Mycoplasma suis and Mycoplasma parvum (formerly Eperythrozoon spp.) are uncultivated, wall-less bacteria of swine that parasitize the surface of erythrocytes. The presence of two distinct species in pigs was established by cross-inoculation studies. Furthermore, they differ in size (M. suis varies from 1 µm to 2.5 µm whereas M. parvum is smaller at 0.5 µm) and degree of parasitemia (with M. suis, many parasites are often observed, whereas with M. parvum, the parasitemia is low).

M. suis can produce a clinical hemolytic anemia in young pigs under natural conditions, but infections with M. parvum do not cause overt disease. The clinical syndrome associated with M. suis infection has been called the ictero-anemia of pigs. The disease may appear as severe acute anemia with fever, icterus, anorexia, depression and muscle weakness. Parasitemia is high during the early stage of clinical disease but disappears rapidly as the reticulocyte count rises. Subclinical disease may compromise breeding performance and weight gain. Transmission is by the common hog louse. The disease is diagnosed by identification of the parasite in blood smears, serology (IHA and ELISA) and PCR-based techniques.