One million children die before their fifth birthday from diarrhea. The eukaryotic parasite Entamoeba histolytica is one of the top 10 causes of diarrhea in the developing world. The outcome of an E. histolytica infection is variable and can result in either asymptomatic carriage, immediate or latent disease. Our preliminary studies suggest that there is a link between parasite genetics and disease;we identified two single nucleotide polymorphisms (SNPs) infrequent in diarrheal isolates but common in strains that asymptomatically colonize children. Our hypothesis is that variation in the E. histolytica genome influences virulence and disease outcome. Innovation: The extensive genetic polymorphism found in trophozoites in clinical isolates, have made it difficult to identify the genetic changes that define the virulence potential of this parasite. The existence of a biorepository of E. histolytica positive stool samples (collected during a longitudinal study of enteric disease) and advances in high-throughput sequencing, make it now possible for us to study this parasite at a population level. Approach: An ongoing study of the enteric pathogens infecting children who live in the urban slum of Mirpur, Bangladesh, has collected E. histolytica positive stool samples. These were obtained from both asymptomatically colonizing ameba and those responsible for E. histolytica associated diarrhea. In this study we will first sequence the whole genome and transcriptome of cultured strains to identify common E. histolytica SNPs. We will then use the study samples to investigate whether an association exists between the virulent amebic strains and the parasite SNP genotype. Investigator: Dr. Gilchrist is an Assistant Professor of Research Division of Infectious Diseases and International Health. Her research has focused on using molecular methods to understand the biology and pathogenic phenotype of enteric parasites. She is co- author on the paper describing the sequenced E. histolytica genome, and for her studies on the gene regulation of E. histolytica motility she developed the first E. histolytica Affymetrix microarrays. Environment: Dr. Gilchrist's lab is in a uniquely supportive environment, as there is substantial institutional expertise, and support for work on enteric diseases of global significance at the Division of Infectious Diseases at the University of Virginia. Her collaborator include Dr. R. Haque at the International Centre for Diarrhoeal Diseases Research, Dhaka, Bangladesh (ICDDR,B) and Dr. W. Petri at UVA who are co-PI's of an ongoing longitudinal study of the enteric pathogens infecting children in Dhaka, Bangladesh. Dr. E. Caler, leader of the NIAID E. histolytica genomic and sequencing project at JCVI, Maryland will collaborate on the sequencing of ameba strains. Dr. Gilchrist's other colleagues at UVA include Dr. I. K. M. Ali, who developed the original E. histolytica genotyping system, and Dr. E. Houpt, an expert in the development of enteric pathogen diagnostics.
Severe diarrhea kills an estimated 1.3 million children before their 5th birthday. Amebic dysentery and liver abscesses, caused by Entamoeba histolytica are considered by the WHO to be a major health problem in the developing world. Disease however occurs in only a minority of infections. In this work we propose to use a multilocus sequence typing system to identify the E. histolytica genetic changes that result in a predisposition to cause disease.