(NEMATHELMINTHES)Class: Nematoda

(Round worm)

Dr. Gamal Allam

Ascariasis

Dr. Gamal Allam

Learning outcomes

• By the end of the lecture, you should be able to:1- Mention causal agent of Ascariasis.2- Mention systematic position of Ascaris lumbricoides.3- Mention geographic distribution of Ascariasis.6- Explain life cycle of Ascaris lumbricoides.7- Mention habitat of Ascaris lumbricoides.8- Mention mode of infection by Ascaris lumbricoides.9- Mention pathology and clinical features of Ascariasis.10- Diagnose Ascariasis.

Dr. Gamal Allam

Suggested Reading

• http://www.dpd.cdc.gov/dpdx/HTML/ Ascariasis.htm

Dr. Gamal Allam

Causal Agents

• Ascariasis is a parasitic disease caused by Ascaris lumbricoides.

• Ascaris lumbricoides is the largest nematode (roundworm) parasitizing the human intestine.

Dr. Gamal Allam

Systematic position

• Phylum: Aschelminthes• Class: Nematoda

e.g. Ascaris lumbricoides

Dr. Gamal Allam

Geographic Distribution

• Ascaris lumbricoides is the most common human helminthic infection.

• Worldwide distribution.• Highest prevalence in tropical and subtropical

regions, and areas with inadequate sanitation.

Dr. Gamal Allam

MorphologyAdult worm:• It is the largest nematode parasitizing the human

intestine. • The male measures 20 cm, and the female 25 -35 cm in

average length.• The adult is creamy white in colour• It has a club-shaped oesophagus• The posterior end of the male is curved ventrally; it has

one set of genitalia provided with two retractile.• The posterior end of the female is straight; it has two sets

of genitalia.

Dr. Gamal Allam

Ascaris lumbricoides

Dr. Gamal Allam

Egg: There are 3 types of eggs:• a- Fertilized egg : 60x45μ, oval in shape, yellowish brown in colour

with two coverings , outer mamillated and inner thick egg shell and containing immature ovum.

• b- Unfertilized egg: 90x45μ, long and narrow, less mamillated layer and thin egg shell and containing refractile granules. These eggs are laid by unfertilized or single female.

• c-Decorticated egg: When the mamillated layer is lost, the fertile or infertile egg is said to be decorticated.

Dr. Gamal Allam

Life cycle

Dr. Gamal Allam

Life Cycle

2nd stage Rhabditiform larva

Dr. Gamal Allam

Life cycle Habitat: The adult worms live loosely attached to the mucous

membrane of the small intestine of man by its lips.

Immature eggs pass in the faeces, the average daily output of a

female worm is 200,000 eggs.

Under favourable environmental conditions in the soil

(temperature 25ºC, humidity 70% and oxygen) a rhabditiform

larva develops inside the egg in about two weeks.

The first moult occurs after one week giving the second-stage

larvae.

Dr. Gamal Allam

Life cycle …. cont. The infective stage is the egg containing 2nd stage larva.

Mode of infection: Man is infected by ingestion of the

infective eggs containing 2nd stage larva with water or raw

vegetables or contaminated hand.

The eggs hatch in the upper small intestine liberating their

rhabditiform larvae which penetrate the intestinal wall to

reach the venules or lymphatics to the liver then to the right

side of the heart to the lungs where they break out the lung

capillaries into the alveoli.

Dr. Gamal Allam

Life cycle …. cont.• In the lungs the larvae undergo second and

third moults, then pass to the bronchi, ascend the trachea to the glottis and pass down the oesophagus to the small intestine.

• In the intestine they undergo a fourth moult and become adults and the eggs appear in faeces about 2 months after infection.

• Life span of adult is about 12 to 18 months.

Dr. Gamal Allam

Mode of infection

• Humans become infected by swallowing Embryonated eggs containing 2nd stage Rhabditiform larva

Dr. Gamal Allam

Clinical Features

• Although infections may cause stunted growth.• Adult worms usually cause no acute

symptoms.• High worm burdens may cause abdominal pain

and intestinal obstruction.• Migrating adult worms may cause

symptomatic occlusion of the biliary tract.• Also oral expulsion may occur in very high

worm burden.

Dr. Gamal Allam

Ascaris lumbricoides

Dr. Gamal Allam

Clinical Features…….cont.

Dr. Gamal Allam

Laboratory Diagnosis

• Microscopic identification of Fertilized and unfertilized Ascaris lumbriocoides eggs in stool of the infected human is diagnostic for Ascariasis.

Dr. Gamal Allam

Laboratory Diagnosis…..cont.

fertilized egg unfertilized egg

Dr. Gamal Allam

Laboratory Diagnosis…..cont.

Embryonated eggsfertilized egg eggsDr. Gamal Allam

1-Embryonated egg is the infective stage of:Ascaris lumbricoides2- Intestinal obstruction is caused by: Ascaris lumbricoides

Dr. Gamal Allam

Thank you

Dr. Gamal Allam