There is a need for new, effective, and less toxic treatments for leishmaniasis, an infectious disease caused by Leishmania protozoa and is a major cause of suffering and morbidity in much of the developing world. Imiquimod, an immune-response modifier, has recently been approved by the Food and Drug Administration for the treatment of genital warts caused by human papillomaviruses. Imiquimod initiates a local immune reaction, including the stimulation of macrophages, resulting in resolution of human papillomavirus infection and regression of the viral lesion. Since imiquimod activates a number of immune cells, including macrophages, which are the only host cells of Leishmania species, an investigation was done to determine whether it induces leishmanicidal properties in infected macrophages in vitro and in vivo in a mouse model. Imiquimod and a related compound, S-28463, effectively stimulated leishmanicidal activity in macrophages; moreover, imiquimod stimulated signal transduction associated with inducing nitric oxide synthesis in macrophages.

Within the mammalian host, Leishmania donovani is an obligatory intracellular protozoan that resides and multiplies exclusively in the phagolysosomes of macrophages. The outcome of this infection is governed by the interaction between Leishmania and macrophage molecules that ultimately effect the expression of genes within both cells. To explore the effect of this intracellular infection on macrophage gene expression, a cDNA expression array analysis was performed to compare gene expression profiles in noninfected and L. donovani-infected macrophages. In this manner, it was possible to examine the effect of infection on the expression of several hundred well-characterized host cell genes in an unbiased manner. Interestingly, ∼40% of the genes whose expression was detected in macrophages were down-regulated during infection with L. donovani. However, several genes were also induced during the infection process, some of which could play a role in recruitment of additional macrophages to the site of infection. Taken together, the general suppression of gene expression in addition to the selective induction of key genes is likely to play an important role in allowing the parasite to survive and proliferate within its host macrophage cell.

Plasmodium vivax is now the predominant species causing malarial infection and disease in most non-African areas, but little is known about its transmission efficiency from human to mosquitoes. Because the majority of Plasmodium infections in endemic areas are low density and asymptomatic, it is important to evaluate how well these infections transmit. Using membrane feeding apparatus, we fed Anopheles dirus with blood samples from 94 individuals who had natural P. vivax infection with parasitemias spanning four orders of magnitude. We found that the mosquito infection rate is positively correlated with blood parasitemia and that infection begins to rise when parasitemia is >10 parasites/μl. Below this threshold, mosquito infection is rare and associated with very few oocysts. These findings provide useful information for assessing the human reservoir of transmission and for establishing diagnostic sensitivity required to identify individuals who are most infective to mosquitoes.

We used the loop-mediated isothermal amplification (LAMP) method developed by our group for malaria diagnosis with genus-specific and species-specific primers for the four human malaria parasites at a field clinic in comparison with standard microscopy. Among 110 blood samples collected from the malaria clinic in Thailand, LAMP detected 59 of 60 samples positive by microscopy (sensitivity = 98.3%) and none of the 50 microscopy-negative samples (specificity = 100%). Negative predictive value (NPV) and positive predictive value (PPV) of LAMP were 98% and 100%, respectively. These results indicate that LAMP is an effective tool for malaria diagnosis at a field clinic in a field setting.

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