1. Soil-Transmitted Helminths
Elaine C. Jong MD
Clinical Professor of Medicine
University of Washington
Infectious Diseases
Travel & Tropical Medicine
April, 2013

2. Helminth Infections: Magnitude Of The Problem
Ascaris, Enterobius
1 billion infections each
Trichuris, hookworm
million each
Schistosomiasis
200 million
Filariasis (W. bancrofti)
115 million
Strongyloides
million
Paragonimus
21 million
Onchocerciasis
17.8 million
Loa loa
3-13 million
Opisthorchis
10 million
Clonorchis
7 million
Fasciola hepatica
2 million

3. Worm Kingdom Nematodes= Roundworms Cestodes= Tapeworms
Ascaris lumbricoides (common roundworm)
Ancylostoma duodenale and Necator americanus (hookworm)
Trichuris trichiura (whipworm)
Strongyloides stercoralis
Enterobius enterobium (pin worm)
Cestodes= Tapeworms
Trematodes= Flukes

4. Questions
What are the main risk factors for soil-transmitted helminths (STH)?
What are some of the impacts of STH on human health?
What are effective interventions to interrupt the transmission of disease?
What is the accepted approach to diagnosis and treatment of STH in less-developed areas where such infections are highly endemic?
How does this differ from the usual standard of care in the United States?

5. Overview: Helminth Infections
May be asymptomatic
May be an incidental finding in lab exam of clinical specimens
Symptoms and disease usually associated with heavy worm burdens
With a few exceptions, most worms are unable to multiply in their host
Heavy worm burdens therefore tend to be the result of repeated infections over time
Worms can live for years in a human host—
>20 years in the case of certain flukes

6. Overview: Helminth Infections-2
May be associated with gastrointestinal symptoms:
diarrhea, abdominal discomfort, abnormal stools, rectal irritation/ itching
May cause malnutrition and pediatric growth retardation in endemic areas
May affect productivity in adulthood
May be associated with striking peripheral blood eosinophilia
during larval migratory stages, or
location of either adult worms or eggs in tissues outside the intestinal lumen

7. STH Transmission

8. Helminth infections, growth, and anemia
Transmission of helminth infection
Accumulation of worm burden
Malabsorption
Gastrointestinal blood loss
Chemical messages to host
Iron-
deficiency anemia
Poor growth
Poor
cognitive
development
Adapted from Chwaya HM, Stoltzfus RJ. In: Drompton DWT et al (eds), Controlling disease due to helminth infections. Geneva, WHO, p.34

9. 1.3 billion Ascaris infections worldwide
Source: de Silva NR et al.,
2003. TRENDS in
Parasitology.19:

10. Ascaris Infections
Ascaris lumbricoides—common helminth infection with ~1.3 billion persons infected
71% in Asia: China, India, SE Asia
13% in Latin America & Caribbean
8% sub-Saharan Africa
Eggs relatively resistant to drying or extremes of temperature
Larvae migrating through the lungs cause eosinophilic inflammation
Heavy worm burdens in children may cause intestinal obstruction
Migrating and ectopic worms: intestinal perforation, bile duct obstruction, peritonitis, appendicitis, etc.

11. Source: Jong EC, Stevens, DA
Source: Jong EC, Stevens, DA. (eds) Netter’s Infectious Diseases 1e, Elsevier, 2012.

12. From: Teaching Slide Collection, Medical Parasitology, Markell & Voege

13. Ascaris adults DPDx-CDC: www.dpd.cdc.gov./dpdx
Courtesy of Prof. E.C.Jong
DPDx-CDC:

16. 500-900 million hookworm infections worldwide
Source: de Silva NR et al.,
2003. TRENDS in
Parasitology.19:

17. HOOKWORM INFECTIONS
Iron-deficiency anemia is the hallmark of chronic hookworm disease
Adult hookworms inhabit the upper half of the small intestine
Attach and suck blood with the aid of an organic anticoagulant
Ancylostoma duodenale = mL/ day/ worm
Necator americanus = 0.03 mL/ day/ worm
Additional blood loss from bleeding at sites of attachment
Blood loss and compensatory volume expansion
Microcytic hypochromic anemia
Hypoalbuminemia
Cardiovascular changes in severe cases

