Moniezia and Thysanosoma

The large cestodes Moniezia and Thysanosoma in cattle and sheep, and occasionally free-ranging ungulates, are found around the world, including in Canada.  Adult Moniezia live in the small intestine, and Thysanosoma in the small intestine and biliary system.  The life cycle is indirect, involving free-living oribatid mites as intermediate hosts.  Infection of cattle and sheep is by ingestion of these mites containing cysticercoids.  These cestodes are generally considered essentially non-pathogenic unless present in very large numbers and/or in otherwise stressed animals.  The adult parasites are sometimes shed spontaneously in the fall, and their appearance in the faeces is often of (usually unwarranted) concern to farmers.

Phylum: Platyhelminthes
Class: Cestoidea
Cohort: Cestoidea
Subcohort: Eucestoda
Infracohort: Saccouterina
Order: Cyclophyllidea
Family: Anoplocephalidae

Among tapeworms of importance in veterinary medicine, the closest relatives of Moniezia and Thysanosoma are the genera Anoplocephala and Paranoplocephala of horses.
 

Adult Moniezia species measure up to 600 cm in length and 15 mm (M. expansa) or 25 mm (M. benedeni) in width. The scolex of both species has four circular suckers, but no rostellum or hooks. Each mature segment contains two sets of reproductive organs but only one uterus. At the posterior margin of each segment of M. expansa there is a transverse row of discrete inter-proglottidal glands; in M. benedeni these glands form a centrally-placed, continuous band. Most of these features are visible microscopically in cleared and mounted or stained specimens. Mature and gravid segments are wider than they are long.

Adult Thysanosoma are up to approximately 30 cm in length and 10 mm in width. The scolex is similar to Moniezia and there are two sets of reproductive organs in each segment but only a single uterus.  In gravid segments of Thysanosoma, however, the eggs are located in small "packets", similar to Dipylidium in dogs.  There is a clearly visible fringe along the posterior margin of each segment (Thysanosoma is known as the fringed tapeworm).

Eggs of the two species of Moniezia are up to approximately 70 µ in diameter and are irregular in shape. Each egg contains a hexacanth larva enclosed in a pyriform apparatus, which has the appearance of an ice cream cone.

Eggs of Thysanosoma are grouped in para-uterine organs (similar to Dipylidium caninum in dogs) measuring approximately 175 µ by 145 µ and each containing six to twelve eggs. The eggs of Thysanosoma do not have a pyriform apparatus.

Moniezia species occur in ruminants in most parts of the world, M. benedeni primarily in cattle and M. expansa in cattle and sheep. Thysanosoma actinoides (the sole species in the genus) occurs in cattle, sheep and deer in the Americas.

The hermaphrodite adults live in the small intestine (Moniezia) or small intestine and bile ducts (Thysanosoma) of their ruminant hosts. Eggs in the feces are ingested by free-living oribatid (Moniezia) or psocid (Thysanosoma) mite intermediate hosts, in which the infective cysticercoids develop. Infection of the ruminant is by ingestion of infected mites.

Life Cycle: Moniezia and Thysanosoma

In Canada, transmission of Moniezia and Thysanosoma occurs during the summer, and parasite burdens increase into the late summer and fall, when parts of adult parasites may be shed in the feces. The young are more likely to have heavy infection than are older animals.

Neither genus of tapeworm is thought to be associated with adverse effects in cattle or sheep, although it is possible that very heavy infections in young or otherwise stressed animals may be a problem.

The detection of eggs on fecal flotation, or of portions of adult parasites in feces, are the best methods.

Because of the assumed generally low pathogenicity of the both genera of tapeworms, treatment and control of Moniezia or Thysanosoma in cattle or in sheep are not usually a concern.  Albendazole (VALBAZEN) at the normal therapeutic dose and extralabel fenbendazole (PANACUR, SAFE-GUARD) at 2X the normal therapeutic dose are effective for Moniezia.

Additional information on the products mentioned is available from the Compendium of Veterinary Products (Twelfth Edition, 2011), or from the manufacturers.

Neither Moniezia nor Thysanosoma are known to be zoonotic.