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Parasitology helmith 2011
- 1. Clinical Parasitology: Helminths Mercury Y. Lin, MD FCAP LCDR MC USN Laboratory Department
- 2. 2 CME Disclaimer • Educational information within this presentations is believed to be accurate as of time of presentation. • The following presentation will discuss general approaches and concepts to clinical parasitology and should not to be misconstrued as a "Standard". • Consultation with additional published guidelines, reference materials and clinical experts are recommended.
- 3. 3 Before we start. What do you need to know about stool ova & parasite? • Interfering substances - bismuth, barium (wait 7-10 days), antimicrobial agents (wait 2 weeks), gall bladder dye (wait 3 weeks after procedure). • Submit fresh stool (lab will add formalin). • Do not freeze or refrigerate stool sample* • Repeat studies maybe needed due to erratic shed rates of some parasites.
- 4. 4 classification of human parasites • Nematodes (roundworms) – Intestinal – Blood and tissue • Cestodes (tapeworms) – Intestinal – Tissue (larval stage) • Trematodes (flukes/flatworms) – Intestinal – Liver/lung – blood • Protozoa – Intestinal • Amebae • Flagellates • Ciliates • Apicomplexa (coccidia) – Blood/tissue • Flagellates • Amebae • apicomplexa Helminths
- 5. 5 Classification of Helminths Nematodes (roundworms) Cestodes (tapeworms) Trematodes (flukes) Shape Cylindrical Segmented plane Unsegmented plane Body cavity Yes No No Digestive tract Complete No Incomplete Sex Male or female hermaphrodites hermaphrodites (except Schistosoma)
- 6. Intestinal nematodes (roundworms) Most easily recognized from of intestinal parasite: large size and cylindrical, unsegmented body Live primarily as adults in intestine and confirmed by identification of egg in feces Ascaris lumbricoides Enterobius vermicularis Trichuris trichiura Hookworms Ancylostoma duodenale A. ceylanicum Necatur americanus Strongyloides stercoralis Anisakis simplex
- 7. Ascaris lumbricoides largest nematode (roundworm) parasitizing the human intestine. (Adult females: 20 to 35 cm; adult male: 15 to 30 cm.) The most common human helminthic infection. Worldwide distribution. Highest prevalence in tropical and subtropical regions, and areas with inadequate sanitation. Occurs in rural areas of the southeastern United States.
- 8. Ascaris lumbricoides Fecal-oral infection Ingested egg releases larvae which penetrates duodenal wall, enters blood and goes to liver, heart and pulmonary circulation; grow in alveoli, then coughed up, swallowed back to intestine Eggs released into soil where they become infectious
- 9. Ascaris lumbricoides Although infections may cause stunted growth, adult worms usually cause no acute symptoms. High worm burdens may cause abdominal pain and intestinal obstruction. Migrating adult worms may cause symptomatic occlusion of the biliary tract or oral expulsion. During the lung phase of larval migration, pulmonary symptoms can occur (cough, dyspnea, hemoptysis, eosinophilic pneumonitis - Loeffler’s syndrome). Treatment of ascariasis are albendazole* with mebendazole, ivermectin*, and nitazoxanide as alternatives.
- 10. Enterobius vermicularis a.k.a.: human pinworm. (Adult females: 8 to 13 mm, adult male: 2 to 5 mm.) Humans are considered to be the only hosts of E. vermicularis. A second species, Enterobius gregorii, has been described and reported from Europe, Africa, and Asia. For all practical purposes, the morphology, life cycle, clinical presentation, and treatment of E. gregorii is identical to E. vermicularis. Infections more frequent in school- or preschool-children and in crowded conditions. More common in temperate than tropical countries. The most common helminthic infection in the United States (estimated 40 million persons infected).
- 13. Enterobius vermicularis Infection maybe asymptomatic. The most typical symptom is perianal pruritus, especially at night, which may lead to excoriations and bacterial superinfection. Occasionally, invasion of the female genital tract with vulvovaginitis and pelvic or peritoneal granulomas can occur. Other symptoms include anorexia, irritability, and abdominal pain. Laboratory diagnosis: “Scotch-tape test,” or Falcon Paddle Treatment with pyrantel pamoate (“PIN-X”). Also personal hygiene prevent reinfection/laundry bedding.
