests that the EBA(aa1085-96) peptide is involved in a second binding step, independent of sialic acid. Antibody recognition of this peptide sequence may protect against merozoite invasion, but only a small proportion of sera from adults from different areas of malaria transmission showed antibody reactivities to the EBA(aa1076-96) peptide, indicating that this sequence is only weakly immunogenic during P. falciparum infections in humans. However, Tanzanian children with acute clinical malaria showed high immunoglobulin G reactivity to the EBA(aa1076-96) peptide compared to children with asymptomatic P. falciparum infections. The EBA(aa1076-96) peptide sequence from EBA-175 induced antibody formation in mice after conjugation of the peptide with purified protein derivative. These murine sera inhibited EBA(aa1076-96) peptide binding to glycophorin A.