Cryptosporidium spp., although technically divided into C. parvum and C. hominis, is actually comprised of up to 20 different species, all of which can be found in humans and other animals. Humans can acquire the infection through direct contact with infected humans or other animals or through contaminated water or food. Cryptosporidium spp. are found throughout the world and in a variety of environments. The incidence of Cryptosporidium infections is highest in children under five, as well as the elderly in nursing homes. It is also common among immunocompromised patients and is sometimes a presenting symptom of individuals with HIV/AIDS.
Cryptosporidium spp. has the typical sporozoan life cycle, and they spend the majority of it in the epithelial cells of the gastrointestinal organs. The life cycle is shown below.
Immunocompetent individuals will have symptoms of diarrhea (sometimes watery and frothy) that can alternate with constipation, nausea, and low-grade fever. They will generally recover spontaneously. However, in immunocompromised patients, diarrhea can be chronic and life-threatening. HIV/AIDS patients' symptoms will worsen as their CD4 lymphocyte count decreases.
Microscopic diagnosis depends on finding oocysts in the stool, which is difficult using routine procedures and is not a recommended method. Concentration techniques will increase the yield of oocysts. It is much better to stain the smear with an acid-fast stain such as Ziehl-Neelson or Kinyoun (image to the right; oocysts are red and approximately 4–6 μm). Note the small size, only Microsporidia are smaller. A more sensitive method of detection is using an assay such as a direct fluorescent antibody procedure (DFA) or an immunoassay. Also, molecular methods are useful, and detection of Cryptosporidium is part of several commercial molecular-based assays.
