a disease of animals caused by the cestode Thysaniezia of the family Avitellinidae Spasskii (Thysanosomidae), an intestinal parasite of sheep, cattle, and some wild animals. Thysanieziasis occurs in the countries of the eastern hemisphere that have a moderate or warm climate, including the USSR, where it affects sheep. The causative agent of the disease is Thysaniezia giardi, a milky-white organism that measures as much as 5 m in length and 10 mm in width; the organism consists of a head, neck, and numerous segments. The life cycle of the parasite has not been studied.
Sheep more than one year old are particularly susceptible to infection. Sluggishness, salivation, and loss of coordination are the main symptoms of the disease. Epizootics usually occur among sheep in winter and fall. The animals on infected farms are given niclosamide or tin arsenate.