T. canis and T. cati pose a significant health hazard to people. Thousands of people become infected with Toxocara in the United States per year. How do people become infected? Humans become infected when they ingest infective eggs from the soil or from their hands or another object. Large numbers of the eggs can accumulate in the soil where dogs and cats are allowed to defecate. The eggs are sticky, and can collect on the hands and under the fingernails of people. Children, and others who may not have good hygiene, are most prone to becoming infected.
Remember, Toxocara eggs need to be in the environment approximately two weeks, before becoming infective, so direct contact with an infected animal generally does not result in transmission. However, young puppies may continually contaminate their entire litter area, and may even have infective eggs stuck to their coats. Adults and children who handle the bitch or puppies or who clean the area may be especially at risk.
If a human ingests Toxocara eggs, the subsequent larvae can migrate through the person's tissues. This condition is called 'visceral larva migrans.' The larvae most commonly migrate through the liver, lungs, and brain. They can cause severe inflammation and actual mechanical damage to the organs. Signs of this disease include an enlarged liver, intermittent fever, loss of weight and appetite, and a persistent cough. Asthma or pneumonia may develop.
A unique form of this disease is called 'ocular larva migrans.' Larvae migrate through the eyes and can cause vision loss or even blindness. Ocular larva migrans usually occurs in children 7-8 years old, whereas, visceral larva migrans occurs in children ages 1-4 years. The reason for the difference among ages is unknown.
To prevent human infection, good hygiene is extremely important. Teach children, especially, to wash their hands after playing and before eating. Do not let children play in areas where dogs or cats may have defecated. Cats should not be allowed to use sandboxes or the garden as litter boxes. Worm your pets as recommended, keep the environment clean, and control rodent populations.
