Disease / Pathology
Toxocara canis/cati causes the disease called toxocariasis. An uncommon yet possibly serious parasitic infection in humans where humans are not the natural host.
Location in the Host
Toxocara canis/catis infectious eggs are accidentally ingested by humans which are considered accidental hosts. Undercooked meat/viscera (beef-chicken- lamb-duck) of infected animals can also serve as a source of infection. The definitive hosts are either dogs (T. canis) or cats (T. cati). The eggs will eventually hatch in the human intestine where they will penetrate the intestinal wall. Once they penetrate the intestinal wall they enter the circulation to be transported to various areas of the body such as the liver, muscle, heart, brain, eyes, etc. Because humans are not a natural host there is no further development of the larvae. However they do produce localized inflammatory responses and migratory damage to the areas they enter.
Geographic Distribution
Toxocara canis/cati is found worldwide.
Life Cycle
Toxocara canis/cati have a life cycle that has either the dog or the cat as the definitive host. Generally younger dogs and cats are most vulnerable. Paratenic hosts (an optional intermediate host in which the larvae usually enters passively along with ingested food but do not develop and as a result the eggs are not shed by these host) for both species include numerous species of mammals and birds. In the image below the rabbit is representative of the paratenic host.
Morphology & Diagnosis
Toxocara canis/catis eggs are shed in the feces of dogs/cats. They have a unique pitted surface appearance, round to oval, and are approximately 80-85 um in size The eggs are not shed by humans as they are paratenic hosts and therefore the detection of eggs in human feces is not diagnostic. Diagnosis can be made by the patient’s clinical signs and the detection of IgG antibodies to Toxocara by commercially available indirect enzyme immunoassay tests.
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