Intestinal nematode infections- Trichuris, Enterobius, Ancylostoma

Introductory lecture for MBBS on Nematode infections.

1. Intestinal Nematode Infections Trichuris , Enterobius and Ancylostoma

2. TriChuriS TriChiura It was first described by Linnaeus in 1771 It is also called as whipworm as the adult worm resembles to a handle of a whip Human infection is mostly confined to T. trichiura and very rarely T . suis (pig whipworm) and T. vulpis ( dog whipworm) 71 species of Trichuris are recorded so far

3. Epidemiological determinants Habitat: large intestine of man ( mainly cecum and appendix ) Distribution: Warm & Moist climate. Worldwide; Global prevalence in humans is approximately 604 millions Adult worm It is whip shaped . Anterior three-fifth is thin, hair like, coiled ( like rope of a whip ) and posterior two-fifth is short and thick

4. Morphology Egg Barrel shaped surrounded by a shell, bear mucus plug at both the poles ( 50–54 μ m long and 22–23 μ m wide) Bile stained; yellowish brown in colour (in saline mount) Floats in saturated salt solution

5. Life cycle Host: Humans Infective form: Embryonated eggs Mode of transmission : Men (usually children) acquire infection by ingestion of contaminated food and water containing embryonated egg

6. Adults Laying Unembryonated Egg Within 2–3 months, the female worms following fertilization start laying unembryonated eggs Diagnostic form: Unembryonated egg; Non-infective It takes about 28 days to become embryonated Embryonation occurs at 25°C in warm and moist condition Life cycle

7. Pathogenicity/Clinical Features I.P. 70-90 days Eosinophilia Heavy infections: Mechanical distortion & Allergic response by the host Abdominal pain, anorexia Trichuris dysentery syndrome Iron deficiency anemia due to blood loss Recurrent rectal prolapse Growth retardation and impaired cognitive function

8. Lab diagnosis Stool Examination Preservative: Formalin is preferred over polyvinyl alcohol to preserve the stool samples Whip shaped adult worms of 3–5 cm long, are occasionally seen on proctoscopy

9. Management Other findings: Peripheral blood eosinophilia (< 15%) Increased serum IgE level Treatment: Mebendazole (500 mg once) or albendazole (400 mg daily for three doses) Ivermectin (200 mg/kg daily for three doses)

10. Enterobius Vermicularis Enterobius vermicularis is also called as pin worm or threadworm It is described first by Leuckart , in 1865 E. vermicularis is the only species

11. Epidemiology Globally, around 209 million people are infected by pinworms The prevalence is maximum in school children between the age of 5 and 14 years Factors promoting infection Over crowding and impaired hygiene, poor personal care It has been said that: “ You had the infection as a child, you have it now and you will again get it when you have children”

12. Morphology Habitat: The adult worm remains attached to the large intestine (cecum, appendix and adjacent portion of colon) by their mouth end Adult worm: It is small, white and thread like ( hence named as threadworm )

13. Morphology Eggs Shape: Oval or planoconvex (one side is plain and the other side is flat because it is compressed laterally) Size: 50–60 μm long × 20–30 μm wide Surrounded by: Double layered egg shell Not bile stained, Colorless in saline mount Embryonated when passed fresh; contains a tadpole larva inside Floats in saturated salt solution

14. Life cycle Host: Humans are the only host Infective form: Embryonated eggs are infective to man Mode of transmission: Men ( usually children ) acquire infection by ingestion of embryonated eggs containing larva by: Ingestion of eggs contaminated with fingers due to inadequate hand washing or nail biting habit

15. Endogenous autoinfection retrograde migration of the larva hatched from the eggs in the perianal skin Autoinfection Exogenous autoinfection eggs cause intense irritation of the perianal skin and scrapping of the area leads to contaminated finger

16. Life cycle

17. Life cycle Development in Man Eggs hatch out releasing the larvae in the cecum and develop into adult worms Gravid female worms fully filled with eggs migrate to large intestine (rectum, colon) and start laying eggs on the perianal skin The eggs are embryonated and are the infective stage to man Female worm live for about 2 months but because of the autoinfection the cycle continues

18. Pathogenicity and Clinical Features Asymptomatic: Most of the infections are asymptomatic Symptomatic patients: Females/Children/Young adults Cardinal symptoms: Perianal pruritus often worse at night as a result of the nocturnal migration of the female worm Excoriation of the perianal skin and bacterial superinfection may occur Abdominal pain and weight loss Migration of the worm: Rarely, pinworms invade the female genital tract, causing vulvovaginitis and pelvic or peritoneal granulomas

19. Laboratory diagnosis Wet mount of perianal swab collected by cellophane tape method or NIH swab method detects planoconvex eggs containing larvae The female worms lay eggs in the perianal area ; not in rectum. Hence eggs are rarely detected by stool examination So the eggs deposited in the perianal skin are collected by applying cellophane tape or its modification called, NIH swab

20. Cellophane Tape Method Eggs are detected by the application of clear cellulose acetate tape to the perianal region before the child goes for bath The tape is then applied on the clear glass slide The slide is observed under microscope for the detection of pin worm eggs

21. NIH Swab Method It is devised in National institute of health, USA It consists of a glass rod attached to a cellophane tape by a rubber band The other end of the glass rod is fixed by a rubber stopper and kept in a test tube The cellophane part of the glass rod is rolled over the perineal and perianal skin area to collect the sample After the tape is transferred to a slide, microscopic examination will detect Enterobius eggs

22. Management One of the following drugs can be given: Mebendazole (100 mg once) Albendazole (400 mg once) or Pyrantel pamoate (11 mg/kg once; maximum , 1 g ) Treatment of household members is advocated to eliminate asymptomatic reservoirs of potential reinfection Prevention By improving personal hygiene such as proper washing of bed clothes and hand washing

