Epizootic Lymphangitis

• Histoplasma capsulatum var. farciminosum
  • Similar to H. capsulatum

• Occurs in horses, donkeys and mules
• 90% occurs in horses

• Occurs in Europe, Africa and Asia
  • Eradicated from the UK but is still under the notifiable Diseases of Animals Act

• Chronic disease

• Highly contageous
  • Spread by direct contact or indirect, e.g. through infected grooming equipment, biting flies

• Once established in a population it is very difficult to eradicate
  • Long incubation peroid
  • New cases can develop weeks or months after the infection appears to have been eradicated

• Affects the lymph nodes, lymph vessels and skin
  • Mostly of the neck and limbs

• Causes ulcerative, nodular lesions
  • Dissemination occurs
  • Pulmonary disease can occur
  • Ulcers rupture, discharging blood-stained pus for several weeks

• Oval or pear shaped cells
  • Double contoured
  • Dimorphic
    • Grows in the yeast phase at 37°C and in the mycelial phase at room temperature
  • Growth is slow, taking up to 8 weeks
  • At room temperature, thick-walled chlamydospores can be seen
  • Orgnaisms can usually be seen in swollen leucocytes

• Can be stained using Gram, Giemsa, H & E and 10% Methylene Blue followed by Carbol Fuchsin

• Enzyme-linked immunosorbant assay can be used to detect the fungi

• Life-long immunity follows recovery from infection

• Treatment included potassium iodide, hamycin and Amphotericin B
  • Vaccination has also proven to be effective
  • Injection of hyperimmune serum around skin lesions has been proven to be effective