Parasitology-Lec 3 Nematodes 2

PARASITOLOGY LECTURE 3 - NematodesNotes from lecture, Zeibig (’97) and Murray (’98)USTMED ’07 Sec C – AsM

OUTLINE IN THE STUDY OF PARASITE

I. Nomenclature and synonymsII. Geographic distributionIII. MorphologyIV. Life cycleV. Pathology in the hostVI. Clinical symptomatologyVII. Laboratory diagnosisVIII. TreatmentIX. Preventive measures

GENERALITIES

helminths are multicellular and contain internal organ systems

nematodes are commonly known as the intestinal roundworms

Morphology and Life Cycle Notes

- members of the class nematoda may assume three basic morphologic forms: egg, larvae, and adult worms

- eggs vary in size and shape- the developing larvae located inside fertilized

eggs emerge and continue to mature; they are typically long and slender

- sexes are separate- the adult female worms are usually larger than the

adult males- the adults are equipped with complete digestive

and reproductive systems- life cycles of the nematodes are similar yet

organism specific- infection may be initiated in one of two primary

ways:1. ingestion of the infected eggs2. by burrowing through the skin of the foot

- the adult worms reside in the intestine where they concentrate on obtaining nutrition and reproduction

- adult females lay eggs in the intestine- eggs may be passed into the stool; once outside

the body, the larvae inside the eggs warm, moist soil and 2-4 weeks to mature

Laboratory Diagnosis

- through recovery of eggs, larvae and occasional adult worms

- the specimens of choice vary by species and include cellophane tape preparations taken around the anal opening, stool, tissue biopsies and infected skin ulcers

- ELISA is available for the diagnosis of select nematode organisms

Pathogenesis and Clinical Symptoms

- the following factors may contribute to the ultimate severity of a nematode infection

1. the number of worms present2. the length of time the infection persists3. overall health of the host

- with one exception, all of the nematodes may cause intestinal infection symptoms at some point during their invasion of the host

- symptoms include: abdominal pain, diarrhea, nausea, vomiting, fever and eosinophilia

- other symptoms: skin irritation, formation of blisters, muscle involvement

ASCARIS LUMBRICOIDES

I. Nomenclature and synonyms

Ascaris lumbricoides (as’kar-is/lum-bri-koy’deez) Common names: Large Intestinal Roundworm,

Roundworm of Man

II. Geographic distribution

most common intestinal helminth infection in the world

susceptible are warm climates and areas of poor sanitations

in the US frequency is greatest in the Appalachian Mountains and surrounding areas in the east, west and south

III. Morphology

Unfertilized Egg

decorticated unfertilized egg

unfertilized eggFertilized Egg

very corticated mature egg mature egg

corticated mature eggAdults

adult male

adult femaleIV. Life cycle

1. infection begins following the ingestion of infected eggs that contain viable larvae

2. inside the small intestine the larvae emerge from the eggs

3. the larvae complete a liver-lung migration by first entering the blood via penetration through the intestinal wall

4. first “stop” is the liver5. continues through the blood stream to

second “stop,” the lung6. once inside the lung, the larvae burrow

their way through capillaries into the alveoli

7. migration to bronchioles8. larvae are transferred through coughing

into the pharynx9. are swallowed and returned to the

intestines adult worms take up residence in the small

intestine adults multiply and a number of resulting

undeveloped eggs (up to 250,000/day) are passed in the feces

soil provides the necessary conditions for the eggs to embryonate

infective eggs remain viable for years eggs are not easily destroyed by chemicals Infective stage: embryonated eggs

V. Pathology in the host

a worm can migrate into the bile duct and liver and damage tissue

because the worm has a tough, flexible body, it can occasionally perforate the intestine, creating peritonitis with secondary bacterial infection

the adult worms do not attach to the intestinal mucosa but depend on constant motion to maintain their position w/in the bowel lumen

migration of worms to the lungs can produce pneumonitis resembling an asthmatic attack

migration can occur in response to fever, drugs other than those used to treat ascariasis and some anesthetics

pulmonary involvement is related to the degree of

hypersensitivity induced by previous infections and the intensity of the current exposure and may be accompanied by eosinophilia and O2 desaturation

a tangled bolus of worms in the intestines may cause obstruction, perforation and occlusion of the appendix

