RESUMEN
BACKGROUND: A potential problem for malaria vaccine development and testing is between-host variation in antibody responses to specific malaria antigens. Previous work in adults in an area highly endemic for Plasmodium falciparum in Papua New Guinea found that genetic regulation partly explained heterogeneity in responsiveness. We have now assessed the relative contributions of environmental and genetic factors in total IgG responses to specific malaria antigens in children, and quantified temporal variation within individuals of total IgG responses. METHODS: Total IgG responses against schizont extract, merozoite surface protein-1, merozoite surface protein-2, ring-infected erythrocyte surface antigen, and SPf66 were measured by ELISA. Variance component analysis was used to estimate the variation explained by genetic and environmental factors in these antibody responses. Intra- and inter-class correlations of antibody responses within relative pairs were estimated. We adjusted for age, P. falciparum density, sex and village differences either within or prior to the analysis. RESULTS: For all malaria antigens, temporal variation in the total IgG response was the predominant source of variation. There was substantial familial aggregation of all IgG responses, but it remained unclear how much this clustering was attributable to genetic factors and how much to a common environment in the household. The remaining variance, which could not be explained by either of the above, was very small for most of the antigens. CONCLUSIONS: Temporal variation and clustering of immune responses to specific malaria antigens need to be taken into account when planning, conducting and interpreting immuno-epidemiological and vaccine studies.
Asunto(s)
Inmunoglobulina G/inmunología , Vacunas contra la Malaria/inmunología , Malaria/inmunología , Animales , Formación de Anticuerpos , Antígenos de Protozoos/inmunología , Niño , Ensayo de Inmunoadsorción Enzimática , Femenino , Humanos , Inmunoglobulina G/análisis , Inmunoglobulina G/genética , Masculino , Linaje , Plasmodium falciparum/inmunología , Factores de TiempoRESUMEN
A Phase I safety and immunogenicity study with a three-component blood-stage malaria vaccine was conducted in adult male subjects living in an endemic area of Papua New Guinea. The preparations were recombinant proteins which corresponded to parts of the two merozoite surface proteins of Plasmodium falciparum (MSP1 and 2), and of the ring-infected erythrocyte surface antigen (RESA). The three proteins were emulsified with the adjuvant Montanide ISA720. Ten subjects were injected twice (four weeks apart) with the vaccine formulation and two with the adjuvant alone. Mild pain at the site of injection was reported by about half of the subjects but no systemic reaction related to the formulation occurred. There was a sharp rise in geometric mean stimulation index after the second dose compared to baseline for MSP1 and RESA, while the rise was small for MSP2. Geometric mean antibody titres increased for MSP1 during the study, whereas they hardly changed for MSP2 and RESA. The vaccine formulation was safe when used in an already immune population. The vaccine induced good cellular responses, especially for MSP1 and RESA. Boosting of humoral responses was weak, probably because of high baseline antibody levels.
Asunto(s)
Anticuerpos Antiprotozoarios/biosíntesis , Antígenos de Protozoos/inmunología , Vacunas contra la Malaria/inmunología , Proteína 1 de Superficie de Merozoito/inmunología , Plasmodium falciparum/inmunología , Proteínas Protozoarias/inmunología , Vacunación , Adyuvantes Inmunológicos , Adulto , Animales , Anticuerpos Antiprotozoarios/inmunología , Citocinas/sangre , Citotoxicidad Inmunológica , Humanos , Inmunización Secundaria , Vacunas contra la Malaria/efectos adversos , Malaria Falciparum/prevención & control , Masculino , Manitol/análogos & derivados , Manitol/inmunología , Persona de Mediana Edad , Ácidos Oléicos/inmunología , Papúa Nueva Guinea , Plasmodium falciparum/crecimiento & desarrollo , Seguridad , Linfocitos T/inmunología , Vacunación/efectos adversosRESUMEN
Serum levels of reactive nitrogen intermediates (RNI; nitrate + nitrite), interferon gamma (IFN gamma) and tumour necrosis factor (TNF) were measured in 177 Papua New Guinean children with different clinical manifestations of malaria. The groups investigated were asymptomatic parasitaemic, mild malaria, cerebral malaria survivors and cerebral malaria non-survivors. The levels of TNF were highest among the cases of cerebral malaria who died and lowest among the asymptomatic parasitaemic children (mean log TNF levels 2.183 pg/mL vs. 1.455 pg/mL; P = 0.001). Similarly, the levels of IFN gamma were highest among the cerebral and lowest among the asymptomatic patients (mean log TNF levels 0.338 pg/mL vs 0.054 pg/mL; P < 0.0001). RNI levels were high among both the asymptomatic parasitaemic group and those who died due to cerebral malaria (mean log RNI levels 1.56 microM vs. 1.412 microM; P = 0.18). The ratio of RNI to TNF, however, was significantly higher among the asymptomatic parasitaemic children and lowest among those who died due to cerebral malaria (mean log (RNI:TNF) ratio 0.118 vs. -0.789; P < 0.001). We concluded that the ratio of serum RNI to serum TNF is a more useful indicator of outcome of falciparum malaria in this population than the absolute levels of either alone.