18. Source: Jong EC, Stevens, DA
Source: Jong EC, Stevens, DA. (eds) Netter’s Infectious Diseases 1e, Elsevier, 2012.

19. Hookworm Symptoms Pruritic erythema (“Ground Itch”)
Pulmonary symptoms during larval migration to the gut
Transient gastroenteritis-like syndrome as adult hookworms attach to the intestinal mucosa
Eosinophila noted in 30-60% of infected patients

20. Who’s who?

21. 500-900 million whipworm infections worldwide
Source: de Silva NR et al.,
2003. TRENDS in
Parasitology.19:

22. Whipworm Infections
million Trichuris trichiura infections worldwide
Approximately same distribution as Ascaris
Ingestion of eggs in contaminated vegetables or soil
Inhabit the caecum & colon causing inflammation, hemorrhagic patches
Each female worm produces ~10,000 eggs per day passed in the feces
Heavy infection can cause growth retardation, malnutrition, rectal prolapse

23. Source: Jong EC, Stevens, DA
Source: Jong EC, Stevens, DA. (eds) Netter’s Infectious Diseases 1e, Elsevier, 2012.

24. Trichuris trichiura adult female
Source: CDC Parasitology Diagnositic Web Site

28. Strongyloides infections
Strongyloides stercoralis causes chronic infections that are often silent
Elevation of peripheral blood eosinophils
Soil transmitted life cycle
Autoinfection life cycle
Can complete life cycle without leaving the human host
Filariform larvae in fecal stream may penetrate peri-rectal skin causing rash “cutaneous larva currens”
Infection may be self-perpetuating for decades after leaving endemic area
Hyperinfection occurs in immune-compromised hosts
Dissemination with local inflammation, enteritis, pneumonitis, microabscesses

29. Source: Jong EC, Stevens, DA
Source: Jong EC, Stevens, DA. (eds) Netter’s Infectious Diseases 1e, Elsevier, 2012.

30. Patient with cutaneous larva currens rash
Courtesy of Prof. E.C.Jong

31. From: Teaching Slide Collection, Medical Parasitology, Markell & Voege

32. Strongyloides stercoralis filariform larva
Source: CDC Parasitology Diagnositic Web Site

33. Enterobius vermicularis
Ubiquitous infection of children (estimated 1.3 billion infections worldwide)
Adults live in the caecum, gravid females migrate to the rectal area at night
Common cause of perianal itching
Appendicitis
Peritonitis
Vulvovaginitis
Eggs mature after 4-6 hours outside intestine and become infective
Fecal-oral spread on fingers and fingernails

34. Source: Jong EC, Stevens, DA
Source: Jong EC, Stevens, DA. (eds) Netter’s Infectious Diseases 1e, Elsevier, 2012.

35. Clinical Summary: Soil-Transmitted Helminths
Light infections may be asymptomatic
Heavy worm burdens may be associated with
Gastrointestinal symptoms: diarrhea, abdominal discomfort, abnormal stools, rectal irritation/ itching
Malnutrition, pediatric growth retardation, and anemia: resulting from malabsorption and gastrointestinal blood loss
Cognitive impairment

37. Clinical Summary: STH, p.2
Infections may be associated with striking peripheral blood eosinophilia
Larval migratory stages
Location of either adult worms or eggs in tissues outside the intestinal lumen
Infections do not lead to protective immunity
Heavy worm burdens usually acquired from repeated exposure in contaminated environments
Children acquire heavy worm burdens from contact with the ground and poor hygiene
Strongyloidiasis is unique—once infected, worm burdens may persist/ increase through autoinfection cycle

38. Parasite Diagnosis Identification of gross specimens
Stool for ova & parasite microscopic exam
Wet mount
Trichrome stain
Serology tests
Not for routine STH diagnosis
May be useful for extra-intestinal helminthic infections
Strongyloidiasis (Strongyloides stercoralis)
Trichinosis (Trichinella spiralis)
Toxocara canis/ catis

