Ticks that spread Lyme disease used to be confined to the warmer regions of the US. As the climate warms, scientists see a spread of deer ticks, ixodes scapularis, to regions once too cold for the tick to survive in winter. So named because of their habit of parasitizing white-tailed deer, these blood-suckers transmit a number of diseases affecting humans besides Lyme disease, such as anaplasmosis, babesiosis, and the rare Powassan virus disease. The tick is hardy, able to survive frost, and in the spring one of the first invertebrates to become active as it searches for a blood meal.Cases of Lyme disease, a debilitating infectious disease that can cause paralysis, joint pain, swelling, fatigue, and memory loss have doubled to about 30,000 per year. Usually, the initial symptom is an expanding rash at the site of the bite. Ticks, normally found in the southeast have spread to the upper Midwest, New England and eastern Canada. Increased outdoor recreation by housebound human seeking to escape their monotony, has increased exposure to potential infection. Warmer winters have allowed ticks to feed later into autumn, increasing their chance of surviving winter; in spring females lay hundreds of eggs in the leaf litter. Ticks that have infested an area are transmitting new bacteria-based diseases such as anaplasmosis and Powassan virus disease, which can be fatal. Lyme disease can be treated with antibiotics, not always easily, and symptoms can linger for months. The best defense is to avoid tick bites with protective clothing and insect repellent containing DEET. Check dogs for ticks and apply tick repellent.