Asunto(s)
Interferón gamma/sangre , Malaria Falciparum/diagnóstico , Óxido Nítrico/sangre , Factor de Necrosis Tumoral alfa/análisis , Biomarcadores/sangre , Preescolar , Femenino , Humanos , Masculino , Papúa Nueva Guinea , PronósticoRESUMEN
The interaction between malnutrition and malaria is complex and there is evidence that malnutrition decreases the susceptibility to malaria. To investigate the relation between anthropometric measurements and subsequent malaria morbidity and to examine whether the effect observed was due to interaction with host immunity, we followed for 1 y a cohort of 136 children aged 10 to < 120 mo in Wosera, East Sepik Province, Papua New Guinea. At baseline, 21% were stunted, 10% were wasted, and 5% were both stunted and wasted. After adjustment for age and use of bed nets, height-for-age z score (HAZ) at baseline predicted the number of clinical episodes of falciparum malaria during the following year: incidence rate increased with increasing HAZ. Humoral responses to specific malarial antigens were lowest in the wasted children. The prevalence of lymphoproliferative responders was not significantly different between well-nourished and undernourished children. In contrast, the prevalence of cytokine producers was higher in the undernourished than in the well-nourished children. Our findings support the view that stunting but not wasting protects against falciparum malaria. The mechanism may be related to an improved ability of malnourished children to produce certain cytokines in response to stimulation by specific malarial antigens.
Asunto(s)
Antropometría , Malaria Falciparum/epidemiología , Formación de Anticuerpos , Antígenos de Protozoos/aislamiento & purificación , Niño , Preescolar , Estudios de Cohortes , Estudios Transversales , Citocinas/sangre , Susceptibilidad a Enfermedades , Humanos , Inmunidad Celular , Lactante , Estudios Longitudinales , Malaria Falciparum/inmunología , Nueva Guinea/epidemiología , Trastornos Nutricionales/complicaciones , Estado NutricionalRESUMEN
In this review we summarise the arguments that inflammatory cytokines, triggered by material released from the parasite at schizogony (malarial toxin), might induce the illness and pathology seen in malaria. These pro-inflammatory cytokines can generate inducible nitric oxide synthase and cause nitric oxide to be released, as can low concentrations of malarial toxin itself provided interferon-gamma, which has only low activity in the absence of malarial toxin, is present. We suggest here that recently described hypermetabolic functions of these mediators provide a much more plausible explanation for malarial hyperlactataemia and hypoglycaemia, the chief prognostic indicators in falciparum malaria, than does hypoxia secondary to mechanical blockage of vessels by sequestering parasites, which is the dominant current theory. We also review the arguments that rationalise, through these mediators, the reversibility of the coma of cerebral malaria. Although not yet tested at a cellular level, the proposal that nitric oxide generated in cerebral vascular walls contributes to this coma continues to gather indirect support. In addition, new evidence incriminating nitric oxide in the mechanism of tolerance to endotoxin rationalises the raised nitric oxide generation seen in malarial tolerance.
