Ticks are small parasitic arachnids (same class as spiders).  In veterinary medicine, ticks pose a major source of infection for ehrlichia (e.canis, e.equi, e.platys, e. risticii, e.ewingii), Rocky Mountain Spotted Fever (Rickettsia rickettsii), tularemia (francisella turarensis diagnosed in California's Tulare county), Lyme disease (Borrelia burgdorferi), and multiple other disorders.