What is Epizootic Lymphangitis ?

 Epizootic lymphangitis is a contagious disease of the skin, lymphatic vessels and nodes of the limbs, neck and chest of horses and other equid species. It is caused by a fungus (Histoplasma capsulatum var farciminosum) and is responsible for chronic weight loss and progressive debility in affected animals. Epizootic lymphangitis is not endemic in the United States.

Clinical Signs: Four forms of epizootic lymphangitis are described. Two or more forms of the disease can occur concurrently in the same animal. 

Skin form 

  • Most commonly encountered form of epizootic lymphangitis 
  • Following the introduction of the mycelial or yeast phase of the fungus through a wound, broken or abraded skin, the organism spreads via the lymphatics to the regional lymph nodes, in some cases involving the internal organs. 
  • The initial lesion is usually a chancre-like papule that develops along the course of a superficial lymphatic vessel, eventually becoming a pyogranulomatous nodule that ulcerates. 
  • The lesion undergoes alternate periods of discharging and partial healing before finally closing over with scar formation. It can take two to three months for this to occur. 
  • Although the commonest sites of lesions are the forelimbs, neck and chest, lesions may be distributed over the entire body in advanced cases of the disease. 
  • Severely affected equines exhibit anorexia, deterioration in condition and lameness in cases of joint involvement.

Ocular form 

  • Less frequently observed and very rarely becomes generalized 
  • Most common in donkeys 
  • Granulomatous proliferation of conjunctival sac that protrudes out of medial lacrimal puncta; this can lead to blockage of lacrimal duct 
  • Blepharospasm, conjunctivitis and ocular discharge
  • Swelling of the eyelids
  • Extension to periorbital tissues where it results in a granulomatous reaction
  • Frequent complications in advanced cases, corneal ulceration, panophthalmitis and myiasis

Respiratory form 

  • Lesions usually confined to upper respiratory tract 
  • Papules/nodules develop on nasal mucosa; these ulcerate giving rise to granulating ulcers 
  • Lesions may extend to the trachea, bronchial tree and the lungs
  • Mucopurulent nasal discharge, coughing and dyspnea in advanced cases of the disease 

Diagnosis: A provisional clinical diagnosis of epizootic lymphangitis is made by microscopic examination of pus preferably aspirated from an unruptured lesion or a biopsy sample from an affected lymph node or skin lesion. Culture can be attempted but it takes four to eight weeks for development of colonies. Serum agglutination test titers >1:80 are considered positive for infection.

Treatment: Amphotericin B is the drug of choice.

Prevention: Isolation and increased biosecurity are the chief way to prevent spread of the fungus.