Asunto(s)
Malaria/etiología , Animales , Metabolismo de los Hidratos de Carbono , Citocinas/fisiología , Humanos , Hipoglucemia/etiología , Tolerancia Inmunológica , Mediadores de Inflamación/fisiología , Ácido Láctico/sangre , Malaria/inmunología , Malaria/fisiopatología , Malaria Cerebral/etiología , Óxido Nítrico/fisiologíaRESUMEN
Plasmodium vivax Duffy binding protein (DBP) is a conserved functionally important protein. P. vivax DBP is an asexual blood-stage malaria vaccine candidate because adhesion of P. vivax DBP to its erythrocyte receptor is essential for the parasite to continue development in human blood. We developed a soluble recombinant protein of P. vivax DBP (rDBP) and examined serologic activity to it in residents of a region of high endemicity. This soluble rDBP product contained the cysteine-rich ligand domain and most of the contiguous proline-rich hydrophilic region. rDBP was expressed as a glutathione S-transferase (GST) fusion protein and was isolated from GST by thrombin treatment of the purified fusion protein bound on glutathione agarose beads. P. vivax rDBP was immunogenic in rabbits and induced antibodies that reacted with P. vivax and Plasmodium knowlesi merozoites. Human sera from adult residents of a region of Papua New Guinea where malaria is highly endemic or P. vivax-infected North American residents reacted with rDBP in an immunoblot and an enzyme-linked immunosorbent assay. The reactivity to reduced, denatured P. vivax rDBP and the cross-reactivity with P. knowlesi indicated the presence of immunogenic conserved linear B-cell epitopes. A more extensive serologic survey of Papua New Guinea residents showed that antibody response to P. vivax DBP is common and increases with age, suggesting a possible boosting of the antibody response in some by repeated exposure to P. vivax. A positive humoral response to P. vivax DBP correlated with a significantly higher response to P. vivax MSP-1(19). The natural immunogenicity of this DBP should strengthen its usefulness as a vaccine.
Asunto(s)
Antígenos de Protozoos , Proteínas Portadoras/análisis , Moléculas de Adhesión Celular/análisis , Plasmodium vivax/inmunología , Proteínas Protozoarias/análisis , Proteínas Protozoarias/inmunología , Receptores de Superficie Celular/análisis , Adolescente , Adulto , Anciano , Animales , Formación de Anticuerpos , Secuencia de Bases , Proteínas Portadoras/inmunología , Moléculas de Adhesión Celular/inmunología , Niño , Preescolar , Reacciones Cruzadas , Humanos , Lactante , Vacunas contra la Malaria , Persona de Mediana Edad , Datos de Secuencia Molecular , Plasmodium knowlesi/inmunología , Conejos , Receptores de Superficie Celular/inmunología , Proteínas Recombinantes de Fusión/análisis , Proteínas Recombinantes de Fusión/inmunología , SolubilidadRESUMEN
A prospective study in 207 children aged 0.5-15 years was carried out to examine the relationship between cellular responses to Plasmodium falciparum ring-infected erythrocyte surface antigen (RESA) and malaria infection and morbidity. The prevalence of lymphoproliferative response to RESA was 13%, IFN-gamma prevalence was 40% and IL-4 prevalence was 22%. Only the IFN-gamma, response to RESA increased significantly with age. When proliferation or stimulation of either cytokine was used to assess T-cell activation the overall frequency of responders increased to 55%. The proliferative and IFN-gamma response to RESA were positively associated. Although there was no association between any of the CMI responses to RESA and concurrent morbidity the prevalence of IL-4 response to RESA was significantly lower in children who experienced clinical malaria in the following year. These results coupled with our earlier data showing a negative relationship between humoral responses to RESA and malaria morbidity support the inclusion of RESA in a subunit vaccine against malaria.
Asunto(s)
Antígenos de Protozoos/inmunología , Enfermedades Endémicas , Interleucina-4/inmunología , Malaria/inmunología , Plasmodium falciparum/inmunología , Proteínas Protozoarias/inmunología , Linfocitos T/inmunología , Adolescente , Animales , División Celular , Células Cultivadas , Niño , Preescolar , Estudios de Cohortes , Humanos , Lactante , Interferón gamma/inmunología , Leucocitos Mononucleares/citología , Malaria/epidemiología , Papúa Nueva Guinea/epidemiología , Estudios Prospectivos , Proteínas Recombinantes de Fusión/inmunologíaRESUMEN
BACKGROUND: No comprehensive data on the clinical features and the prognosis of cerebral malaria in the South Pacific are available at present. We conducted a prospective study in children with cerebral malaria to assess the case fatality rate (CFR) in the region and to identify potential risk factors for death. METHODS: We recruited 134 children admitted to the Madang General Hospital between April 1991 and October 1993 with a strictly defined diagnosis of cerebral malaria. Besides clinical examination, we collected a blood sample for parasitological haematological and biochemical assessment. RESULTS: The CFR was 11.9% and the prevalence of residual neurological sequelae at discharge was 1.5%. The proportion of children presenting with deep coma (12%) or hypoglycaemia (17%) was lower in our study than in African ones, where severe complications are more frequent. Also mortality associated with hypoglycaemia on admission was lower. Clinical or laboratory conditions significantly associated with death were deep coma, malarial anaemia and hyperleucocytosis. CONCLUSIONS: All conditions associated with deep coma, such as shock, hypoglycaemia and acidosis, should be corrected. Also prompt administration of blood transfusions to patients with anaemia is likely to reduce the occurrence of death in Papua New Guinean children with cerebral malaria.
