Cryptosporidiosis. Coloured scanning electron micrograph (SEM) of a small intestine infected with Cryptosporidium parvum (round green dots). This is a parasitic protozoan that is usually transmitted to humans from farm animals through milk and water. The release of a toxin results in abdominal cramps and severe diarrhoea. The disease can cause death if the immune system is weakened, such as in AIDS (acquired immune deficiency syndrome) patients. Magnification: x190 at 6x7cm size.