Parasites are transmitted to people through oral ingestion of parasite eggs from a contaminated environment, through hookworm larvae penetrating the skin, or from accidentally ingesting a flea infected with a tapeworm. Contamination occurs when people accidentally put dirty hands in their mouths. People, particularly children, can be exposed to parasites at work or play in contaminated soil, such as a sandbox or garden. Parasite eggs cannot be seen by the naked eye but are present wherever there are feces from an infected animal. Sometimes fruits and vegetables growing close to or in the ground, such as strawberries and carrots, are contaminated. If not carefully washed, they can be a source of human infection as well.