Can a Tapeworm Come Out of Your Rectum and Then Go Back in the Rectum Again

General Concepts

Clinical Manifestations

Adult Tapeworms: Developed worms are found in the small-scale intestine; these infections are unremarkably well tolerated or asymptomatic, but may crusade abdominal distress, dyspepsia, anorexia (or increased ambition), nausea, localized hurting, and diarrhea.

Larval Tapeworms: Larvae locate in extraintestinal tissues and produce systemic infections with clinical furnishings related to the size, number, and location of cysts. Taenia solium cysticercosis (infection with the cysticercus larval stage) is often asymptomatic and chronic; neurocysticercosis, ophthalmic cysticercosis, and subcutaneous and muscular cysticercosis are, however, ofttimes reported. Echinococcus granulosus hydatid larvae may class massive cysts in liver, lungs, and other organs, including long bones and the central nervous system.

Structure

Adults, which mature sexually in the definitive or concluding host, are ribbon-shaped, multisegmented, hermaphroditic flatworms; each segment has a complete male and female reproductive organisation. An anterior holdfast organ (the scolex) is followed past a germinative portion ("cervix") and segments at successively later stages of development. Larvae encyst in various tissues of the intermediate host; larval cysts contain i or many scoleces of futurity adult worms.

Multiplication and Life Cycle

The tapeworm's life cycle involves a definitive and 1 or more intermediate hosts (except for the 1-host cycle of Hymenolepis nana). Each blazon of cycle has specialized larval forms (cysticercus, cysticercoid; coenurus, hydatid; coracidium, procercoid, plerocercoid).

Pathogenesis

Pathology due to adult worms results from the physical presence and action of the large worms (Taenia species), occasional erosive action (causing local inflammation) by scolex hooks (T solium, H nana), or reduced host intake of vitamin B₁₂ (Diphyllobothrium latum). Allergic reactions may also be responsible for symptoms such equally headache, dizziness, inanition, and anal and nasal pruritus.

Host Defenses

Developed worms are probably only weakly immunogenic, although some evidence exists for a cell-mediated host response; moderate eosinophilia and increased IgE may occur. Hymenolepis nana, in contrast, elicits a strong allowed response when directly infected by the eggs, since the larvae develop within the villi (meet page 1105). Larvae arm-twist strong immunity against reinfection that is derived from both cell-mediated and humoral responses induced by antigenic stimulation of tissues.

Epidemiology

Infective larvae are caused by eating contaminated raw or undercooked meat, grains, or fish. Taenia solium cysticercosis or H nana can be transmitted in a straight cycle via ingestion of eggs from homo carrion. Echinococcus eggs from dog or fox fur cause human hydatid disease (humans are the intermediate host; canids are the definitive hosts). Reinfection with adult tapeworms is common; second infections with larvae are rare. T solium cysticercosis may exist acquired by autoinfection; internal autoinfection with H nana from a cysticercoid infection is possible.

Diagnosis

Adult Worms:Taenia infections are diagnosed by finding gravid segments in stool specimens; the eggs of these species are indistinguishable. Other species are diagnosed on the basis of eggs in stool specimens.

Larval Worms: Cysts in tissues may be identified in biopsy specimens, past radiography (calcified cysts), and by computed tomography (encephalon cysts). Serology (indirect hemagglutination, ELISA) is useful only of variable sensitivity and specificity. A history of travel in owned areas is often of not bad importance.

Command

Meat should be cooked thoroughly or frozen at -ten°C for 10 days; beefiness and pork should be inspected for Taenia ("measly meat"); man feces should not contaminate drinking water; sheepdogs should be treated and should non be fed sheep viscera. Humans may be treated with praziquantel or niclosamide.

Introduction

Tapeworms are ribbon-shaped multisegmented flatworms that dwell as adults entirely in the human small intestine. The larval forms lodge in peel, liver, muscles, the central nervous system, or whatever of various other organs. Their life cycles involve a specialized pattern of survival and transfer to specific intermediate hosts, by which they are transferred to another human host. Each pattern is feature of a given tapeworm species.

In general, the common gut-dwelling developed cestodes are well adapted to the human host, induce few symptoms, and only rarely cause serious pathology. This reality belies innumerable fearsome and largely counterfeit stories of tapeworms stealing food and causing ravenous hunger (far more commonly, the appetite is depressed). Larval cestodes, all the same, develop in human organs or somatic tissues exterior of the gut and are therefore far more pathogenic.

