3. WHAT IS TOXOCARIASIS?
Toxocariasis is an infection transmitted from animals to
humans (zoonosis) caused by the parasitic roundworms
commonly found in the intestine of dogs (Toxocara canis)
and cats (T. cati).
The soil of parks and playgrounds is commonly
contaminated with the eggs of T canis, and infection may
cause human disease that involves the liver, heart, lung,
muscle, eye, and brain.
4. WHO IS AT RISK FOR TOXOCARIASIS?
Anyone can become infected with Toxocara. Young
children and owners of dogs or cats have a higher
chance of becoming infected.
5. EPIDEMIOLOGY
Toxocariasis is a worldwide infection.
Humans are accidental hosts of Toxocara
Ways of Transmission: Fecal Oral. Dogs and cats that are infected
with Toxocara can shed Toxocara eggs in their feces. You or your
children can become infected by accidentally swallowing dirt that
has been contaminated with dog or cat feces that contain
infectious Toxocara eggs. Although it is rare, people can also
become infected from eating undercooked meat
containing Toxocara larvae.
6. MORTALITY/MORBIDITY
Toxocariasis is almost always a benign, asymptomatic, and self-
limiting disease, although brain involvement can cause severe
morbidity. Brain involvement can evoke meningitis, encephalitis, or
epilepsy.
Ocular involvement may cause loss of visual acuity or unilateral
blindness.
Pulmonary and hepatic forms can cause protracted symptoms if
the patient does not receive treatment.
7. AGE
CDC studies have shown that transmission
of Toxocara larvae is most common in young children and
persons younger than 20 years.
Toxocariasis is predominantly a disease of children,
typically those aged 2-7 years.
Ocular toxocariasis is most common in older children and
young adults.
8. MORPHOLOGY
Both species produce eggs that are brown and pitted. T. canis eggs
measure 75-90 µm and are spherical in shape, whereas the eggs of T.
cati are 65-70 µm in diameter and oblong. Second stage larvae hatch
from these eggs and are approximately 0.5mm long and 0.02mm
wide. Adults of both species have complete digestive systems and
three lips, each composed of a dentigerous ridge.
Adult T. canis are found only within dogs and foxes and the males are
4–6 cm in length, with a curved posterior end. The males each have
spicules and one “tubular testis.” Females can be as long as 15 cm, with
the vulva stretching one third of their bodylength. The females do not
curve at the posterior end.
T. cati adult females are approximately 10 cm long, while males are
typically 6 cm or less. The T. cati adults only occur within cats, and
male T. cati are curved at the posterior end.
9. PATHOPHYSIOLOGY
Adult worms of the Toxocara species live in the small intestine of dogs
and puppies and range from 4-12 cm in length. Almost all puppies are
infected at or soon after birth. During the summer, in wet
conditions, Toxocara eggs are embryonated in 2-5 weeks and become
infective. They survive for years in the environment, and humans
typically ingest the eggs via oral contact with contaminated hands. Once
introduced into the human intestine, the eggs decorticate, releasing the
larvae. The larval form is visible only under a microscope because it is
less than 0.5 mm in length and 0.02 mm wide. The larvae penetrate the
bowel wall and migrate through vessels to the muscles, liver, and lung
and sometimes to the eye and brain.
10.
11. Cats, dogs and foxes can become infected with Toxocara through the
ingestion of eggs or by transmission of the larvae from a mother to her
offspring.Transmission to cats and dogs can also occur by ingestion of
infected accidental hosts, such as earthworms, cockroaches, rodents, rabbits,
chickens, or sheep.
Eggs hatch as second stage larvae in the intestines of the cat, dog or fox host
(for consistency, this article will assume that second stage larvae emerge
from Toxocara eggs, although there is debate as to whether larvae are truly in
their second or third stage of development). Larvae enter the bloodstream
and migrate to the lungs, where they are coughed up and swallowed. The
larvae mature into adults within the small intestine of a cat, dog or fox, where
mating and egg laying occurs. Eggs are passed in the feces and only become
infective after several weeks outside of a host. During this incubation period,
molting from first to second (and possibly third) stage larva takes place within
the egg. In most adult dogs, cats and foxes, the full lifecycle does not occur,
but instead second stage larvae encyst after a period of migration through the
body. Reactivation of the larvae is common only in pregnant or lactating cats,
dogs and foxes. The full lifecycle usually only occurs in these females and their
offspring.
12. Second stage larvae will also hatch in the small intestine of an
accidental host, such as a human, after ingestion of infective eggs.
