Diagnosis and treatment Pythiosis is suspected to be heavily underdiagnosed due to unfamiliarity with the disease, the rapid progression and morbidity, and the difficulty in making a diagnosis. Symptoms often appear once the disease has progressed to the point where treatment are less effective. As the organism is neither a bacterium, virus, nor fungus, routine tests often fail to diagnose it. In cytology and histology, the organism does not stain using Giemsa, H&E, or Diff-Quick, but the hyphae are outlined by surrounding tissue. GMS staining is required to identify the hyphae in slides, and highlights the lack of septation which helps distinguish the organism from fungal hyphae. Granulomatous inflammation with numerous eosinophils is suggestive that the hyphae are oomycetes rather than fungi, which are less likely to attract eosinophils. The symptoms are usually nonspecific and the disease may not be included in a differential diagnosis in human medicine, though it is familiar to veterinarians. Biopsies of infected tissues are known to be difficult to culture, but can help narrow the diagnosis to several different organisms. A definite diagnosis is confirmed using ELISA testing of serum for pythiosis antibodies, or by PCR testing of infected tissues or cultures. Due to the poor efficacy of single treatments, pythiosis infections are often treated using a variety of different treatments, all with varying success. Most successful treatments include surgery, immunotherapy, and chemotherapy. Aggressive surgical resection is the treatment of choice for pythiosis. Because it provides the best opportunity for cure, complete excision of infected tissue should be pursued whenever possible. When cutaneous lesions are limited to a single distal extremity, amputation is often recommended. In animals with gastrointestinal pythiosis, segmental lesions should be resected with 5-cm margins whenever possible. Unfortunately, surgical excision of tissue and amputation do not guarantee complete success and lesions can reappear. So, surgery is often followed by other treatments. An immunotherapy product derived from antigens of P. insidiosum has been used successfully to treat pythiosis. Case reports indicate the use of the following chemotherapy treatments with varying success: potassium iodide, amphotericin B, terbinafine, itraconazole, fluconazole, ketoconazole, natamycin, posaconazole, voriconazole, prednisone, flucytosine, and liposomal nystatin. References Dog diseases Horse diseases Pythium