The adult cestodes arm-twist little host inflammatory or allowed response in contrast to the stiff responses elicited past the larval stages in tissues. Adult cestodes are often acquired by ingestion of meat from intermediate hosts. Extraintestinal infection with larvae results from ingestion of eggs of fecal origin. Diagnosis of infection with adult cestodes is based on identification of eggs and segments (proglottides) in carrion. Larval infections are more difficult to appraise; serology and biopsy are helpful. Command depends on sanitation, personal hygiene, and thorough cooking of meat and fish.

Taenia saginata, The Beef Tapeworm

Clinical Manifestations

The clinical manifestations of infection with adult T saginata tapeworms are bars to occasional nausea or vomiting, appetite loss, epigastric or umbilical hurting, and weight loss. Moderate eosinophilia may develop. A agonizing manifestation of T saginata infection is the agile crawling of the muscular segments out of the anus. Rarely, intestinal perforation may occur from the scolex of Taenia, or proglottides may be vomited and and so aspirated.

Structure

Adults are ribbonlike, flattened, segmented, hermaphroditic flatworms v to 10 one thousand long, consisting of scolex, neck, and immature, mature, and ripe segments in linear sequence. The distinctive morphologic and physiologic properties of the adult tapeworm reflect on the 1 paw their remarkable specialization for survival in the vertebrate intestine, and on the other hand their massive reproductive powers which are made possible by the multiple sexual units, the proglottides or segments. This ensures the worm species against the enormous rate of loss of the segments or eggs passed in the carrion, with merely the about remote probability of whatever i egg succeeding in reaching an intermediate host and being transferred to another homo. The terminal one-third to 1-half of the worm'southward length consists of gravid (egg-filled) segments. These segments are muscular and tin can crawl caterpillar-way through the anal sphincter to the outside environment—which renders them available to their herbivore intermediate hosts.

The larval cyst of T saginata—the cysticercus—is a pea-sized, fluid-filled cyst, which develops in the muscles of the intermediate host. Within the cyst is a single inverted scolex, formed from a germinative portion of the inner cyst wall (Fig. 89-ane).

Effigy 89-1

Larval types plant in the taeniid tapeworms. . (From Muller R: Worms and Disease: A transmission of Medical Helminthology. William Heinemann Medical Books, London, 1975, with permission.)

Multiplication and Life Bike

Figure 89-2 illustrates the life cycle of T saginata. Gravid segments break off from the worm and are carried in the fecal bolus or by their own crawling activity to the soil. The segments move abroad from the bolus and adhere to grass. If ingested by a bovine intermediate host, the segments are digested open in the gut, each releasing 50,000 to 100,000 eggs. The eggs hatch, each releasing a six-hooked larva, the oncosphere (likewise called the hexacanth), which penetrates the gut wall and reaches the muscles via the apportionment. There the oncosphere fills with fluid and develops into the 8-mm cysticercus. If a homo eats raw or undercooked infected beef, the cysticercus is digested free and inverts the scolex, which attaches to the wall of the small intestine and begins to bud off the long chain of segments. In about 3 months the worm reaches four-five thou in length and gravid segments begin to pass through the anus. The worm is long-lived, surviving 5 to 20 years or more than.

Effigy 89-2

Life cycles of Taenia solium and T saginata. . (a) The port (pig) tapeworm (outer developmental cycle); (b) the beef (cattle) tapeworm (inner developmental bike). A. Final host: humans only. Tapeworm in the small intestine

Pathogenesis

Rare intestinal blockage or penetration accept been reported, just pathology is usually inconsequential—although the psychological distress at passing motile segments may exist extreme.

Host Defenses

Because of its express contact with the epithelial lining, the gut-habitation adult tapeworm induces little host inflammatory, allergic, cell-mediated, or humoral response. The sucking action of the scolex appears to have relatively limited immunogenic event. The long life bridge of the worm suggests the absence of an constructive inhibitory mechanism.

Epidemiology

Taenia saginata, the commonest big tapeworm of humans, is transmitted as cysticerci in beef ("measly beef"). Partially cooked, smoked, or pickled beef can be infective, although raw beef (steak tartare) is the commonest bearer of infection, as witnessed by the frequency of taeniasis in countries such as Ethiopia and Argentina where raw or undercooked beef is often eaten.

Big worms may abound by 15 to xxx cm a day in the human being gut, passing ten segments daily, which may convey up to a million eggs a 24-hour interval into the environment throughout the long life span of the worm. Eggs may also be found in pastures flooded by human sewage or on which human sewage is used as fertilizer.

