The neck continually produces proglottids, each one containing a reproductive tract; mature proglottids are full of eggs, and fall off to leave the host, either passively in the feces or actively moving. All tapeworms are hermaphrodites, with each individual having both male and female reproductive organs. Humans are subject to infection by several species of tapeworms if they eat undercooked meat such as pork (Taenia solium), beef (T. saginata), and fish (Diphyllobothrium), or if they live in, or eat food prepared in, conditions of poor hygiene (Hymenolepis or Echinococcus species). The unproven concept of using tapeworms as a slimming aid has been touted since around 1900. Diversity and habitat
All 6,000 species of Cestoda are parasites, mainly intestinal; their definitive hosts are vertebrates, both terrestrial and marine, while their intermediate hosts include insects, crustaceans, molluscs, and annelids as well as other vertebrates.T. saginata, the beef tapeworm, can grow up to 20 m (65 ft); the largest species, the whale tapeworm Tetragonoporus calyptocephalus, can grow to over 30 m (100 ft). Species with small hosts tend to be small. For example, vole and lemming tapeworms are only 13–240 mm (0.5–9.4 in) in length, and those parasitizing shrews only 0.8–60 mm (0.03–2.36 in). Anatomy
Cestodes have no gut or mouth and absorb nutrients from the hosts alimentary tract through their specialised neodermal cuticle, or tegument, through which gas exchange also takes place.
Episodic ataxia (EA) is an autosomal dominant disorder characterized by sporadic bouts of ataxia (severe discoordination) with or without myokymia (continuous muscle movement). There are seven types recognized but the majority are due to two recognized entities. Ataxia can be provoked by psychological stress or startle, or heavy exertion, including exercise. Symptoms can first appear in infancy. There are at least six loci for EA, of which 4 are known genes. Some patients with EA also have migraine or progressive cerebellar degenerative disorders, symptomatic of either familial hemiplegic migraine or spinocerebellar ataxia. Some patients respond to acetazolamide though others do not. Signs and symptoms
Typically, episodic ataxia presents as bouts of ataxia induced by startle, stress, or exertion. Some patients also have continuous tremors of various motor groups, known as myokymia. Other patients have nystagmus, vertigo, tinnitus, diplopia or seizures. Cause
The various symptoms of EA are caused by dysfunction of differing areas. Ataxia, the most common symptom, is due to misfiring of Purkinje cells in the cerebellum. This is either due to direct malfunction of these cells, such as in EA2, or improper regulation of these cells, such as in EA1. Seizures are likely due to altered firing of hippocampal neurons (KCNA1 null mice have seizures for this reason). Pathophysiology
EA1: KCNA1
Type 1 episodic ataxia (EA1) is characterized by attacks of generalized ataxia induced by emotion or stress, with myokymia both during and between attacks. This disorder is also known as episodic ataxia with myokymia (EAM), hereditary paroxysmal ataxia with neuromyotonia and Isaacs-Mertens syndrome.