Giardia

Giardia (dʒiːˈɑrdiə or ˈdʒɑrdiə) is a genus of anaerobic flagellated protozoan parasites of the phylum Metamonada that colonise and reproduce in the small intestines of several vertebrates, causing the disease giardiasis. Their life cycle alternates between a swimming trophozoite and an infective, resistant cyst. Giardia were first described by the Dutch microscopist Antonie van Leeuwenhoek in 1681. The genus is named after French zoologist Alfred Mathieu Giard. Like other diplomonads, Giardia have two nuclei, each with four associated flagella, and were thought to lack both mitochondria and Golgi apparatuses. However, they are now known to possess a complex endomembrane system as well as mitochondrial remnants, called mitosomes, through mitochondrial reduction. The mitosomes are not used in ATP synthesis the way mitochondria are, but are involved in the maturation of iron-sulfur proteins. The synapomorphies of genus Giardia include cells with duplicate organelles, absence of cytostomes, and ventral adhesive disc. About 40 species have been described from different animals, but many of them are probably synonyms. Currently, five to six morphologically distinct species are recognised. Giardia lamblia (=G. intestinalis, =G. duodenalis) infect humans and other mammals, G. muris is found from other mammals, G. ardeae and G. psittaci from birds, G. agilis from amphibians and G. microti from voles. Other described (but not certainly valid), species include: Giardia ardeae Giardia beckeri Giardia beltrani Giardia botauri Giardia bovis Giardia bradypi Giardia canis Giardia caprae Giardia cati Giardia caviae Giardia chinchillae Giardia dasi Giardia equii Giardia floridae Giardia hegneri Giardia herodiadis Giardia hyderabadensis Giardia irarae Giardia marginalis Giardia melospizae Giardia nycticori Giardia ondatrae Giardia otomyis Giardia pitymysi Giardia pseudoardeae Giardia psittaci Giardia recurvirostrae Giardia sanguinis Giardia serpentis Giardia simoni Giardia sturnellae Giardia suricatae Giardia tucani Giardia varani Giardia viscaciae Giardia wenyoni Many different species of Giardia exist, so to differentiate between species, very specific PCR (Polymerase Chain Reactions) have been developed to detect specific Giardia spp.