- 14. Trichuris trichiura a.k.a.: human whipworm 3rd most common round worm of humans (approx 800 million infected worldwide). Infections more frequent in areas with tropical weather and poor sanitation practices, and among children. Trichuriasis occurs in the southern United States. No animal reservoir Fecal oral
- 16. 16 Trichuris trichiura Most frequently asymptomatic. Heavy infections, especially in small children, can cause gastrointestinal problems (abdominal pain, diarrhea, rectal prolapse) and possibly growth retardation. Confirm diagnosis with microscopic identification of whipworm eggs in feces. Treatment with mebendazole or albendazole.
- 17. Ancylostoma duodenale, Necatur americanus (Human hookworms) Hookworm is the second most common human helminthic infection (after ascariasis). Both N. americanus and A. duodenale are found in Africa, Asia and the Americas. Necator americanus predominates in the Americas and Australia, while only A. duodenale is found in the Middle East, North Africa and southern Europe.
- 18. Hookworms are difficult to distinguish, and differs only in mouth morphology. Other hookworms infecting animals may also invade and parasitize humans (A. ceylanicum, A. caninum) or can penetrate the human skin (causing cutaneous larva migrans), but do not develop any further (A. braziliense, A. caninum, Uncinaria stenocephala).
- 19. Ancylostoma duodenale, Necatur americanus (Human hookworms) (intestinal hookworm infection)
- 20. zoonotic infection with other hookworms (cutaneous larval migrans)
- 21. Ancylostoma duodenale, Necatur americanus (Human hookworms) Iron deficiency anemia (caused by blood loss at the site of intestinal attachment of the adult worms) is the most common symptom of hookworm infection. respiratory symptoms can be observed during pulmonary migration of the larvae. Microscopic identification of eggs in the stool is the most common method for diagnosing human hookworm infection. Cutaneous larval migrans is usually diagnosed clinically as there are no serologic tests for zoonotic hookworm infections. Larvae may be seen in stained tissue sections, but low yield as parasites are usually not found in the visible track. In countries where hookworm infection is prevalent, light infections are often not treated. In the United States, hookworm infections are generally treated with albendazole. Cutaneous larva migrans is a self-limiting infection but can be treated with albendazole or ivermectin
- 22. Strongyloides stercoralis are more complex than that of most nematodes as it can alternation between free-living and parasitic cycles, and its potential for autoinfection and multiplication within the host. Occur in tropical and subtropical areas, but cases also occur in temperate areas (including the South of the United States). Seen in rural areas, institutional settings, and lower socioeconomic groups.
- 24. Strongyloides stercoralis Frequently asymptomatic. Gastrointestinal symptoms include abdominal pain and diarrhea. Pulmonary symptoms (including Loeffler’s syndrome) can occur during pulmonary migration phase. Diagnosis rests on the microscopic identification of larvae in the stool or duodenal fluid (Enterotest). Examination of serial samples may be necessary because stool examination is relatively insensitive. Serum Strongyloides IgG ELISA is commercially availabe. Treatment of uncomplicated strongyloidiasis is ivermectin.
- 25. 25 Anisakis simplex Worldwide, with higher incidence in areas where raw fish is eaten (e.g., Japan, Pacific coast of South America, the Netherlands). Anisakiasis is caused by the accidental ingestion of larvae of the nematodes (roundworms) Anisakis simplex and Pseudoterranova decipiens. Within hours after ingestion of infected larvae, violent abdominal pain, nausea, and vomiting may occur. Occasionally the larvae are coughed up. If the larvae pass into the bowel, a severe eosinophilic granulomatous response may also occur 1 to 2 weeks following infection, causing symptoms mimicking Crohn's disease. Adequately cooking fish (60° C) or freezing (-20° C for seven days or -35° C for 15 hours) before ingestion will kill anisakid helminths.
