Cryptosporidiosis - Pathogenesis

Pathogenesis

The oocysts are ovoid or spherical and measure 5 to 6 micrometers across. When in flotation preparations they appear highly refractile. The oocysts contains up to 4 sporozoites that are bow-shaped.

As few as 2 to 10 oocysts can initiate an infection. The parasite is located in the brush border of the epithelial cells of the small intestine. They are mainly located in the jejunum. When the sporozoites attach the epithelial cells’ membrane envelops them. Thus, they are “intracellular but extracytoplasmic”. The parasite can cause damage to the microvilli where it attaches. The infected human excretes the most oocysts during the first week. Oocysts can be excreted for weeks after the diarrhea subsides.

The immune system reduces the formation of Type 1 merozoites as well as the number of thin-walled oocysts. This helps prevent autoinfection. B cells do not help with the initial response or the fight to eliminate the parasite.