The larvae will then migrate through the organs and tissues of the
accidental host, most commonly the lungs, liver, eyes, and brain.
Since L2 larvae cannot mature in accidental hosts, after this period
of migration, Toxocara larvae will encyst as second stage larvae.
13. SYMPTOMS :
Ocular toxocariasis: Ocular toxocariasis occurs
when Toxocara larvae migrate to the eye. Symptoms and signs of
ocular toxocariasis include vision loss, eye inflammation or damage
to the retina. Decreased visual acuity, seeing floaters or bubblelike
images . Typically, only one eye is affected.
Visceral toxocariasis: Visceral toxocariasis occurs
when Toxocara larvae migrate to various body organs, such as the
liver or central nervous system. Symptoms of visceral toxocariasis
include fever, fatigue, decreased appetite, restlessness, hives,
history of seizures, coughing, wheezing, or abdominal pain.
14. PHYSICAL
Tenderness in the right upper quadrant or hepatomegaly may be present in patients with liver
involvement.
With pulmonary involvement, wheezing may be heard. Breath sounds may be decreased if a
pleural effusion is present.
Patients with ocular involvement may present with the following:
Retinal detachment due to traction caused by retinal fibrosis
Peripapillary inflammation
Peripheral retinal exudates
Gliotic mass in peripheral retina
Vitreoretinal traction band in peripheral retina
15. FUNDUSCOPIC EXAMINATION OF THE RIGHT EYE OF A PATIENT WITH
OCULAR TOXOCARIASIS SHOWING RHEGMATOGENOUS RETINAL
DETACHMENT.
16. THREE SYNDROMES OF TOXOCARA INFECTION ARE GENERALLY
RECOGNIZED, AS FOLLOWS:
In children, covert toxocariasis is a mild, subclinical, febrile illness.
Symptoms can include cough, difficulty sleeping, abdominal pain,
headaches, and behavioral problems. Examination may reveal
hepatomegaly, lymphadenitis, and/or wheezing.
Visceral larva migrans is caused by the migration of larvae through
the internal organs of humans and the resulting inflammatory
reaction. A constellation of symptoms develops, including fatigue,
anorexia, weight loss, pneumonia, fever, cough, bronchospasm,
abdominal pain, headaches, rashes, and, occasionally, seizures.
Examination may reveal hepatomegaly, lymphadenitis, and/or
wheezing. Occasionally, pleural effusions develop. Chronic
urticaria has been described. Severe cases can lead
to myocarditis or respiratory failure.
17. Ocular larva migrans, which is caused by migration of larva into the
posterior segment of the eye, tends to occur in older children and
young adults. Patients may present with decreased vision, red eye,
or leukokoria (white appearance of the pupil). Granulomas
and chorioretinitis can be observed in the retina, especially at the
macula. Unilateral visual loss, retinal fibrosis, retinoblastoma, and
retinal detachment occur. Serum antibodies to Toxocara are often
absent or present in low titers.
18. RISK FACTORS OF TOXOCARIASIS INCLUDE THE FOLLOWING:
Living with or raising dogs and cats
Eating without handwashing
Infection via contact with soil from a yard, sandbox,
park, or playground
19. DIAGNOSIS
Laboratory Studies
The diagnosis of toxocariasis requires a high index of suspicion and depends on
serologic testing (eg, ELISA, immunoblot).
Peripheral blood eosinophilia is the most important finding; however, it may be
absent in patients with ocular or covert toxocariasis.
Serum total IgE: Patients with toxocariasis often have a marked increase in total IgE
levels.
ELISA with Toxocara excretory-secretory antigen (TES-Ag) may show the following:
An elevated anti–TES-Ag IgE level indicates acute infection or progressive
inflammation caused by toxocariasis.
An increase in the immunoglobulin G (IgG) level confirms a past or present infection
with minimum inflammation.
In ocular toxocariasis, an IgG or IgE titer is lower because the worm burden is smaller.
ELISA with aqueous fluid is therefore useful when ocular toxocariasis is suspected.
20. IMAGING STUDIES
Chest radiography
In a patient with pulmonary involvement, chest radiography may show multiple
pulmonary nodules with surrounding ground-glass opacities, or possibly pleural
effusion.
Ultrasonography
Ultrasonography reveals multiple hypoechoic areas in the liver.
CT scan
Hepatic lesions are of low density.
Pulmonary involvement manifests as multiple pulmonary nodules and surrounding
ground-glass opacities or, rarely, pleural effusion.