- 27. 27 Anisakis simplex Diagnosis can be made by gastroscopic examination during which the 2 cm larvae are visualized and removed, or by histopathologic examination of tissue removed at biopsy or during surgery. The treatment of choice is surgical or endoscopic removal. Dolphin stomach
- 28. Tissue & Blood Nematodes Trichinella spiralis Filarial worms Wuchereria bancrofti Brugia malayi Onchocerca volvulus Loa loa
- 29. Tissue & Blood Nematodes Filarial worms Wuchereria bancrofti (tropical areas worldwide) Brugia malayi (limited to Asia) Wuchereria bancrofti
- 30. Tissue & Blood Nematodes Onchocerca volvulus (a.k.a.: River Blindness) mainly in Africa, with additional foci in Latin America and the Middle East.
- 31. Cestodes (tapeworms) Taenia solium Taenia saginata Diphyllobothrium latum Cestodes are flat and ribbonlike with heads armed with organs for attachment (scolex) All are hermaphroditic with male and female reproductive organs in each mature protoglottid (indiv segments together make strobila) No digestive system, food is absorbed from host intestine Eggs are nonoperculated (except D.latum) Infections with larval stages are always in tissues usually by ingestion of eggs passed in feces (cysticercus, hydatid cyst)
- 32. Taenia solium (pork tapeworm) Taenia solium (pork tapeworm) is the main cause of human cysticercosis. Prevalent in Africa, India, SE Asia, China, Mexico, Latin America. Because pigs are intermediate hosts of the parasite, completion of the life cycle occurs in regions where humans live in close contact with pigs and eat undercooked pork. Human cysticercosis is acquired by ingesting T. solium eggs shed in the feces of a human T. solium tapeworm carrier, and thus can occur in pts that neither eat pork nor share environments with pigs.
- 33. Taenia Saginatum (beef tapeworm) Eggs same as T.solium. Proglottid 15-30 branches on uterine system
- 35. Taenia spp.
- 36. Diphyllobothrium latum (fish tapeworm) Worldwide, cool lake regions where freshwater fish eaten raw or pickled Usu asx Infection associated with pernicious anemia b/c parasite absorbs vitamin B12 Complicated life cycle with up to three hosts (freshwater fish last)
- 39. Echinococcus granulosus Human echinococcosis (hydatid disease) is caused by the larval stages of cestodes of the genus Echinococcus. Echinococcus granulosus causes cystic echinococcosis, the form most frequently encountered; E. multilocularis causes alveolar echinococcosis. Hooklets or “Bat'leth Sign”
- 40. Bat'leth
- 42. Echinococcus granulosus E. granulosus occurs practically worldwide, and more frequently in rural, grazing areas where dogs ingest organs from infected animals. E. multilocularis occurs in the northern hemisphere, including central Europe and the northern parts of Europe, Asia, and North America. Echinococcus infections remain silent for years before the enlarging cysts cause symptoms in the affected organs (liver, biliary duct, lung, brain, bone, heart). The diagnosis of echinococcosis relies mainly on findings by ultrasonography and/or other imaging techniques supported by positive serologic tests (ELISA IgG, IgE Ab). Treatment is surgery + albendazole to prevent recurrence.
- 43. Dipylidium caninum (dog tapeworm) (double-pored dog tapeworm) mainly infects dogs and cats, but is occasionally found in humans. Worldwide. Human infections have been reported in Europe, the Philippines, China, Japan, Argentina, and the United States. Most infections with Dipylidium caninum are asymptomatic. Pets may exhibit behavior to relieve anal pruritis (such as scraping anal region across grass or carpeting).
