Lyme disease is probably the biggest concern of horse owners at the moment. Lyme disease was at first thought not to affect horses--but unfortunately, that has turned out to be untrue. A large percentage of exposed horses do not demonstrate any symptoms; but those who do might suffer fever, a subtle, shifting lameness (which often baffles handlers and veterinarians), swelling of the limbs, a reluctance to move (which can mimic "tying-up"), laminitis, inflamed eye tissues, lethargy, and skin and muscle hypersensitivity. If left untreated, horses can develop a blue-green discoloration of the cornea and yellowing of the eye's normal white sclera, as well as eventual hepatitis and/or nephritis and chronic arthritis. The disease also can cause abortion in broodmares and be transferred across the placenta to foals in utero.