Colombian field isolates of Plasmodium falciparum were analyzed for genetic diversity. Fifty-three samples were collected as thick smears from patients living in Panguí, an isolated area with low migration. While the samples were being collected, Panguí was experiencing an epidemic outbreak of malaria. The samples were typified using nested polymerase chain reaction (PCR) amplification of block 2 of the merozoite surface protein 1 (MSP1) gene and nested PCR with mutation-specific primers for position 108 of the dihydrofolate reductase enzyme gene. The results for the circulating population of parasites in Panguí show low diversity-four allelic forms-using MSP1 as a marker, a fact that contrasts with data reported for certain Asian and African zones. A high percentage of mixed infections was observed, as was high complexity of the infection. No differential distributions were found for any allelic type.
Calcium is an important factor in the invasion of the erythrocyte by Plasmodium falciparum. We have proposed that the entrance of the cation into the erythrocyte might be a messenger that triggers a series of molecular events leading to invasion. Other authors have proposed that the site of action of the calcium is extracellular. We show herein that the invasion is inhibited by intracellular calcium chelators and that the inhibition depends on the intracellular concentration of the chelators and on the calcium concentration in the medium.
ResumenUno de los elementos indispensables para desarrollar estrategias terapéuticas contra la malaria es establecer los niveles y distribución geográfica de la resistencia de Plasmodium falciparum a medicamentos; desafortunadamente los métodos disponibles en la actualidad no son adecuados para hacer una búsqueda de la resistencia a nivel epidemiológico. En este trabajo se adecuó una prueba radiométrica"in vitro"para detectar resistencia de FI falciparum a varios medicamentos simultáneamente; este ensayo permite hacer una determinación cuantitativa de la resistencia, tiene corta duración comparado con la prueba "in vivo" y facilita el análisis de un gran número de muestras en corto tiempo. Aunque el ensayo no puede ser aplicado sobre muestras de pacientes que hayan tomado antimaláricos recientemente y es necesario que los aislamientos se desarrollen en condiciones de cultivo "in vitro", el desconocimiento de las bases moleculares de la resistencia a cloroquina, amodiaquina, mefloquina, quinina y halofantrina, lleva al uso de la prueba radiométrica ya que no requiere la identificación directa de un gen o de un producto génico.Palabras clave: Plasmodium falciparum, resistencia, pruebas in vitro, antimaláricos Modification of a Radiometric Microtest to detect Plasmodium falciparum Resistance to Several Drugs Summary The development of strategies to control malaria requires precise knowledge about the drug-resistant parasite levels and geographical distribution. Unfortunately currently available methods are not fully adequate for these parameters to be established. This paper describes the improvement of a radiometric micro-test to detect resistance to several drugs. This test is easy, rapid and permits analysis of numerous samples in a short time. A molecular assay is not currently available for the determination of resistance because the molecular mechanisms behind chloroquine, amodiaquine, mefloquine, quinine or halofantrine resistance remain obscure. Under these circumstances, we recommend the use of the modified microtest for them.
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