In the CNS, granulomas appear cortically or subcortically, showing a hyperintense
appearance on proton density and T2-weighted images.
21. The image on the left is a posteroanterior chest radiograph in a patient with toxocariasis. The
image on the right is a CT scan of the patient with toxocariasis showing multiple pulmonary
nodules with surrounding ground-glass opacities at first visit.
22. OTHER TESTS
An immunoblot is more specific than ELISA when bands from 24-
35 kD are considered out of typical 7-band patterns (24, 28, 30, 35,
132, 147, 200 kD).
Funduscopic examination should be performed in patients
suspected of having acute toxocariasis.
23. PROCEDURES
Biopsy is rarely performed to confirm the presence
of Toxocara larvae.
A needle biopsy of the liver is required for
histologic diagnosis in cases of liver involvement;
however, some results are false-negative because
lesions in the liver are very small.
24. HISTOLOGIC FINDINGS
The encapsulated larvae can be found in the liver,
lung, brain, and/or enucleated eye. The larvae occur
in a matrix of epithelioid cells surrounded by a
fibrous capsule with weak inflammatory reactions.
In ocular toxocariasis, a mobile larva can be directly
observed under the retina.
25. Diagnostic Considerations
Eosinophilic lung infiltrates may be due to other
helminths, to fungi, or to allergic reactions to
Differential Diagnoses
Hepatitis A
26. TREATMENT (ANTHELMINTIC DRUGS )
Mebendazole (Vermox)
Emverm: 100 mg PO q12hr for 3 days; if cure is not achieved 3 wk after
treatment, a second course of treatment is advised
Vermox: 500 mg PO as a single dose
DOC. Adverse effects are negligible, except headaches during early therapy.
These symptoms are from metabolites secreted from nematodes that are
killed by the drug. Causes worm death by selectively and irreversibly blocking
uptake of glucose and other nutrients in susceptible adult intestines where
helminths dwell.
27. Albendazole (Albenza)
400 mg PO once
Second DOC if mebendazole is difficult to obtain. Decreases
ATP production in the worm, causing energy depletion,
immobilization, and, finally, death.
Diethylcarbamazine citrate (Hetrazan) 100mg
Synthetic organic compound highly specific for several
common parasites. Does not contain any toxic metallic
elements. Not recommended as the DOC because of more
severe adverse effects. Recommended if therapy with
mebendazole fails or mebendazole is not available.
28. Chemotherapy: the treatment of choice in most
patients with liver, lung, or eye involvement.
Occasionally, ocular involvement requires ocular
surgery.
Corticosteroids, are prescribed in severe cases of VLM
or if the patient is diagnosed with OLM.
Surgical Care
For liver or lung involvement, no surgical care is
required.
For ocular involvement with retinal detachment, laser
treatment may be considered.
29. CONSULTATIONS
A consultation with an ophthalmologist is indicated in cases of
ocular larva migrans.
Consultation with a neurologist is indicated in cases of brain
involvement with neurologic symptoms or seizures.
Consultation with an infectious disease specialist may be indicated
when questions exist regarding the indications for and selection of
treatment for visceral larva migrans.
30. PREVENTION OF TOXOCARIASIS?
Take your pets to the veterinarian to prevent infection with Toxocara.
Your veterinarian can recommend a testing and treatment plan for
deworming.
Wash your hands with soap and water after playing with your pets or
other animals, after outdoor activities, and before handling food.
Teach children the importance of washing hands to prevent infection.
Do not allow children to play in areas that are soiled with pet or other
animal feces.
Clean your pet’s living area at least once a week. Feces should be either
buried or bagged and disposed of in the trash. Wash your hands after
handling pet waste.
Teach children that it is dangerous to eat dirt or soil.
31. COMPLICATIONS
Decreased visual acuity may occur if ocular toxocariasis is
not identified and treated.
Retinal detachment due to ocular involvement may cause
unilateral visual loss.
Seizures may result from cerebral involvement.
32. PROGNOSIS
Toxocariasis is generally a self-limited disease. The
prognosis is good when adequately treated, except
in some patients with ocular or cerebral
involvement.
33. PATIENT EDUCATION
Properly de-worm kittens and puppies.
Pets should undergo periodic stool examinations by a veterinarian,
and they should be treated if examination findings are positive
for Toxocara eggs.
Do not bring stray dogs or cats home. If such animals are brought
home, they should be examined by a veterinarian for toxocariasis.
Focus on personal hygiene. If dogs or cats have been in the yard,
consider it contaminated. Wash hands after lawn work or
gardening.
