Lymphangitis is inflammation of the lymphatic vessels. These are low-pressure vessels similar to veins that collect the fluid that surrounds cells and return it to the bloodstream. Lymphangitis is usually caused by a bacterial infection that spreads to the lymphatic vessels.
Pigeon Fever (False Strangles)
Infection causing lymphangitis in horses can occur following infection with Corynebacterium pseudotuberculosis bacteria. The bacteria probably enter by way of skin wounds including injections, insect bites, or by contact with contaminated tack or grooming equipment. The condition is commonly known as pigeon fever, but is also called false strangles, pigeon breast, and dry land distemper. Pigeon fever in horses causes an infection of the lower limbs (ulcerative lymphangitis), inflamed and pus-filled sores in the chest region, and contagious acne. It is a common infectious diseases of horses in California and is increasingly seen in other dry, western states of the US. In these areas, infections are seasonal, with a peak in late summer and fall. Healing often occurs without treatment or with limited topical treatment. Abortion and infection of the mammary glands may also occur. In rare cases the internal organs may be affected.
Signs of the ulcerative lymphangitis caused by pigeon fever develop slowly and may include painful inflammation, small lumps or swellings, and slow-healing sores, especially on the fetlock. Occasionally, the swelling extends up the entire limb. The discharge is odorless, thick, greenish white, and blood-tinged. Usually, only one leg is involved. The sores and swelling progress slowly, and the condition can become longterm with relapses.
Other signs of pigeon fever include widespread or localized swellings, swelling and inflammation of the skin on the lower abdomen, lameness, sores that drain pus, fever, weight loss, and depression. An increase in white blood cells may be present. A high or prolonged fever may indicate complications such as multiple or internal pus-filled sores, or whole-body infection and abortion. Pus-filled sores can be large, up to 8 inches (20 centimeters) in diameter before rupturing, and take months to heal. Weight loss, colic, or lack of coordination may be signs of internal sores. Inflamed skin sores are painful and mildly itchy with a loss of hair, discharge, and crusting. They are also slow to heal.
To confirm the diagnosis of this disease, your veterinarian will take samples of material from the sores. Tests will then be done in a laboratory to identify the organism involved. Because the signs of this disease can easily be confused with infection by other bacteria, fungi, or worms, it is important to identify the bacteria so that proper treatment can be started.
Lymphangitis and early pus-filled swellings are often treated with hot packs, poultices, or flushing with water (hydrotherapy). In many cases, small sores are pierced to let the pus out and then flushed with iodine solution. Your veterinarian can recommend the most effective treatment for your horse. Large sores usually require surgery. For skin lesions and grossly contaminated limbs, veterinarians usually prescribe a daily scrubbing with a shampoo that contains iodine. Medications to relieve pain and promote healing may be needed. General supportive and nursing care is also important. If treatment is successful, the swelling gradually goes down over days or weeks. Severe or untreated cases often become longterm, and scarring and hardening of the tissue of the leg occurs.
Unhygienic and wet conditions increase the risk of infection, particularly of the lower legs and abdomen. Maintaining good hygiene and avoiding prolonged exposure of horses to damp or wet conditions may help limit infections. However, the disease occurs even under excellent management conditions.
Last full review/revision July 2011 by Peter H. Holmes, BVMS, PhD, Dr HC, FRCVS, FRSE, OBE; Nemi C. Jain, MVSc, PhD; Susan M. Cotter, DVM, DACVIM (Small Animal, Oncology); Wayne K. Jorgensen, BSc, PhD; Sarah E. Payne, DVM, DACVIM