39. Drugs for STH Treatment
Ascaris
Trichuris
Hookworm
Strongyloides
Pyrantel pamoate
(Antiminth)¹ √
Mebendazole (Vermox)²
Thiabendazole (Mintezol)³
( √ )
Albendazole
(Albenza)ª
Ivermectin
(Stromectol)§
√ (intestinal stages only)
¹Paralysis of worm nervous system; ²Inhibition of microtubules, glucose depletion;
³Inhibition of helminth-specific fumarate reductase; ªInhibition of cytoplasmic microtubules;
§ bind glutamate-gated chloride ion channels increasing membrane permeability to chloride ions resulting in paralysis

40. WHO (1997) MODEL LIST OF ESSENTIAL DRUGS
FOUR ANTIPARASITIC DRUGS LISTED:
Albendazole
Levamisole
Mebendazole
Pyrantel pamoate

41. Individual Diagnosis & Treatment
Stool ova and parasite exam (O&P)
Treat with drug of choice
Best drug available
FDA-approved, off label use
Investigational new drug protocol/ orphan drug
Repeat O&P for test of cure or fecal egg count reduction (FECR) 4 or more weeks after therapy

42. WHO community treatment (May 2001, resolution 54.19)
“Deworming campaigns” involve presumptive treatment of high-risk groups
Routine screening of stool specimens is labor-intensive and not practical in many settings
Use of WHO drugs at de-worming doses associated with negligible and self-limiting side effects
Target high risk groups (school-age children & women of child-bearing age) (selective treatment)
Treat all persons (mass treatment) with “preventive chemotherapy” in particular regions
Survey for severe adverse reactions related to the widespread distribution of antihelminthic drugs

43. Summary of STH Prevention
Hand washing
Wearing shoes
Behavior/ education
Personal hygiene
Geophagia
Latrines
Individual treatment
Targeted mass treatment

44. Articles
Andrade C, Alava T, De Palacio IA, et al. Prevalence and intensity of soil-transmitted helminthiasis in the city of Portoviejo (Ecuador). Mem Inst Oswaldo Cruz, 96:1075-9, 2001.
Glickman LT, Camara AO, Glickman NW, et al. Nematode intestinal parasites of children in rural Guinea, Africa: prevalence and relationship to geophagia. Int J Epidemiol, 28:169-74, 1999.
Guyatt HL, Brooker S, Kihamia CM, et al. Evaluation of efficacy of school-based anthelmintic treatments against anaemia in children in the United Republic of Tanzania. Bull World Health Organ, 79: Epub 2001 Oct 24.
Kawai K, Saathoff E, Antelman G, et al. Geophagy (Soil-eating) in relation to anemia and helminth infection among HIV-infected pregnant women in Tanzania.
Kirwan P, Asaolu SO, Molloy SF, et al. Patterns of soil-transmitted helminth infection and impact of four-monthly albendazole treatments in preschool children from semi-urban communities in Nigeria: a double-blind placebo-controlled randomised trial. BMC Infect Dis ;9:20.

45. Ndyomugyenyi R, Kabatereine N, Olsen A, et al
Ndyomugyenyi R, Kabatereine N, Olsen A, et al. Efficacy of ivermectin and albendazole alone and in combination for treatment of soil-transmitted helminths in pregnancy and adverse events: a randomized open label controlled intervention trial in Masinid district, western Uganda. Am J Trop Med Hyg ; 79:
Steinman P, Utzinger J, Du Z-W, et al. Efficacy of single-dose and triple-dose albendazole and mebendazole against soil-transmitted helminths and taenia spp.: a randomized controlled trial. PLoS ONE. 2011; 6(9): e doi: /jounal.pone
Vercruysse J, Behnke JM, Albonico M, et al. Assessment of the antihelminthic efficacy of albedazole in school children in seven countries where soil-transmitted helminths are endemic. PLoS Negl Trop Dis. 2011; 5(3): e949. doi: /journal.pntd
Watson JL, Herrin BR, John-Stewart G. Deworming helminth co-infected individuals for delaying HIV disease progression. Cochrane Database Syst Rev ; (3):CD
Ziegelbauer K, Speich B, Mäusezahl, et al. Effect of sanitation on soil-transmitted helminth infection: systematic review and meta-analysis. PLoS Med. 2012; 9(1):e doi: /journal.pmed