C. canis, C. felis, C. meleagridis, and C. muris can also cause disease in humans. Cryptosporidium is capable of completing its life cycle within a single host, resulting in microbial cyst stages that are excreted in feces and are capable of transmission to a new host via the fecal-oral route. Other vectors of disease transmission also exist.The pattern of Cryptosporidium life cycle fits well with that of other intestinal homogeneous coccidian genera of the suborder Eimeriina: macro- and microgamonts develop independently; a microgamont gives rise to numerous male gametes; and oocysts serving for parasites spreading in the environment. Electron microscopic studies made from the 1970s have shown the intracellular, although extracytoplasmic localization of Cryptosporidium species.These species possess a number of unusual features:
an endogenous phase of development in microvilli of epithelial surfaces
two morphofunctional types of oocysts
the smallest number of sporozoites per oocyst
a multi-membraneous "feeder" organelleDNA studies suggest a relationship with the gregarines rather than the coccidia. The taxonomic position of this group has not yet been finally agreed upon. The genome of Cryptosporidium parvum was sequenced in 2004 and was found to be unusual amongst Eukaryotes in that the mitochondria seem not to contain DNA. A closely related species, C. hominis, also has its genome sequence available. CryptoDB.org is a NIH-funded database that provides access to the Cryptosporidium genomics data sets. Transfer
Infection is through contaminated material such as earth, water, uncooked or cross-contaminated food that has been in contact with the feces of an infected individual or animal.
The host immune response involves cytotoxic (CD8-positive) T cells against infected B lymphocytes, resulting in enlarged, atypical lymphocytes (Downey cells).When the infection is acute (recent onset, instead of chronic), heterophile antibodies are produced.Cytomegalovirus, adenovirus and Toxoplasma gondii (toxoplasmosis) infections can cause symptoms similar to infectious mononucleosis, but a heterophile antibody test will test negative and differentiate those infections from infectious mononucleosis.Mononucleosis is sometimes accompanied by secondary cold agglutinin disease, an autoimmune disease in which abnormal circulating antibodies directed against red blood cells can lead to a form of autoimmune hemolytic anemia. The cold agglutinin detected is of anti-i specificity. Diagnosis
Diagnostic modalities for infectious mononucleosis include:

Persons age, with highest risk at 10 to 30 years. Medical history, such as close contact with other people with infectious mononucleosis, and the presence and time of onset of "mononucleosis-like symptoms" such as fever and sore throat. Physical examination, including palpation of any enlarged lymph nodes in the neck, or enlarged spleen. The heterophile antibody test is a screening test that gives results within a day, but has significantly less than full sensitivity (70–92%) in the first two weeks after clinical symptoms begin. Serological tests take longer time than the heterophile antibody test, but are more accurate. Physical examination
The presence of an enlarged spleen, and swollen posterior cervical, axillary, and inguinal lymph nodes are the most useful to suspect a diagnosis of infectious mononucleosis.