Adults prefer warm humid places and will leave a host if it dies. Outdoors, fleas are most abundant during humid, rainy summers and are more common outside in the southern United States than in the north. Indoors, warmth and high relative humidities are conducive to large populations. Larvae may undergo arrested development in less than favorable conditions. Medical Importance of Fleas Flea bites vary in effect from short-lived itching welts to an overall rash to symptoms which may last over a year, depending on the sensitivity of the victim.
Young children are more sensitive than older persons.
Commonly, a small red spot appears where the skin has been pierced. Little swelling ensues, but the spot is accompanied by a red halo of irritated skin which usually lasts for several hours to a day. Fleas are vectors of several diseases important to human health including plague, murine typhus, and tularemia. The greatest threat to humans exist when domestic rats are exposed to infection from wild rodents in areas adjacent to human communities. Murine typhus is a mild form of epidemic typhus that is usually spread by the human louse.