Ancylostoma Duodenale Necator Americanus
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Class Nematoda - The Roundworms General Characters • They are un-segmented, elongated and cylindrical. • They have separate sexes with separate appearances. • They have a tough protective covering or cuticle. • They have a complete digestive tract with both oral and anal openings. The nematodes are free living (Majority) or parasites of humans, plants or animals. Nematode The intestinal nematodes – Ascaris – Hook worms The blood- and tissue – Pin worm dwelling nematodes – Whip worm – The filaria – Trichinella Ascaris lumbricoides Distribution: Cosmopolitan in distribution • Rural > urban • Children > adults Morphology: Male adult worm measures 15-20 cm in length. The posterior end is curved ventrally. The female worm measures 20-40 cm in length. Its posterior end is straight. Habitat: Human small Intestine Infective stage: Infective (fertilized) egg Mode of infection: Ingest infective eggs with contaminated water and food Diagnostic Morphology Adult Looks like an earthworm Female (20-35 cm); Male (12-30 cm) 3 lips which carry minute teeth A pair of female and male worms of A. lumbricoides. Notice the vulvar waist(arrow)of the female worm and the coiled end of the male worm. A scanning electron micrograph of Ascaris showing the three prominent “lips” The life cycle of A. lumbricoides Clinical Features and Pathogenicity Depends on: • worm load • The host immune response • Effect of larval migration • Mechanical effects of adult worm • Nutritional deficiencies due to the presence of adult worm Majority of infections are clinically asymptomatic Due to Migrating Larvae( larval ascariasis) • Loeffler’s syndrome Eosinophilic abscesses Lungs - larval migration causes pneumonitis (Loffler’s syndrome) due to immunological(hypersensitive) reaction CLINICAL FEATURERS: Fever, cough, sputum, asthma, eosinophilia On reaching general circulation: Rarely larvae may wander in to the brain, eye or retina causing granuloma Due to Adult worm • Adult worms in their normal habitat cause little pathology • Severe disease if worm burden 100 or > • Heavy infections can cause intestinal colic • Aggregate masses of worms cause Volvulous, Intestinal obstruction. Causing these symptoms: • Blocking the duct orifices • Acute appendicitis • Pancreatic necrosis • Obstructive jaundice • Ascaris liver abscess • Migrate out of the anus or come out the mouth or nose Immuno-pathological effects: •sensitivity to ascaris Ag. •conjunctivitis, urticaria, asthma. •Indirect effects - Micro organisms can by carried by the adult worms on their migration from bowel Effect on Growth and Nutrition: •Protein energy malnutrition. •Low serum proteins. •Vitamin A deficiency •Effect on normal growth and educational development. Diagnosis • Microscopic identification eggs in the stool a direct wet mount examination of the specimen (200,000 eggs/female/day) • Macroscopic identification of adults passed in stool or through the mouth or nose Treatment • Albendazole a single oral dose of 400 mg • Mebenazole 100 mg orally twice daily for 3 days Prevention • Avoid contacting soil that may be contaminated with human feces • Do not defecate outdoors • Dispose of diapers properly • Wash hands with soap and water before handling food • When traveling to areas where sanitation and hygiene are poor, avoid water or food that may be contaminated • Wash, peel or cook all raw vegetables and fruits before eating Hook worms Ancylostoma duodenale Necator americanus Hook Worms • Necator americanus - Sri Lanka, S.Asia, Africa, Pacific region and America • Ancylostoma duodenale - E.Europe, N.Africa, • India, N.China, Japan • Both species overlap in S.E.Asia, Pacific, W.Africa Hook Worms • Disease: Ancylostomiasis • Disribution: Tropical and subtropical areas • Morphology: N.americanus - 1 cm, head sharply bent backwards. Buccal capsule has a pair of ventral cutting plates. A.duodenale – slightly larger head bent backwards in a smooth curve. Buccal capsule has two pairs of teeth • Habitat: Small intestine • Definitive host: Human • Infective Stage: Filariform larva • Transmission: Via Penetration of filariform larvae through the skin (Necator americanus and Ancylostoma duodenale) and orally via the ingestion of contaminated food (Ancylostoma duodenale) May migrate to the mammary gland and are excreted via milk and infect the child L3 5th day Obligatory lung migration Non feeding,move on to top soil L2 rhab.larva (3rd day) Free living,actively feeding L1 Shade,warmth, sandy soil 24 hours IP= 4-7 weeks Pathogenesis Larvae at the site of entry vesiculation and pustulation (ground itch) Can be secondarily infected due to severe itching Asthma and bronchitis during migration, can cause pneumonitis but less severe than ascariasis Adults: Hook worm Anaemia Symptoms- mucous surface & skin become pale. Palpitation, breathlessness Chronic blood loss. active Iron deficiency Anaemia Hypoalbuminaemia Treatment Mebendazole or Flubendazole Pryantel pamoate Bephenium hydroxynaphthoate Supportive treatment: iron, vitamins and high protein diet. Laboratory Diagnosis • By demonstrating characteristic eggs in faeces. In ‘old’ stool samples Rhabditiform larvae may be found • Clinical picture and anemia in endemic area Prevention and Control • Avoidance of indiscriminate defaecation & use of foot wear • provision of hygienic latrines, treatment of infected persons& health education Enterobius vermicularis Pin Worm or Thread Worm Enterobius vermicularis • Geographical distribution -worldwide high prevalence in cold climates. • Location in host - Adults are loosely attached to the mucosa of the large intestine • Morphology - creamy white, 1cm, spindle shaped • Infective stage: Embryonated egg • Mode of infection: By direct infection from a patient (Fecal-oral route). Autoinfection: the eggs are infective as soon as they are passed by the female worm. If the hands of the patient get contaminated with these eggs, he/she will infect him/herself again and again. Aerosol inhalation from contaminated sheets and dust. Retro infection: where some of the pinworm larvae which hatch on the anus return to the gastrointestinal tract of the original host, leading to a very high parasitic load as well as ensuring continued infestation. Life Cycle Eggs become infective within 6 hours of laying Clinical Pictures • The migration of the worms causes allergic reactions around the anus and during night it causes nocturnal itching (pruritus ani) and enuresis. • The worms may obstruct the appendix causing appendicitis. Diagnosis: • Demonstration of eggs by: • NIH (National Institute of Health, USA) swab • Scotch Tape method a clear adhesive cellulose tape is applied to the anal area early in the morning before bathing or defecation • Eggs are usually collected in the folds of skin around the anus. Rarely appear in the stools Treatment: • Flubendazole or Mebendazole • Piperazine • Pyrivinium pamoate • White precipitate ointment to relieves itching and kills female worms. .