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)


Strongyl_larva2_DPDx.JPG (159621 bytes) wuchereriamf-chmai.jpg (14459 bytes)
intestinal-- Strongyloides larva systemic-- microfilaria (Wuchereria)

  Transmission and Clinical Complications

Large Intestine   transmission complications
Trichuris (whipworm) oral hemorrhagic colitis
Enterobius (pinworm) oral perianal itch
Small intestine    
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
Toxocara canis
(visceral larva migrans)
oral eosinophilia, hepatomegaly, cough, fever
Dx: serology
Wuchereria bancrofti or Brugia malayi (lymphatic filariasis) mosquito vector elephantiasis, chyluria or hydrocoele
Dx: microfilaria in blood, serology, antigen capture
Onchocera volvulus
(river blindness)
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

Treatment:  Wuchereria, 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
                                                                       egg fertilization
                                                                       embryo in egg
                                                                        4 molts


Bowel nematodes - with adults in bowel
Trichuris trichiura
                                   Ancylostoma duodenale
and Necator americanus
                                   Enterobius vermicularis
                                   Strongyloides stercoralis
                                   Enterobius vermicularis

mapworm.jpg (97013 bytes)                                       

       Tissue nematodes - adults or larval stage in tissue
        Trichinella spiralis, native etc
                      Toxocara canis
(visceral larva migrans)
                      Filaria - Wuchereria bancrofti
                                   Brugia malayi
                                   Onchocerca volvulus

                            Loa loa


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.

trichurisadult-chmai.jpg (9509 bytes) trichurisegg-chmai.jpg (22910 bytes)
 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

pinwor1.jpg (17764 bytes) pinwor2.jpg (13314 bytes)
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

asc_lum_adult_dpdx.jpg (31333 bytes)
adult female 20-35 cm long
asc_lum_fertinfert_dpdx.jpg (46461 bytes)
eggs ~68 mÁ long
ascarisadult-chengmai.jpg (17765 bytes)
adults from one child

AscariasisLifeCyclecdc.gif (26250 bytes)

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

strongadult-chmai.jpg (2830 bytes) Strongyl_larva2_DPDx.JPG (159621 bytes)
adult        filariform (invasive) larva

 WB00938_.GIF (1017 bytes) most asymptomatic
 WB00938_.GIF (1017 bytes) GI - peptic ulcer like symptoms, diarrhea rarely, cutaneous larvae currens (trunkal itchy dermatitis)
 WB00938_.GIF (1017 bytes)  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

WB00938_.GIF (1017 bytes) stool examination . NB: difficult to find strongyloides
WB00938_.GIF (1017 bytes) duodenal aspirate or Enterotest duodenal string test
WB00938_.GIF (1017 bytes) serology (the most sensitive)
WB00938_.GIF (1017 bytes) culture of stool (Harada-Mori or Baerman) allows "free living" strongyloides to multiply
WB00938_.GIF (1017 bytes)  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

nematoHW.jpg (5946 bytes)h
mouth of Ancylostoma duodenale
hookworm-filarlarvae-chmai.jpg (7450 bytes)
filariform larva
hookworm_egg2_dpdx.jpg (24625 bytes)
egg 60 x 40 mÁ  

  WB00938_.GIF (1017 bytes)  
usually assymptomatic 90%
  WB00938_.GIF (1017 bytes)   heavy infections (20 - 100 worms)
  WB00938_.GIF (1017 bytes)   iron deficiency anemia
  WB00938_.GIF (1017 bytes)   malnutrition from protein loss
  WB00938_.GIF (1017 bytes)   rarely itch at skin entry site

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.

Pathology Nematodes.jpg (9724 bytes)

Treatment albendizole, ivermectin.

Laboratory procedures for diagnosing intestinal helminths
Stool ova and parasite (O & P) examination

1. Direct microscopic (without a concentration technique) examination: not very sensitive

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.

           nema-cesta_fig4cdc.gif (55924 bytes)             


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 hookworm Enterobius
Toxocara Strongyloides Ascaris
Fasciola Trichuris

Trichinella spiralis, nativa (Trichinosis, Trichinellosis)

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

trichinella_larv2_dpdx.jpg (17180 bytes) trichinella-adult-chmai.jpg (8744 bytes)
larva extracted from muscle adult from intestine wall

 WB00938_.GIF (1017 bytes)  Early (1-2 weeks) -      abdominal pain, diarrhea

  WB00938_.GIF (1017 bytes) Midterm (2-6 weeks) - myalgia, muscle weakness, facial and periferal edema, rash; sometimes encephalitis and myocarditis

  WB00938_.GIF (1017 bytes) Long term (months) -  usually assymptomatic despite presence of trichinella "cysts"

 WB00938_.GIF (1017 bytes)   clinical picture with laboratory support (eosinophilia and raised creatine phosphokinase (CK)
 WB00938_.GIF (1017 bytes)   microscopic examination of muscle biopsy
 WB00938_.GIF (1017 bytes)   serology

trichinella-musc-chmai.jpg (25165 bytes)
larva in muscle cell at biopsy

Treatment: steroids and mebendizole or albendazole

Problems: education of meat consumer
                     lack of good drug

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 liver.

: In man larvae are 0. 5 mm long; egg in dog feces, looks like a round Ascaris egg.

                                                        toxocara_canis_eggs.jpg (15769 bytes)  Toxocara  eggs

 WB00938_.GIF (1017 bytes)  Hepatomegaly, pneumonitis, encephalitis, fever and eosinophilia in heavy infections
 WB00938_.GIF (1017 bytes)  Retinal lesion (similar to retinoblastoma) or focal retinitis when single larva reaches retina

 WB00938_.GIF (1017 bytes)  Clinical syndrome with very high eosinophilia
 WB00938_.GIF (1017 bytes)  Serology
 WB00938_.GIF (1017 bytes)  Nothing in stools

Steroids and  albendizole

Problems: - Control of dog and cat feces in parks and sandboxes
                      - Diagnosis difficult because of nonspecificity of symptoms

Other Nematodes

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