The Nematodes

The Nematodes Ascaris lumbricoides Common name: Giant intestinal round worm Disease: Human ascariasis

Morphology  It is the largest and the most common nematode in man.  15-30 cm by 3 mm (male).  20-45 cm by 5 mm (female).  Creamy white or pinkish worm.  Cylindrical, elongated, tapering gradually at the anterior end.

Ascaris lumbricoides adult male and female © Dr Peter Darben, Queensland University of Technology clinical parasitology collection. Used with permission

Diagnostic Features  Smooth finely striated cuticle with faint longitudinal white lateral lines. Which is seen as a whitish streak along the entire length of the body.  Terminal mouth with trilobate lips and a small triangular buccal cavity

An adult Ascaris worm. Diagnostic characteristics: tapered ends; length 15-35 cm (the females tend to be the larger ones). This worm is a female, as evidenced by the size and genital girdle (the dark circular groove at bottom area of image). Worm passed by a female child in Florida. CDC DPDx Parasite Image Library

 The male has a ventrally curved papillated posterior extremity with 2 copulatory spicules.  The female has paired reproductive organs on the posterior 2/3.  And in the anterior and middle third is a depression wherein a vagina is located.

Ova  There are two types of ova:  Fertilized: broadly ovoid, golden brown in color. – A. vitelline membrane: an inner nonpermeable, lipoidal layer. – B. glycogen membrane: thick, transparent middle layer. – C. Albuminous/ mammillary coat: outermost layer.

A fertilized Ascaris egg, still at the unicellular stage, as they are when passed in stool. Eggs are normally at this stage when passed in the stool (Complete development of the larva requires 18 days under favorable conditions).

Eggs, unfertilized (left) and fertilized (right). Patient seen in Haiti. CDC DPDx Parasite Image Library

 Unfertilized: generally larger and longer, elongated or sometimes irregular in shape.  With 2 layers, relatively thinner glycogen membrane and irregular coating of albuminous layer.  The vitilline layer is absent.  If mammilary coat is absent it is called decorticated.

Larva hatching from an egg. CDC DPDx Parasite Image Library

Life cycle



Fertilized ovasoil 2 weeksembryonation ingestedcirculationheart and lungsesophagus>SI

Pathology  A. Larval Migration to lungs can produce: – Pneumonitis resembling asthmatic attack accompanied by marked eosinophilia (ascaris pneumonitis of loeffler’s syndrome).

Clinical manifestations: Asthmatic type of respiration, cough, urticaria, rash,edema of the lips and eosinophilia.

Ascaris lumbricoides larva in section of lung (H&E) © Dr Peter Darben, Queensland University of Technology clinical parasitology collection. Used with permission

 B. Pathology due to Adult Worm.  Abdominal pain, diarrhea, nausea, loss of appetite.  Serious and sometimes fatal effects due to erratic migration of adult worms. They maybe regurgitated and vomited and may escape through the nostrils.

 Ascaris may pass the larynx and may lead to suffocation.  Or they may reach the lungs and produce pulmonary gangrene or may pass the uestachian tube and provoke otitis media.  They may invade the bile duct, gall bladder, liver and appendix.

Diagnosis  Diagnosis is made by finding the eggs in the feces, fertilized or unfertilized by performing DFS, kato-thick, kato-katz or concentration technique.

 Stool examination may give negative findings in the following conditions: – When the patient is actually free from Ascaris infection. – Worms are still immature in the lumen. – During larval migration – When only male worms are present in the intestine.

Treatment  Piperazine citrate, pyrantel pamoate, mebendazole, albendazole, levimazole.  Piperazina and pyrantel pamoate are used these days because these drugs have a neuromuscular blocking effect on the parasite causing paralysis.

 Toxocara canis and Toxocara catti  Common name: Dog ascaris and Cat ascaris  Disease: toxocariasis/visceral larval migrans

Life cycle

Pathology  Larval migrans can produce hemorrhage, necrosis and granuloma of the site.  Eosinophilia, liver damage, pulmonary inflammation, and ocular problems has been observed.  Among children anemia with high WBC count.

Diagnosis  Diagnosis is usually stablsihed on clinical grounds.  Examination of egg in the stool of the patient is not useful because the egg laying adults are not present.  However, examination of fecal material from infected pets often supports the diagnosis.

Treatment  Because the clinical course of VLM is so variable, it is very difficult to evaluate efficacy of any treatment. Since the infection is self limited. Only severe cases needs to be treated. Thiabendazole appears to shorten the course of the disease.

