Targeting a Reticulocyte Binding Protein and Duffy Binding Protein to Inhibit Reticulocyte Invasion by Plasmodium vivax.

Plasmodium vivax merozoite invasion is restricted to Duffy positive reticulocytes. Merozoite interaction with the Duffy antigen is mediated by the P. vivax Duffy binding protein (PvDBP). The receptor-binding domain of PvDBP maps to an N-terminal cysteine-rich region referred to as region II (PvDBPII). In addition, a family of P. vivax reticulocyte binding proteins (PvRBPs) mediates interactions with reticulocyte receptors. The receptor binding domain of P. vivax reticulocyte binding protein 1a (PvRBP1a) maps to a 30 kD region (PvRBP1a30). Antibodies raised against recombinant PvRBP1a30 and PvDBPII recognize the native P. vivax antigens and inhibit their binding to host receptors. Rabbit IgG purified from sera raised against PvRBP1a30 and PvDBPII were tested individually and in combination for inhibition of reticulocyte invasion by P. vivax field isolates. While anti-PvDBPII rabbit IgG inhibits invasion, anti-PvRBP1a30 rabbit IgG does not show significant invasion inhibitory activity. Combining antibodies against PvDBPII and PvRBP1a30 also does not increase invasion inhibitory activity. These studies suggest that although PvRBP1a mediates reticulocyte invasion by P. vivax merozoites, it may not be useful to include PvRBP1a30 in a blood stage vaccine for P. vivax malaria. In contrast, these studies validate PvDBPII as a promising blood stage vaccine candidate for P. vivax malaria.

Infecciones maláricas en individuos asintomáticos en la población indígena Jivi, Amazonas, Venezuela / Asymptomatic malaria infection in the indigenous Jivi population, Amazonas state, Venezuela

Se evaluó la presencia de infecciones maláricas en individuos asintomáticos en la población Jivi de Puente Parhueña. El estudio fue de tipo prospectivo en tres momentos. El diagnóstico parasitológico se realizó mediante el examen convencional de gota gruesa y extendido (GGE) y la reacción en cadena de la polimerasa (PCR). El diagnóstico por microscopia indicó 2% (5/261) de láminas positivas en Abril, 1% (3/274) en Septiembre y 4% (5/135) en Diciembre. La PCR para Plasmodium spp., fue 46% (26/57) en abril, 49% (28/57) en Septiembre y 35% (20/57) en Diciembre. En los tres momentos predominó la presencia de P. vivax. La prueba de ELISA demostró 72% (41/57) seroreactivos en Abril, 53% (30/57) en Septiembre y 60% (34/57) en Diciembre. En Puente Parhueña habitan individuos con infecciones maláricas asintomáticos, con persistencia de anticuerpos antimalaricos, que probablemente representan un reservorio de gametocitos dentro de la comunidad.

The study was carried out to determine the present malaria infection in the asymptomatic Jivi people of Puente Parhueña. The study was prospective over three periods of time. The parasitological diagnoses were from thick and thin blood smears (GGE) and polymerase chain reaction (PCR). The antibody search was performed by ELISA. Microscopy of the slides detected the following positive results: 2% (2/261) April, 1% (3/274) September and 4% (5/135) December. Detection of Plasmodium by PCR was 46% (26/57) in April, 49% (28/57) in September y 35% (20/57) in December. Plasmodium vivax infected individuals predominated during these 3 times. Positives for ELISA were 72% (41/57) in April, 53% (30/57) September and 60% (34/57) December. The study demonstrated that people living in Puente Parhueña presented asymptomatic malaria infection with malaria antibodies persistence which likely represents a gametocyte potential reservoir for infection among the population.