VI. Clinical symptomatology

Asymptomatic : patients infected with a small number of worms (5-10) will often remain asymptomatic

Ascaris/Roundwrom infection : patients who develop symptomatic ascariasis may be infected with as few as a single worm

o Intestinal phase may produce tissue damage;

secondary bacterial infection may occur following worm perforation

Px infected w/ many worms may exhibit vague abdominal pain, vomiting, fever and distention

Discomfort from adult worms exiting the body through anus, mouth or nose may occur

Protein malnutritiono Pulmonary phase

Low-grade fever Cough Eosinophilia Pneumonia Asthmatic reaction

VII. Laboratory diagnosis

specimen of choice for the recovery of Ascaris lumbricoides eggs is stool

adult worms may be recovered in several specimen types, depending on the severity of infection, including the small intestine, gall bladder, liver and appendix

adult worms may be present in stool, womited, or removed from external nares

ELISA is also available

VIII. Treatment

several medications:o mebendazoleo pyrantel pamoateo levamisoleo peperazine citrate

intestinal tract obstructiono combo of drug therapy and nasogastric

suction, or surgery pulmonary discomfort

o corticosteroids

IX. Preventive measures

Avoidance of using human feces as fertilizer Proper sanitation and personal hygiene

HOOKWORM

NECATOR AMERICANUS/ANCYLOSTOMA DUODENALE

GENERALITIES “hookworm” refers to Necator americanus and

Ancyclostoma duodenale 2 primary differences between the two organisms

o geographic distributiono adult worms of each have minor

morphologic differenceso eggs, larvae stages are indistinguishable


Necator americanus (ne-kay’tur/ah’merr”i-kay’nus)

Common name: New World Hookworm

Ancylostoma duodenale (an”si’los’tuh’muh/dew”o-de-nay’lee)

Common name: Old World Hookworm

II. Geographic distribution/Epidemiology

nearly ¼ of the world population is infected w/ hookworm

frequency of hookworm is high in warm areas where the inhabitants practice poor sanitation practices

mixed infections w/ any combo of hookworm, Trichuris and Ascaris is possible because all organisms require the same soil conditions

Necator is primarily found in North and South America

o Also exist in China, India and Africa Ancylostoma is a parasite of the Old World

o Found in Europe, China, Africa, South America and Caribbean

III. Morphology

Eggs

Hookworm egg 400x

Hookworm egg

Rhabditiform Larvae

Hookworm rhabditiform larva

Hookworm rhabditiform larva 400x close up of buccal cavity

Filariform Larvae

short esophagus

Pointed tail

Hookworm filariform larva

Adults

Necator americanus adult male

Necator americanus buccal capsule

Ancyclostoma duodenale adult female

IV. Life cycle

1. humans contract hookworm when third-stage filariform larvae penetrate through the skin, particularly into areas such as unprotected feet

2. inside the body, the filariform larvae migrate to the lymphatics and blood system

3. blood carries the larvae to the lungs where they penetrate capillaries and enter alveoli

4. migration of larvae continues into the bronchioles where they are coughed into the pharynx, swallowed and deposited into the intestines

maturation occurs in the intestine adults live and multiply in the S.I. females lay 10,000 to 20,000 eggs per day eggs are passed into the outside environment via

feces first-stage rhabditiform larvae emerge from eggs

w/in 24-48 hrs in warm, moist soil larvae continue to develop by molting two times Infective stage: third-stage filariform larvae


human phase of hookworm life cycle is initiated when a filariform (infective form) larva penetrates intact skin

egg laying is initiated 4 to 8 weeks after the initial exposure and can persist for 5 years

on contact w/ soil, the rhabditiform (noninfective) larva are released from the eggs

the rhabditiform larva develop into filariform w/in 2 weeks

both species have mouthparts designed for sucking blood from injured intestinal tissue