Diagnosis

Adult infections tin be diagnosed past identifying segments in the carrion. The species of Taenia can be identified but by the segments, considering their eggs are identical. The uterus of Tsaginata usually forms 12 to 20 branches on each side of the chief uterine stem, whereas there are 7 to 10 branches in the smaller and relatively wider T solium segment (meet Fig. 89-two).

Command

Inspection of beef for cysticerci is the all-time preventive mensurate. Beef must be thoroughly cooked in owned areas—to at least 56°C throughout the meat, which may be difficult to accomplish with big cuts of fatty meat, particularly pork. Freezing at 10°C for x days usually is lethal to Taenia cysticerci, but they can withstand 70 days at 0°C.

Treatment is readily available for the abdominal adult worms. Niclosamide, is a nonabsorbed oxidative phosphorylation inhibitor that kills the scolex and anterior segments on contact, later which the worm is expelled. Praziquantel, a constructed isoquinoline-pyrazine derivative, is an equally effective and relatively nontoxic cesticidal compound. Since the scolex is usually but non e'er destroyed, and a new worm can regenerate if the scolex and a minute portion of the neck survive, the patient should be observed for several months, as egg-begetting segments tin reappear in ten-12 weeks.

Taenia solium, The Pork Tapeworm

Clinical Manifestations

The clinical effects of adult T solium infection are similar to those acquired past T saginata.

Construction

The scolex of T solium differs from that of T saginata in possessing an anterior circle of sharply spined hooks arranged in a double row. These are under muscular control and work with the four suckers to attach to the gut wall. Equally described above, gravid segments of Tsolium can be distinguished from those of T saginata by the number of outpocketing branches of the uterus. The adult worm is usually 3 to 5 m long. Gravid segments tend to be less muscular and more square than those of T saginata.

Multiplication and Life Wheel

As shown in Figure 89-two, the life cycle of T solium is similar to that of T saginata except that the hog is the principal intermediate host. Because the gravid segments are less motile than those of T saginata, they are unremarkably eliminated in the fecal matter and remain in the fecal bolus (which increases the run a risk of infecting pigs, which are coprophagous).

Of peachy clinical importance is the fact that humans who ingest eggs from human feces, every bit distinct from cysticerci in undercooked pork, may develop the larval infection just as pigs do, resulting in the serious disease cysticercosis.

Pathogenesis

The hooked scolex of T solium may crusade greater abdominal disturbance, pain, and inflammatory response than that caused by T saginata, but symptoms are still mostly balmy and the pathology minor. Still, T solium larval infection (cysticercosis) is a potentially unsafe systemic infection, the degree of impairment depending on the site and number of cysticerci that develop. Infection almost unremarkably occurs in the central nervous arrangement (CNS). Information technology is besides frequently plant in muscles and subcutaneous tissues. The earth of the centre is as well a mutual site. In the CNS, the larvae most often occupy the brain hemispheres. They may also be found in the cisternae and ventricles. Hydrocephalus may consequence from obstacle of cerebrospinal fluid flow. Infection in specific sites tin can induce epilepsy, mental disturbances, or a meningeal syndrome. Nevertheless, upwards to one-half of CNS infections are thought to be asymptomatic. Subsequently expiry of the scolex inside the cyst—often years afterward infection—the sheathing becomes fibrosed or calcified.

Host Defenses

Owing to the systemic migration and tissue localization of the cysticerci, cysticercosis elicits considerable host sensitization. This response is usually bereft to block the initial infection simply probably renders the normal host immune to a subsequent ane. Much of the damage from cysticercosis is caused by the severe inflammatory host response that occurs after the death and disruption of the parasite .

Epidemiology

A remarkable and tragic attribute of T solium infection is the ability of this worm to develop both developed and larval stages in humans. If T solium eggs are ingested (from fecally contaminated water or by anus-to-mouth transfer of infective eggs), they may hatch in the gut and spread systemically, causing human being cysticercosis. Information technology appears likely (although information technology is unproven) that human cysticercosis may also be acquired when reverse peristalsis, induced by developed T solium in the gut, returns gravid segments into the duodenum, where the eggs hatch and release invasive oncospheres. Cysticerci develop to say-so in well-nigh 3 months and may live many years. Cysticerci that dice may become calcified, rendering them demonstrable by radiography.

Human cysticercosis is a serious and widespread affliction, being particularly common in Latin America. The affliction is frequently found among Mexican agricultural workers in California and other Western states. Human cysticercosis apparently cannot develop from eggs of T saginata.

