Effect of hydroxyethyl starch (HES) in reducing parasite load in experimental visceral leishmaniasis

Leishmania donovani primarily infects phagocytic cells of the reticuloendothelial system. Hydroxyethyl starch (HES) has been shown to concentrate transiently in these organs. The effect of HES administration was assessed upon infection and also upon vaccination against this parasite. Animals received HES intraperitoneally thrice weekly, either alone (HES) or with a subcutaneous immunization protocol utilizing aluminum hydroxide and killed parasites (ALP-HES). Controls were untreated (NT) or received only the vaccination protocol (ALP). Results showed that animals treated with HES alone exhibited significantly fewer parasites as compared to untreated animals (p less than 0.001). The ALP animals also were protected against infection but demonstrated greater parasite burdens than HES animals. Immunized animals which also received HES demonstrated infection levels similar to those treated with HES alone, thus negating any synergistic effect. The reason for increased protection against L. donovani infection in animals treated with HES is not clear, but it may result from a transient increase in host resistance.