BackgroundUp to 40% of the world's population is at risk for Plasmodium vivax malaria, a disease that imposes a major public health and economic burden on endemic countries. Because P. vivax produces latent liver forms, eradication of P. vivax malaria is more challenging than it is for P. falciparum. Genetic analysis of P. vivax is exceptionally difficult due to limitations of in vitro culture. To overcome the barriers to traditional molecular biology in P. vivax, we examined parasite transcriptional changes in samples from infected patients and mosquitoes in order to characterize gene function, define regulatory sequences and reveal new potential vaccine candidate genes.Principal FindingsWe observed dramatic changes in transcript levels for various genes at different lifecycle stages, indicating that development is partially regulated through modulation of mRNA levels. Our data show that genes involved in common biological processes or molecular machinery are co-expressed. We identified DNA sequence motifs upstream of co-expressed genes that are conserved across Plasmodium species that are likely binding sites of proteins that regulate stage-specific transcription. Despite their capacity to form hypnozoites we found that P. vivax sporozoites show stage-specific expression of the same genes needed for hepatocyte invasion and liver stage development in other Plasmodium species. We show that many of the predicted exported proteins and members of multigene families show highly coordinated transcription as well.ConclusionsWe conclude that high-quality gene expression data can be readily obtained directly from patient samples and that many of the same uncharacterized genes that are upregulated in different P. vivax lifecycle stages are also upregulated in similar stages in other Plasmodium species. We also provide numerous examples of how systems biology is a powerful method for determining the likely function of genes in pathogens that are neglected due to experimental intractability.

Plasmodium vivax causes 25-40% of malaria cases worldwide, yet research on this human malaria parasite has been neglected. Nevertheless, the recent publication of the P. vivax reference genome now allows genomics and systems biology approaches to be applied to this pathogen. We show here that whole-genome analysis of the parasite can be achieved directly from ex vivo-isolated parasites, without the need for in vitro propagation. A single isolate of P. vivax obtained from a febrile patient with clinical malaria from Peru was subjected to whole-genome sequencing (30× coverage). This analysis revealed over 18,261 single-nucleotide polymorphisms (SNPs), 6,257 of which were further validated using a tiling microarray. Within core chromosomal genes we find that one SNP per every 985 bases of coding sequence distinguishes this recent Peruvian isolate, designated IQ07, from the reference Salvador I strain obtained in 1972. This full-genome sequence of an uncultured P. vivax isolate shows that the same regions with low numbers of aligned sequencing reads are also highly variable by genomic microarray analysis. Finally, we show that the genes containing the largest ratio of nonsynonymous-to-synonymous SNPs include two AP2 transcription factors and the P. vivax multidrug resistance-associated protein (PvMRP1), an ABC transporter shown to be associated with quinoline and antifolate tolerance in Plasmodium falciparum. This analysis provides a data set for comparative analysis with important potential for identifying markers for global parasite diversity and drug resistance mapping studies.

Macrophages play a central role in mycobacterial pathogenesis. Recent work has highlighted the importance of diverse macrophage types and phenotypes that depend on local environment and developmental origins. In this review, we highlight how distinct macrophage phenotypes may influence disease progression in tuberculosis. In addition, we draw on work investigating specialized macrophage populations important in cancer biology and atherosclerosis in order to suggest new areas of investigation relevant to mycobacterial pathogenesis. Understanding the mechanisms controlling the repertoire of macrophage phenotypes and behaviors during infection may provide opportunities for novel control of disease through modulation of macrophage form and function.

Risk, severity, and outcome of infection depend on the interplay of pathogen virulence and host susceptibility. Systematic identification of genetic susceptibility to infection is being undertaken through genome-wide association studies, but how to expeditiously move from genetic differences to functional mechanisms is unclear. Here, we use genetic association of molecular, cellular, and human disease traits and experimental validation to demonstrate that genetic variation affects expression of VAC14, a phosphoinositide-regulating protein, to influence susceptibility to serovar Typhi ( Typhi) infection. Decreased VAC14 expression increased plasma membrane cholesterol, facilitating docking and invasion. This increased susceptibility at the cellular level manifests as increased susceptibility to typhoid fever in a Vietnamese population. Furthermore, treating zebrafish with a cholesterol-lowering agent, ezetimibe, reduced susceptibility to Typhi. Thus, coupling multiple genetic association studies with mechanistic dissection revealed how VAC14 regulates invasion and typhoid fever susceptibility and may open doors to new prophylactic/therapeutic approaches.

Opportunities for improved disease reporting are identified by describing physicians' reporting knowledge and practices as well as reporting knowledge and specimen referral patterns among clinical laboratories in the state of Georgia. In 2005, a sample of physicians(n = 177) and all Georgia clinical laboratories (n = 139) were surveyed about reporting knowledge and practices. Knowledge was greater among physicians who received their medical degree before 1980 (P = .04), accessed e-mail (P< .01), used the Internet to obtain public health information (P < .01), and reported frequently (P= .06). Increased knowledge was not associated with training in reporting (P = .14). Physicians were often unaware of reporting procedures and mechanisms and often did not report because they believed others would report (52%). Laboratory representatives (56%) more often received training on disease reporting than physicians (32%). All laboratories sent some specimens for diagnostic testing at reference laboratories and 35% sent the specimens outside of Georgia. Physicians'characteristics may affect reporting knowledge independent of training on disease reporting, and increased knowledge is associated with increased reporting. Investigation of physician characteristics that contribute to improved reporting, such as an active engagement with public health, could help to guide changes to reporting-related training and technology. Reporting by other health care providers and physicians' perceptions that others will report both indicate that studies of all reporting stakeholders and clear delineation of reporting responsibilities are needed. Extensive specimen referral by laboratories suggests the need for coordination of reporting regulations and responsibilities beyond local boundaries.