5/31/13 Ascaris lumbricoides - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Ascaris_lumbricoides 1/4

Ascaris lumbricoides

An adult female Ascaris worm.

Scientific classification

Kingdom: Animalia

Phylum: Nematoda

Class: Secernentea

Order: Ascaridida

Family: Ascarididae

Genus: Ascaris

Species: A. lumbricoides

Binomial name

Ascaris lumbricoides

Linnaeus, 1758

Ascaris lumbricoidesFrom Wikipedia, the free encyclopedia

Ascaris lumbricoides is the giant roundworm of humans,belonging to the phylum Nematoda. An ascarid nematode, it isresponsible for the disease ascariasis in humans, and it is the largestand most common parasitic worm in humans. One sixth of the humanpopulation is estimated to be infected by Ascaris lumbricoides or

another roundworm .[1] Ascariasis is prevalent worldwide and moreso in tropical and subtropical countries.

It can reach a length of up to 35 cm.[2]

Contents

1 Life cycle2 Morphology

3 Epidemiology

4 Infections

4.1 Symptoms

4.2 Prevention4.3 Details of infection process

5 Diagnosis and treatment

6 References

7 External links

Life cycle

Ascaris lumbricoides, or "roundworm", infections in humans occurwhen an ingested fertilised egg becomes a larval worm thatpenetrates the wall of the duodenum and enters the blood stream.From here, it is carried to the liver and heart, and enters pulmonarycirculation to break free in the alveoli, where it grows and molts. In 3weeks, the larvae pass from the respiratory system to be coughed up, swallowed, and thus returned to the smallintestine, where they mature to adult male and female worms. Fertilization can now occur and the female producesas many as 200,000 eggs per day for a year. These fertilized eggs become infectious after 2 weeks in soil; they can

persist in soil for 10 years or more.[3]

The eggs have a lipid layer, that makes them resistant to the effects of acids and alkalis as well as other chemicals.

This resilience helps to explain why this nematode is such a ubiquitous parasite.[4]

Morphology

5/31/13 Ascaris lumbricoides - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Ascaris_lumbricoides 2/4

Fertile egg as can be seen in a

microscope

Fertile egg in human faeces (detail)

Ascaris lumbricoides is characterized by its great size. Males are 2–4 mm in diameter and 15–31 cm long. The males' posterior end is curvedventrally and has a bluntly pointed tail. Females are 3–6 mm wide and20–49 cm long. The vulva is located in the anterior end and accounts forabout a one third of its body length. Uteri may contain up to 27 millioneggs at a time with 200,000 being laid per day. Fertilized eggs are oval toround in shape and are 45-75 micrometers long and 35-50 micrometerswide with a thick outer shell. Unfertilized eggs measure 88-94

micrometers long and 44 micrometers wide.[5]

Epidemiology

More than 2 billion people are affected by this infection.[3] In the UnitedStates there is a reported prevalence of 0.8% of the total population asof 1987. Ascaris lumbricoides eggs are extremely resistant to strongchemicals, desiccation, and low temperatures. The eggs can remain

viable in the soil for several months or even years.[5]

Eggs of A. lumbricoides have been identified in archeological coprolitesin the Americas, Europe, Africa, the Middle East, and New Zealand, the

oldest ones being more than 24,000 years old.[6]

Infections

Infections with these parasites are more common where sanitation is

poor[7] and raw human feces are used as fertilizer.

Symptoms

Often, there are no symptoms with an A. lumbricoides infection.However, in the case of a particularly bad infection, symptoms mayinclude bloody sputum, cough, fever, abdominal discomfort, passing

worms, etc.[8][9]

Prevention

Preventing any fecal-borne disease requires educated hygienic habits/culture and fecal treatment systems once ayear. This is particularly important with ascaris because its eggs are one of the most difficult pathogens to kill(second only to prions), and the eggs commonly survive 1–3 years. Ascaris lives in the intestine where it lays eggs.Infection occurs when the eggs, too small to be seen by the unaided eye, are eaten. The eggs may get ontovegetables when improperly processed human feces of infected people are used as fertilizer for food crops.Infection may occur when food is handled without removing or killing the eggs on the hands, clothes, hair, rawvegetables/fruit, or cooked food that is (re)infected by handlers, containers, etc. Bleach does not readily kill Ascariseggs but it will remove their sticky film, to allow the eggs to be rinsed away. Ascaris eggs can be reduced by hotcomposting methods, but to completely kill them may require rubbing alcohol, iodine, specialized chemicals,cooking heat, or "unusually" hot composting (for example, over 120 degrees Fahrenheit for 24 hours [1]

5/31/13 Ascaris lumbricoides - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Ascaris_lumbricoides 3/4

Infertile egg

(http://weblife.org/humanure/chapter8_7.html)).