Diagnosis

Diagnosis of adult worm infection is similar to that for T saginata. Cysticercosis is difficult to diagnose and ordinarily requires radiologic, serologic, and clinical cess. Subcutaneous nodules tin unremarkably be felt or observed, and can exist sampled past biopsy. The enzyme-linked immunosorbent assay (ELISA) is useful, especially with the purified antigens that are at present available. Plain radiographs of soft tissues may demonstrate the oval or elongated cysts (4-10 mm × 2-5 mm) if they are wholly or partially calcified. Cysts in muscles are usually aligned with the fibers. Soft tissue or encephalon calcifications are strongly indicative of cysticercosis. Plainly skull films may show cerebral calcifications or bespeak intracranial hypertension. Computed tomography is the most useful procedure, every bit it detects calcified and noncalcified cysts besides as edema or intracranial hypertension.

Control

The command of infection of humans as definitive hosts is the same every bit that for T saginata, except that the command measures apply to pork not beef. In add-on, man sewage from infected individuals may contaminate the source of drinking water. The eggs are highly resistant and tin withstand many months of environmental exposure over a broad temperature range. Treatment for adult T solium is the same as for T saginata.

Cysticercosis may crave surgery for ophthalmic or brain involvement, only chemotherapy should precede surgery when possible. Tissue infection can be treated with albendazol (taken with a fat meal to increase assimilation or praziquantel (combined with corticosteroids to reduce the inflammatory response to the dead cysticerci). Praziquantel should non be used for ocular or spinal cord infections.

Taenia multiceps, The Coenurus Tapeworm

The adult worm of Taenia multiceps is institute in dogs or wild canids. The larva is a bladderworm with multiple scoleces—from a few to 100 or more than—in an encysted vesicle. This vesicle, unremarkably two - 5 cm in diameter, is chosen a coenurus (Fig. 89-one). The usual intermediate host is the sheep. Human infection tin occur from accidental ingestion of dog feces containing the eggs.

Infection in humans normally occurs in the brain in temperate areas, and in the center or subcutaneous tissues in tropical areas. Diagnosis and handling are similar to those for Echinococcus infection, which may be difficult to distinguish from coenurus infection. Treatment is importantly surgical, although the drugs used for cysticercosis may also be effective against coenurus infection.

Echinococcus granulosus, The Hydatid Tapeworm

Clinical Manifestations

Echinococcosis (hydatid disease) results from the presence of one or more than massive cysts, or hydatids, which tin develop in any tissue site, including the liver, lungs, heart, brain, kidneys, and long bones. The clinical manifestations of this infection therefore vary profoundly, depending on the site and size of the cyst, but resemble those of a slow-growing tumor that causes gradually increasing pressure. Infections in the liver, lungs, or subcutaneous tissue sites may exist asymptomatic for many years, but pressure level effects eventually develop. In sensitive or vital areas, hydatids produce a panoply of symptoms, chiefly attributable to mechanical compression or blocking furnishings but also include collapse of infected long basic, blindness, and epileptiform seizures. The rupture of a hydatid cyst may induce sudden anaphylactic shock in a previously asymptomatic individual.

Structure

Developed E granulosus tapeworms are relatively infinitesimal, consisting of 3 to 5 segments, and commonly are less than one cm long. Dogs and wild canids are the only final hosts in which the adults are found, oftentimes adhering in great numbers to the small intestinal mucosa. The scolex has iv suckers and is crowned with a circumvolve of spines equally in T solium. It is followed past a germinative neck region, one developing segment, and commonly ane gravid segment containing several hundred eggs.

The hydatid larva is institute in sheep, in many other herbivores—and in humans. In humans the cyst is tiresome-growing, but in a period of years may accomplish a diameter of xxx cm with a ane mm thick, laminated sheath surrounded by fibrous reactive host tissue. The cyst is usually fluid-filled and, if viable, has a germinative inner lining from which many thousands of scoleces are budded off into the lumen or remain attached to the germinative wall (Fig. 89-1). The floating scoleces often enlarge, become vesicular, and develop into daughter floating colonies within the parent cyst. These in plow may bud off a third generation of cysts within themselves. The result is an enclosed sac containing myriads of future adult worms ready to infect a domestic dog or other susceptible carnivore that feeds on the hydatid-infected animal and the scolex-filled cyst fluid.

