STRONGYLOIDES STERCORALIS

Question 1

What’s the common name for strongyloides stercoralis?

Answer 1

Threadworm (although in some countries this common name refers to Enterobius vermicularis)

The smallest nematode & is aetiologic agent of Strongylodiasis

Question 2

Epidemiology of S. stercoralis

Answer 2

Warm climates

Question 3

Habitat of S.stercoralis:

Answer 3

①Adults in wall of intestine(duodenum & jejunum)
➁larvae can be found throughout the body
③Parasitic females may invade lung epithelium and reproduce

Question 4

MORPHOLOGY OF S.STERCORALIS:

Answer 4

①Female worms
➁Male worms
③Eggs
④Larvae
Both and male worms have a well developed digestive system.

Question 5

Female S.stercoralis morphology:

Answer 5

Females are thin, transparent & about 2.5 mm long .
*The female reproductive system contains paired uteri, vagina & vulva. Gravid female uteri contain thin­ walled transparent ovoid eggs
*Ovoviviparous with a lifespan of 3 to 4 months, may persist due to autoinfection!

Question 6

Male S.stercoralis morphology:

Answer 6

Male worms are shorter & broader than females measuring 0.6–1 mm in length.
*They have copulatory spicules which penetrate the female during copulation.
*They do not invade the intestinal wall & usually not seen in human infection

Male worms eliminated from the bowel soon after the females begin to oviposit(lay eggs).
However, the majority of females are probably parthenogenetic ( lay fertilized eggs without males).

Question 7

Egg of S.stercoralis morphology:

Answer 7

*Are oval & measure 50–60 µm in length.
*Seen within the uterus of gravid female.
*eggs hatch out to rhabditiform larva (1st stage larva) soon after being layed.
*Hence it is the larva & not the egg which is excreted in feces & detected during stool examination

Question 8

Larvae of stercoralis morphology:

Answer 8

Rhabditiform Larva (L1 stage) and Filariform larva (L3 stage)

Question 9

Rhabditiform Larva (L1 stage)

Answer 9

*Eggs hatch out to form L1 larva in the small intestine.
*Most common form of the parasite found in the feces.
*L1 larva migrates into the lumen of the intestine & excreted in feces.
*Has ‘double bulb’ oesophagus

Question 10

Filariform Larva (L3 stage)

Answer 10

*L1 larva moults twice to become the L3 larva.
*It is the infective stage of the parasite to man
*Has long, slender oesophagus

Question 11

Life Cycle of S.stercoralis:

Answer 11

Has a parasitic cycle & a free-living soil cycle where it can persist for long periods in soil.

Question 12

Natural host:

Answer 12

Man but dogs & cats are found infected with morphologically similar strains

Question 13

Mode of infection:
.

Answer 13

1. Penetration of skin by filariform larva when a person walks barefoot in contaminated soil.
2. Internal autoinfection in colon – L3 penetrate mucosa of colon.
3. External autoinfection: L3 penetrate perianal, and perineal area

Question 14

In the free-living cycle:

Answer 14

①Rhabditiform larvae are passed in the stool of an infected definitive host
➁develop into either infective filariform larvae (direct development)
⑥or free-living adult males and females
③that mate and produce eggs
④from which rhabditiform larvae hatch
⑤and eventually become infective filariform (L3) larvae
⑥The filariform larvae penetrate the human host skin to initiate the parasitic cycle

This second generation of filariform larvae cannot mature into free-living adults and must find a new host to continue the life cycle

Question 15

Parasitic cycle:

Answer 15

⑥Filariform larvae in contaminated soil penetrate human skin when skin contacts soil
⑦and migrate to the small intestine
⑧It has been thought that the L3 larvae migrate via the bloodstream and lymphatics to the lungs, where they are eventually coughed up and swallowed. However, L3 larvae appear capable of migrating to the intestine via alternate routes (e.g. through abdominal viscera or connective tissue).
⑧In the small intestine, the larvae molt twice and become adult female worms . ⑨The females live embedded in the submucosa of the small intestine and produce eggs via parthenogenesis (parasitic males do not exist) , which yield rhabditiform larvae.
①The rhabditiform larvae can either be passed in the stool
⑩or can cause autoinfection

Question 16

Pathogenicity & Clinical Features

Answer 16

①S. stercoralis generally cause benign & asymptomatic disease.
➁Blood eosinophilia & larvae in stool may be the only indications of infn.
③Severe & even fatal disease may occur in those with defective immune response.
④Clinical disease may have skin, pulmonary & intestinal manifestations.