A. duodenale has chitinous teeth N. americanus has shearing chitinous plates


Asymptomatic Hookworm infection: does not exhibit clinical symptoms

Hookworm Disease/Ancylostomiasis/Necatoriasis : patients who are repeatedly infected may develop intense allergic itching at the site of hookworm penetration known as ground itch; other symptoms:

Sore throat Bloody sputum Wheezing Headache Mild pneumonia w/ cough

o Intestinal phase Symptoms depend on # of

worms present Chronic infections (light worm

burden ~500 eggs/g feces) Vague mild GI

symptoms Slight anemia Weight loss or

weakness Acute infections (greater than

5000 eggs/g feces) Diarrhea Anorexia Edema Pain Enteritis Epigastric discomfort Patients may develop a

microcytic hypochromic iron deficiency

Weakness Hypoproteinemia

Mortality due to blood loss


primary means is by recovery of the eggs in stool samples

larvae may mature and hatch from the eggs in stool that has been allowed to sit at room temperature w/o additive fixatives

recovery and examination of the buccal capsule is necessary to determine the specific hookworm organism

reverse enzyme immunoassay for specific IgE

VIII. Treatment

drugs of choice : mebendazole or pyrantel pamoate

for asymptomatic infections : iron replacement and/or other dietary therapy (proteins, iron, vitamins)


similar to those of Ascaris proper sanitation, fecal disposal prompt treatment personal protection

STRONGYLOIDES STERCORALIS


Strongyloides stercoralis (stron”ji-loy’deez/stur”kor-ray’lis)

Common name: Threadworm

II. Geographic distribution

found predominantly in tropics and subtropicsIII. Morphology

Eggs

Rhabditiform Larvae

rhabditiform larva 400x

Strongyloides stercoralis rhabditiform larva

Strongyloides stercoralis rhabditiform larva, close-up of anterior end showing a typical short buccal cavity

Filariform Larvae

Strongyloides stercoralis filariform larvaAdult

IV. Life cycle

unlike in the hookworm life cycle, where eggs are the primary morphologic form seen in feces, in the threadworm life cycle rhabditiform larvae are usually passed in the feces

eggs are only occasionally found the rhabditiform larvae develop directly into the

third-stage infective filariform larvae (in soil) remaining phases of the threadworm life cycle

mimic those of the hookworm there are 3 possible routes threadworms may

take in their life cycles:

o direct a skin-penetrating larvae enters

the circulation and follows the pulmonary course

adults develop in the small intestine

adult females burrow into the mucosa of the duodenum, and reproduce parthogenetically

@ female produces about 1 dozen eggs/day

eggs hatch w/in the mucosa and releaserhabditiform larvae into the lumen of the bowel

rhabditiform larvae are distinguished from hookworms by:

short buccal capsule large genital

primordium rhabditiform larvae are passed

into the stool and may either: develop into filariform

and continue the direct cycle

develop into free-living adult worms and initiate indirect cycle

o indirect Rhabditiform larvae are passed

into the outside environment (soil) and mature into free-living adults that are nonparasitic

Adult females produce eggs that develop into the rhabditiform larvae

Larvae mature and transform into the filariform at w/c time they may either initiate a new indirect cycle or become infective

Several generations of this nonparasitic existence may occur before new larvae become skin-penetrating

o Autoinfection Occurs when the rhabditiform

larvae develop into the filariform stage inside the intestine of the host

Penetrate the intestinal or perianal skin and follow the course through the circulation and pulmonary structures-coughed-swallowed (become adults)

The larvae may then enter the lymphatics or blood stream

Persist for years and can lead to hyperinfection and massive or disseminated, fatal infection

