Lecture 4. Nematodes (Roundworm): Intestinal
|LECTURE 1 Introduction and Intestinal Protozoa Notes||Lecture Powerpoint (.pdf)||Printable handout (.pdf)|
|LECTURE 2 Malaria Notes||Lecture Powerpoint (.pdf)||Printable handout (.pdf)|
|LECTURE 3 Systemic Protozoa Notes||Lecture Powerpoint (.pdf)||Printable handout (.pdf)|
|LECTURE 4 Intestinal Helminths Notes||Lecture Powerpoint (.pdf)||Printable handout (.pdf)|
|LECTURE 5 Filaria and schistosoma Notes||Lecture 5 Powerpoint (.pdf)||Printable 5 handout (.pdf)|
|LECTURE 6 Other trematodes and cestodes Notes||Lecture 6 Powerpoint (.pdf)||Printable 6 handout (.pdf)|
|intestinal-- Strongyloides larva||systemic-- microfilaria (Wuchereria)|
Transmission and Clinical Complications
|Trichuris (whipworm)||oral||hemorrhagic colitis|
|Enterobius (pinworm)||oral||perianal itch|
|Ascaris (round worm)||oral||small intestine obstruction|
|Strongyloides (thread worm)||percutaneous and autoinfection||duodenitis, cutaneous larva currens,
hyperinfection in immunocompromised
|Ancylostoma & Necator (hookworms)||percutaneous||iron deficiency anemia|
Diagnosis: stool examination for
larvae (strongyloides) or eggs (the rest)
Treatment: albendizole or ivermectin (strongyloides) or mebendazole (the rest)
|Worm||transmission||clinical picture & diagnosis|
|Trichinella spiralis or nativa||raw pork, bear, walrus||myositis, diarrhea
Dx. eosinophilia, raised CPK, serology
(visceral larva migrans)
|oral||eosinophilia, hepatomegaly, cough, fever
|Wuchereria bancrofti or Brugia malayi (lymphatic filariasis)||mosquito vector||elephantiasis, chyluria or hydrocoele
Dx: microfilaria in blood, serology, antigen capture
|black fly vector||itchiness, persistant skin nodules, blindness
Dx: adults in skin nodules, microfilaria in skin biopsies (snips)
|Loa loa (eye worm)||horse fly vector||Calabar swellings (3-4 days), eye worm
Dx: microfilaria in blood
Diagnosis: blood or tissue examination for microfilaria; serology for Trichinella and Toxocara
Onchocerca, Loa- ivermectin, diethylcarbamazine, albendizole
Trichinosis, Toxocara- albendizole
The helminths (from the Greek meaning worm) are higher, multicellular forms of
parasite with specialized organs. There are two basic groups:
Nematodes - roundworms
Platyhelminths - flatworms - cestodes (tapeworm)
- trematodes (fluke)
- round in cross section
- bilaterally symmetrical
- variable size - 1 mm to 1 meter
- organs - digestive, nervous, excretory, cuticle, muscle, sexual
- develops by molting (shedding cuticle
- separate sexes
- reproduction and development: egg
embryo in egg
Bowel nematodes - with adults in bowel
Ancylostoma duodenale and Necator americanus
nematodes - adults or larval stage in tissue
Trichinella spiralis, native etc
Toxocara canis (visceral larva migrans)
Filaria - Wuchereria bancrofti
Trichuris trichiura (Whipworm)
- about 350 million infected, in some areas 90-100% of population
- restricted to warm climate by necessity for egg to embryonate on moist warm soil for10-14 days before becoming infective
- spread: fecal - oral (esp. via foods and hands)
- life cycle: people infected by swallowing embryonated egg egg hatches in small intestine attaches to colonic epithelium and matures to egg laying in 3 months.
|adult female, approx. 45 mm||eggs approx. 52 mu long|
- clinical: 99% assymptomatic
- heavy load gives diarrhea, dysentery, anemia, rectal prolapse
- examine stool (standard techniques) - pathognomonic egg
- mebendizole, albendizole
- lack of cost effective control methods in LDC (least developed countries)
Enterobius vermicularis (Pinworm)
-very common in all geographic areas - 20%+ in Toronto's children
- spread: fecal - oral; eggs can survive days to weeks in environment
- infected by swallowing egg which hatches after contact with stomach acid and matures to adult which then resides in lumen of caecum (from egg to adult maturation in 15-43 days) . Female migrates onto perianal skin to lay eggs at night.
