Cell Biology of Parasitism

Nancy Guillen

In 1995, over 52 million death around the world, 17 millions correspond to infectious diseases, mainly in the developping countries. The growing impact of infectious diseases due to parasites prompts us to study the relationship between parasites and human cells. We are interested in intestinal infections because the intestinal tract is continually challenged by microbial pathogens. Dhiarrea lead to 4% death and 5% handicaps over the world. Host-pathogen cross-talk in the intestine constitutes an attractive model to study microbial pathogenicity and is of major clinical interest since these infections affect the greater part of human population,. The hematophage amoeba, Entamoeba histolytica is the etiologic agent of one of the pathologies: amoebiasis, an infectious disease accounting for 50 million clinical cases each year and responsible for 100 000 deaths. Usually, intestine colonisation by E. histolytica is asymptomatic but in certain unknown conditions, the equilibrium of the host-parasite interaction is impaired. The parasite invades the colonic mucosa causing ulcerations and amebic colitis, and may from there pass via the blood stream to the liver where it can cause life-threatening hepatic abscesses. Humans are the unique reservoir of this parasite that multiplies and differentiates in the colon leading to cyst formation. The cysts are excreted in the faeces; they are the resistant form of the parasite, which allows environmental survival. A new contamination is thus due to faecal-oral transmission. Water is the principal route of contamination, by its direct ingestion without decontamination or by the ingestion of contaminated uncooked vegetables. Amoebiasis incidence is high in developing countries due to insufficient sanitary conditions. Several European groups require development of diagnostics and therapies against amoebiasis. These include in particular travelers, military personnel and members of governmental and non-governmental humanitarian organizations. Also, in European countries in situations where hygiene is sub-optimal (mental health institutions and prisons) cases of amoebiasis have been known to occur, the incidence is low but growing. For instance, a recent emergence in the Georgian Republic underlines the vulnerability of a whole community faced with this infection.

The infectious agent is the cyst (attached micrograph) widely spread due to the contamination of food and water.

The vegetative agent is the trophozoite (attached micrograph), which lives, multiplies and differentiates into a cyst in the human colon.

The pathogenic agent is the ‘activated’ trophozoite, which migrates, invades the intestine, kills human cells and phagocytoses them.
The disease, amoebiasis, has two clinical manifestations: intestinal colitis and the formation of liver abscesses.

For more information : The Entamoeba Homepage