Eggs of Toxocara canis. These eggs are passed in dog feces, especially puppies' feces. Humans do not produce or excrete eggs, and therefore eggs are not a diagnostic finding in human toxocariasis! The egg to the left is fertilized but not yet embryonated, while the egg to the right contains a well developed larva. The latter egg would be infective if ingested by a human (frequently, a child). CDC DPDx Parasite

Toxocara canis (Dog Roundworm) egg, embryonated © Dr Peter Darben, Queensland University of Technology clinical parasitology collection. Used with permission

 Trichuris trichiura  Common name: whipworm  Disease: trichuriasis

Morphology  Adult  They attach to the cell wall of the cecum.  Colored or pinkish, the anterior end is attenuated, whip-like, while the posterior end is more robust.  3.5-5 cm ( female) straight post. End  3-4.5 cm ( male) coiled 3600 with a sheathed single spicule.

Trichuris trichiura adult male and female © Dr Peter Darben, Queensland University of Technology clinical parasitology collection. Used with permission

Ova  barrel shaped/lemon shaped/football shaped or Japanese lantern shape.  With a prominent bipolar plugs on both ends.  The shell is thick and composed of three layers. With a yellowish outer and a transparent inner layer.

Egg of Trichuris trichuria as seen on wet mount. The diagnostic characteristics are: a typical barrel shape two polar plugs, that are unstained size: 50-54 µm by 22-23 µm. The external layer of the shell of the egg is yellow-brown (in contrast to the clear polar plugs). The egg is unembryonated, as eggs are when passed with the stool. CDC DPDx Parasite Image Library

Life cycle

 Eggssoil 3 weeksembryonationingestedlarvaececum

Hookworms  A. Necator americanus  Common name: new world hookworm, american hookworm  Disease: necatoriasis, uncinariasis, tropical anemia, “laziness”

 B. Ancylostoma duodenale  Common name: old world hookworm  Disease: ancylostomiasis, miner’s anemia

 C. Ancylostoma braziliense  Common name: cat hookworm  Disease: cutaneous larva migrans, creeping eruption

 D. Ancylostoma caninum  Common name: dog hookworm  Disease: cutaneous larva migrans, creeping eruption

 Necator americanus is small and has a tendency to go against the general body curvature, hence a hook is formed (S shaped)  The buccal capsule is provided with a semilunar cutting plates.

 They are also provided with long cephalic or amphidial gland that secretes a potent anticoagulant and promotes the flow of blood.  The bursa copulatrix is longer than broad with a bidigitate or a bipartite dorsal ray with long slender copulatory spicules that are fused at the tip to form a delicate barb.

Morphology  Ancylostoma duodenale: contour tends to follow the general body curvature of the body hence looks like letter C.  Large buccal capsule, equipped with two pairs of ventral teeth.

 The male worms have a fan like organelle at the posterior portion known as copulatory bursa/bursa copulatrix which is short and broad with tripartite or tridigitate dorsal ray with a pair of simple, long, bristle like copulatory spicule, plain and free at the tip.

 Ancylostoma braziliense one of the smaller species of hookworm with a pair of large teeth and a pair of inconspicuous median teeth in buccal capsule.  The bursa copulatrix is almost as broad as long and is supported by short lateral rays.

 Ancylostoma caninum is common parasite of dogs. They have a wide buccal capsule bearing three pairs of ventral teeth. The cephalic or amphidial gland of the worm secretes anticoagulant that delays coagulation of blood. Long moderately slender rays supports the male bursa.

Life cycle

 Eggssoillarva hatchesrhabditiform(with open mouth/feeding stage)filariform(longer, with close mouth, non-feeding stage and with protective sheath)skincirculationheart and lungesophagusSI

Ova  Hookworm egg provided with a very thin egg shell ( with germ cell in the process of segementation 2-8 cell stages)

Hookworm eggs examined on wet mount (eggs of Ancylostoma duodenale and Necator americanus cannot be distinguished morphologically).

Hookworm filariform larvae © Dr Peter Darben, Queensland University of Technology clinical parasitology collection. Used with permission

Necator americanus adult male, posterior end © Dr Peter Darben, Queensland University of Technology clinical parasitology collection. Used with permission

Dental Pattern    

N.A A.B A.C A.D

0 1 3 2

N.americanus   



Dorsal Ray Copulatory spicules

Copulatory spicules

bidigitate (bipartite) ends with a barb

A. duodenale

tridigitate (tripartite) simple, bristle like, plain and free at the tip

A.braziliense A. caninum broad as long long moderately slender rays

Pathology  Ground itch/ dew itch percutaneous entry of the infective filariform larvae often characterized by itching sensation or dermatitis. It is often severe and also known as ground itch or dew itch.

 Pulmonary lesion/wakana disease is caused by passive pulmonary migration of larval stages of hookworm. Symptoms may be similar to ascaris pneumonitis.

Creeping eruption/ cutaneous larva migrans the infective laval stage can enter human skin but cannot pass below stratum germinativum producing serpiginous tunnel in this stratum. Common among larvae that do not normally infect human such as A.braziliense and A.caninum.

 Hookworm anemia  adult worm suck the host’s blood and mucosal substances.  Microcytic hyopochromic anemia  May cause hemorrhage to intestinal worm

 Hypoalbuminemia  due to combined loss of blood, lymph and protein.