S. stercoralis differs from the life cycle of hookworms in three aspects:

1. eggs hatch into larvae in the intestine before they are passed in feces

2. larvae can mature into filariform in the intestines and cause autoinfection

3. a free-living, nonparasitic cycle can be established outside the human host


Heavy worm loads may involve the biliary and pancreatic ducts, the entire small bowel and colon

o Causes inflammation and ulceration leading to epigastric pain and tenderness, vomiting, diarrhea and malabsorption

Symptoms mimicking peptic ulcer disease coupled w/ peripheral eosinophilia

Individuals w/ chronic strongyloidiasis are at risk of developing severe, life-threatening hyperinfection syndrome if the host-parasite balance is disturbed by any drug or illness that compromises the immune status

Hyperinfection syndrome:o Seen in individuals immunocompromised

by malignancies and those undergoing corticosteroid therapy

o Also observed in Px who have undergone solid organ transplantation and in malnourished people

o Intestinal symptoms: diarrhea, malabsorption, and electrolyte abnormalities

o Fatal complications: bacterial sepsis, meningitis, peritonitis and endocarditis

Loss of cellular immune function may be associated w/ the conversion of rhabditiform larvae to filariform larvae, followed by dissemination of the larvae via the circulation to virtually any organ

Extraintestinal infection involves the lung and includes bronchospasm, diffuse infiltrates and cavitation

Widespread dissemination that involves the abdominal lymph nodes, liver, spleen, kidneys, pancreas, thyroid, heart, brain and meninges


Asymptomatic: patients infected w/ only a light infection often remain asymptomatic

o Usually seen in intestinal infections Strongyloidiases/Threadworm infection:

o Most common symptoms include diarrhea and abdominal pain

o Also exhibit urticaria accompanied by eosinophilia

o Additional intestinal symptoms may occur such as vomiting, constipation, weight loss, and variable anemia

o Malabsorption syndrome for Px w/ heavy infection

o Site of larvae penetration may become itchy and red

o Recurring allergic reactionso When larvae migrate to the lungs, Px

may develop pulmonary symptomso Pneumonitis from migrating larvaeo Immunocompromised persons

Severe autoinfections lead to spread of larvae throughout the body

Increased secondary bacterial infections

Death


diagnostic eggs, often indistinguishable from those of hookworm, may be present in stool samples from patients suffering from severe diarrhea

stool concentration with zinc sulfate has successfully recovered these eggs

rhabditiform larvae may be recovered in fresh stool samples and duodenal aspirates

careful screening of feces is necessary to differentiated rhabditiform larvae of hookworm from Strongyloides

Enterotest and ELISA Sputum samples have yielded Strongyloides

larvae in patients suffering from disseminated disease

VIII. Treatment

Thiabendazole although not always successful Alternative medications include: albendazole and

ivermectin


same as hookworm proper handling and disposal of fecal material and

adequate protection of the skin from contaminated soil

GNATHOSTOMA SPINEGERUM (SPINIGERUM)* can’t find any chapter or topic that discusses this parasite. The closest was in reference to the Copepods of the phylum Arthropoda…

GENERALITIES The arthropods are the largest of the animal phyla Phylum Arthropoda comprises invertebrate

animals w/ a segmented body, several pairs of jointed appendages, bilateral symmetry, and a rigid, chitinous exoskeleton that is molted periodically as the animal grows

Arthropods develop from eg to adult by a process known as metamorphosis

They pass through several distinct morphological stages including egg, larvae, pupa and adult

5 important classeso Chilopodao Pentastomidao Crustacea

Copepods Decapods (crabs, crayfish)

o Arachnidao Insecta

Copepods are small, simple aquatic organisms lack a carapace, have one pair of maxillae, and

have 5 pairs of biramous swimming legs are intermediate host in the life cycle of several

human parasites including:o Dracunculus medinensiso Diphyllobothrium latumo Gnathostoma spinigerumo Spirometra species

Epidemiologyo Worldwide distributiono Serve as intermediate hosts for

helminthic diseases in the US and Canadao Human infections result from ingesting

water contaminated with copepods or from eating the raw or insufficiently cooked flesh of infected fish

-fin-

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Parasitology-Lec 3 Nematodes 2