Asunto(s)
Malaria Cerebral/mortalidad , Niño , Preescolar , Coma/etiología , Coma/mortalidad , Intervalos de Confianza , Estudios Transversales , Femenino , Hematócrito/estadística & datos numéricos , Hemoglobinas/análisis , Humanos , Lactante , Recuento de Leucocitos , Funciones de Verosimilitud , Modelos Logísticos , Malaria Cerebral/sangre , Malaria Cerebral/complicaciones , Malaria Cerebral/fisiopatología , Masculino , Oportunidad Relativa , Papúa Nueva Guinea/epidemiología , Prevalencia , Estudios Prospectivos , Índice de Severidad de la EnfermedadRESUMEN
A prospective study in 207 children aged 0.5-15 years was carried out in a highly endemic area of Papua New Guinea to examine the relationship between cellular responses to Plasmodium falciparum merozoite surface protein 2 (MSP2) and malaria infection and morbidity. In vitro proliferation, IFN-gamma and IL-4 induction were measured against two recombinant proteins of MSP2, FC27 and 3D7 as well as against a form of the 3D7 MSP2 lacking the central repetitive sequences (d3D7). The prevalence of proliferative response was generally low, 6% for FC27, 9% for 3D7 and 11% for d3D7. A higher prevalence of IL-4 response was obtained being 27% for FC27, 34% for 3D7 and 30% for d3D7 while the prevalence of IFN-gamma response was 13%, 15% and 18%, respectively. There was no correlation between age and proliferative responses; in contrast cytokine production increased with age for all three antigens. When proliferation or stimulation of either cytokine was used to assess T-cell activation the frequency of responders increased to 39%, 47% and 46% for FC27, 3D7 and d3D7 respectively. Analysis of the relation of T cell responses to concurrent infection and morbidity showed that lymphoproliferative response only to d3D7 was significantly associated with parasitaemia; while lymphoproliferative responses to all 3 MSP2 antigens were highest in the group of clinical malaria cases. There was no significant correlation between proliferation or cytokine production to MSP2 and concurrent or subsequent malaria morbidity.
Asunto(s)
Antígenos de Protozoos , Antígenos de Superficie/inmunología , Citocinas/biosíntesis , Malaria Falciparum/inmunología , Plasmodium falciparum/inmunología , Proteínas Protozoarias/inmunología , Linfocitos T/inmunología , Adolescente , Animales , Niño , Preescolar , Estudios Transversales , Enfermedades Endémicas , Humanos , Lactante , Interferón gamma/biosíntesis , Interleucina-4/biosíntesis , Activación de Linfocitos , Malaria Falciparum/epidemiología , Papúa Nueva Guinea/epidemiología , Estudios Prospectivos , Proteínas Recombinantes de Fusión/inmunologíaRESUMEN
Serum from 41 of 92 children admitted to Madang Hospital, Papua New Guinea, with cerebral malaria, previously assessed for serum levels of reactive nitrogen intermediates (RNI: nitrate plus nitrite), were re-assessed for creatinine levels on the day of admission. Further analysis of RNI levels on day 21 compared to day 0 was carried out. Children with the highest RNI levels on admission, and with the longest duration of coma, did not have elevated creatinine levels. The highest levels of creatinine occurred among those with the lightest coma and creatinine levels were similar in those with short (< 48 h) and long (> 48 h) duration of coma. Between days 0 and 21, RNI decreased in 30 of 57 children, increased in 23, and did not change in 4. There was a significant relationship between the decrease in RNI relative to the level of RNI on admission and the duration of coma. For children with a coma duration < 48 h (48/57), there was no difference between the numbers showing an increase or a decrease in RNI level, but 6 of the 9 children with coma duration > 48 h showed a decrease in RNI greater than 50% of the RNI levels on admission. None of these 9 children had elevated creatinine levels. Elevated RNI levels in severe cases were thus not associated with renal function in these children in Papua New Guinea.