- organism: adult female approx. 10 mm long; egg approx. 55 Ám long
pinworm egg 50-60 Ám
|pinworm adult 8-13 mm|
- most asymptomatic
<10% anal pruritus; rarely vaginitis
-less then 10% found in stools, i.e. not a useful examination;
-best is pinworm swab - cellophane tape swab, or sticky paddle
- mebendizole, albendazole, pyrantel pamoate
- insensitivity of pinworm swabs (intermittent deposition of eggs) : eradication of infection from rest of family.
Ascaris lumbricoides (Roundworm)
-About 650 million infected worldwide mainly tropics. Transmission is faecal-oral; egg very resistant, can survive years
-egg ingested, hatches in duodenum; larvae penetrate intestine wall, enter blood vessels and embolize through liver to lungs. They then migrate into airspaces, up trachea and are swallowed, taking up permanent adult residence in the small intestine; ~ 2 months from egg to mature adult
adult female 20-35 cm long
eggs ~68 mÁ long
adults from one child
Adult worms1 live in the lumen
of the small intestine. A female may produce up to 240,000 eggs
per day, which are passed with the feces 2. Fertile eggs embryonate and become infective after
18 days to several weeks 3, depending on the environmental conditions (optimum: moist, warm,
shaded soil). After infective eggs are swallowed 4, the larvae hatch 5, invade the intestinal
mucosa, and are carried via the portal, then systemic circulation to the lungs 6 . The larvae
mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree
to the throat, and are swallowed 7. Upon reaching the small intestine, they develop into adult
worms 1. Between 2 and 3 months are required from ingestion of the infective eggs to oviposition
by the adult female. Adult worms can live 1 to 2 years. (CDC 1999)
- related to number of worms; small numbers asymptomatic
- large numbers of adults in intestine -- obstruction, pains
- at times adults migrate into bile duct, up esophagus or through surgical anastomoses of intestine
- cause malnutrition if in large numbers
Diagnosis: stool examination for eggs
Treatment: mebendizole, albendazole
Strongyloides stercoralis (Threadworm)
The only important helminth that can complete its life cycle in the human host and hence increase its numbers. Special problem in immunocompromized because of this. Mainly a tropical parasite because requires warm moist soil for transmission.
Transmission: skin contact with invasive larvae in soil.
Larvae passed into soil in human feces where mature in several days to skin invasive (filariform) larvae. Can exist for months in soil "free living" by completing life cycle without contact with human host man. Larvae penetrate skin, move via blood vessels to lung, invade airspace, move up bronchi, are swallowed, and then penetrate small intestinal mucosa where they mature to adults in submucosa. They deposit eggs in submucosa and these hatch and migrate into intestinal lumen. Small numbers of larvae get into blood vessels and circulate again to produce more adults (internal autoinfective cycle) or invade perianal skin and enter blood vessels to eventually produce new adults (external autoinfective cycle).
Organism: female adult - 2.7 mm long, rhabditiform larvae approx. 0.38 mm, filariform larvae approx. 0.6 mm long
|adult||filariform (invasive) larva|
GI - peptic ulcer like symptoms, diarrhea rarely, cutaneous larvae currens (trunkal itchy dermatitis)
hyperinfection (disseminated strongyloides) in immunocompromised; spread of larvae to peritoneum, lung, CNS with contamination of those organs with gram negative bacteria; transmural small intestine spread of larvae and bacteria with necrosis of intestine
stool examination . NB: difficult to find strongyloides
duodenal aspirate or Enterotest duodenal string test
serology (the most sensitive)
culture of stool (Harada-Mori or Baerman) allows "free living" strongyloides to multiply
agar plate tracking
Treatment: albendazole, ivermectin
Problems: diagnostic techniques not sensitive
untreated it persists for life
Ancylostoma duodenale and Necator americanus
Epidemiology: transmission by contact of skin with soil contaminated with larvae.
Biology: eggs in feces hatch and mature as larvae in warm moist soil; develops into to
infective (filariform) larvae in 7 days. Filariform larvae penetrate skin of host (e.g.
bare feet), circulate to lungs where they penetrate alveoli, move up bronchi and are
swallowed. Then, as adults, they attach by mouth to small intestinal mucosa and suck
blood. (Necator 0.03 ml/day, Ancylostoma 0.15 ml/day). Prepatent period (time
from skin penetration to egg production) is 4-5 weeks. Adults can live 5-15 years.
