Protozoan infection (giardiasis) in human intestinal lumen (Giardia sp.), coloured transmission electron micrograph (TEM). Vegetative phase called trophozoite that develops from a cyst infection in the small intestine. Giardia lamblia, a human parasite of the gastrointestinal tract. The organism is spread by direct contact or through contaminated food and water. Giardia spp. are pear-shaped, with hair-like flagella for motility. They cause the disease giardiasis (or lambliasis), an infection of the small intestine most common in tropical areas. Giardia spp. attaches by means of sucking discs to microvilli in the human intestine. Abdominal cramps, swelling, diarrhoea and nausea may occur. Magnification: x1, 870 when shortest axis printed at 25 millimetres.