Toxocara canis
Thanh T. and Dhool M.
Taxonomic Consideration
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Kingdom:Animalia
Phylum: Nematoda
Class: Rhabditea
Order: Ascaridida
Family: Ascarididae
Genus: Toxocara
Species: canis
Characteristics
•The Ascarids are typically very large, stout
intestinal worms.
•They frequently have three prominent lips
surrounding their oral opening.
•The life cycle is usually direct
Referred to as "roundworm”
video
Introduction
•Geographic region: Worldwide
•Definitive host: Dogs and other canids
•Paratenic host: Rodents
•Accidental host- Human
•Toxocara canis is a worldwide distributed
helminth parasite of the dogs and other
canids.
•T. canis is gonochorist (which means the sex
of the parasite is present on different
worms—opposed to hermaphroditism
A puppy can be born infected with T.
canis. Dormant juveniles in the mother
are activated by the host hormones in
late pregnancy and reenter the
circulatory system where they are
carried to the placenta, there they
penetrate through the fetal
bloodstream, where they do a
complete lung migration.
Introduction continue..
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If the host is a young puppy and has no
prior infection, the worms hatch and
migrate though the portal system and
lungs and back into the intestines.
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If the host is an older dog the juveniles
do not complete the lung migration,
they wander the body and eventually
enter a developmental arrest.
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T. canis can infect its host via a
transmammory route (which is through
the mother’s milk), however this is less
common.
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If a female dog is lactating and ingests
infective juvenile eggs then they can
complete the migration and produce a
patent infection.
Morphology
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Adult T. canis have a round body
with spiky cranial and caudal parts,
covered by yellow cuticula.
Cranial part of the body contains
two lateral alae (length 2–2.5 mm,
width 0.2 mm).
Male worms measure 9–13 × 0.2–
0.25 cm and female worms 10–18
× 0.25–0.3 cm.
T. canis eggs have oval or spherical
shape with granulated surface,
thick-walled, and measures from
72 to 85 μm
Life cycle of Toxocara canis
The Life Cycle of T. canis
Life cycle continued…
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Unembroyonated eggs are released in the feces and forms embryo in the external
environment.
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Once ingested by dogs the infective eggs hatch and release larvae that penetrates the
gut wall and migrate to various tissues where they encyst (if the dogs is older than 5
weeks). Older dogs are often asymptomatic.
In younger dogs, the larvae migrate through the lungs, bronchial tree, and esophagus;
adult worms develop and oviposit in the small intestine.
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In the older female dogs, the encysted stages are reactivated during pregnancy, and
can infect puppies via the transplacental and transmammary routes in which small
intestine adult worms become established.
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Thus, infective eggs are excreted both by lactating bitches(female dogs) and puppies.
However in older male dogs the parasite meets a dead end, because the adult male
will not shed eggs in the feces and are not affected if they ingest the eggs.
Life cycle continued..
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Humans are accidental hosts who
become infected by ingesting
infective eggs in contaminated soil.
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After ingestion, the eggs hatch and
larvae penetrate the intestinal wall
and are carried by the circulation to
a wide variety of tissues (liver, heart,
lungs, brain, muscle, eyes). While
the larvae do not undergo any
further development in these sites,
they can cause severe local reactions
(such as inflammation) that are the
basis of toxocariasis.
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The two main clinical presentations
of toxocariasis are visceral larva
migrans (VLM) and ocular larva
migrans (OLM)*.
Visceral Larva Migrans
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Occurs when a juvenile of several species of nematodes gain entry to an improper
host and begin a typical tissue migration
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They do not complete the normal migration but undergo developmental arrest and
begin an extended, random wandering through various organs and tissues of the
body, affected organs can include the liver, heart (causing myocarditis), brain, and the
CNS (causing dysfunction, seizures, and coma).
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The VLM remains unapparent in most cases. Symptomatic cases are most frequently
observed in children aged two to five years.
Visceral Larva Migrans Symptoms
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Physical symptoms: includes fatigue, anorexia, weight loss, pneumonia, fever, cough,
bronchospasm, abdominal pain, headaches, rashes, and, occasionally seizures
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The clinical symptoms :depend on the localization and degree of pathological
changes and include non-specific and varied conditions such as eosinophilia,
leukocytosis, hepatomegaly, mild gastrointestinal disorders, asthmatic attacks,
pneumonic symptoms, urticarial skin changes, central nervous disorders with
paralyses
Ocular larva Migrans
•Ocular larva migrans, is caused by migration of larva into the posterior segment of
the eye, tends to occur in children and young adults. Patients may present with
decreased vision, red eye, or leukokoria (white appearance of the pupil). Granulomas
and choriorentinitis (inflammatation of the the uveal tract of the eye), Unilateral visual
loss, retinal fibrosis, retinoblastoma (common primary ocular malignancy/ eye cancer
of children) and retinal detachment occur.
•Clinically, serum antibodies to Toxocara are often absent or present in low titers.
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Diagnosis and Treatment
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ELISA using secretory excretory antigen
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Finding Toxocara larvae within a patient is the only definitive diagnosis for
toxocariasis, however biopsies to look for second stage larvae in humans are generally
not very effective
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Liver biopsy might demonstrate the characteristic granuloma surrounding a juvenile
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High levels of eosinophils are present, especially if they had previous parasitic
infection
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Mebendazole is effective on patient with severe symptoms
Prevention and Control
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Clean your pet’s living area at least once a
week. Feces should be either buried or
bagged and disposed of in the trash.
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Do not allow children to play in areas that
are soiled with pet or other animal stool
and cover sandboxes when not in use to
make sure that animals do not get inside
and contaminate them.
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Wash your hands with soap and warm
water after playing with your pets or other
animals, after outdoor activities, and
before handling food.
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Teach children the importance of washing
hands to prevent infection and that it is
dangerous to eat dirt or soil.
Dirt is not a
good way to
incorporate
minerals into
your diet!
Quick Review
• What are the Definitive host:
Dogs and other canids
• What kind of Host are rodents:
Paratenic host
• How do humans get infected by
T.canis:
Ingesting infecting soils containing
eggs
• How do puppies get infected:
ingesting infected eggs, through
transplacental route, and
transmammory route(RARE!)
Toxocara free = happy puppies and
happy babies 
References
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http://en.wikipedia.org/wiki/Toxocara_canis
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http://en.wikipedia.org/wiki/Toxocariasis
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http://emedicine.medscape.com/article/229855-overview
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http://emedicine.medscape.com/article/1222849-overview
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http://www.novatec-id.com/products/infectious-diseases/worms/toxocara-canis/
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http://animal.discovery.com/invertebrates/monsters-inside-me/toxocariasis-toxocararoundworm/