Adult female 12 mm long (A.d); ova approx. 60 mu long
Adult female 10 mm long (N.a); ova approx. 65 mu long
mouth of Ancylostoma duodenale
egg 60 x 40 mÁ
usually assymptomatic 90%
heavy infections (20 - 100 worms)
iron deficiency anemia
malnutrition from protein loss
rarely itch at skin entry site
Diagnosis: Stool examination for ova
Treatment: mebendizole, albendazole
Problems: Lack of cost effective LDC (least developed country) control
Cutaneous Larva Migrans
Ancylostoma caninum, Ancylostoma braziliensis etc.
Non-human (dog, cat etc) hookworms that penetrate human skin (as does human hookworm) but cannot go further. Migrate and produce serpiginous itchy traits in subcutaneous tissue.
Treatment albendizole, ivermectin.
Laboratory procedures for diagnosing intestinal
Stool ova and parasite (O & P) examination
1. Direct microscopic (without a concentration technique) examination: not very sensitive
2. Kato technique: uses glycerin mixed with stool which "clears" (makes transparent) fecal debris making eggs visable. Can be used for counting eggs/gram feces.
3. Concentration techniques:
i. zinc sulfate solution flotation - eggs float to top of solution
ii. formal ethyl acetate sedimentation
4. Culture: Harada
Mori or Baerman culture or charcoal culture - only Strongyloides will multiply in
an incubated stool specimen - increases numbers of larvae and sensitivity of microscopy.
Increased blood eosinophil counts are normal host response to helminth
infection; not seen in protozoan infections
|very high (30-80% of WBC)||moderate (10-30% of WBC)||low or absent (0-10% of WBC)|
Trichinella spiralis, nativa
Common in geographic areas where undercooked pork is eaten, in the Arctic where raw walrus is eaten and among bear hunters in North America; 5-15% of North American population infected at some time.This is a zoonosis infecting most carnivorous mammals; especially pigs, bear, walrus, and rats. Man infected by eating Trichinella infected uncooked meat.
Encysted larvae in meat, when eaten, excyst (hatch) and penetrate into small intestine submucosa where they mature to adults in 1-2 weeks producing larvae which penetrate blood vessels and diseminate to all muscles. There, they cause inflammation and encyst in muscle cells (not cardiac), remaining viable and quiet for many years. Adult female is 5 mm.long
|larva extracted from muscle||adult from intestine wall|
Early (1-2 weeks) - abdominal pain, diarrhea
Midterm (2-6 weeks) - myalgia, muscle weakness, facial and periferal edema, rash; sometimes encephalitis and myocarditis
Long term (months) - usually
assymptomatic despite presence of trichinella "cysts"
clinical picture with laboratory support (eosinophilia and raised creatine phosphokinase (CK)
microscopic examination of muscle biopsy
larva in muscle cell at biopsy
Treatment: steroids and mebendizole or albendazole
Problems: education of meat consumer
lack of good drugs
Toxocara Canis (Visceral Larva Migrans)
Epidemiology: This is a zoonotic roundworm with the dog as reservoir. Uncommon human infection but consequences serious. Transmission is dog fecal (dog)-oral (human) .
Dog feces especially in sandboxes and parks where children play. Eggs in soil viable and infective for several months.
Biology: Adult has cycle in dog the same as Ascaris in man. Man an accidental
"dead end" host. Eggs ingested by man/child, hatch after stomach passage and
larvae migrate through small intestinal wall into vasculature and then to liver and lungs
and beyond. Do not mature to adults but cause local inflammation especially in
Organism: In man larvae are 0. 5 mm long; egg in dog feces, looks like a round Ascaris egg.
Hepatomegaly, pneumonitis, encephalitis, fever and eosinophilia in heavy infections
Retinal lesion (similar to retinoblastoma) or focal retinitis when single larva reaches retina.
Clinical syndrome with very high eosinophilia
Nothing in stools
Treatment: Steroids and albendizole
Problems: - Control of dog and cat feces in parks and sandboxes
- Diagnosis difficult because of nonspecificity of symptoms
1. Anisakis sp: Salt water fish (cod, herring etc) roundworm that when ingested produces a nematode inflammatory mass in stomach of raw fish consumer or eosinophilic gastritis (mainly Japan, Holland).
2. Angiostrongylus cantonensis: nematode of amphibians producing eosinophilic meningitis (mainly SE Asia).
3. Gnathostoma spinigerum: nematode of cat producing migratory local subcutaneous
swelling, and at times encephalomyelitis (mainly SE Asia).
4. Capillaria philippinensis: small intestine nematode producing diarrhea and malabsorption (Philippines).
5. Bayliascaris procyonis: Raccoon nematode in North America producing a visceral larva migrans like Toxocaris (above) but with severe encephalitis