Parasitology helmith 2011

Clinical Parasitology: Helminths

Mercury Y. Lin, MD FCAPLCDR MC USN

Laboratory Department

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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.

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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.

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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

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Classification of Helminths

Nematodes (roundworms)

Cestodes (tapeworms)

Trematodes (flukes)

Shape Cylindrical Segmented plane Unsegmented planeBody cavity Yes No NoDigestive tract Complete No Incomplete

Sex Male or female hermaphrodites hermaphrodites

(except Schistosoma)

Intestinal nematodes (roundworms)

Most easily recognized from of intestinal parasite: large size and cylindrical, unsegmented bodyLive primarily as adults in intestine and confirmed by identification of egg in feces

Ascaris lumbricoidesEnterobius vermicularisTrichuris trichiuraHookworms

Ancylostoma duodenaleA. ceylanicumNecatur americanus

Strongyloides stercoralisAnisakis simplex

Ascaris lumbricoideslargest 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.

Ascaris lumbricoidesFecal-oral infectionIngested 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

Ascaris lumbricoidesAlthough 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.

Enterobius vermicularisa.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).

Enterobius vermicularis

Appendix

Enterobius vermicularis

Enterobius vermicularisInfection 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.

Trichuris trichiuraa.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

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Trichuris trichiura

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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.

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.

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).


(intestinal hookworm infection)

zoonotic infection with other hookworms

(cutaneous larval migrans)


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

Strongyloides stercoralisare 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.

Strongyloides stercoralis

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.

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Anisakis simplexWorldwide, 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.

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Anisakis simplex

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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

Tissue & Blood Nematodes

Trichinella spiralisFilarial worms

Wuchereria bancroftiBrugia malayi

Onchocerca volvulusLoa loa


Filarial wormsWuchereria bancrofti (tropical areas worldwide)Brugia malayi (limited to Asia)

Wuchereria bancrofti


Onchocerca volvulus (a.k.a.: River Blindness)mainly in Africa, with additional foci in Latin America and the Middle East.

Cestodes (tapeworms)

Taenia soliumTaenia saginataDiphyllobothrium 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)

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.

Taenia Saginatum (beef tapeworm)

Eggs same as T.solium.

Proglottid 15-30 branches on uterine system

Taenia spp.

Diphyllobothrium latum (fish tapeworm)

Worldwide, cool lake regions where freshwater fish eaten raw or pickledUsu asx

Infection associated with pernicious anemia b/c parasite absorbs vitamin B12

Complicated life cycle with up to three hosts (freshwater fish last)

Diphyllobothrium latum (fish tapeworm)

Echinococcus granulosusHuman 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”

Bat'leth

Echinococcus granulosus

Echinococcus granulosusE. 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.

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).

Dipylidium caninum (dog tapeworm)

Trematodes (flukes)Flat, fleshy leaf shaped wormComplicated 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)

Fasciolopsis buskilargest 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

Fasciolopsis buski

Adult flukeegg

Fasciolopsis buski

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.

Fasciola hepatica (sheep liver fluke)

Adult flukeEgg: virtually indistinguishable From F. bruski

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


Adult flukeEgg

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.

Paragonimus westermani (Oriental lung fluke)

Paragonimus spp egg from bronchial alveolar lavage @ 1000x

Adult fluke

SchistosomesS. mansoniS. haematobiumS. Japonicum

Differ from other flukesMale and femalesNo operculum on eggsObligate intravascular organismsNot eaten (vegetation,fish,crustaceans), instead infected by skin penetrating cercariae

SchistosomesS. mansoni

Most widespread, Africa, Saudi, Brazil, Venezuela, West IndiesReservoir hosts include primates, marsupials, rodentsResides in the small branches of the inferior mesenteric vein near lower colonEggs deposited in bowel (GI symptoms) and eggs can go to portal vein (liver symptoms)Egg has a sharp lateral spine

S. japonicumFound only in China, Japan, Philippines, IndonesiaReservoirs include domestic animals, cats, dogs, cattle, horses pigsResides in branches of superior mesenteric vein around small intestineInvolves GI and liver and brainEggs spherical with inconspicuous spine

S. haematobiumOccurs in Africa, Asia, Portugal, India, EgyptReservoirs include monkeys, baboons, chimpsDevelop in liver and migrate to vesicle, prostatic and uterine plexusEggs deposit in bladder Associated with squamous cell carcinoma of bladderEggs with terminal spine

SchistosomesClinical: 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

Schistosoma mansoni

egg

Schistosoma japonicum

egg

Schistosoma haematobium

egg

Schistosomes

Gallbladder wall

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References

• Center of Disease Control & Prevention (http://dpd.cdc.gov atlas)

• Ash & Orihel's Atlas of Human Parasitology (5th Ed.)

Questions?

http://dpd.cdc.gov/

http://dpd.cdc.gov/

Parasitology helmith 2011

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