Trichuris trichiuria

Phylum: Nemathelminthes
Class: Nematoda
Order: Trichurata
Genus: Trichuris
Species: Trichuris trichiuria

eggs of trichuris trichuria

Geographical Distribution

• World wide distribution.
• Most common intestinal nematodes in South East Asia.

Morphology

• Size of adults:
• Male : 30 - 45 mm long.
• Female : 35 - 50 mm long.
• Male have a single spicule which is surrounded by sheath.
• The anterior 3/5 in elongated and thin, the posterior 2/5 is fleshy and bulbous.
• The adults are mainly located in the caecum.
• Eggs are barrel-shaped, brownish in colour and have a transparent blister like plugs at both ends.
• In the soil, the eggs become infective in about 3 weeks.

Trichuris trichiura (a) female (b) male

Life Cycle

• Infection occurs by ingesting embryonated eggs.
• The larva penetrates the gut wall and return to the lumen to mature into adult.
• Worms attached themselves by threading their anterior ends into the mucus membrane.
• The posterior end hangs free in the lumen.
• The development in the host takes about 3 months to complete.

Life Cycle

Diagnosis

• Present of barrel-shaped eggs in the faeces.
• Sigmoidscope or proctoscope my show worms attached to the mucus membrane.
• Intact worm may be passed out in the faeces.

Strogyloides stercoralis

Phylum: Nemathelminthes
Class: Nematoda
Order: RhabditataFamily: Strogylidae
Genus: Strogyloides
Species: Strogyloides stercoralis

Necator americanus & Ancylostoma duodenale

Phylum: Nemathelminthes
Class: Nematoda
Order: Strogylata
Species: Necator americanus, Ancylostoma duodenale

Geographical Distribution

• N. americanus is usually found in moist Tropical regions such as South East Asia, Africa and America.
• A. doudenale is found in dryer and colder regions like North India, Pakistan, North China, Middle East and North Africa.

Morphology

• Adults are cylindrical with head bent sharply backward (hooked appearance).
• The male is smaller and possess a bursa at the posterior end.
• The eggs of various species are indistinguishable.
• Eggs are ovoid with thin transparetn shell.
• Size of eggs: 75 um x 36 um.
• When passed in the host intestine, they are single celled.
• In the faeces, they are at 4 - 8 celled stage.

hookworm egg

  

Ancylostoma duodenale	Necator americanus
First identified in Italy	First identified in Texas, USA
Old world hookworm	New world hookworm
Larger (male 8-11mm)	Smaller (male 7-9mm)
Anterior end bent in same direction of general curvature of body	Anterior end bent in opposite direction of general curvature of body
Prominent buccal capsule with 2 pairs of teeth	Smaller buccal capsule with 2 pairs of semilunar cutting plates
Vulva opens at junction of middle and posterior 1/3	Vulva opens a little in front of the middle
Copulatory spicules not fused	Copulatory spicules fused at ends to form a barbed tip
Lifespan 2-7years	Lifespan 4-20yrs
Ground itch less common	Ground itch more common

Hookworm Life Cycle

• Eggs are passed in the stool, and under favorable conditions (moisture, warmth, shade), larvae hatch in 1 to 2 days.
• The released rhabditiform larvae grow in the feces and/or the soil, and after 5 to 10 days (and two molts) they become become filariform (third-stage) larvae that are infective.
• These infective larvae can survive 3 to 4 weeks in favorable environmental conditions. On contact with the human host, the larvae penetrate the skin and are carried through the veins to the heart and then to the lungs.
• They penetrate into the pulmonary alveoli, ascend the bronchial tree to the pharynx, and are swallowed.
• The larvae reach the small intestine, where they reside and mature into adults.  Adult worms live in the lumen of the small intestine, where they attach to the intestinal wall with resultant blood loss by the host.
• Most adult worms are eliminated in 1 to 2 years, but longevity records can reach several years.

Enterobius vermicularis

Phylum: Nemathelminthes
Class: Nematoda
Order: Ascaroidea
Family: Ozyuridae
Genus: Enterobius  
Species: Enterobius vermicularis

Ascaris lumbricoides

Geographical Distribution

• This is one of few parasites which is more prevalent in the temperate regions of the world than the tropic.
• Children are more often involved.
• Groups living together like families, hostels, army camps etc.

Morphology

• Size of adults;
• Male : 5 mm long and 0.1 - 0.2 mm in diameter.
• Female : 13 mm long and 0.3 - 0.5 mm in diameter.
• Anterior end has 3 small lips without dentitions.
• The esophagus has a globular swelling at the posterior end.
• Gravid female has 2 distended uteri which almost fill the whole body.
• Male has curved tail and a spicule.
• The cuticle has a distinct cervical alae.
• The eggs appear flattened on one side.
• Egg has thick transparent shell. Unembrionated when passed out but become infective within a few hours.

Enterobius vermucularis egg

Enterobius vermucularis adults

Life Cycle

• The adults are mainly located in the caecal region.
• Female deposit eggs on the anus and perianal skin.
• Infection occurs by inhaling and swallowing the eggs.
• Autoinfection occurs by contamination of the fingers.
• There is no visceral migration.
• Larva matures into the adult in the lumen of the intestinal tract.
• Life cycle is completed in 6 weeks.

Life cycle

Ascaris lumbricoides

Phylum: Nemathelminthes
Class: Nematoda
Order: Ascaroidea
Family: Acaridae
Genus: Ascaris (Linnaeus 1758)
Species: Ascaris lumbricoides

ascaris lumbricoides adult

Habitat

• Adult: in the intestine (normally in small intestine).
• The worm may migrate to ectopic site.

Geographical Distribution

• The distribution is cosmopolitan, but more frequently in the warm and moist climate.

Morphology

• The mature worm is cylindrical with tapering ends.
• The male is smaller; 12 - 31 cm long and 2 - 4 mm wide and has a curved tail.
• The female 20 - 35 cm long and 3 - 6 mm wide.
• The head has 3 lips.
• The eggs when freshly passed, it is not infective and contains a single cell.
• This eggs is surrounded by irregular albumin coat.
• The eggs acquire a brownish colour from the bile pigment.
• The larva may be seen in infective lungs.

Ascaris lumbricoides adults

   

unfertilized and fertilized eggs

Life Cycle

• Adult worms live in the lumen of the small intestine.
• A female may produce approximately 200,000 eggs per day, which are passed with the feces.
• Unfertilized eggs may be ingested but are not infective.  Fertile eggs embryonate and become infective after 18 days to several weeks, depending on the environmental conditions (optimum: moist, warm, shaded soil). 
• After infective eggs are swallowed, the larvae hatch, invade the intestinal mucosa, and are carried via the portal, then systemic circulation to the lungs.
• The larvae mature further in the lungs (10 to 14 days), penetrate the alveolar walls, ascend the bronchial tree to the throat, and are swallowed.
• Upon reaching the small intestine, they develop into adult worms.
• Between 2 and 3 months are required from ingestion of the infective eggs to oviposition by the adult female.
• Adult worms can live 1 to 2 years.

Life Cycle