INSTITUTE OF PULIC HEALTH, DHAKADepartment of Laboratory Medicine

BSc in Health Technology (Laboratory)- 1st Year

HELMINTHOLOGYLecture No. 03(Ancylostoma duodenale)

By

Sk. MIZANUR RAHMANAssistant Bacteriologist, MBL, IPH

MS in Biotechnology & Genetic Engineering (UODA)MS in Microbiology (SU)

MPH in Epidemiology (SUB)

Introduction

• Hookworms are the voracious blood feeders of the nematode world.

• Two principal species that infect around 900 million people on earth are:

• Necator americanus known as the american killer also known the new world hookworm.

• Ancylostoma duodenale known as the old world hookworm.

Ancylostoma duodenale• Associated with miners because

mines offer an ideal habitat for egg and juvenile development due to constancy in temperature and humidity.

• It was known to cause a serious anemia in miners.

• Has two ventral plates, each with large teeth that are fused at their bases. A pair of small teeth is found in the depths of the capsule. The needlelike specules have simple tips and are never fused distally.

Definitive host• Human• No Intermediate host

Bucal cavity 2 ventral plates and two large teeth

Size of female 10-13

Size of male 8-11mm

Position of vulva 1/3 from posteriorEgg production 25000/ day

Penetration through skin Yes

Longevity 5 years

Ancylostoma duodenale

Geographic distribution

• A.duodenale is the indigenous hookworm of the north-temperate zone of the eastern hemisphere. it is confined in southern Europe, northern Africa, India, China and southern Asia.

• N.americanus is the new world worm. the “American killer,” was first discovered in Brazil and then Texas, but it was later found indigenous in Africa, India, Southeast Asia, China, and southwest Pacific islands.

Morphology

• Adult

– Cylindrical with the head bent sharply backwards

– Males are smaller than the females and possess a

bursa at their posterior end

Morphology: Adults

Ancylostoma duodenale • Female is 10-13 mm in length

by 0.6 mm in diameter• Males are 8-11 mm by 0.4 mm• Posterior end has an

umbrella-shaped bursa with riblike rays

• Two pairs of curved teeth on the ventral wall of its buccal capsule

Scanning electron micrograph of the oral opening of Ancylostoma duodenale, another species of human hookworm. Note the presence of four cutting "teeth," two on each

side.

Adult mouthpart of Necator americanusNote : The large buccal capsule is open dorsally with one pair of cutting plate

teeth.

Life cycle

First stage larva: hatches out from the egg in 24 to 48 hours Actively feeds on organic debris and bacteria in the soil 2nd stage larva: on the third day3rd stage larva: on the fifth day filariform; enclosed in a sheath does not feed; actively motile.

The third stage larva initiates the infection by penetrating the skin and passing into blood circulation. Through the blood it is carried to the right heart and then to pulmonary blood vessels. It soon breaks out of the pulmonary blood vessels into the alveoli.

Life Cycle cont--

Life cycle cont--• Eggs are passed with feces. Eggs hatch in about 48 hours under favorable

conditions such as (moist soil, protection from direct sun rays and temperature about 25°C.

• The first-stage larva feed upon bacteria in the feces about three days and then molt to second-stage larva. First and second stage larva have a rhabditiform esophagus. After 5-10 days they molt and become filariform third-stage larva that are infective.

• These infective larva can survive 3-4 weeks in favorable environmental conditions. 25 -15°C at 0°C death occurs rapidly. They move to the surface of the soil and wave back and forth which increases the chance to contact host. When they contact with the human host, the larva penetrate the skin and are carried through the veins to the heart and then to the lungs, break through into air sacs, to the trachea and are swallowed. The larva reach the small intestine, where they reside and mature in to adults.

• Hookworms have evolved strategies to evade the host’s defense system, and several of these has been discovered.

• Ancylostoma spp. Secrete a neutrophil inhibition factor that interferes with activation of neutrophils.

