Toxocara canis Sidney Milliron Aaron Bettenhausen.
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Transcript of Toxocara canis Sidney Milliron Aaron Bettenhausen.
Toxocara canis
Sidney MillironAaron Bettenhausen
Taxonomy
• Kingdom: Animalia • Phylum: Nematoda • Class: Secernentea • Order: Ascaridida • Family: Toxocaridae • Genus: Toxocara • Species: Toxocara canis
Geographic range
• World wide distribution• Found commonly in all domestic dogs and
other canids• Possible to have prenatal infections of puppies
Hosts• Primary host is dogs• Adults are infected upon
infestation of embryonated eggs, or by eating rodents infected with visceral larva migrans
• Worms can penetrate the placenta and infect unborn puppies
• Puppies can be born infected• Puppies can also become
infected via the transmammary route
Other hosts• If a rodent eats the embryonated
eggs the worms will hatch and begin migration before going dormant
• If the rodent is then eaten by a dog the dog can become infected
• Rodent acts as paratenic host• Rodents develop visceral larva
migrans• Humans who ingest the eggs also
develop visceral larva migrans
Egg
• Eggs– Brownish– Almost spherical – Surficial pits– Unembryonated
when laid
Larvated Eggs – Infective Stage
Larvae
• Found in Intestines, Circulatory, Lungs and Esophagus of Hosts
Adults
• Adults– Large (M=4-
6cm; F=6.5-15+cm)
– Have 3 lips– Prominent
cervical alae in both sexes
3 Prominent Lips
Life Cycle
• Adult worms live in small intestine of their host– Produces prodigious numbers of eggs
• Eggs are passed in feces• Develop into L3 in 5-6 days under optimal
conditions
Canine Oral ingestion • In Puppies:– Worms hatch and migrate through the portal system
and lungs – Get swallowed and find their way back to intestine– Can be fatal to puppies due to malnutrition
• In older dogs (secondary immune response)– Juveniles do not complete the lung migration – Wander through the body, eventually entering a
developmental arrest for a long periods– Most adult dogs show no symptoms when infected and
gain an increased immunity to reinfection as they age
Life Cycle
Infection during canine pregnancy
• Dormant juveniles are activated by host hormones late in pregnancy
• Reenter the circulatory system– Carried to placentas
• Penetrate through to the fetal bloodstream– Complete lung migration en route to the intestine
• Juveniles can also be passed by the trasmammary route, in mother’s milk
Other routes
• If a rodent or other mammal eats embryonated eggs– Juveniles begin to migrate but then become
dormant and continues it’s developmental arrest• If rodent is eaten by a dog– Worms promptly migrate through the lungs to the
intestine or into tissues to continue their wait, depending on age.
Visceral Larva Migrans
• Occurs when nematode gains entry into paratenic host– They do not complete the normal migration but
undergo developmental arrest– Begin an extended, random wandering through
various organs and tissues of the body
Pathogenesis
• Juveniles provoke a delayed-type hypersensitivity reaction in paratenic hosts– Eventually they will find their way to the brain– In other tissues, juveniles will form a granuloma – Can cause chronic ocular inflammation, as well as
retinal granulomas – Rarely can cause eosinophilic meningoencephalitis
Visceral Larva Migrans
• Occurs when a mammal other than the intended host (Dogs) ingest the eggs
• Worms hatch and begin migration but eventually undergo developmental arrest
• Worms begin a randomly wandering through the body• Can be caused by a number of different species
however Toxocara canis is the most common species that causes this disease in humans
• In experimental hosts juvenile worms seem to prefer residing in the brain.
Symptoms in Humans
• Fever, pulmonary symptoms, hepatomegaly, and eosinophilia
• Worms migrate indiscriminately to and from any organ including but seem to prefer the liver
• Can cause blindness if they migrate to the eye• Can cause neurological symptoms• Extent of tissue damage is proportional to the
numbers of juvenile worms in the body
Prevalence of infection
• In the united states 4.6-7.3% of children ages 1 to 11 years old have Visceral Larva migrans
• Up to 30% infection has been found in African American children of low socioeconomic status
• Up to 34% infection has been found in Irish school children
• In some developing tropical countries the rates of infection among children can be around 50 to 80%
Diagnosis
• An ELISA using secretory-excretory antigens• A liver biopsy might reveal a juvenile
surrounded by a granuloma• Infected patients may present with high
eosinophilia
Treatment and Control
• Mebendazole• Periodic deworming of household pets• Proper disposable of animal feces• Don’t let your dog eat rodents• Covering sandpits in public parks when not in
use