- 44. Dipylidium caninum (dog tapeworm)
- 45. Trematodes (flukes) Flat, fleshy leaf shaped worm Complicated life cycle starting with snail as intermediate host (some have 2nd int host) Two suckers – oral and ventral Hermaphrodites (except schisto) Fluke eggs have a “lid” called an operculum (except schisto)
- 46. Fasciolopsis buski largest intestinal fluke of humans. Geographic distribution: Asia and the Indian subcontinent, especially in areas where humans raise pigs and consume freshwater plants. Clinical: Most infections are asymptomatic. In heavier infections, symptoms include diarrhea, abdominal pain, fever, ascites, anasarca and intestinal obstruction. Dx: microscopic identification of eggs, or more rarely of the adult flukes, in the stool or vomitus. The eggs are indistinguishable from those ofFasciola hepatica. Tx: Praziquantel
- 49. Fasciola hepatica (sheep liver fluke) Human infections with F. hepatica are found in areas where sheep and cattle are raised, and where humans consume raw watercress, including Europe, the Middle East, and Asia. Possible symptoms: Liver irritation, hepatomegaly, RUQ pain, fever, chills, eosinophilia, hepatitis, biliary obstruction, portal cirrhosis Dx: Microscopic identification of eggs is useful in the chronic (adult) stage. Antibody detection tests are useful especially in the early invasive stages, when the eggs are not yet apparent Tx: Fasciola hepatica infections may not respond to praziquantel. The drug of choice is triclabendazole with bithionol as an alternative.
- 50. Fasciola hepatica (sheep liver fluke) Adult fluke Egg: virtually indistinguishable From F. bruski
- 51. Clonorchis sinensis (Chinese liver fluke) Endemic areas are in Asia including Korea, China, Taiwan, and Vietnam. From consuming undercooked or pickled freshwater fish containing metacercariae Symptoms: usually mild and asympt; severe infection (↑flukes in bile ducts) will cause fever, pain, jaundice, hepatomegaly, cholecystitis, cholangitis chronic infection can cause adenocarcinoma of bile ducts
- 52. Clonorchis sinensis (Chinese liver fluke) Adult fluke Egg
- 53. Clonorchis sinensis (Chinese liver fluke)
- 54. Paragonimus westermani (Oriental lung fluke) More than 10 species of Paragonimus genus are reported to infect humans, the most common is P. westermani, the oriental lung fluke. Paragonimus westermani is distributed in southeast Asia and Japan Clinical symptoms: -Acute phase : diarrhea, abdominal pain, fever, cough, urticaria, hepatosplenomegaly, pulmonary abnormalities, eosinophilia. -Chronic phase, pulmonary symptoms (cough, expectoration of discolored sputum, hemoptysis, and chest radiographic abnormalities). Possible CNS involvement in severe disease. Diagnosis: exam of eggs in stool or sputum (but present 2 to 3 months after infection), Ab detection of P. westermani antigen via serologic assays (westernblot or enzume immunoassay). Tx: Praziquantel, Bithionol.
- 55. Paragonimus westermani (Oriental lung fluke) Paragonimus spp egg from bronchial alveolar lavage @ 1000x Adult fluke
- 56. Schistosomes S. mansoni S. haematobium S. Japonicum Differ from other flukes Male and females No operculum on eggs Obligate intravascular organisms Not eaten (vegetation,fish,crustaceans), instead infected by skin penetrating cercariae
- 57. Schistosomes S. mansoni Most widespread, Africa, Saudi, Brazil, Venezuela, West Indies Reservoir hosts include primates, marsupials, rodents Resides in the small branches of the inferior mesenteric vein near lower colon Eggs deposited in bowel (GI symptoms) and eggs can go to portal vein (liver symptoms) Egg has a sharp lateral spine S. japonicum Found only in China, Japan, Philippines, Indonesia Reservoirs include domestic animals, cats, dogs, cattle, horses pigs Resides in branches of superior mesenteric vein around small intestine Involves GI and liver and brain Eggs spherical with inconspicuous spine S. haematobium Occurs in Africa, Asia, Portugal, India, Egypt Reservoirs include monkeys, baboons, chimps Develop in liver and migrate to vesicle, prostatic and uterine plexus Eggs deposit in bladder Associated with squamous cell carcinoma of bladder Eggs with terminal spine
- 58. Schistosomes Clinical: most infections are asymptomatic. Acute schistosomiasis (Katayama's fever) may occur weeks after the initial infection, especially by S. mansoni and S. japonicum. Manifestations include fever, cough, abdominal pain, diarrhea, hepatosplenomegaly, and eosinophilia. Microscopy of eggs is the most practical initial method for diagnosis. Stool examination should be performed when infection with S. mansoni or S. japonicum is suspected, and urine examination should be performed if S. haematobium is suspected. Special specimen prep techniques can increase diagnostic sensitivity. Tx: praziquantel , oxamniquine
- 63. 63
- 64. 64 References • Center of Disease Control & Prevention (http://dpd.cdc.gov atlas) • Ash & Orihel's Atlas of Human Parasitology (5th Ed.) Questions?