Multiplication and Life Wheel

Echinococcus granulosus causes a zoonosis; the developed is a parasite of canids. The dog-sheep bike (Fig. 89-3) is the ane almost germane to humans Other animate being cycles, such equally dog-camel, dog-horse, wolf-moose, wolf- or coyote-deer, too occur, each with a caste of specific host-parasite accommodation, as well as a distinct geographic range. Eggs passed by the dog tin can be ingested by sheep or other herbivores, or past humans who have shut contact with feces-contaminated dog fur. Within the sheep or human intermediate host, the eggs hatch, the oncospheres penetrate the gut, migrate, and ultimately 1 or several may form the enormous hydatid cysts. Because the scoleces in the hydatid fluid resemble sand grains, they are chosen hydatid sand. If a cyst bursts within the human body, it can give ascent to dozens of new cysts—limited, in most cases, by a strong cellular allowed response of the host.

Effigy 89-iii

Life cycles of Echinococcus granulosus and E multiocularis. A. Final host: dog (and other canids) 1.a. Echinococcus granulosus (beside it, the worm is reproduced approximately half its natural size)

Pathogenesis

Jaundice and portal hypertension can issue from pressure furnishings of a cyst in the liver; hemoptysis and dyspnea from a lung cyst; and acute inflammatory effects may follow brain or spinal cord infections.

Host Defenses

The migrating and growing larvae, and antigens that leak from the cyst, induce a strong immune response—but rarely one capable of penetrating and destroying the cyst. Ruptured cysts may crusade anaphylaxis and the advent of new cysts in other sites, suggesting an active but ineffectual immune response.

Epidemiology

Echinococcus granulosus is well-nigh common in temperate sheep-raising areas: southern South America, the southern and primal Russia, East Africa, and the western United States. The source of most human being infections is sheepdog feces containing E granulosus eggs (which often adhere to the fur of dogs petted by humans). Killed sheep fed to dogs maintain the infection; sheep ingest eggs with canis familiaris feces in their grazing. Other species of Echinococcus are too establish in Africa, Southward America, and elsewhere, sustained past similar canid-prey relationships.

Diagnosis

Symptoms of a tumorlike, slowly growing mass with eosinophilia are strongly suggestive, peculiarly in an endemic sheep-raising area. Isolated hooks in the sputum suggest rupture of a lung cyst. The serologic tests that are currently most useful are indirect hemagglutination, latex agglutination, and ELISA. However, both faux positives and fake negatives are frequent and may have unsafe repercussions (see Morris and Richard, 1992; Schantz et al., 1990). Ultrasound imaging (US), magnetic resonance (MR), and computed centric tomography (CT) have profoundly improved the diagnosis of deep-seated lesions and also can demonstrate avascular fluid-filled cysts. Radiographs are less precise or useful, although they demonstrate the hollow cyst areas.

Command

Constructive control is chiefly epidemiologic: denying sheep dogs access to carcasses of infected sheep, obligatory testing and treatment of all sheep dogs, prevention of contact of children with possibly infected sheep dogs, and widespread instruction on the danger and method of spread of hydatid affliction.

Handling is importantly by surgical resection (with extreme care to avoid or decontaminate spillage). Recent work suggests that a long class of albendazole may kill the scoleces within the cyst and even reduce the size of the cyst. Long, continued use of mebendazole has also proved constructive, although the results are variable. A recent approach involves percutaneous puncture under sonographic guidance, aspiration of cyst fluid, instillation of a protoscolecidal amanuensis such every bit 95% methanol or cetrimide, and respiration (PAIR), along with albendazole treatment to reduce the danger of subsequently renewed affliction from spillage (run across Giorgio et al., 1992).

Echinococcus multilocularis, The Multiloculate or Alveolar Hydatid Tapeworm

Echinococcus multilocularis, which normally follows a fox-rodent wheel in northern Siberia and Due north America, is occasionally conveyed to human being fur trappers via fox pelts. In humans information technology causes a often fatal form of echinococcosis. The appearance and life bike of this cestode closely resemble those of E granulosus, except for the restricted range and small number of hosts. The cyst, even so, is extremely dangerous as it lacks the laminated membrane that confines the cyst of Due east granulosus, and develops an invasive, uncontrolled series of connected chambers (hence the designation "multiloculate" and the alternative proper noun alveolar hydatid). Information technology therefore resembles a malignant growth, capable of budding off to cause metastatic spread. The primary cyst normally forms in the liver. The affliction is unremarkably diagnosed late, when it is inoperable, and ends fatally. Early radiologic imaging by United states, CT, or MR is essential. Serological tests, particularly with purified E multilocularis antigens, are sensitive and highly specific. Treatment with mebendazole, albendazole, or praziquantel, and surgery should follow.

