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ORDER CYCLOHPYLLİDEA Family Taeniidae : the Adults Are, in Most

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ORDER CYCLOHPYLLİDEA Family Taeniidae : the Adults Are, in Most 1 ORDER CYCLOHPYLLİDEA Family Taeniidae : The adults are, in most case, large tapeworms and are found in carnivores (domestic and wild) and human in the small intestine. Genera of importance are Taenia and Echinococcus. The scolex has an armed rostellum with a concentric double rows of hooks ( the important exception is Taenia saginata whose scolex is unarmed). The gravid segments are longer than they are wide. The metacestode stages are a cysticercus, coenurus, hydatid cyst , tetrathyridium, cysticercoid and strobilocercus and these occurs in mammals, arthropods, amphibians and reptiles . The egg, as seen outside the host’s body, is small and spherical, and the embryophore consists of the typical double layer, outer vitelline and inner chitinous. In this family, the apperance of the embryophore in optical section is of radial striation. The outer shell is lost in the uterus of the tapeworm, and is not seen in diagnostic material, and its colour is brown. Genus Taenia : The members of the genus Taenia are large tapeworms comprising a number of species. It has the essential morphological characters of the family, with a double row of hooks on the scolex, and single genital pore. In the proglottids, the genital pores open alternately on either side in successive proglottids, but not regularly so. Usually there are numerous testes. The ovary is in the hinder parts of the proglottids. The uterus has a median longitudinal stem with lateral brnches that may themselves be branched. Differentiation is usually based on the size of the scolex, the size of the rostellum and number of hooks, and on the morphology of the genital system within the mature segments. The larval stages themselves are very simply diagnosed morphologically becase of the wide range of forms, and biologically because of their high selectivity for particular intermediate hosts and tissues. The adults of Taenia are usually of minor importance in domestic animals, and it is the larval stages which are of veterinary interest. The basic life cycle of taeniidae: the gravid segments are passed in the faeces, singly or in short lengths, and the embryophores are broken down in the digestive organs ( stomach, abomasum or small intestine etc.) of the intermediate hosts. The free oncosphere migrates actively into the intestinal mucosa using its six hooks and reaches the bloodstream, in which it may be carried to any organ, tissue and cavity. It has highly selective tissue requirements, and only if it arrives in its predilection tissue will it develop. The larva (metacestode ) has usually reached its fully infective form in two or three months from ingestion, and final host ingests the predilection tissue containing it. Most of larval stages can survive until the death of the intermediate host for several days - years, an important factor in an epidemiological system where carrion-feeding carnivores exist. Species : Taenia saginata The adult tapeworms is usually 5-8 m long, rarely up to 15 m. The scolex has neither a rostellum nor hooks. Gravid segments are 16-20 mm long by 4-7 mm wide and the uterus has 15-35 lateral branches on either side. In cattle , the mature cysticercus, C. bovis, is greyish- white, oval, about 0.5-1.0 cm long and filled with fluid in which the invaginated scolex clearly visible. As in the adult tapeworm, it has neither rostellum nor hooks. 2 Prediction side : Small intestine ( T. saginata ; in definitive host ); muscle (Cysticercus bovis – metacestode stage - larva stage ; in intermediate host ) Final hosts : Human Intermediate hosts : Cattle, although other ruminants can serve as intermediate hosts Life cycle : In infected human pass millions of eggs daily, either free in the faeces or as intact segments each containing about 250.000 eggs, and these can survive on the pasture for several months. After ingestion by suitable bovine, the oncosphere travel via the blood to striated muscle. It is firsly grossly visible about 2 weeks later as a pale semi-transparent spot about 1.0 mm in diameter, but it is not infective to human until about 12 weeks when it has reach its full size around 1.0 cm. By then it is enclosed by in a thin fibrous capsule but despite this capsule the scolex can usually still be seen. The longevity of the cysts range from weeks to years. When they die they are usually replaced by a caseous crumbly mass, which may become calcified, and both living and dead cysts are frequently in the same carcass. Human become infected by ingesting raw or inadequately cooked meat. Development to patency takes 2-3 months. Pathogenesis and clinical signs : Most people who become infected with T. saginata, which is usually a single tapeworm , remain asymptomatic. Some symptoms, such as diarrhea, abdominal-pain, change appetite, and slight weight loss, may be experienced by T. saginata. In addition, symptoms including dizziness, vomiting, and nausea