Notas del editor
- Flukes: incomplete digestive tract “Manus”
- Egg of A. lumbricoides with larva inside and Larva of A, lumbricoides hatching from an egg.
- * This drug is approved by the FDA, but considered investigational for this purpose.
- Cross-section of an adult female E. vermicularis . Note the presence of the alae (blue arrow), intestine (green arrow) and ovaries (black arrows). Eggs of E. vermicularis in a wet mount
- Eggs are deposited on perianal folds . Self-infection occurs by transferring infective eggs to the mouth with hands that have scratched the perianal area . Person-to-person transmission can also occur through handling of contaminated clothes or bed linens. Enterobiasis may also be acquired through surfaces in the environment that are contaminated with pinworm eggs (e.g., curtains, carpeting). Following ingestion of infective eggs, the larvae hatch in the small intestine and the adults establish themselves in the colon . The time interval from ingestion of infective eggs to oviposition by the adult females is about 1 month. The life span of the adults is about 2 months. Gravid females migrate nocturnally outside the anus and crawling on the skin of the perianal area . The larvae contained inside the eggs develop (the eggs become infective) in 4 to 6 hours under optimal conditions . Retroinfection, or the migration of newly hatched larvae from the anal skin back into the rectum, may occur but the frequency with which this happens is unknown.
- eggs are 50-55 micrometers by 20-25 micrometers. They are football-shaped, thick-shelled and possess a pair of polar “plugs” at each end
- unembryonated eggs are passed with the stool . In the soil, the eggs develop into a 2-cell stage , an advanced cleavage stage , and then they embryonate . After ingestion (soil-contaminated hands or food), the eggs hatch in the small intestine, and release larvae that mature and establish themselves as adults in the colon . The adult worms (approximately 4 cm in length) live in the cecum and ascending colon. The adult worms are fixed in that location, with the anterior portions threaded into the mucosa. Female worms in the cecum shed between 3,000 and 20,000 eggs per day. The life span of the adults is about 1 year.
- Ancylostoma caninum larvae have also been implicated as a cause of diffuse unilateral subacute neuroretinitis. Eggs of Ancylostoma and Necator are microscopically indistinguishable
- Eggs are passed in the stool , and under favorable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days. The released rhabditiform larvae grow in the feces and/or the soil and become filariform larvae that are infective . These infective larvae can survive 3 to 4 weeks in favorable environmental conditions. On contact with the human host, the larvae penetrate the skin and are carried through the blood vessels to the heart and then to the lungs. They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed . The larvae reach the small intestine, where they reside and mature into adults. Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall with resultant blood loss by the host . Most adult worms are eliminated in 1 to 2 years, but the longevity may reach several years. Some A. duodenale larvae, following penetration of the host skin, can become dormant (in the intestine or muscle). In addition, infection by A. duodenale may probably also occur by the oral and transmammary route. N. americanus, however, requires a transpulmonary migration phase.
- Normal definitive hosts for these species are dogs and cats. The cycle in the definitive host is very similar to the cycle for the human species. Humans may also become infected when filariform larvae penetrate the skin . With most species, the larvae cannot mature further in the human host, and migrate aimlessly within the epidermis, sometimes as much as several centimeters a day. Some larvae may persist in deeper tissue after finishing their skin migration.
- Left: Rhabditoid larva of S. stercoralis in an unstained wet mount of stool. Notice the rhabditoid esophagus (blue arrow) and prominent genital primordium (red arrow). Right: Adult female parasite in human small intestine. Notice parasite’s intestine (red arrow) and ovaries (blue arrows).
