Strongyloides stercoralis (Threadworm)

1. Strongyloides stercoralis(Threadworm) Audra Spring

2. Morphology It’s a nematode, so it has two larval forms: • Filariform larvae • (pathogenic form) Rhabditiform larvae (non-infective form)

3. Morphology The size and shape of the worm are dependent on whether it’s parasitic or free-living. • Free-living females – 1 mm by 60 µm • Parasitic females – 2.2 mm by 45 µm • Eggs – 55 µm by 30 µm

4. Epidemiology Found worldwide • An estimated 50 to 100 million cases Favors warmer tropical and subtropical climates Endemic in sub-Saharan Africa, Latin America, southeast Asia, and the southeastern United States

5. Epidemiology • Worms can be free-living in the soil or live in a host. • Only females are parasitic. • The definitive host is humans, but may also affect other primates and dogs

6. Life Cycle Dirt Skin Blood Feces Autoinfection Intestine Heart Lungs

8. Strongyloidiasis • Strongyloides stercoralis has a direct parasitic life cycle, meaning it can complete its entire life cycle in the definitive host. • This causes an autoinfection in the human, because the worm keeps infecting them without ever leaving. • Disseminated strongyloidiasis, or hyperinfection, occurs in immunocomprised victims when the worms spread throughout the body, leading to sepsis and secondary bacterial infections. • Hyperinfection has an 85% fatality rate.

9. Symptoms • Commonly asymptomatic • But symptoms may include: 1. Gastrointestinal (diarrhea, abdominal pain, malabsorption) 2. Respiratory (coughing, wheezing) 3. Dermatologic (ground itch, rash) 4. Anemia • People with weaker immune systems such as elderly people and children are more susceptible. • Immunosuppressed patients have further complications (disseminated strongyloidiasis and hyperinfection). • Infection is diagnosed primarily by stool samples, but string tests may also be used

10. Treatment The drug of choice is thiabendazole, with and eradication rate of 70-90%. • Side effects, such as dizziness, drowsiness, and gastrointestinal problems Albendazole and ivermectin are alternatives, with a 60-90% eradication rate. • These have fewer side effects than thiabendazole. All antihelminthic drugs that either kill the worm on contact, change the permeability of their membranes, or paralyze them

11. Prevention Properly dispose of human wastes. Wear Shoes. …Don’t eat dirt.

12. References • Sing, Andreas, Lorenz Leitritz, Johannes R. Bogner, and Jürgen Heesemann,. “First-Glance Diagnosis of Strongyloides stercoralis Autoinfection by Stool Microscopy.” Journal of Clinical Microbiology. May 1999: p. 1610-1611, Vol. 37, No. 5. 11 October 2006. <http://jcm.asm.org/cgi/content/full/37/5/1610> • Lehman, Don. “Strongyloides stercoralis.” Diagnostic Parasitology. 1999. University of Delaware. 1 October 2006. <http://www.udel.edu/medtech/dlehman/medt372/S-strong.html> • “Taxonomy, Common Name, Disease.” Strongyloides stercoralis. College of Agricultural and Environmental Sciences. 1 October 2006. <http://ucdnema.ucdavis.edu/imagemap/nemmap/ENT156HTML/nemas/strongyloidesstercoralis> • “2-Nematodes: Hookworms (Ancylostoma duodenale, Necator americanus) & Strongyloides stercoralis.” Columbia University. 1 October 2006. <http://64.233.161.104/search?q=cache:e3OfkQy-GEIJ:healthsciences.columbia.edu/dept/ps/2007/para/old/PD2_lczanko.pdf+morphology+strongyloides+stercoralis&hl=en&gl=us&ct=clnk&cd=3> • Zepf, Bill. “Strongyloides stercoralis Infection Can Be Fatal.” American Family Physician. 15 March 2002. FindArticles.com. 1 October 2006. <http://findarticles.com/p/articles/mi_m3225/is_6_65/ai_84072809> • “Strongyloidiasis.” Library Identification of Parasites of Public Health Concern. 26 September 2005. Centers of Disease Control. 1 October 2006. <http://www.dpd.cdc.gov/dpdx/HTML/Frames/S-Z/Strongyloidiasis/body_Strongyloidiasis_page1.htm>