They usually settle near the top of the soil in a silt layer, which protects them from destruction by sunlight. Toxocara eggs are very hardy and can survive for years, resisting the most perilous weather conditions of rain and snow. There are no chemicals that can kill all the toxocara eggs in soil. While contaminated soil is the primary direct source of infection, children can become infected from the coat of a puppy who has been playing in contaminated soil. Antibiotics and immuno-suppresive drugs are a big problem of parasite infections.
Parasites are opportunistic invaders.
When the intestinal system is in healthy balance, there is less opportunity for parasitic infestation. Antibiotics, however, kill bacteria indiscriminately, both the good and the bad, upsetting the natural ecology of the gastrointestinal tract and vagina. This often leads to yeast overgrowth and trichomoniasis. Trichomonas vaginalis is a microscopic parasite that causes foul-smelling vaginal discharge, a burning sensation, and inflammation. It is sexually transmitted and when passed to a male partner can cause non-specific urethritis.