- Free-living cycle: The rhabditiform larvae passed in the stool (see "Parasitic cycle" below) can either molt twice and become infective filariform larvae (direct development) or molt four times and become free living adult males and females that mate and produce eggs from which rhabditiform larvae hatch . The latter in turn can either develop into a new generation of free-living adults (as represented in ), or into infective filariform larvae . The filariform larvae penetrate the human host skin to initiate the parasitic cycle (see below) . Parasitic cycle: Filariform larvae in contaminated soil penetrate the human skin , and are transported to the lungs where they penetrate the alveolar spaces; they are carried through the bronchial tree to the pharynx, are swallowed and then reach the small intestine . In the small intestine they molt twice and become adult female worms . The females live threaded in the epithelium of the small intestine and by parthenogenesis produce eggs , which yield rhabditiform larvae. The rhabditiform larvae can either be passed in the stool (see "Free-living cycle" above), or can cause autoinfection . In autoinfection, the rhabditiform larvae become infective filariform larvae, which can penetrate either the intestinal mucosa (internal autoinfection) or the skin of the perianal area (external autoinfection); in either case, the filariform larvae may follow the previously described route, being carried successively to the lungs, the bronchial tree, the pharynx, and the small intestine where they mature into adults; or they may disseminate widely in the body.
- Enterotest (“string test”): swallow a gelatin capsule attached to a long string. The end of the string remains outside the mouth and is taped to your cheek. The capsule dissolves in the stomach and the string passes into the upper part of the small intestine. same method as used for detecting giardia.
- Larvae of Trichinella in muscle tissue.
- Filariasis is caused by nematodes (roundworms) that inhabit the lymphatics and subcutaneous tissues. Infective larvae are transmitted by infected biting arthropods during a blood meal.
- Coiled microfilaria of O. volvulus, in a skin nodule
- Left: proglottid of T. solium, stained with carmine. Note the number of primary uterine branches (<13). Right: eggs of Taenia spp. are indistinguishable from each other and measure 30-35 micrometers in diameter with radial striation.
- T. saginata adults usually have 1,000 to 2,000 proglottids, while T. solium adults have an average of 1,000 proglottids. The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces. T. saginata may produce up to 100,000 and T. solium may produce 50,000 eggs per proglottid respectively.
- Treatment for taeniasis is Praziquantel.
- Left: proglottids of D. latum, showing the rosette-shaped ovaries. Right: Diphyllobothrium spp. eggs are oval or ellipsoidal and range in size from 55 to 75 µm by 40 to 50 µm
- Eggs released in develop into free swimming larva, coracidium which is ingested by crustaceans, then develps to larval from; crustacean eaten by fish and larvae develop in muscle (infective larva in fish is sparganum) which is eaten by other fish, mammals or man. Treatment of diphyllobothriasis: Praziquantel or Niclosamide.
- Left: degenerating protoscolex with hooklets Right: Echinococcus multilocularis in liver tissue, stained with hematoxylin and eosin (H&E).
- Echinococcus granulosus resides in the small bowel of the definitive hosts (dogs). Gravid proglottids release eggs that are passed in the feces. After ingestion by a suitable intermediate host (under natural conditions: sheep, goat, swine, cattle, horses, camel), the egg hatches in the small bowel and releases an oncosphere that penetrates the intestinal wall and migrates through the circulatory system into various organs, especially the liver and lungs. In these organs, the oncosphere develops into a cyst that enlarges gradually, producing protoscolices and daughter cysts that fill the cyst interior. The definitive host becomes infected by ingesting the cyst-containing organs of the infected intermediate host. After ingestion, the protoscolices evaginate, attach to the intestinal mucosa , and develop into adult stages in 32 to 80 days. The same life cycle occurs with E. multilocularis (1.2 to 3.7 mm), with the following differences: the definitive hosts are foxes, and to a lesser extent dogs, cats, coyotes and wolves; the intermediate host are small rodents; and larval growth (in the liver) remains indefinitely in the proliferative stage, resulting in invasion of the surrounding tissues. Human infection is accidental, dead-end intermediate hosts.
- E. granulosus IgG detection is an important tool for diagnosing hydatid disease, since infected individuals do not exhibit fecal shedding of E. granulosus eggs.
- Note the double set of reproductive organs per proglottid. 2 sets of genital pores, vas deferens, testes, uterus, ovary,