Asunto(s)
Creatinina/sangre , Malaria Cerebral/sangre , Nitratos/sangre , Nitritos/sangre , Biomarcadores/sangre , Niño , Preescolar , Coma/etiología , Femenino , Humanos , Malaria Cerebral/complicaciones , Masculino , Papúa Nueva Guinea , Factores de TiempoRESUMEN
The prevalence and concentration of IgG antibodies to defined Plasmodium falciparum antigens were assessed in serum samples of 97 children with cerebral malaria and 146 children with uncomplicated malaria. The antigens used included the schizont extract, ring-infected erythrocyte surface antigen, the C-terminal region of merozoite surface antigen-1 (MSA-1) (BVp42), and three recombinant proteins of MSA-2 (FC27, 3D7, and d3D7). Parasite isolates from 24 children with cerebral malaria and 22 children with uncomplicated malaria were genotyped for MSA-1 and MSA-2. The distribution of parasite genotypes belonging to the different allelic families was similar in both the cerebral and uncomplicated malaria groups. There were higher antibody levels to antigens derived from the infecting parasite genotype than to heterologous genotypes, but this difference was only statistically significant for antibody against the d3D7 antigen among children infected with the 3D7 parasite genotype (mean log = 4.72 versus 3.45 antibody units [AU]; P = 0.029). Those who died were more likely to be infected with the FC27 genotype and had lower antibody levels to MSA-2 of the 3D7 type than had cerebral malaria patients who survived (mean log = 2.94 versus 3.79 AU; P = 0.049). Antibodies against parasites of the 3D7 genotype are associated with a better prognosis among children with cerebral malaria partly because these children are more likely to be infected with parasites of this genotype rather than the FC27 genotype, which appears to be more virulent.
Asunto(s)
Anticuerpos Antiprotozoarios/biosíntesis , Antígenos de Protozoos/inmunología , Malaria Cerebral/inmunología , Malaria Falciparum/inmunología , Plasmodium falciparum/inmunología , Enfermedad Aguda , Adolescente , Animales , Antígenos de Superficie/genética , Antígenos de Superficie/inmunología , Niño , Preescolar , Femenino , Genotipo , Hemoglobinas/análisis , Humanos , Inmunoglobulina G/biosíntesis , Lactante , Recuento de Leucocitos , Malaria Cerebral/parasitología , Malaria Falciparum/parasitología , Masculino , Proteína 1 de Superficie de Merozoito , Plasmodium falciparum/genética , Precursores de Proteínas/genética , Precursores de Proteínas/inmunología , Proteínas Protozoarias/genética , Proteínas Protozoarias/inmunologíaRESUMEN
Isolates of Plasmodium falciparum obtained from 12 children attending different health facilities in the Madang Province, Papua New Guinea were typed for allelic variants of merozoite surface protein-1 and merozoite surface protein-2. Blood was obtained just before treatment with either amodiaquine or chloroquine and at intervals following treatment. All patients examined were found to be infected with genetically different parasites. Nine of the children were found to have single infections while three had mixed infections. In all patients, parasites reappearing in the blood following treatment had the same genotype as parasites in the primary infection. These results indicate that parasites reappearing in the blood following treatment were the result of true recrudescence and not new infections.
Asunto(s)
Antígenos de Protozoos , Malaria Falciparum/parasitología , Plasmodium falciparum/efectos de los fármacos , Alelos , Animales , Niño , Preescolar , Resistencia a Medicamentos/genética , Femenino , Frecuencia de los Genes , Variación Genética , Genotipo , Humanos , Masculino , Proteína 1 de Superficie de Merozoito , Plasmodium falciparum/clasificación , Plasmodium falciparum/genética , Precursores de Proteínas/genética , Proteínas Protozoarias/genética , RecurrenciaRESUMEN
A prospective community study in a highly malaria endemic area of Papua New Guinea found that infection with multiple Plasmodium falciparum genotypes was an indicator of lowered risk of subsequent clinical attack. The results suggest that concurrent or very recent infections provide protection from superinfecting parasites. The finding of an association between reduced risk of clinical malaria and infection with parasites of merozoite surface protein 1 (MSP-1) type RO33 or MSP-2 type 3D7 further suggests that the concomitant immunity is, at least in part, a consequence of a response to these major merozoite surface proteins.