Question 17

Skin manifestations of Strongyloides infection

Answer 17

*Dermatitis with erythema & itching at site of penetration of L3 larva occur.
*In sensitized individuals, there may be an allergic response.
*Pruritus & urticarial lesions particularly around the perianal skin & buttocks are symptoms of chronic strongyloidiasis.
*larva migrans do occur = larva currens or racing larva, 10cm/hour

Question 18

Pulmonary Manifestations of Strongyloidiasis

Answer 18

*Small hemorrhages may occur in the alveoli & bronchioles as larva escape pulmonary capillaries .
*Bronchopneumonia may be present, which may progress to chronic bronchitis & asthmatic symptoms in some patients.
*Larva of Stongyloides may be found in the sputum of these patients

Question 19

Intestinal Manifestations of strongyloidiasis

Answer 19

*Epigastric pain & hunger pangs in acute stage resembling peptic ulcer or malabsorption syndrome.
*Mucus diarrhea is often present.
*Extensive sloughing of mucosa causing dysenteric stools occur in heavy infn.
*Other manifestations include protein-losing enteropathy and paralytic ileus.

Question 20

Hyperinfection

Answer 20

*Refers to extensive internal reinfection leading to large numbers of adult worms in intestines, lungs & larvae in various tissues & organs.
*Common in immunosuppressed persons
*Defective cell-mediated immunity predispose to this condition
*Filariform larvae may enter arterial circulation & lodge in various organs e.g. heart, lungs, brain, kidney, pancreas, liver & lymph nodes.
*CNS involvement lead to brain abscess & meningitis.
*Peritonitis is also a major fatal complications.
*Circulating larvae may carry intestinal bacteria causing septicemia

Question 21

Diagnosis of Strongylodiasis

Answer 21

1. Clinical diagnosis– diarrhoea with epigastric pain,high eosinophilia.
2. Definitive diagnosis – Microscopy
   *Direct wet mount of stool: Demonstration of L1 larvae in freshly passed stools most important for specific diagnosis.
   *Concentration methods: formol ether concentration method or Baermann’s funnel gauze method.
   *Larvae may be present in sputum, duodenal aspirates & jejunal biopsies.
   *Stool Culture esp when larvae are scanty using Agar plate culture & Charcoal culture method.
   *Serological tests e.g ELISA although has a downside of extensive cross­-reactions with other helminth infns

Question 22

Treatment of Strongyloidiasis

Answer 22

All cases whether symptomatic or not need to be treated to prevent severe invasive disease.
*Ivermectin (200 mg/kg daily for 2 days) more effective than Albendazole.
*Disseminated disease need extended treatment with Ivermectin for atleast 5–7 days.
*Absence of eosinophilia is a poor prognostic sign in hyperinfection.

Question 23

Prevention of Strongyloidiasis

Answer 23

1. Sanitary disposal of human excreta
   -long voided feces or surface water specially dangerous.
2. Treat all cases specifically
3. Rule out Strongylodiasis before treatment with immunosuppressives.
4. 30 year old infection in absence of exposure reported – autoinfection.

Question 24

ZOONOTIC STRONGYLOIDIASIS

Answer 24

*Wild or domestic animals as definitive /natural hosts.
*Do not cause patient infections.
*Causes cuteneous larva migrans and urticaria in man

Question 25

STRONGYLOIDES FUELLERBORNI

Answer 25

*Parasite of Old World monkeys, Zoonotic
*First human case – Zimbabwe
*Papua New Guinea.
*Zambia

Known as SWOLLEN BELLY SICKNESS

Question 26

MORPHOLOGY of S.fuellerborni

Answer 26

Eggs in stool, not larvae
Eggs resemble hookworm eggs.
Freeliving female with post vulvar constriction

Question 27

Transmission S.fuellerborni

Answer 27

*Similar to S.stercoralis
*Trans-mammary in infants implied –14th day after birth infants develop infection.

Question 28

Pathogenesis of S.fuellerborni

Answer 28

*Similar to S.stercoralis (with a very huge egg load)
*Abdominal symptoms with oedema – “swollen belly sickness”as a result of protein loss.
*Respiratory distress and abdominal distension symptoms.

Question 29

Diagnosis of S. fuellerborni

Answer 29

*Demonstration of ova in feces
*Copro culture of eggs to adults, and their identification.

Question 30

Treatment of S.fuellerboni

Answer 30

*Thiabendazole
*Mebendazole
*Clinical management – in hyperproteinaemia

Question 31

Prevention of S.fuellerborni

Answer 31

*Sanitary disposal of human excreta
*Control of monkey populations
*Treat all cases specifically

Question 32

DIPLOSCAPER CORONATA

Answer 32

1. Lives in decaying matter and sewage beds
2. Facultative parasite of man
3. Males rarely found – parthenogenesis reproduction
4. Worms found in human urine and stomach contents
5. Worms acquired from decaying vegetation.

Question 33

RHABDITIS

Answer 33

1. Resemble free-living Strongyloides
2. Life cycle free-living – but no fllariform larval form
   3.Can live in ulcerated damaged skin and organs
3. Contaminators of food and drink
4. In human larvae found in itching cutaneous papules- resemble craw-craw, female urine.

Question 34

MELOIDOGYNE JAVANICA
Syn Heterodera incognita

Answer 34

1. Plant parasitic Nematodes found in roots and stem of many edible plants
2. Eggs and larvae in feces after ingestion of infected plants
3. Eggs thin shelled, elongate ovoid, flattened on one side
4. Mistaken for infertile eggs of Ascaris or hookworm eggs.