RESUMEN
A parasitological, clinical, serological and molecular cross-sectional study carried out in a highly endemic malaria area of Rio Negro in the Amazon State, Brazil, revealed a high prevalence of asymptomatic Plasmodium vivax infection. A total of 109 persons from 25 families were studied in five villages. Ninety-nine inhabitants (90.8%) had at least one previous episode of malaria. Serology showed 85.7% and 46.9% of positivity when P. falciparum antigens and P. vivax MSP-1, respectively, were used. Twenty blood samples were PCR positive for P. vivax (20.4%) and no P. falciparum infection was evidenced by this technique. No individual presenting positive PCR reaction had clinical malaria during the survey neither in the six months before nor after, confirming that they were cases of asymptomatic infection. Only one 12 year old girl presented a positive thick blood smear for P. vivax. This is the first description of asymptomatic Plasmodium infection in this area studied.
Asunto(s)
Malaria Vivax/epidemiología , Plasmodium vivax , Adolescente , Adulto , Anciano , Animales , Anticuerpos Antiprotozoarios/sangre , Brasil/epidemiología , Niño , Preescolar , Estudios Transversales , ADN Protozoario/análisis , Ensayo de Inmunoadsorción Enzimática , Femenino , Humanos , Malaria Vivax/diagnóstico , Masculino , Persona de Mediana Edad , Plasmodium vivax/genética , Plasmodium vivax/inmunología , Reacción en Cadena de la Polimerasa , PrevalenciaRESUMEN
A parasitological, clinical, serological and molecular cross-sectional study carried out in a highly endemic malaria area of Rio Negro in the Amazon State, Brazil, revealed a high prevalence of asymptomatic Plasmodium vivax infection. A total of 109 persons from 25 families were studied in five villages. Ninety-nine inhabitants (90.8 percent) had at least one previous episode of malaria. Serology showed 85.7 percent and 46.9 percent of positivity when P. falciparum antigens and P. vivax MSP-1, respectively, were used. Twenty blood samples were PCR positive for P. vivax (20.4 percent) and no P. falciparum infection was evidenced by this technique. No individual presenting positive PCR reaction had clinical malaria during the survey neither in the six months before nor after, confirming that they were cases of asymptomatic infection. Only one 12 year old girl presented a positive thick blood smear for P. vivax. This is the first description of asymptomatic Plasmodium infection in this area studied.
Um estudo seccional parasitológico, clínico, sorológico e molecular, realizado em uma área altamente endêmica para malária, no Rio Negro, Estado do Amazonas, revela alta prevalência de infecção assintomática por Plasmodium vivax. Um total de 109 pessoas de 25 famílias residentes em cinco comunidades do Rio Padauiri, afluente do Rio Negro, foram estudadas. Noventa por cento dos habitantes (90,8 por cento) tinham tido pelo menos um episodio prévio de malária. A sorologia mostrou 85,7 por cento e 46,9 por cento de positividade quando antígenos de P. falciparum e P. vivax MSP-1, foram respectivamente usados. Vinte amostras de sangue submetidas ao PCR foram positivas para P. vivax (20,4 por cento), entretanto, nenhuma foi positiva para o P. falciparum por esta técnica. Nenhum paciente com PCR positivo durante o inquérito e seis meses antes ou depois teve manifestações clínicas de malária, portanto, podemos afirmar que eram assintomáticos. Somente uma criança de 12 anos de idade teve gota espessa positiva para P. vivax. Esta é a primeira descrição de infecção assintomática por Plasmodium na área estudada.
Asunto(s)
Humanos , Animales , Masculino , Femenino , Preescolar , Niño , Adolescente , Adulto , Persona de Mediana Edad , Malaria Vivax/epidemiología , Plasmodium vivax , Anticuerpos Antiprotozoarios/sangre , Brasil/epidemiología , Estudios Transversales , ADN Protozoario/análisis , Ensayo de Inmunoadsorción Enzimática , Malaria Vivax/diagnóstico , Reacción en Cadena de la Polimerasa , Prevalencia , Plasmodium vivax/genética , Plasmodium vivax/inmunologíaRESUMEN
The recent evolution of Plasmodium falciparum is at odds with the extensive polymorphism found in most genes coding for antigens. Here, we examined the patterns and putative mechanisms of sequence diversification in the merozoite surface protein-2 (MSP-2), a major malarial repetitive surface antigen. We compared the msp-2 gene sequences from closely related clones derived from sympatric parasite isolates from Brazilian Amazonia and used microsatellite typing to examine, in these same clones, the haplotype background of chromosome 2, where msp-2 is located. We found examples of msp-2 sequence rearrangements putatively created by nonreciprocal recombinational events, such as replication slippage and gene conversion, while maintaining the chromosome haplotype. We conclude that these nonreciprocal recombination events may represent a major source of antigenic diversity in MSP-2 in P. falciparum populations with low rates of classical meiotic recombination.
Asunto(s)
Antígenos de Protozoos/genética , ADN Protozoario/genética , Vacunas contra la Malaria , Plasmodium falciparum/genética , Plasmodium falciparum/aislamiento & purificación , Proteínas Protozoarias/genética , Alelos , Animales , Antígenos de Protozoos/inmunología , Secuencia de Bases , Brasil , Mapeo Cromosómico , Cromosomas , Simulación por Computador , ADN Protozoario/química , Evolución Molecular , Conversión Génica , Genes de Insecto , Marcadores Genéticos , Haplotipos , Desequilibrio de Ligamiento , Cadenas de Markov , Repeticiones de Microsatélite , Datos de Secuencia Molecular , Plasmodium falciparum/inmunología , Proteínas Protozoarias/inmunología , Análisis de Secuencia de ADNRESUMEN
Four variants of merozoite surface protein 2 (MSP-2) of Plasmodium falciparum were used in serology to examine whether changes in repeat units affect its recognition by antibodies during infection with parasites of known MSP-2 types. The results indicate that variation in MSP-2 repeats may represent a mechanism for parasite immune evasion.