Hymenolepis nana, The Dwarf Tapeworm

Clinical Manifestations

Hymenolepis nana infections are oft asymptomatic, especially in lite cases. Heavy infections can induce enteritis with nausea and vomiting, diarrhea, abdominal pain, and dizziness. Massive infection with several thousand worms may follow autoreinfection.

Structure

These small worms, xv to l mm long, have minute segments that are wider than long, a foursucker scolex with a retractable spined anterior rostellum, and concluding gravid segments that break upward and release their egg load later they are defenseless up in the fecal bolus.

The larval form is a cysticercoid, a tailed construction that has a withdrawn scolex and lacks a fluid filled bladder. Typically, Hymenolepis larvae are found in insect or crustacean intermediate hosts—with the sole and remarkable exception of H nana, whose cysticercoid larvae can develop either in an insect or in the pocket-sized intestinal villi of its homo (or rodent) final host.

Multiplication and Life Wheel

The life bike of this parasite is shown in Effigy 89-four. Infection is caused most commonly from eggs in the carrion of another infected individual, which are transferred in food, past contaminated fingers, or in sewage-contaminated drinking h2o.

Figure 89-4

Life cycle of Hymenolepis nana. A. Concluding host: humans (likewise dog, rodents) 1. Hymenolepis nana, sexually mature worm, well-nigh 1/two natural size

The ingested eggs hatch in the duodenum, and the oncospheres penetrate only into the villi (Fig. 89-five). At that place, each oncosphere forms a cysticercoid larva that emerges, 4 to 5 days later, into the gut lumen as a young scolex and cervix; the scolex attaches to the mucosa, the neck proceeds to strobilate, and the worm reaches full size in five to ten days. The adult worm sheds gravid terminal segments, which disintegrate in the intestine, releasing eggs that are passed in the feces. When these eggs are ingested by another (nonimmune) human, this directly or one-host life cycle begins again. Worms live but a curt time, mayhap iv to 6 weeks. Rodents also can harbor these worms and may serve as reservoir hosts, infecting humans via their pellets.

Figure 89-5

Diagrammatic section of an adult and larval H nana in the gut of a mouse. . In heavy infections in this host, much of the mucosal lining is abraded. (From Muller R: Worms and Disease: A Transmission of Medical Helminthology. William Heinemann Medical Books, (more...)

Remarkably, an indirect, two-host wheel may also occur, involving grain beetles, fleas, or other insects that feed on contaminated rodent droppings. Insects that ingest the H nana eggs tin can serve as hosts for the cysticercoid larvae. Humans who accidentally ingest infected grain beetles (some of which, such as Tribolium, are but ii to 3 mm long) digest the cysticercoid costless; digestive enzymes then human action on the cysticercoid to release the scolex, which attaches and develops by this indirect bike into an adult worm identical to that acquired by the directly life cycle.

A third mode of infection is by internal infection or autoreinfection. Eggs from worms acquired in an initial infection—probably via the indirect, insect wheel, which is nonimmunizing (see Host Defenses, below)—can hatch, invade the villi, and produce a second generation of worms. Since many eggs can be involved, this pathway tin lead to massive infection with several 1000 worms.

Pathogenesis

Fiddling or no pathology occurs from development of cysticercoids in the villi, and just after a heavy infection (perhaps produced by autoreinfection) practice symptoms develop from the adult worms. Children may be particularly subject to massive worm loads and show the nigh astringent intestinal symptoms.

Host Defenses

The tissue phase of the directly bicycle of H nana infection (Figs. 89-four and 89-5) initiates a profound cellular and humoral response, rendering most hosts immune to subsequent infection (as demonstrated experimentally in rodents). In dissimilarity, the indirect bicycle through infected insects does not involve mucosal embryogenesis in humans and induces fiddling or no immunity, even permitting occasional massive internal reinfection to occur. The immune response is seldom constructive confronting the initial infection because the tissues have already been invaded and a protective cyst formed past the fourth dimension the response develops.

Epidemiology

Hymenolepis nana is probably the commonest human cestode, owing to its wide distribution, specially in crowded areas, such as Bharat and China. The direct infectiousness of the eggs frees the parasite from its quondam dependence upon an insect intermediate host, making rapid infection and person-to-person spread possible. The curt life bridge and rapid class of development also facilitate the spread and fix availability of this worm. Congested areas, 24-hour interval-care centers, and crowded institutions such as prisons frequently have loftier levels of infection with H nana, despite its strong immunizing capacity and short life span.

