parasitology-lec 3 nematodes 2
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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
I. Nomenclature and synonyms
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
V. Pathology in the host
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
VI. Clinical symptomatology
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
VII. Laboratory diagnosis
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)
IX. Preventive measures
similar to those of Ascaris proper sanitation, fecal disposal prompt treatment personal protection
STRONGYLOIDES STERCORALIS
I. Nomenclature and synonyms
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
V. Pathology in the 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
VI. Clinical symptomatology
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
VII. Laboratory diagnosis
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
IX. Preventive measures
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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