Details of infection process

Infections happen when a human swallows water or food contaminatedwith unhatched juveniles. The juveniles hatch in the duodenum (1stsection of small intestine). They then penetrate the mucosa andsubmucosa and enter venules or lymphatics. Next they pass through theright heart and into pulmonary circulation. They then break out of thecapillaries and enter the air spaces. Acute tissue reaction occurs whenseveral worms get lost during this migration and accumulate in otherorgans of the body. The juveniles migrate from the lung up the respiratorytract to the pharynx where they are swallowed. They begin producingeggs within 60–65 days of being swallowed. These are produced withinthe small intestine where the juveniles mature. It might seem odd that theworms end up in the same place where they began. One hypothesis toaccount for this behavior is that the migration mimics an intermediate host, which would be required for juveniles ofan ancestral form to develop to the third stage. Another possibility is that tissue migration enables faster growth and

larger size, which increases reproductive capacity.[10]

Diagnosis and treatment

Most diagnoses are made by identifying the appearance of the worm or eggs in feces. Due to the large quantity ofeggs laid, physicians can diagnose using only one or two fecal smears.

Infections can be treated with drugs called ascaricides. The treatment of choice is Mebendazole. The drug functionsby binding to tubulin in the worms' intestinal cells and body-wall muscles. Nitazoxanide and ivermectin can also be

used.[5]

References

1. ^ Harhay MO, Horton J, Olliaro PL (February 2010). "Epidemiology and control of human gastrointestinal parasitesin children" (http://www.future-drugs.com/doi/abs/10.1586/eri.09.119?url_ver=Z39.88-

2003&rfr_id=ori:rid:crossref.org&rfr_dat=cr_pub%3dpubmed). Expert Review of Anti-infective Therapy 8 (2):219–34. doi:10.1586/eri.09.119 (http://dx.doi.org/10.1586%2Feri.09.119). PMC 2851163(//www.ncbi.nlm.nih.gov/pmc/articles/PMC2851163). PMID 20109051(//www.ncbi.nlm.nih.gov/pubmed/20109051).

2. ^ "eMedicine - Ascaris Lumbricoides : Article by Aaron Laskey"(http://www.emedicine.com/EMERG/topic840.htm). Archived(http://web.archive.org/web/20080127165320/http://www.emedicine.com/EMERG/topic840.htm) from the originalon 27 January 2008. Retrieved 2008-02-03.

3. ̂a b Murray, Patrick R.; Rosenthal, Ken S.; Pfaller, Michael A. Medical Microbiology, Fifth Edition. United States:Elsevier Mosby, 2005

4. ^ Piper R (2007). Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, Greenwood Press.

5. ̂a b c Roberts, Larry S.; Janovy, John Jr. Foundations of Parasitology, Eight Edition. United States: McGraw-Hill, 2009

6. ^ Dridelle R. Parasites. Tales of Humanity's Mostly Unwelcome Guests. Univ. of California, 2010. p. 26.ISBN 978-0-520-25938-6.

5/31/13 Ascaris lumbricoides - Wikipedia, the free encyclopedia

en.wikipedia.org/wiki/Ascaris_lumbricoides 4/4

7. ^ "DPDx - Ascariasis" (http://www.dpd.cdc.gov/dpdx/html/Ascariasis.htm). Archived(http://web.archive.org/web/20080224051907/http://www.dpd.cdc.gov/DPDx/HTML/Ascariasis.htm) from theoriginal on 24 February 2008. Retrieved 2008-02-03.

8. ^ http://www.nlm.nih.gov/medlineplus/ency/article/000628.htm

9. ^ http://www.stanford.edu/group/parasites/ParaSites2005/Ascaris/JLora_ParaSite.htm#Symptoms

10. ^ Read, A.F.; Skorping, A. 1995. The Evolution of Tissue Migration by Parasitic Nematode Larvae. Parasitology111:359-371

External links

Ascaris lumbricoides Video - DAVE Project (http://daveproject.org/duodenum-ascaris-lumbricoides/2004-05-10/)

Retrieved from "http://en.wikipedia.org/w/index.php?title=Ascaris_lumbricoides&oldid=555937738"

Categories: Nematodes Parasites Animals described in 1758

This page was last modified on 20 May 2013 at 12:29.

Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply.By using this site, you agree to the Terms of Use and Privacy Policy.

Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.