Nematode (Round Worm)

Nematodes Dr. Rafal Al-Saigh
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Nematode (Round Worm)
It is estimated that 25% of the world s population is infected with this
nematode.
Ascaris lumbricoides
(Intestinal round worms of humans)
A. Lumbricoides is the giant roundworm of human, belonging to the phylum
Nematode. It is the largest and most common parasitic worm in human.
It is responsible for the disease called Ascariasis in small intestine of human.
Ascariasis is prevalent worldwide and more so in Tropical and Subtropical
countries.
Ascariasis can occur at all ages, but is more prevalent in 5-9 years old group.
The incidence is higher in poor rural population.
The adult females of this species can measure up to 18 inches long (males are
generally shorter)
Morphology
The adult worm: is the largest round worm parasitizing the human intestinal
tract. It is elongated, cylindrical, and tapers both anteriorly & posteriorly to
relatively blunt conical ends. The head is provided with three fleshy lips.
The digestive & reproductive organs float inside the body cavity which contains
an irritating allergic fluid .The irritant action is due to the presence of atoxin
called a scarone or a scarase.
Egg:The fertilized egg of Ascaris lumbricoides at the time of oviposition is
spherical or sub-spherical, measures 65-75um X 35-50um & consists of the
following observable structures:
1-A coarsely granular, spherical ovum that usually does not completely fill the
shell.
2-A thin inner most membrane that is highly impermeable.