The ‘neglected enteric protists’: Cryptosporidium, Giardia and Entamoeba

The title of my presentation is The 'Neglected Enteric Protists': Cryptosporidium, Giardia, and Entamoeba. I am Prof. Sitara Ajjampur based at The Wellcome Trust Research Laboratory at Christian Medical College in Southern India where we have been carrying out various studies on enteric infections for several decades in endemic populations primarily young children with early childhood diarrhea. Today I will be discussing the three enteric parasitic infections that cause a very high burden of disease globally. But more so, in low-resource settings and in very young children in these settings who do not have access to safe water and sanitation.

Cryptosporidium is an apicomplexan protist, meaning that it belongs to the same family as malaria and toxoplasma. Numerous species with host specificity have been described and among these, 20 of 44 species have been shown to infect humans. Among these different species, Cryptosporidium parvum and Cryptosporidium hominis are the two major species responsible for over 90% of human infections. Zoonotic species can also cause infections and have been reported from several different countries. The distribution of zoonotic species varies by setting. The commonly reported species, which include C.meleagridis, usually from birds, C.felis, which is from cats, C.canis, which is from dogs, and C.muris, which is from rodents, are usually acquired from domestic pets or livestock. Cryptosporidium is transmitted in multiple ways and the infectious stage is a sporulated oocyst. The multiple modes of transmission include contaminated food and water, from person-to-person, and as well as mentioned above, a zoonotic mode. Once swallowed, these sporozoites released from the oocyst attach and invade the intestinal epithelium, usually the terminal ileum, within minutes, and reside in a parasitophorous vacuole that is intracellular but extracytoplasmic. Infection leads to disruption of the brush border, crypt hypoplasia, and inflammation. Recent research has led to an updated understanding, both of the immunology and the life cycle of this parasite that will be described in more detail on the talk on cryptosporidiosis. If we can look at the image here, this is from a child with diarrhea from the community. Here, you can make out oval to spherical acid fast oocysts that are four to six microns in size.