Cestoda known as ‘Tapeworms’ MLS 602: General and Medical Microbiology Lecture: 12 Edwina Razak [email protected] Learning Objectives • Describe the general characteristics of cestodes. • Identify different genus and species in the Class Cestoda which causes human infection. • Discuss morphology, mode of transmission and life cycle. • Outline the laboratory diagnosis and treatment. Introduction • Inhabit small intestine • Found worldwide and higher rates of illness have been seen in people in Latin America, Eastern Europe, sub-Saharan Africa, India, and Asia. • Cestodes: Digestive system is absent • Well developed muscular, excretory and nervous system. • hermaphrodites (monoecious) and every mature segment contains both male and female sex organs. • embryo inside the egg is called the oncosphere (‘hooked ball’). Structural characteristics Worms have long, flat bodies consisting of three parts: head, neck and trunk. • Head region called the scolex, contains hooks or sucker-like devices. Function of scolex: enables the worm to hold fast to infected tissue. Neck region is referred as region of growth where segments of the body are regenerated. • The trunk (called strobila) is composed of a chain of proglottides or segments. • Gravid proglottides contains testes and ovaries. Is the site where eggs spread . • Rostellum is small button-like structure on the scolex of “armed” tapeworms from which the hooks protrude. It may be retractable. Structural Characteristics • 1.Scolex or head. • 2. Neck, leading to the region of growth below, showing immature segments. • 3. Mature segments • 4. Gravid segments filled with eggs Medically important tapeworms are classified into the following: ORDER: Pseudophyllidean ORDER: Cyclophyllidean tapeworms tapeworms 1. Genus Taenia 1. Diphyllobothrium latum, the a. T. saginata, the beef tapeworm. fish tapeworm Adult worm in human intestine Adult worm in human intestine b. T. solium, the pork tapeworm. Adult worm in human intestine. 2. Sparganum mansoni, S. Larval form also can cause disease in man proliferum (cysticercus cellulosae) • Larval stages in tissues, causing 2. Genus Echinococcus Sparganosis. a. E. granulosus the dog tapeworm. Larval form causes hydatid disease in man. b. E. multilocularis Larval stage causes alveolar or multilocular hydatid disease. Medically important tapeworms are classified into the following: 3. Genus Hymenolepis 4. Genus Dipylidium a. H. nana, the dwarf tapeworm. D. caninum, the double-pored dog Adult and larval stages in human tapeworm. Adult rarely in human intestine. intestine. b. H. diminuta, the rat tapeworm. 5. Genus Multiceps Adult worm rarely in human M. multiceps and other species. intestine. Larval stage may cause coenurosis in man. DIPHYLLOBOTHRIUM LATUM • Fish Tapeworm disease • Longest human parasite some measuring 60 feet in length. • Two intermediate hosts: 1. Shrimplike crustaceans called copepod 2. Fish • Scolex is spatulate or spoon- shaped DIPHYLLOBOTHRIUM LATUM DIPHYLLOBOTHRIUM LATUM Pathogenesis Laboratory Diagnosis • Most infections are asymptomatic. • Eggs in stool: Single shell with operculum at one end and a knob on the other. • Rarely, it causes severe cramping, abdominal Treatment: • pain, vomiting, weakness and weight Niclosamide loss. Praziquantel • Pernicious anemia can also result Prevention due to interference of vitamin B12 Prohibiting the disposal of untreated absorption in jejunum. sewage into fresh water /lakes. Personal protection: cooking of all fresh water fish. SPARGANOSIS • infection by sparganum (plerocercoid larva) • ingestion of cyclops containing procercoid larva, uncooked meat or application of raw flesh of infected animal on skin or mucosa. • Two species are : Spirometra mansoni and S. proliferum. • Diagnosis is only after surgical removal of the worm. Found in subcutaneous tissue, peritoneum, abdominal viscera and brain. Taenia species • The cestodes Taenia saginata (beef • Taenia solium taeniasis is less tapeworm), T. solium (pork tapeworm) and T. frequently symptomatic than Taenia asiatica (Asian tapeworm). saginata . The main symptom is often • Taenia solium can also cause cysticercosis. the passage (passive) of proglottids. • Taenia saginata and T. solium are worldwide • Taenia saginata taeniasis produces in distribution. Taenia solium is more prevalent in poorer communities where only mild abdominal symptoms. The humans live in close contact with pigs and eat most striking feature consists of the undercooked pork. passage (active and passive) of • Taenia asiatica is limited to Asia and is seen proglottids. Occasionally, appendicitis mostly in the Republic of Korea, China, or cholangitis can result from Taiwan, Indonesia, and Thailand. migrating proglottids. Life Cycle Disease • Cysticercosis is the disease • Taeniasis, which is an intestinal associated with the development infection with the adult tapeworm. of the larval form (cysticercus) of Humans acquire intestinal the pork tapeworm, Taenia infections with T. solium after solium, within an intermediate