Strongyloides stercoralis

By: Mahamed Yassin & Zakariya Salah

Fun Facts!!

Carries 60-85% mortality rate for immunocomprimised patients.

Adult females may live up to 5 years and continue the reproductive cycle.

Strongyloides is the only helminth to secrete larvae (and not eggs) in feces

Unlike most parasitic worms, Strongyloides stercoralis has a heterogonic life cycle.

First described in the nineteenth century in French soldiers returning home from expeditions in IndoChina.

Taxonomy Kingdom: Animalia

Phylum: Nematoda

Class: Secernentea

Order: Rhabditida

Family: Strongyloididae

Genus: Strongyloides

Species: S. stercoralis

Morphology(parasitic vs. free-living)

Parasitic females can grow up to 2.5mm long with blunt ends and males = 0.9mm. females filariform esophagus

covers 1/3 of body length. Ovary is didelphic and opens at vulva (2/3 of bodies length)

Free living adults approx. 1 mm long. *female slightly larger than male Both sexes have rhabditiform

esophagus. Female has didelphic ovary with vulva mid way of body.

Geographic Range

Endemic Tropics and subtropics

Also can occur in temperate climates Likes warm moist climates

significance Africa, Tropical America, Pacific

Islands and parts of North America

Widespread in Eastern Europe and Mediterranean region.

*about 1% of world population is infected

Host

Definitive host: Humans, dogs,cats

Intermediate Host: None

Reservoir Host: Dog, monkey. Might use other mammals, like the two above.

Life Cycle

Life Cycle

L3 stage penetrates skin

Enters bloodstream and migrates to pulmonary capillaries

Once in alveoli of lung, it is taken to throat where it is swallowed

Inside small intestine it matures into adult female by molting 2X

Female undergoes asexual reproduction and lay eggs that will hatch into rhabditiform.

From there they either exit the body or molt 2X more into filariform.

Filariform either penetrates intestinal wall or perianal skin, thus starting the infection all over again.

Life Cycle

Rhabditiform in the soil either develop into filariform (2X molting) or adults (4X molting).

The free-living male and female produce eggs

Eggs can either molt into infective filariform or adults

The adult worms only live through one copulation cycle in the wild. But inside humans (only females there) adults can survive longer.

Pathogenesis

Acute strongyloidiasis Wheezing Low-grade fever Epigastric tenderness

Chronic strongyloidiasis Chronic urticaria Larva currens

Severe strongyloidiasis Diffuse abdominal tenderness; abdominal distension;

hyperactive, hypoactive, or absent bowel sounds; vomiting; hematemesis; and hematochezia

Altered mental status and meningismus (if CNS involvement) Rash, Cough, respiratory distress, wheezing, hemoptysis, and

crackles Fever, chills

Symptoms

Minor infections can be asymptomatic but usually one or more of the following symptoms occur: Anemia, cough,

constipation, diarrhea, nausea, stomach ach, vomiting, weight loss

Immunosupressed and immunocomprimised patients: DEATH, distension,

shock, septicemia, neurological and pulmonary commplications

Treatment and diagnosis

stool samples will confirm the presence of this parasite. Other techniques used include direct fecal smears, culturing fecal samples on agar plates, serodiagnosis through ELISA.

Treatment includes Ivermectin is the drug of first choice for treatment because of higher tolerance in patients.

Thiabendazole and Albendazole are also sometimes used.

Control

The ideal method would be prevention by improved sanitation (proper disposal of feces), practicing good hygiene (washing of hands), etc..

Stay away from moist soil, do not work or play with contaminated water/soil.

References

http://www.dpd.cdc.gov/dpdx/html/imagelibrary/Strongyloidiasis_il.htm

http://animaldiversity.ummz.umich.edu/site/accounts/information/Strongyloides_stercoralis.html

http://emedicine.medscape.com/article/788652-overview

http://www.parasitesinhumans.org/strongyloides-stercoralis.html