Asunto(s)
Enfermedades Endémicas , Malaria Falciparum/epidemiología , Plasmodium falciparum/clasificación , Adolescente , Distribución por Edad , Animales , Niño , Preescolar , Estudios de Cohortes , Estudios Transversales , Genotipo , Humanos , Lactante , Malaria Falciparum/parasitología , Morbilidad , Papúa Nueva Guinea/epidemiología , Plasmodium falciparum/genética , Reacción en Cadena de la Polimerasa , Prevalencia , Estudios ProspectivosRESUMEN
A prospective longitudinal study to examine the relationship between cellular immune responses to the synthetic malarial peptide SPf66 and malaria infection and morbidity was carried out in 187 children aged 0.5-15 years in the Wosera area of Papua New Guinea. Cellular responses were assessed by proliferation and stimulation of cytokines representing the Th1 and Th2 cell subsets (interferon gamma [IFN gamma] and interleukin-4 [IL-4]. Most children (66%) did not respond to SPf66 by any measure. Among the responders, the highest response was obtained for IL-4 (19%) followed by IFN gamma (10%), and the least for proliferation (5%). Analyses of the relation of T cell response to malaria infection showed that the IFN gamma response to SPf66 was positively correlated with parasite density (r = 0.27, P = 0.001). There was no association between the cellular response to SPf66 and concurrent or subsequent malaria morbidity, whichever clinical definition was used. Thus none of these cellular immune responses predicted efficacy of SPf66 in this highly endemic area.
Asunto(s)
Enfermedades Endémicas , Vacunas contra la Malaria/inmunología , Malaria Falciparum/inmunología , Vacunas Sintéticas/inmunología , Adolescente , Niño , Preescolar , Estudios de Cohortes , Fiebre/inmunología , Humanos , Inmunidad Celular/inmunología , Lactante , Interferón gamma/sangre , Interleucina-4/sangre , Estudios Longitudinales , Papúa Nueva Guinea , Parasitemia/inmunología , Estudios ProspectivosRESUMEN
Autoimmune disease is generally rare in tropical rural populations. Plasma concentrations of nitrite plus nitrate (reactive nitrogen intermediates), reflecting high nitric-oxide production somewhere in the body, can be high in patients who have cerebral malaria, but even higher in symptom-free parasitised individuals, who are termed malaria-tolerant. We propose that the nitric oxide causing high serum levels of reactive nitrogen intermediates in malaria-tolerant individuals is generated in macrophages during the establishment and maintenance of malarial tolerance, and makes autoimmune disease rare in many tropical rural populations by minimising proliferation of autoreactive T cells. Conversely, innately low levels of nitric-oxide generation in these populations, selected by malarial disease in tropical areas, could rationalise their high frequency of autoimmune disease and hypertension when living in western societies.
Asunto(s)
Enfermedades Autoinmunes/epidemiología , Tolerancia Inmunológica , Malaria/inmunología , Óxido Nítrico/metabolismo , África/epidemiología , Enfermedades Autoinmunes/inmunología , Humanos , Terapia de Inmunosupresión , Macrófagos/inmunología , Macrófagos/metabolismo , Malaria/parasitología , Malaria Cerebral/metabolismo , Malaria Cerebral/parasitología , Nitratos/sangre , Óxido Nítrico/fisiología , Nitritos/sangre , Linfocitos T/inmunología , Clima TropicalRESUMEN
In this study, we present an analysis of the Plasmodium vivax MSP-1 polymorphic region 5 and identify a new recombinant gene element. In clinical isolates from Papua New Guinea (PNG), the P. vivax MSP-1 gene type was characterized by restriction fragment length polymorphisms and by Southern blot oligonucleotide hybridizations using probes to type-specific sequences. There were three pairs of dimorphic gene elements in the MSP-1 polymorphic region 5; four of the eight potential different combinations of sequence elements for this region have been identified. The center gene segment was the most polymorphic, especially for the glutamine (Q) repeat element with virtually every gene containing a different length of Q repeats, a finding consistent with database sequence information. The frequencies of all of the polymorphic MSP-1 gene elements were approximately equal except for the first segment, which was biased 10:1 for the Type II (Sal-1 type) versus Type I (Belem type) gene segment. In fact, only one combination (I/Q/S) of the genetic elements containing the type I gene segment for polymorphic region 5 was identified, a finding consistent with sequences reported to gene data banks. Considering only the multiplicity of MSP-1 gene types, 38% of the patients were identified as having multiple infections; when correlated with the circumsporozoite protein and the Duffy antigen binding protein gene types, the multiple infection rate increased to 65% of 23 isolates characterized. Increased age was the only clinical parameter that positively correlated with multiclonal infections and there was no other apparent bias or linkage of gene types among the three loci. These data identify multiple clonal populations of P. vivax in the PNG population and potentially a high rate of concurrent infections in clinical cases. The extreme polymorphism of the MSP-1 polymorphic region 5 suggests that frequent recombination occurs within this gene. The bias in frequency for one recombinant gene motif indicates that intrinsic host or parasite factors may engender increased frequency of one genetic element over another. Failure to identify this type of discrete clonal marker as well as reliance on a single marker can mask the true multiclonal nature of an infection and lead to underestimation of the multiplicity of infection.
