HOOKWORMS Flashcards
Why are they called hook worm?
Due to cervical curvature
Name the two species of hookworms that are human parasites.
Necator americanus - Also called the American or the ‘New World hookworm.
Ancylostoma duodenale - Also called the ‘Old World’ hookworm.
Epidermiology of hookworms
Throughout the tropics
Necator americanus Epidermiology
Literally means the ‘American murderer’.
Geographical distribution- South America, Southern Africa, Southern India, Northern Australia, Southern States of USA.
Habitat of N. americanus:
adult worms live in the small intestines, mostly the jejunum, less often in the duodenum & infrequently in the ileum.
Attached to mucosa, but may attach to new sites during feeding.
Morphology of N. americanus
Adult form(male and female) and eggs
Adult form of N. americanus morphology:
*Adult worms are slightly smaller than A.duodenale & pinkish or creamy grey.
*Buccal capsule is smaller with 2 pairs of semilunar cutting plates instead of teeth like A. duodenale.
*They have an excretory & oesophageal glands for exodigestion, also excretes anticoagulant.
*Contraction of oesophageal muscles draws blood & anchors worms to the intestinal wall
Male N. americanus male morphology:
*Males are slightly smaller than females being 7–9 mm by 0.3 mm.
*Posterior end of the male has copulatory bursa which is long & wide. The copulatory spicules are fused at the ends to form a barbed tip.
Female N. americanus male morphology:
*Females being 9–11 mm by 0.4 mm.
*Female worms have a vulva placed in the middle and anterior of the body.
N. americanus eggs:
identical with those of A. duodenale.
Life cycle of N. americanus:
*similar to that of A. duodenale
Lifespan of Necator is much longer being about 4–20 years compared to Ancylostoma with 2–7 years
Ancylostoma Duodenale Epidermiology
*Prevalent along the Mediterranean coast of Europe & Africa, northern India, China and Japan.
Habitat of A. duodenale:
similar to americanus mostly the jejunum, less often in the duodenum & infrequently in the ileum.
Adult A. duodenale worm morphology:
*Relatively stout and cylindrical worms.
*Appear pale pink or greyish white, however may appear reddish brown due to ingested blood.
*The body is curved with the dorsal aspect concave and the ventral aspect convex.
*The buccal capsule is reinforced with a hard chitin-like substance carrying 6 teeth; 4 teeth ventrally & 2 dorsally.
Morphology of male A. duodenale worm:
*Male worm is smaller than female worm 8-11 mm in length & 0.4 mm thick.
*Posterior end of the male is expanded into a copulatory bursa.
*The cloaca into which the rectum & genital canal open is situated within the copulatory bursa.
Morphology of female A. duodenale worm:
*Female worm is larger, 10 to 13 mm long & 0.6 mm thick.
*Female posterior end is conoid with a sub-terminal anus situated ventrally.
*Vulva opens ventrally at junction of the middle & posterior thirds of the body.
*Has a vagina leading to two closely coiled ovarian tubes which occupy posterior & middle parts of the worm.
*During copulation the male attaches its copulatory bursa to the vulva.
Characteristics of hookworm eggs
*Eggs are identical for both species.
*Oval or elliptical in shape & colorless(Not bile stained).
*Surrounded by a thin transparent hyaline shell membrane.
*The egg contains an unsegmented ovum when released by the worm in the intestine.
*During passage down the intestine the ovum develops(becomes segmented with 4 or 8 blastomeres).
*A clear space btn the segmented ovum & the egg shell exist.
*Both species have high fecundity with duodenale laying 25000-30000 eggs/day & Americanus producing 9000 eggs/day.
Life Cycle of Hookworms
*Life cycle is the same for both species.
*Definitive host: Humans are the only natural host.
*Infective form: Is the 3rd stage filariform larva.
*Adult worms inhabit the small intestine by attaching to the mucous membrane by means of mouth parts.
*Eggs containing segmented ova are passed in feces of infected person & not immediately infective to humans.
*Embryo develops inside the eggs deposited in the soil under ideal conditions
*rhabditiform larva hatches out of the egg & grows in size by feeding on bacteria & other organic matter in the soil.
*It then moults twice to become the non-feeding 3rd-stage infective Filariform larva.
Infective larva can live in the soil for 5–6 weeks.
Transmission of Hookworm
①Cutaneous – (3rd stage) or L3 filariform larvae penetrate thru skin follicles in the unshod state or bare hands e.g farmers/Miners.
➁Oral route – swallowed filariform larvae thru contaminated vegetables or fruits become infective without lung passage(Tissue phase is bypassed) .
③Cases of transmammary/transplacental transmission has been reported for Ancylostoma.
*Galactogenic hookworm infection not demonstrated in human hookworm except only suggested by high neonatal hookworm incidence.
*larvae are carried via venous circulation to the right side of the heart & to the lungs.
*Larva penetrate pulmonary capillaries into the alveoli, migrate up the respiratory tract to the pharynx & are swallowed to reach the small intestine.
*During migration or on reaching the esophagus, they undergo third moulting.
*Final moulting occur in the small intestine with devt of the buccal capsule by which they attach themselves to the small intestine & grow into adults.
