Ticks are the main carriers of many protozoan diseases, including piroplasmosis. The protozoa in most cases survive from one generation of ticks to successive generations by infecting their eggs. Some ticks also spread diseases caused by bacteria, viruses, and rickettsia. A viral disease sometimes spread by ticks is the Western stain of equine encephalomyelitis. Lyme disease Tiny deer ticks can spread Lyme disease, a bacterial infection.
Deer ticks are about half the size of the American dog tick.
Lyme disease is a growing problem in several areas of the country, affecting humans, horses, dogs, cattle, cats, and other mammals. It was first recognized in the United States in 1975 after a mysterious outbreak of a unique form of arthritis in people. The disease was named after one of the towns in Connecticut in which the illness appeared. Stephen W. Barthold, Ph.D., director of the Center for Comparative Medicine at the University of California-Davis, has been studying these bacteria for a number of years. These ticks and the bacteria they carry are not selective about the hosts they latch onto, Barthold said, and they infect mice, birds, and people, among others.