eating undercooked pork host. The usual definitive host, can containing cysticerci. serve as accidental intermediate • Cysts evaginate and attach to the hosts following ingestion of small intestine by their scolices. infectious eggs. Adult tapeworms develop to • Note that cysticercosis is only maturity and may reside in the acquired from the fecal-oral route small intestine for years (ingestion of eggs), not via the ingestion of cysticerci in undercooked pork. Clinical Presentation • Cysts, called cysticerci, can develop Cysts in the brain or spinal cord: in the muscles, the eyes, the brain, and/or the spinal cord. Symptoms • Cause the most serious form of the caused by the cysts depend on the disease, called neurocysticercosis location, size, number, and stage of • May cause no symptoms the cysts. • May cause seizures and/or Cysts in the muscles: headaches (these are more • Generally do not cause symptoms common) • May also cause confusion, difficulty • May cause lumps under the skin, with balance, brain swelling, and which can sometimes become excess fluid around the brain (these tender are less common) • May cause stroke or death Laboratory Diagnosis • Recovery of the gravid segments or the eggs from the stool . • formol-ether sedimentation method . • Eosinophilia usually occurs during the early stage of cysticercosis • indirect haemagglutination test Scolex of T.soilum and T.saginata • T.solium • T.saginata Treatment and Control Treatment: Niclosamide and Mebendazole Prevention • People who have tapeworm infections can infect themselves with the eggs and develop cysticercosis (this is called autoinfection). They can also infect other people if they have poor hygiene and contaminate food or water that other people swallow. Thus these two measures can be taken to prevent spread of infection: • Through cooking of meat (above 57°C) • Proper disposal of human excrete. Other Tapeworm diseases ECHINOCOCCUS GRANULOSUS Morphology • the dog tapeworm, humans and • adult worm measures 3-6 mm in sheep are intermediate hosts length (up to 1 cm) • Definitive hosts are canines e.g. • has scolex, neck and strobilla (3 dogs, wolves, foxes and coyotes. proglottides) • Causes hydatid disease • scolex is pyriform, with 4 suckers • Found in temperate rather than and a prominent rostellum bearing tropical region two circular rows of hooklets. • Echinococcus multilocularis- • the terminal proglottid is longer alveolar or multilocular hydatid and wider than the rest of the disease and definitive hosts are worm and contains the branched rodents. uterus filled with eggs. Life cycle and pathogenecity • Oncosphere hatch in duodenum or • The cysts may be large, filled with small intestine into embryos clear fluid and contain (oncosphere) which: • Characteristic protoscolices ♦ Penetrate wall (immature forms of the head of the ♦ Enter portal veins parasite). • Migrate via portal blood supply to • These mature into developed organs: eg: lungs, liver, brain etc., scolices, which are infective for thus, causing extra -interstitial dogs. infections. • In these organs, larvae develop into hydatid cysts. Echinococcus granulosus Hydatid cyst Other Features Mode of human infection Clinical features • Ingestion of eggs by the following • Asymptomatic infection is ways: common, but in symptomatic i) Ingestion of water or vegetables patients polluted by infected dog feces. ♦ It may cause cough - with ii) Handling or caressing ,kissing hemoptysis in lung hydatid disease. infected dogs where the hairs are ♦ Hepatomegaly - with abdominal usually contaminated with eggs. pain and discomfort ♦ Pressure -from expanding cyst ♦ Rupture of cyst - severe allergic reaction - anaphylaxis. Diagnosis: X-ray or other body scans ♦ Demonstration of protoscolices in cyst after operation ♦ Serology Treatment: Surgery Albendazole Hymenolepis nana • Dwarf worm about 25mm Mode of infection long 1. Ingestion of egg with • Lives in small intestine contaminated raw vegetables. 2. Direct infection from a patient • Hymenolepis diminuta (rat 3. Auto infection: the eggs of H. nana tapeworm) are infective as soon as they are • scolex has 4 suckers and a passed with feces by the patient. retractile rostellum with a 4. If the hands of the patient are single row of hooklets contaminated by these eggs, she/he infects herself/himself again and again. Pathogenicity • Light infections produce no symptoms. In fairly heavy infections, children may show lack of appetite, abdominal pain and diarrhoea. H.diminuta differs from H. nana in that: ♦ The adult worm measures about 10-60 cm ♦ The rosetellum on the head has no hooks ♦ In the mature segment, there are two testes at one side and another testis on the other side. Summary • Cestodes are third class of tapeworms in the phylum Platyhelminthes • Long flat bodies , head region and ribbon like series of segments. • Scolex- attachment to the infected tissue • Proglottids- contains reproductive organs and is filled with fertilized eggs. • No digestive system but absorbs food from the host intestine..