Ascariasis

October 6, 2009Presented by Melissa Torres

Photo extracted from: http://emedicine.medscape.com/article/212510

Soil transmitted helminths

• Parasite nematodes– Infection from contact with eggs/ larvae in soil

– Human to human direct transmission is impossible*

• Nematodes include– Roundworms, whipworms, and hookworms

– Common to be infected with all three worms

• One of the world’s most important causes of physical and intellectual growth retardation.

What is Ascariasis?

• Most common helminthic disease– Estimated worldwide prevalence of 25%

– 0.8-1.22 billion people

• Usually asymptomatic

• Most prevalent in children– Highest prevalence = 2 to 10 year olds

– Highest intensity = 5 to 15 year olds

Symptomatic Ascariasis

• May manifest into–Growth retardation– Pneumonitis/ verminous pneumonia– Intestinal obstruction–Hepatobiliary and pancreatic injury– Eosinophilia*

Climate is an important factor

• Warm and moist climates– Latin America and Caribbean

– Sub-Saharan Africa

–Middle East and north Africa

– India

– South Asia

– East Asia and Pacific Islands

– China

A. lumbricoides

Extracted from Soil-transmitted helminth infections: ascariasis, trichuriasis, and hookwormFigure 1: Adult male and female soil-transmitted helminths

Extracted from http://en.wikipedia.org/wiki/Ascaris_lumbricoides

Ascaris lumbricoides• Largest of nematodes infecting humans• Highest daily egg output• Shortest lifespan

Extracted from Soil-transmitted helminth infections: ascariasis, trichuriasis, and hookwormTable 2: Characteristics of the soil-transmitted helminths: adult worms of greatest public-health significance

Ascaris lumbricoides

Extracted from Soil-transmitted helminth infections: ascariasis, trichuriasis, and hookwormFigure 2: Soil transmitted helminth eggs

Fertilized eggs•Contain a zygote•And a thick eggshell consisting of four layers

Egg shed facts:

• Humans with ascariasis can shed in their faeces– Fertilized eggs only• 45% of infected persons

– Unfertilized eggs only• 20% of infected persons

– Or fertilized and unfertilized eggs• 40% of infected persons

Ascaris suum

• Swine nematode– Difficult to distinguish from A. lumbricoides

• Possibility of zoonotic infection– In well developed countries

– Little evidence shown on transmission of porcine ascariasis to humans

Life Cycle

Diagnosis

• Stool examination– Kato-Katz fecal smear– McMaster method

• Ultrasonography and endoscopy– ECRP

Photo extracted from http://www.lnrcancernetwork.nhs.uk/images/ERCP.jpg

Treatment

• Drug therapy– Adult worms only!

• Benzimidazole anthelminthic drugs– Albendazole = DOC– Mebendazole

• During pregnancy– Pyrantel pamoate

Albendazole

http://commons.wikimedia.org/wiki/File:Albendazole_structure.png

Treatment

• Paralyzing vermifuges– pyrantel pamoate– Piperazine– ivermectine

• Nitazoxanide– Primariliy for protozoal

infection

• Vitamin A supplements

Pyrantel pamoate

http://commons.wikimedia.org/wiki/File:Pyrantel_pamoate.png

Surgery

• Deworming – Should be done first

• Intestinal or Bilial surgery– ECRP– Cholecystectomy

Photo extracted from http://www.medscape.com/viewarticle/451597_3

Prevention

• Community control– Difficult to achieve

• Health education– Along with sanitation programs

• Mass treatments– They do not seem to decrease transmission rates

• Vaccine in progress– Nasally administered 16-kd secretory protein

References

1. Bethony, S.B., et al. (2006). Soil transmitted helminth infections: ascariaisis, trichuriasis, and hookworm. The lancet 2006; 367, 1521-1532.

2. Fincham, J.E., et al. (2007). Ascaris, co-infection and allergy: the importance of analysis based on immunological variables rather than egg excretion. Transactions of the Royal Society of Tropical Medicine and Hygiene; 101, 680-682.

3. Haburchak, D.R.. (2008, September 12). Ascariasis. Emedicine. Retrieved September 18, 2009 from http://emedicine.medscape.com/article/212510

4. Peng, W., Zhou, X., & Gasser, R.B.. (2003). Ascaris egg profiles in human faeces: biological and epidemiological implications. Parasitology; 127, 283-290.

5. Sherman, S.C., & Weber, J.M.. (2005). Visual Diagnosis in Emergency Medicine: The CT diagnosis of ascariasis. The Journal of Emergency Medicine; 28, 4, 471-472.

6. Shultz, M.G.. (1982). Ascariasis: nutritional Implications. Review of Infectious Diseases; 4, 815-820.

7. Williams, D., Burke, G., & Hendley, O.J.. (1974) Brief Clinical and Laboratory Observations: Ascariasis: A family disease. The Journal of pediatrics; 853-854

The hygiene hypothesis

• Enhanced TH2 response– Susceptibility versus protection

• “Soil transmitted helminths are though to survive within the host not just by warding off the immune attack, but instead by aggressively subverting the host immune response…” (2006, Bethony et al)