HOOKWORMS

Question 1

Why are they called hook worm?

Answer 1

Due to cervical curvature

Question 2

Name the two species of hookworms that are human parasites.

Answer 2

Necator americanus - Also called the American or the ‘New World hookworm.

Ancylostoma duodenale - Also called the ‘Old World’ hookworm.

Question 3

Epidermiology of hookworms

Answer 3

Throughout the tropics

Question 4

Necator americanus Epidermiology

Answer 4

Literally means the ‘American murderer’.

Geographical distribution- South America, Southern Africa, Southern India, Northern Australia, Southern States of USA.

Question 5

Habitat of N. americanus:

Answer 5

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.

Question 6

Morphology of N. americanus

Answer 6

Adult form(male and female) and eggs

Question 7

Adult form of N. americanus morphology:

Answer 7

*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

Question 8

Male N. americanus male morphology:

Answer 8

*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.

Question 9

Female N. americanus male morphology:

Answer 9

*Females being 9–11 mm by 0.4 mm.
*Female worms have a vulva placed in the middle and anterior of the body.

Question 10

N. americanus eggs:

Answer 10

identical with those of A. duodenale.

Question 11

Life cycle of N. americanus:

Answer 11

*similar to that of A. duodenale

Lifespan of Necator is much longer being about 4–20 years compared to Ancylostoma with 2–7 years

Question 12

Ancylostoma Duodenale Epidermiology

Answer 12

*Prevalent along the Mediterranean coast of Europe & Africa, northern India, China and Japan.

Question 13

Habitat of A. duodenale:

Answer 13

similar to americanus mostly the jejunum, less often in the duodenum & infrequently in the ileum.

Question 14

Adult A. duodenale worm morphology:

Answer 14

*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.

Question 15

Morphology of male A. duodenale worm:

Answer 15

*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.

Question 16

Morphology of female A. duodenale worm:

Answer 16

*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.

Question 17

Characteristics of hookworm eggs

Answer 17

*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.

Question 18

Life Cycle of Hookworms

Answer 18

*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.

Question 19

Transmission of Hookworm

Answer 19

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.

Question 20

HOOKWORM INFECTION & HOOKWORM DISEASE

Answer 20

Both larva & adult worms cause disease.
Cutaneous lesions, Creeping eruption & respiratory manifestations are caused by larvae.

Question 21

①Cutaneous lesions(larvae)

Answer 21

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).

Question 22

➁Creeping eruption ( cutaneous larva migrans). (larvae)

Answer 22

⊛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 .

Question 23

③Respiratory manifestation(larvae)

Answer 23

⊛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.

Question 24

④Intestinal Infection & Hookworm Disease（Caused by adult worms）

Answer 24

⊛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.

Question 25

DIAGNOSIS OF HOOKWORM

Answer 25

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.

Question 26

TREATMENT OF HOOKWORM(Adult Parasites: to reduce worm load）

Answer 26

①Albendazole –300mmg X 3 days doze
➁Mebendazole
③Levamisole
④Pyrantel Pamoate (Combatrin)
⑤Bephium Hydroxynaphthaoate (Alcopar)
⑥Tetrachloroethane-Toxic drug.

Question 27

TREATMENT OF HOOKWORM(Cutaneous Larva Migrans）

Answer 27

①oral Thiabendazole
➁Topical Thiabendazole
③Mebendazole
④10% Metriphonate in petroleum jelly - topically

Question 28

TREATMENT OF HOOKWORM(Hookworm anemia）

Answer 28

①Iron therapy
➁Folic acid
③Parenteral iron – iron-dextrose when patients cannot tolerate iron by mouth or when compliance is poor.

Question 29

ANCYLOSTOMA CEYLANICUM

Answer 29

*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

Question 30

ANCYLOSTOMA BRANZILLIENSE

Answer 30

*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.

Question 31

ANCYLOSTOMA CANINUM

Answer 31

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

Question 32

Other hookworms:

Answer 32

①A. turbaeformi
➁A. malayanum
③A. ceylonicancylostoma
④Uncinaria stenocephala -dogs
⑤Bunostomum phlebotomum - cattle

Question 33

What does hookworm endemicity depend on?

Answer 33

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