Friday, 27 January 2017

Holding on to your host

Moniezia expansa is primarily present throughout ungulates of Europe, Asia, Africa, America and Australia. This parasite has also been found in South American countries, including Peru and Argentina.

Like all cestodes, or tapeworms, M. expansa are flat with multiple segments of proglottids, used for producing gametes for reproduction. The adult bodies lack digestive tracts and are covered with microvilli to increase surface area for the absorption of nutrients. Moniezia expansa adults can reach lengths of 4 to 5 meters and are separated into three sections including the scolex, neck and strobila. The scolex is usually less than 1 millimeter, and contains suckers and hooks to assist in holding on to the host. The small neck produces immature proglottids, while the large strobila (main body) consists of a large chain of mature male and female proglottids.

Moniezia expansa occupies three different environments during its life cycle: the external environment, the body cavity of the intermediate host (oribatid mite), and the intestine of the definitive host (ungulate). First, the eggs of M. expansa exist in the external environment until accidentally ingested by the intermediate host, an oribatid (ground living) mite. The eggs of M. expansa exist in ungulates' feces, most regularly in pastures where these animals feed. The oribatid mite occupies the first inch of turf, hiding during the day, and searching for food at night. Moniezia expansa eggs will then grow and develop to adults in the oribatid mite’s body cavity. Through ingestion of the oribatid mite by ungulates, the adult M. expansa is able to feed on nutrients in the host’s intestine.

Proglottids: a segment of a tapeworm containing both male and female reproductive organs.

Gametes: a mature sexual reproductive cell.

Microvilli: a thin protuberance present in great abundance at the surface of some epithelial cells, thus increasing the surface area available for absorption.

Oribatid mites: a group of mites which live in the top layer of the soil.

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