*Adult worms become sexually mature & start laying eggs after 6 wks post infection however devt arrest may occur & process may take longer(6 months or more).
*In some cases, larvae may be swallowed & may develop directly into adults in the small intestine without a tissue phase.
HOOKWORM INFECTION & HOOKWORM DISEASE
Both larva & adult worms cause disease.
Cutaneous lesions, Creeping eruption & respiratory manifestations are caused by larvae.
①Cutaneous lesions(larvae)
itching sensation by penetrating larvae cause severe local pruritus(allergic reaction),an erythematous papular rash which later become vesicular= “ Ground itch”.
*More common with Necator & self limiting(2-4wks).
➁Creeping eruption ( cutaneous larva migrans). (larvae)
⊛Commonly caused by animal hookworms than human e.g A.braziliense,A. caninum
⊛larvae make serpiginous tunnels in the dermis, travel several mm/day causing itchiness for several weeks or months.
⊛Deep skin eruption .
③Respiratory manifestation(larvae)
⊛Occurs when migrating hookworm larvae break out of pulmonary capillaries into alveoli & cause focal hemorrhages.
⊛Presents as bronchitis & bronchopneumonia with dyspnea & cough.
⊛Rarely Loeffler’s syndrome.
④Intestinal Infection & Hookworm Disease（Caused by adult worms）
⊛Adult worms suck blood leading to microcytic hypochromic anemia.
⊛Patients develops epigastric pain, dyspepsia, vomiting & diarrhea. The stool is bloody or black in colour.
⊛Symptoms & signs of anemia are present: exertional dyspnea, palpitations, dizziness, generalized edema, brittle hair & koilonychias.
*Severe hookworm anemia commonly leads to cardiac failure.
*Mental & physical development retarded in children.
*Hookworm disease is related to worm burden.
5 eggs/mg feces – No clinical disease.
20 egg/mg feces – significant Anemia.
50 eggs/mg feces – massive infection.
DIAGNOSIS OF HOOKWORM
①Demonstration of eggs in feces.
⊛Egg counts give a measure of the intensity of infection.
⊛Modified Kato-Katz smear technique is a useful method for quantitative estimation of eggs in stool.
➁Charcot-Leyden crystals in feaces – in prepatent period
③Free larvae in stored feaces – to be differentiated from other larvae
④Culture of eggs – Harada-Mori test & Coproculture
⑤Blood examination reveals microcytic, hypochromic anemia and eosinophilia.
TREATMENT OF HOOKWORM(Adult Parasites: to reduce worm load）
①Albendazole –300mmg X 3 days doze
➁Mebendazole
③Levamisole
④Pyrantel Pamoate (Combatrin)
⑤Bephium Hydroxynaphthaoate (Alcopar)
⑥Tetrachloroethane-Toxic drug.
TREATMENT OF HOOKWORM(Cutaneous Larva Migrans）
①oral Thiabendazole
➁Topical Thiabendazole
③Mebendazole
④10% Metriphonate in petroleum jelly - topically
TREATMENT OF HOOKWORM(Hookworm anemia）
①Iron therapy
➁Folic acid
③Parenteral iron – iron-dextrose when patients cannot tolerate iron by mouth or when compliance is poor.
ANCYLOSTOMA CEYLANICUM
*Males 8mm. Females 10mm
*Two large teeth, each with a small on each side of the middle line.
*In cats and wild cats, dogs and man to a lesser extent in SE Asia, Phillipines, Taiwan, India
*Does not cause larva migrans in man
*Causes intestinal infection in man and needs to be distinguished from N. americanus and A.duodenale
*Small bursa, as wide as it is long supported
by short lateral rays
ANCYLOSTOMA BRANZILLIENSE
*Found in wild and domestic Cats and dogs in Brazil, Phillipines, India, Thailand, Ceylon, Indonesia, New Guinea
*Males – 8mm, Females – 10mm with distinct angular bend at level of vulva
*Buccal capsule with pair of inconspicuous
median teeth and a pair of outer larger teeth.
ANCYLOSTOMA CANINUM
Dog parasite
*Human parasite in the Phillipines, L3found in skeletal muscle of man in Louisiana.
*Males – 10mm, Females – 14mm
*Large buccal capsule – 3pairs ventral teeth
*Bursa supported by slender rays
*Eggs slightly larger than A. duodenale
*Esophageal (amphidial) glands with proteolytic enzymes
Other hookworms:
①A. turbaeformi
➁A. malayanum
③A. ceylonicancylostoma
④Uncinaria stenocephala -dogs
⑤Bunostomum phlebotomum - cattle
What does hookworm endemicity depend on?
①Continuous infection in the human population
➁Promiscuous defecation ensuring that ova are deposited in favorable soil for extrinsic development
③Appropriate conditions – sandy and humus soil
④Opportunity for the infective larvae to come in contact with bare skin.
⑤Prolonged dry and cold seasons are unsatisfactory for the extrinsic development.
⑥Defecation habits and use of night soil in agriculture ensures inoculation of soils for human exposure.
⑦Temperature is major factor in determining geographical distribution
⊛Necator eggs and larvae tolerates higher temperatures than those of Ancylostoma
⊛Necator is warm climate hookworm
⊛Ancylostoma is cooler climate hookworm
