Toxocariasis
Dogs
Toxocariasis
Toxocariasis is a parasitic infection with the
dog or
cat
roundworm, Toxocara canis or Toxocara cati,
respectively. Ingestion of these worms causes the condition, visceral
larval migrans.
Toxocara canis
Epidemiology
Toxocariasis is a worldwide infection. Epidemiologic surveys show a 2-5%
positive rate in healthy adults from urban Western countries and 14.2-37% in
rural areas. In tropical countries, surveys show a positive rate of 63.2% in
Bali, 86% in
Saint
Lucia, and 92.8% in
Réunion.
Toxocariasis is most commonly a disease of children, typically children aged 2-7
years.
Pathophysiology
Adult worms of the Toxocara species live in the small intestine of dogs and
cats. They range from 4-12 cm in length. Almost all puppies are infected at or
soon after birth. During the summer, Toxocara eggs are shed and become
infective. They survive for years in the environment, and humans typically
ingest the eggs by oral contact with contaminated hands. Once introduced into
the human intestine, the eggs hatch, releasing the larvae. The larval form 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 as well.
Disease severity depends not only on the number of larvae ingested but also
on the degree of allergic reaction. The inflammatory reaction causes epithelial
cells to surround each larva, and, subsequently, a dense fibrous capsule invests
each granuloma.
Features
- Weakness
- Pruritus
- Rash
- Difficulty breathing
- Abdominal pain
- Eosinophilia
- Increased total serum immunoglobulin E (IgE) level
- Elevated antibody titers to T canis
Diagnosis
In suspected cases, diagnosis is confirmed by an increase in the anti-Toxocara
excretory-secretory antigen IgE level
Treatment
Mebendazole or
thiobendazole are the treatments of choice.
Prognosis
Toxocariasis is almost always a benign, asymptomatic, and self-limiting
disease, although brain involvement can cause brain damage, 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.
Prevention
The eggs of Toxocara species are widespread in parks, playgrounds, yards, and
in homes and apartments where the occupants have dogs or cats. Elimination of
eggs from the environment is not possible; therefore, prevention depends on
proper hygiene, including handwashing after contact with pets. Public policies
that have attempted to eradicate Toxocara infection in dogs and cats have had
limited success.
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