• N. americanus secretes acetyl cholinesterase, which inhabits gut peristalsis and possibly is an anti-inflammatory factor.

Pathogenesis cont--

1. Hookworm larvae dermatitis: Penetration of the skin by the filariform larvae may

be asymptomatic in previously uninfected individuals.

However, those experiencing repeated infections develop itching, known as "ground itch" or "dew itch".

Pathogenesis cont--

2. Migration of pre-adult cause temporary pulmonary inflammation:In heavily infected individuals

(i.e., 500-1000 worms), there can be symptoms of pneumonia during the migratory phase in the developmental cycle of these worms

Pathogenesis cont--

3. Abdominal pains, diarrhea, loss of appetite…4. Anemia

– Especially in young children– Hypoproteinemic because of some loss of serum proteins– Iron-deficiency

– Why the small worms can cause anemia?• The pump-like action when worms suck blood• The worms secrete an anticoagulant, which facilitates bleeding• The worms usually change the sites when suck blood

5. Allotriophagy (Geophagy): due to the iron-deficiency

6. Ancylostomiasis in infant

Pathogenesis cont--

Edema, ascites and loss of labour force

Allotriophagy

Symptoms/Clinical Aspects

• Itching of skin as a result of penetration by the larvae.• Congestion in lungs in heavy infections.• Anemia due to loss of blood, particularly if diet is deficient.• Diarrhea• Persons with chronic hookworm disease are debilitated.• Chronic heavy hookworm infection can damage the growth

and development of children.• Hookworm infection has been known to be fatal, particularly

in infants.

Ground itch: The stage of skin penetration Intense itching and dermatitis at the site of entry; between the toesPneumonitis and bronchitis The larval migration through the lungs This is less severe than the Loeffler's syndrome seen during the migration of Ascaris larvae. The final stage of development and attachment to the intestine is often asymptomatic.

Heavy infections: induce microcytic hypochromic anaemia

The blood loss is from sucking by the worm and also from continuing haemorrhage at the site of attachment.

Symptoms/Clinical Aspects cont…..

An Ancylostoma worm results in the loss of 0.15 ml of blood/dayIt is important that there is a difference between hookworm disease and hookworm infection.

Hookworm infection does not necessarily mean that the disease is present, as blood loss produced by light infections can be compensated by adequate food intake. Disease occurs when the intake of food is unable to compensate for the blood loss

Infected children are often oedematous indicating that these is a protein-losing enteropathy as well.

Symptoms/Clinical Aspects cont…..

Skin manifestations

Hookworm infection/disease

• Depends on three factors.1)Number of worms present2)Species of hookworm3)Nutritional conditions of the infected person.

• In general fewer than 25 N.americanus in person will cause no symptoms. 500-1000 result in severe symptoms, and more than 1000 may lead fatal consequences.

• Ancylostoma spp. Suck more blood than N.americanus fewer worms cause greater disease. 100 worms cause severe symptoms.

Transmission

• Hookworm infection is contracted from contact with soil contaminated by hookworm, by walking bare foot or accidentally swallowing contaminated soil.

• Children are at high risk because they play in dirt and often go bare foot.

• Hookworms can’t be spread person to person.

Laboratory diagnosis

• Brine floatation is the method of first choice• Direct fecal smear• Hookworm larvae cultivation is used for

species identification • Hookworm larvae in sputum• CBC, PBF• Histopathology

Laboratory Diagnosis

Microscopic identification of eggs in the stool is the most common method for diagnosing hookworm infection

C: Hookworm egg, advanced cleavage D: Embryonated hookworm egg.

C D

Hookworm rhabditiform larva

Hookworm filariform larva

                                           

    

                                                  

     H G

Section of adult hookworm in small intestine

Prevention

• Proper sanitation practices.• Appropriate fecal disposal.• Do not walk barefoot or contact with bare

hands in areas where hookworms is common or there are likely to be feces in the soil or sand.

Thank you for attention!