Diagnosis

H nana infections can be diagnosed accurately and chop-chop by inspecting the stool for eggs.

Control

Preventing fecal contamination of food and water in institutions and crowded areas is of primary importance. General sanitation and rodent and insect control (especially control of fleas and grain insects) are also essential for prevention of H nana infection. Handling with praziquantel or niclosamide is usually constructive, and can be repeated if necessary.

Hymenolepis diminuta, The Rat Tapeworm

The rat tapeworm, which is larger than H nana (upward to 40 cm long), has a life cycle involving grain insects, similar to the indirect cycle of H nana. H diminuta rarely infects humans, merely may do so if a human eats an insect carrying cysticercoids of this worm. The infection is most common in children, causes a mild diarrhea, is diagnosed by finding the feature eggs in the stool, and is readily treated with praziquantel.

Dipylidium caninum, The Double-Pored Tapeworm

Dipylidium caninum causes a cosmopolitan infection of dogs and cats. Fleas are the intermediate hosts in which the infective cysticercoids develop. Children in shut and continuous contact with pets are occasionally infected as a result of the accidental ingestion of an infected flea. The infection is commonly asymptomatic and is cocky-express, although praziquantel would probably be an effective treatment. Flea command of pets would largely eliminate the infection from household pets and children.

Diphyllobothrium latum, The Wide Fish Tapeworm

Clinical Manifestations

Infection with Diphyllobothrium latum is usually asymptomatic, although occasional diarrhea, abdominal pain, fatigue, vomiting, dizziness, or numbness of fingers and toes may exist present. Eosinophilia develops during the early on stages of worm growth.

Structure

Diphyllobothrium latum is the largest parasite of humans, reaching lengths upward to 10 one thousand and consisting of a chain of iii,000 to 4,000 segments, each up to 2 cm wide. The adult worm, a member of the gild Pseudophyllidea, is characterized by a scolex with a pair of linear sucking grooves instead of suckers and hooks, and by having a rosette-shaped uterus continued to the outside past a uterine pore through which the eggs are passed. Hence, mature segments produce eggs until they die and are shed, rather than by breaking off equally intact egg-filled segments, as in Taenia. Up to a million eggs can exist produced daily. The developmental stages are (1) the ciliated, swimming coracidium that hatches from the egg, (2) the procercoid that develops in the copepod principal host, and (3) the plerocercoid (or sparganum), a nonencysted, nonsegmented larval worm, 20 mm or more in length, found in the fish secondary hosts. The plerocercoid develops into the adult tapeworm in the small intestine of a fish-eating final host, such every bit human, cat, dog, or bear.

Multiplication and Life Cycle

Diphyllobothrium latum is the only adult cestode of humans that has an aquatic life bicycle (Fig. 89-6). Eggs are passed in carrion of an infected human (or bear, dog, cat, wolf, raccoon, or other freshwater fish-eating reservoir host). If passed into lake or swimming water, the eggs develop in two or more weeks (varying with the temperature) and hatch, releasing the spherical ciliated coracidium that contains the oncosphere. When ingested past an advisable water flea (copepods such as Cyclops or Diaptomus), the coracidium sheds the ciliated coat, penetrates into the hemocoel, and changes in 2 to 3 weeks into the 0.5 mm, tailed 2nd-phase embryo, the procercoid. If the infected copepod is and so ingested by a minnow or other fish, the procercoid penetrates the fish gut in a few hours and afterwards develops into a third-stage larva, the plerocercoid or sparganum. Ordinarily, these small infected fish are eaten by larger ones; in each new fish host, the plerocercoid penetrates into the fascia or muscles. Eventually, a large game fish, such as a perch or state highway, is infected; after existence eaten by a human, the fish releases its tapeworm passenger, which attaches and begins adult life. In a few months, the worm is five to 10 m long.

Figure 89-half dozen

Life bike of Diphyllobothrium latum. A. Final host: Humans, dogs, cats (and other fish-eating domesticated and wild animals). Site of the tapeworm: small intestine 1. Egg subsequently it is passed in feces

Pathogenesis

Infection with this tapeworm usually produces no pathology, although the small-scale symptoms noted in a higher place are occasionally present. Megaloblastic anemia ("tapeworm anemia"), which is exacerbated past the worm's uptake of vitamin B12, is now seldom seen, as a result of improved diet, prenatal care, and ready handling. This condition was formerly well-nigh mutual in Republic of finland.