23. Small Intestinal Nematodes: HOOKWORM Hookworm belongs to the family Ancylostomatidae which consists of two species infecting humans : Ancylostoma duodenale Necator americanus The word Ancylostoma is derived from hooked mouth ( Ancylos —hooked, stoma —mouth ) Animal parasites that rarely infect man causes cutaneous larva migrans Ancylostoma braziliensis Ancylostoma caninum Ancylostoma ceylanicum Uncinaria stenocephala

24. Epidemiology Globally, nearly 900 million people are infected . Males and young adults (15–25 years) are commonly affected But the anemia due to the iron loss is more severe in children and pregnant w N . americanus is predominant in south India and A. duodenale in north India Endemic Index Chandler’s index is used in the epidemiological studies of hookworm disease to estimate the morbidity and mortality in the community from hookworm infection ( which depends much upon the worm load )

25. Morphology A. duodenale was first detected by an Italian physician Dubini in 1843 Adult worm

26. Egg Oval shaped, measures 60 μm long × 40 μ m wide Not bile stained , colorless Surrounded by thin, hyaline, translucent egg shell Ovum (embryo) is segmented (four blastomeres ) There is a clear space between the egg shell and the embryo Floats on saturated salt solution Morphology

27. Larva There are four stages of hookworm larva (L1 to L4) First stage larva is called as rhabditiform larva L3 stage larva is called as filariform larva , is the infective form to man Morphology

28. Host: Involves only one host (man). Infective stage: Third stage filariform (L3) larva Mode of transmission: Through penetration of skin by the third stage larva Migratory Phase Intestinal Phase Develop into adults The L3 larvae undergo third molt to form L4 larvae that reach the small intestine where they undergo the final molt to adult worms

29. Life cycle The adult worms attach to the intestinal mucosa by their teeth in buccal capsule In about 5 months following infection, Unembryonated eggs are passed in faeces Development in Soil Embryonation takes place in moist, sandy and warm soil The first stage ( rhabditiform ) larvae hatch out from eggs which then molt twice and finally the infective stage, i.e. L3 (survive upto weeks)

30. Pathogenicity Hookworm has ability to suck blood from the intestinal vessels by : Attaching and making cuts in the intestinal wall by buccal capsule and teeth z Secreting hydrolytic enzymes Releasing anticoagulants like factor VIIa / tissue factor inhibitor Ingestion of extravasated blood It can also penetrate the skin which is facilitated by proteolytic enzymes ( like aspartyl proteases) and hyaluronidase secreted by hookworm

31. Clinical features Affect Due to Migrating Larva: Local lesion (in previously sensitized persons ) Maculopapular dermatitis and rashes (“ ground itch”) at the site of skin penetration Serpiginous tracks may be formed due to subcutaneous migration of the larva Mild transient pneumonitis Affect due to Adultworm in Intestine Asymptomatic Early intestinal phase: epigastric pain, inflammatory diarrhea, Late intestinal phase: iron defi ciency anemia and protein energy malnutrition resulting from blood loss

32. Wakana disease : When L3 larva of A . duodenale is ingested by the oral route, both gastrointestinal (due to larva develop in to adult worm in intestine) as well as pulmonary symptoms (due to larva migrating through pharynx ) are observed Common symptoms include nausea, vomiting, pharyngeal irritation , cough, dyspnea, and hoarseness Clinical features

33. Laboratory diagnosis Stool concentration procedures may be required to detect lighter infections Eggs of A. duodenale and N. americanus are indistinguishable Stool culture: freshly passed stool samples can be cultured where the eggs hatch out to develop to L3 stage filariform larva in 5–7 days Harada Mori filter paper tube method Petridish ( slant culture) technique Baermann funnel technique Other Findings Hypochromic microcytic anemia, Eosinophilia, Hypoalbuminemia

34. Management Antiparasitic drugs: like albendazole ( 400 mg once), mebendazole (500 mg once ), and pyrantel pamoate (11 mg/kg for 3 days) can be given Symptomatic Treatment Mild iron-deficiency anemia can often be treated with oral iron alone. Severe hookworm disease with protein loss and malabsorption warrants nutritional support and oral or parenteral iron replacement School based deworming: It was launched by World Health Organization (WHO) in 2001 which aimed at reducing the hookworm morbidity by giving anthelmintic drugs to at least 75% of school going children

35. MCQ’S Trichuris / Enterobius /Hookworm

36. MCQ 1 The characteristic shape of Trichuris trichiura egg is: A. Oval with a pointed tail B. Barrel-shaped with bipolar plugs C. Spherical with operculum D. Elongated with striations

37. MCQ 2 A child presents with chronic dysentery and rectal prolapse. Which helminth is most likely responsible? A. Ascaris lumbricoides B. Enterobius vermicularis C. Trichuris trichiura D. Taenia solium

38. MCQ 3 The most effective method for diagnosing Enterobius vermicularis is: A. Stool microscopy B. Duodenal aspirate C. Cellophane tape swab (perianal swab) D. Serology

39. MCQ 4 Female Enterobius vermicularis lays eggs in which site? A. Duodenum B. Colon C. Rectum D. Perianal skin

40. MCQ 5 Mode of infection with hookworm is primarily through: A. Ingestion of cysts B. Bite of vector C. Skin penetration by larvae D. Inhalation of ova

41. MCQ 6 The infective form of hookworm is: A. Egg with larva B. Rhabditiform larva C. Filariform larva D. Adult worm

42. MCQ 7 Which of the following clinical features is most characteristic of hookworm infection? A. Nocturnal perianal pruritus B. Dysentery with mucus and blood C. Microcytic hypochromic anemia D. Visceral larva migrans

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