In the eye, the parasites can cause visual loss, and infection of the spine and adjacent leptomeninges can cause paresthesias, pain, or paralysis. Echinococcosis (hydatid disease)
Humans become accidental hosts to worms of the genus Echinococcus, playing no role in the worms biological cycle. This can result in echinococcosis, also called hydatid disease. Humans (usually children) become infected by direct contact with dogs and eating food contaminated with dog feces. Common sites of infection are the liver, the lungs, muscles, bones, kidneys, and the spleen.Eggs hatch in the gastrointestinal tract after the consumption of contaminated food, after which the larvae travel to the liver through portal circulation. Here, the larvae are trapped and usually develop into hydatid cysts. While the liver is the first filter for trapping them, the lungs act as the second filter site, trapping most of the larvae that are not trapped by the liver. Some larvae escape from the lungs to cause cysts in other tissues.When a larva becomes established in tissue, it develops into a "bladderworm" or "hydatid" and can cause various cancer-like cysts that may rupture and interact with nearby organs. Most cases are asymptomatic, and the mortality rate is low, but various complications from these interactions may lead to debilitating illness. Hymenolepiasis
Arthropods are intermediate hosts of Hymenolepis nana, otherwise known as the "dwarf tapeworm," while humans are used as final hosts. Humans become infected and develop hymenolepiasis through eating infected arthropods, ingesting eggs in water inhabited by arthropods, or from dirty hands.
Eucestoda, commonly referred to as tapeworms, is the larger of the two subclasses of flatworms in the class Cestoda (the other subclass is Cestodaria). Larvae have six posterior hooks on the scolex (head), in contrast to the ten-hooked Cestodaria. All tapeworms are endoparasites of vertebrates, living in the digestive tract or related ducts. Examples are the pork tapeworm (Taenia solium) with a human definitive host, and pigs as the secondary host, and Moniezia expansa, the definitive hosts of which are ruminants. Body structure
Adult Eucestoda have a white-opaque dorso-ventrally flattened appearance, and are elongated, ranging in length from a few millimeters to 25 meters. Almost all members, except members of the orders Caryophyllidea and Spathebothriidea, are polyzoic with repeated sets of reproductive organs down the body length, and almost all members, except members of the order Dioecocestidae, are protandral hermaphrodites. Most except caryophyllideans consist of a few to 4000 proglottids (segments) that show a characteristic body differentiation pattern into scolex (head), neck, and strobila.The scolex, located at the anterior end, is a small (usually less than 1 mm) holdfast organ with specific systems for fastening itself to materials: rostrum, acetabula, suckers, bothria, grooves, and hooks. The small neck region, directly behind the scolex, consists of an undifferentiated tissue region of proglottid proliferation, leading into a zone of increasing and continuous proglottid differentiation. As such, the main and largest section of the body, the strobila, consists of a chain of increasingly mature proglottids. These cytological processes are not well understood at present.