Host Defenses

Little or no protective immunity develops, owing to the lack of an intimate tissue phase in the human host. Reinfection is common.

Epidemiology

Infection with the broad fish tapeworm is mutual in temperate and subarctic regions, wherever freshwater fish are eaten raw—every bit in Scandinavia, Siberia, the Great Lakes, Japan, central Europe, and Chile.

Diagnosis

The ovoid, operculated eggs passed in abundance in the human stool are diagnostic. Occasionally, strands of exhausted segments with the characteristic rosette-shaped uteri are also passed.

Control

Plerocercoids in fish are quickly killed by thorough cooking, freezing at -10°C for 15 minutes, or thorough pickling. Treatment of sewage before information technology enters lakes greatly reduces the prevalence of infection, every bit has been demonstrated in Republic of finland. Handling with praziquantel or niclosamide is effective and nontoxic.

Spirometra

Sparganosis is a tissue infection with the sparganum (or plerocercoid) of Spirometra, a genus related to Diphyllobothrium. These two genera accept like life cycles, merely Spirometra commonly utilizes frogs, reptiles, or various small mammals as intermediate hosts, whereas Diphyllobothrium uses fish. In the Southeast Asia, frog flesh (rather than beef steak) is used as a poultice over a wound or blackness centre, which allows the sparganum to clamber into the wound or orbit, initiating a astringent inflammatory response. Humans can also acquire the infection every bit a result of drinking water containing infected Cyclops and possibly from undercooked snake or other infected meat. The procercoids from Cyclops invade the gut wall of the human or beast intermediate host and usually migrate to subcutaneous tissues to form a sparganum, which induces in humans germination of a fibrous 2-cm nodule that encloses and destroys the worm. The nodule tin normally be removed surgically or can be treated with praziquantel if the cyst is inaccessible to surgery.

References

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2. Desnos G, Brochet E, Cristofini P. et al. Polyvisceral echinococcosis with cardiac interest imaged by two-dimensional echocardiography, computed tomography and nuclear magnetic resonance imaging. Am J Cardiol. 1987;59:383. [PubMed: 3812300]

3. Flisser A. Taeniassis and cysticercosis due to Taenia solium. (Review) Progress in Clinical Parasitology. 1994;4:77–116. [PubMed: 7948938]

4. Gemmell MA, Lawson JR, Roberts MG. Control of echinococcosis/hydatidosis. Present state of worldwide progress. Bull WHO. 1986;64:333. [PMC free article: PMC2490883] [PubMed: 3490317]

5. Ito A, Smyth JD: Adult cestodes. In Soulsby EJL (ed): Immune Responses in Parasitic Infections: Immunology, Immunopathology, and Immunoprophylaxis. Vol. 2. Trematodes and Cestodes. CRC Press, Boca Raton, FL, 1987 .

6. Kammerer WS, Schantz PM: Echinococcal illness. In Maguire JH, Keystone JS (ed): Communicable diseases clinics of North America. Parasitic Diseases 7(3):467, Saunders, Philadelphia, 1993 .

7. McCormick GF. cysticercosis—Review of 230 patients. Bull Clin Neurosci. 1985;50:76. [PubMed: 3842090]

8. Morris DL, Richards KS: Hydatid Affliction: Electric current Medical and Surgical Management. Oxford, Butterworth-Heinemann LTD., 1992 .

9. Pawlowski ZS: Cestodiases: taeniasis, cysticercosis, diphyllobothriasis, hymenolepiasis, and others. In Warren KS, Mahmoud AAF (eds): Tropical and Geographical Medicine. second Ed. McGraw-Hill Information Services, New York, 1990 .

10. Schantz PM: Cestode diseases. In Goldsmith R, Heyneman D (ed): Tropical Medicine and Parasitology. Appleton & Lange, East Norwalk, CT, 1989 .

11. Sortelo J, Escobedo F, Penagas P. Albendazole vs praziquantel for therapy of neurocysticercosis. Curvation Neurol. 1988;45:532. [PubMed: 3358706]

12. St. Geme JW, Maldonado YA, Enzmann D. et al. Consensus: diagnosis and management of neurocysticercosis in children. Pediatr Infect Dis J. 1993;12:455. [PubMed: 8345976]

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Source: https://www.ncbi.nlm.nih.gov/books/NBK8399/

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