may also develop in such patients. Laboratory tests often reveal the presence of a moderate oesinophilia. The prognosis is usually good. Although C. bovis may occur anywhere in the striated muscles, the predilection sites, at least from viewpoint of routine meat inspection, are the heart, the tongue and masseter and intercostal muscles. Under natural conditions the presence of cysticerci in the muscle of cattle is not associated clinical signs although, sometimes in massive infections of C. bovis developed severe myocarditis and heart failure associated with developing cysticerci in the heart. Diagnosis : In human, definitive diagnosis depends on identification of the proglottids passed by the patient. The eggs in the stool can be identified only Taenia spp. , because the eggs of all tapeworm in the genus of Taenia look alike. In the intermediate hosts, individual countries have different regulations regarding the inspection of carcasses, but invariably the masseter muscle, tongue and heart are incised and examined and intercosatal muscles and diaghram inspected; triceps muscle is also incised in many counties. The inspection is inevitably a compromise between detection of cysticerci and preservation of the economic value of the carcass. Treatment : All yet there is no licensed drug available that will effectively destroy all the cysticerci in the muscle. In human, the drug of choice praziquantel effective in a single dose administration. Control : As in most parasitic infections of the food animals contagious to man, the first point of attack is the prevention of private slaughter of the animals. In approved abattoirs inspection 3 of carcasses may be undertaken , and though countries vary in the intensity of examination, the essential features are similar. Cooking of the meat is never included in regulations and it should be recognised that, though the thermal death point of C. bovis is only 57°C , this temperature should be reached in the middle of a thick piece of meat. Regulations usually require that infected carcasses are frozen at – 10 °C for at least 10 days, which is sufficient to kill the cysticerci although the process reduces the economic value of the meat. Species : Taenia solium The tapeworm is most prevalent in South and Central America, India, Africa and parts of Far East . It is now uncommon in many developed countries and Islamic countries. The adult tapeworm is 3-5 m long, up to 8 m. The rostellum has four suckers and rostellum bears 22-23 hooks in two rows. Gravid segments are 10-12 mm long and 5-6mm wide. The ovary is in the posterior third of the proglooid and has two lobes with an accessory third lobe. The uterus has 7-12 lateral branches on either side. The name of the larval stage is Cysticercus cellulosa which have morphologically distinct types. The commenest is the ‘cellulosa’ cysticercus which has a fluid-fiiled bladder that is 0.5-1.5 cm in length with an invaginated scolex. The ‘racemose’ form has no evident scolex, but are larger and up to 20 cm in length. Pedilection side : Small intestine ( T. solium- adult tapeworm, in final host); muscle ( Cysticercus cellulosa- larval stage , in intermediate hosts) Final hosts : Human Intermediate hosts : Pig, wild boar, rarely dog and human Life cycle : Gravid segment passed in the feaces, frequently in chains, each contain around 40,000 eggs and because they are non-motile they tend to be concentrated over a small area. After ingestion by susceptible pig the oncosphere travels via the blood to striated muscle. The principal location is the striated muscle, but cysticerci may also develop in other organs, such as lungs, liver, brain and kidney. Human become infected by ingesting raw or inadequately cooked pork containing viable cysticerci. The human, final host, may also act as an intermediated host and become infected with cysticerci . This is most likely to occur from accidental ingestion of T. solium eggs via unwashed hands or contaminated food. There is also, apparently , a minor route of autoinfectionin a person with an adult tapeworm, from the liberation of oncospheres after the digestion of a gravid segment that has entered the stomach from the duodenum by reverse peristaltics. The prepatent period is 2-3 months. Pathogenesis and clinical signs : Cysticerci, comprising a single large cyst and inverted scolex, measure 1-2 cm and easily visible between muscle fibres. The cysticerci are rapidly ensheathed in connective tissue and create a crescentic zone of degenerative lysis around them, thereby allowing room to grow. Pigs are usually slaugtered at an age when all cysticerci are generally still viable. Clinical signs are inapparent in pigs naturally infected with cysticerci and generally insignificant in humans with adult tapeworms. However, when humans are infected with cysticerci, various clinical signs may occur depending on the location of the cysts in the organs, muscle 4 or subcutaneous tissue. Cysticerci may be found in every organs of the body in humas but are most common in subcutaneous tissue, eye and brain.
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