Lymphangitis is a potentially serious equine condition caused by bacterial infection of the lymphatic system. Here’s what you need to know...
Lymphangitis in horses typically appears as a hot, painful, extremely swollen hindleg. It is a potentially serious limb condition, which can cause permanent damage. The cause is uncertain in many cases. In the past it was blamed on bacteria gaining entry inside the limb’s soft tissues, but this is now thought to be only one of several contributing causes. Some cases are thought to be linked to nutrition, as the disease is seen in working horses whose legs filled after being rested over the weekend when fed normal rations, hence the name Monday morning leg. Other cases may develop following an infection, such as a puncture wound. Some cases are linked to specific diseases, for instance the condition purpura haemorrhagica, which can be complication of strangles and/or other diseases.
The name lymphangitis means inflammation of the lymphatics, which is a significant part of the disease. The lymphatic system is a complex network of fine vessels that run parallel to the arteries and veins. These contain lymphatic fluid, or lymph, which drains fluid away from the limbs. These vessels are very fine-walled structures and rely on tiny valves to stop the backflow. At various points there are lymphatic glands, which help to filter the fluid. If the lymphatics become blocked this can cause a dramatic, rapid and painful swelling of the affected area. In the worst cases permanent thickening of the affected limb’s soft tissues may develop and recurrent episodes of the disease. Sometimes the condition is described as cellulitis as this means inflammation of the cells as in many cases it is not just the lymphatics that are involved. Older veterinary text books describe three forms of the condition: sporadic, ulcerative and epizootic. The sporadic form is the one usually seen in the UK. It can come on quickly with the most severe cases deteriorating into the ulcerative form, where fluid can ooze through the skin, due to the extensive internal swelling. Epizootic lymphangitis is an exotic fungal disease seen mostly in working horses, donkeys and mules in Africa, Asia and Eastern Europe.
Signs of lymphangitis in horses
A horse with lymphangitis will typically have a swollen hindlimb that is hot and painful to touch –the forelimbs are rarely affected – and a high temperature, often between 104 °F and 106 °F (40-41 °C), plus severe lameness.
Diagnosis and treatment
The diagnosis of lymphangitis is based on the typical clinical signs.
A swab may be taken from the wound or skin (especially if serum is weeping) for bacterial culture and sensitivity. This allows the targeted use of appropriate antibiotics. The choice of antibiotic is important because of the increase in bacterial resistance; systemic, injectable antibiotics are often used to ensure the full dose is received, rather than risking a sick horse failing to eat antibiotics given in the feed.
Even though many cases of lymphangitis are triggered by infection, a simple course of antibiotics is rarely curative. Sometimes regional perfusion where antibiotics are injected directly into the vessels within the swollen area are used but not always successfully. Intensive aggressive treatment with other anti-inflammatory medication can help, but again may not work as well as one might hope. Other treatments may include diuretics such as frusemide to reduce the fluid, potassium iodide solution (orally for dermatitis) or intravenous DMSO.
In short, medical treatment alone is unlikely to resolve a severe lymphangitis and aggressive use of hydrotherapy, such as using lots of cold hosing or better still an equine spa, if available, can be useful. When the leg is dry, bandaging may be beneficial but may push the swelling up the limb. Controlled exercise is also beneficial.
There has been research done on draft horses that develop a particular form of chronically swollen enlarged lower hind limbs, associated with feather mites. Medical therapy is unrewarding in many cases. Instead specific washes can help, along with massage and special bandaging to compress the swelling. Interestingly it has been reported that draft horses that worked in the shrimp fishing industry have significantly fewer problems with skin lesions and leg swelling due to their daily seawater exercise.
There is another recent interesting study reviewing eight carefully documented horses with hindlimb cellulitis that had been treated with broad-spectrum antibiotics, anti-inflammatories, topical treatments and regional limb perfusions, however only partial improvement of clinical signs was observed with medical therapy alone. These cases showed another option for these particular cases when routine treatments were unsuccessful. This specific set of horses had abscesses located between the cannon bone and the suspensory ligament diagnosed on ultrasound exam, which were then surgically lanced and drained. These were mostly racehorses and they returned to work afterwards. Interestingly the bacteria from the abscesses were cultured and six out of eight isolates showed at least some level of antibiotic resistance, highlighted the seriousness of drug resistance. Going forward we can no longer rely on using different antibiotics to resolve these cases. Instead antibiotics need to be used selectively and responsibly. All treatment options need to be explored once you have a diagnosis, as drugs alone may be insufficient.
Prevention of future bouts of lymphangitis can be difficult, as the condition typically causes some permanent scarring of the limb. Obviously hygiene and cleanliness of the skin has got to be scrupulous with any wounds addressed immediately.
Other steps that can be taken include:
- Keep the horse in regular (daily) exercise – lymphangitis most often affects animals that are not in active work or are experiencing a period of rest
- Treat any wounds immediately, no matter how minor they might seem, by cleaning with an effective dilute antiseptic and applying a barrier wound cream, as recommended by your vet, to keep infection out of small wounds
- Call your vet at the first sign of limb swelling. Early intervention as soon as practical once the first signs appearing is crucial and means you may limit the long-term damage
- Always ensure horses are vaccinated for tetanus as this is another potential complication with any puncture wound.
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