Asunto(s)
Frecuencia de los Genes , Malaria Vivax/parasitología , Plasmodium vivax/genética , Precursores de Proteínas/genética , Proteínas Protozoarias/genética , Secuencia de Aminoácidos , Animales , Antígenos de Protozoos/química , Antígenos de Protozoos/genética , Antígenos de Superficie/química , Antígenos de Superficie/genética , Secuencia de Bases , Southern Blotting , Secuencia Conservada , Cartilla de ADN/química , Humanos , Malaria Vivax/epidemiología , Proteína 1 de Superficie de Merozoito , Datos de Secuencia Molecular , Papúa Nueva Guinea/epidemiología , Plasmodium vivax/química , Plasmodium vivax/inmunología , Reacción en Cadena de la Polimerasa , Polimorfismo de Longitud del Fragmento de Restricción , Precursores de Proteínas/química , Proteínas Protozoarias/química , Recombinación Genética , Secuencias Repetitivas de Ácidos NucleicosRESUMEN
We investigated the prevalence and magnitude of naturally acquired humoral immune response to the major merozoite surface protein (MSP-1) in a malaria-endemic population in Papua New Guinea. A prospective longitudinal study in 0.5-15-year-old children was conducted for one year to examine the relationship between acquired immune response to MSP-1 and subsequent susceptibility to clinical disease. The prevalence and concentration of antibodies to both N-(195A) and C-terminal (BVp42) regions of MSP-1 as well as to the parasite-derived MSP-1 increased with age, with the highest prevalence and concentration of antibodies being detected for the parasite-derived MSP-1 molecule and the C-terminal region of MSP-1. As malaria morbidity decreases with age, a significant negative correlation was observed between antibody levels to both 195A and BVp42 and the incidence rate of clinical malaria. When age and past exposure were corrected for, only antibody concentrations against BVp42 and to a lesser extent parasite-derived MSP-1 were significantly associated with protection from clinical malaria and severe parasitemia. The reduction in the incidence rate of clinical malaria observed in individuals with high antibody concentration to MSP-1 may be due to antibodies directed against epitopes within the C-terminal region of MSP-1.
Asunto(s)
Anticuerpos Antiprotozoarios/sangre , Antígenos de Protozoos/inmunología , Malaria Falciparum/inmunología , Malaria Falciparum/prevención & control , Plasmodium falciparum/inmunología , Precursores de Proteínas/inmunología , Proteínas Protozoarias/inmunología , Adolescente , Factores de Edad , Animales , Formación de Anticuerpos , Niño , Preescolar , Humanos , Inmunidad Innata , Lactante , Estudios Longitudinales , Malaria Falciparum/epidemiología , Malaria Falciparum/parasitología , Proteína 1 de Superficie de Merozoito , Papúa Nueva Guinea/epidemiología , Estudios ProspectivosRESUMEN
Serum levels of reactive nitrogen intermediates (RNI; nitrate plus nitrite) were measured in 92 patients with cerebral malaria in the Madang Province of Papua New Guinea. RNI levels were compared to disease severity and clinical outcome, and correlated with both the depth of coma on admission and its duration. Median levels were higher among children with deeper coma than among those with lighter coma (35.6 microM vs. 16.7 microM; P = 0.008) and also among children with longer duration of coma (72 h; 59.3 microM vs. 19.3 microM; P = 0.004). RNI levels also correlated with clinical outcome, fatal cases having significantly higher RNI levels than survivors (41.2 microM vs. 18.5 microM; P = 0.014). Thus, high RNI levels are associated with indices of disease severity and may predict outcome in children with cerebral malaria. These data are consistent with the hypothesis that nitric oxide is involved in the pathogenesis of coma in human cerebral malaria.
Asunto(s)
Coma/sangre , Malaria Cerebral/sangre , Nitratos/sangre , Nitritos/sangre , Niño , Preescolar , Coma/etiología , Femenino , Humanos , Hipoglucemia/complicaciones , Lactante , Malaria Cerebral/complicaciones , Masculino , Papúa Nueva Guinea , Parasitemia/sangre , Índice de Severidad de la Enfermedad , Resultado del TratamientoRESUMEN
The in vivo response of Plasmodium falciparum parasites to amodiaquine or chloroquine was assessed in children with symptomatic malaria attending different health facilities in the Madang area. Among the 27 subjects who were completely followed up, 4 (15%) were infected with parasites fully susceptible and 23 (85%) with parasites exhibiting some degree of resistance. Out of the latter group, 52% were of RI level, 26% RII and 22% RIII. 14 subjects out of 42 (33%) failed to clear their parasitaemia by day 7 and 92 out of 134 (69%) had persistent or recrudescent parasitaemia at day 21. The level of in vivo resistance was similar for amodiaquine and chloroquine. 86% of the isolates tested in vitro showed resistance to amodiaquine, 86% to chloroquine and 7% to quinine. In ten years the prevalence of resistant isolates in vivo has increased from 47% to 85%. Of more concern is the shift from RI level of resistance to RII and RIII: the proportion of resistant strains that were RI dropped from 90% to 52% over the ten-year period. To determine if the standard antimalarial regimens are still appropriate, there is a need not only to assess the level of parasite resistance but also the prevalence of treatment failure in different parts of Papua New Guinea.
PIP: The in vivo response of Plasmodium falciparum parasites to amodiaquine and chloroquine was assessed in children 1-9 years of age with symptomatic malaria recruited from health centers in Papua New Guinea's Madang area. Among the 27 children who were completely followed up, 4 (15%) were infected with fully susceptible parasites; in the remaining 23 cases (85%), there was some degree of resistance. 52% of parasites in the latter group were RI level, 26% RII, and 22% RIII. There was no correlation between level of resistance and age. 14 out of 42 children (33%) failed to clear their parasitemia by day 7 and 92 out of 134 (69%) had persistent or recrudescent parasitemia at day 21. Both amodiaquine and chloroquine had similar levels of in vivo resistance. 86% of isolates tested in vitro showed resistance to amodiaquine, 86% to chloroquine, and 7% to quinine. In 10 years, the prevalence of resistant isolates in vivo has increased from 47% to 85%. Of particular concern is the finding that the proportion of resistant strains that were RI dropped from 90% to 52% over this decade. The increase of resistance is attributed to indiscriminate use of 4-aminoquinolines in all cases of fever. Needed, to assess whether standard antimalarial regimens are still appropriate, is a review of treatment failure in different parts of Papua New Guinea.
Asunto(s)
Amodiaquina/uso terapéutico , Antimaláricos/uso terapéutico , Cloroquina/uso terapéutico , Malaria Falciparum/tratamiento farmacológico , Plasmodium falciparum/efectos de los fármacos , Quinina/uso terapéutico , Enfermedad Aguda , Animales , Estudios de Casos y Controles , Niño , Preescolar , Resistencia a Medicamentos , Femenino , Estudios de Seguimiento , Humanos , Lactante , Malaria Cerebral/tratamiento farmacológico , Masculino , Papúa Nueva Guinea , Parasitemia/tratamiento farmacológico , Prevalencia , Recurrencia , Insuficiencia del TratamientoRESUMEN
People living in areas endemic for Plasmodium falciparum develop humoral responses which may contribute to protection against clinical disease but the specificity of such protective antibody responses remains to be defined. Antibodies disrupting erythrocyte rosettes have been associated with protection against cerebral malaria, and antibodies agglutinating infected erythrocytes with reduced episodes of clinical disease. We have studied the capacity of serum from Papua New Guinean adults and children with a spectrum of malaria exposure, including children and adults at the time of clinical disease, to disrupt erythrocyte rosettes and cause agglutination of infected erythrocytes. Using a single parasite isolate, almost all sera from adults from highly endemic areas agglutinated infected erythrocytes, and the majority disrupted rosettes, in some cases at greater titres than hitherto described. There was a correlation between rosette disruption and agglutination in highly exposed adults. Rosette disrupting antibodies were equally frequent in children with cerebral and uncomplicated malaria. Antibodies causing rosette disruption were frequent only in adults with a long history of malarial exposure. Rosette disrupting antibodies do not appear to protect Papua New Guinean children or adults against cerebral malaria.