The majority of patients with Blasto are able to be treated with oral anti-fungal medication, but some patients require more aggressive intravenous anti-fungal medication. Because of the tenacious nature of fungi, oral medications are usually required for a minimum of months and are not discontinued until there is certainty that the disease has been cleared from the patient. Intravenous anti-fungal therapy is reserved for severe, life-threatening infections, because of the potential toxicity and expense of the drug.
Treatment of Blastomycosis requires commitment and patience, as it can take weeks to see improvement. Many patients need to be hospitalized early in the course of the disease for fluids, oxygen and pain medications. Most patients who survive the first few weeks after diagnosis will recover, though some have residual effects. It is critical to give all medications as directed and do not discontinue the medication unless there is certainty that the infection is cleared.
Patients with Blasto need to be closely monitored for the first months after diagnosis and are generally followed by an internal medicine specialist. Oral medications are often continued for a minimum of 6 months.
Follow up exams include monitoring of patient progress, medication side effects and clearance of infection. Urine Blasto antigen testing is often used to assess clearance of infection, and several negative tests a few months apart are recommended.
Because medication and follow up recommendations are based on physical exam findings as well as radiographs and lab tests, we recommend that the follow up be done at Veterinary Specialty Center if you and your primary care veterinarian want the internal medicine specialists to continue to make therapeutic recommendations. Discontinuing medications too soon can result in a relapse of the infection. Skip to content. Cause Blastomycosis also often referred to as Blasto is caused by Blastomyces dermatitidis , is a systemic fungal infection that affects dogs and cats.
Clinical Signs The signs of illness will depend on what organs are infected. Saccente M, Woods GL. Clinical and laboratory update on blastomycosis external icon. Clin Microbiol Rev. Blastomycosis in immunocompromised patients external icon. Epidemiology, diagnosis, and treatment of blastomycosis in dogs and cats external icon. Clin Tech Small Anim Pract. Related Links. Other sites. Tissues less commonly infected include the prostate, kidneys, testes, joints, nasal passages, and brain.
Mild normocytic, normochromic, nonregenerative anemia is common, as is moderate leukocytosis characterized by mature neutrophilia or neutrophilia with a left shift.
Perform a thoracic radiographic examination in all dogs with suspected blastomycosis, regardless of whether respiratory signs are evident. Figure 2A. A lateral thoracic radiograph showing a diffuse miliary interstitial pattern in the lung of a dog with blastomycosis.
The lungs will appear normal radiographically in a few dogs with pulmonary parenchymal disease since inflammatory nodules smaller than 5 mm in diameter may not be detected. Figure 2B. A ventrodorsal thoracic radiograph showing a diffuse miliary interstitial pattern in a dog with blastomycosis. Blastomycosis is most reliably diagnosed by demonstrating the organism in cytologic or histologic samples from infected tissues.
Samples from infected sites usually show evidence of pyogranulomatous or purulent inflammation, which should prompt a careful search for yeast cells. Figure 3. A lateral thoracic radiograph showing a focal granuloma arrow in the lung of a dog with blastomycosis.
Figure 4. Cytologic examination of a fine-needle aspirate from an enlarged lymph node in a dog with blastomycosis reveals Blastomyces organisms Wright's-Giemsa stain. Cytologic examination of samples obtained from the lungs by transtracheal aspiration, bronchoalveolar lavage, and transthoracic lung aspiration has been evaluated in the diagnosis of pulmonary blastomycosis.
Figure 5. Blastomyces organisms have been phagocytosed by macrophages in this transtracheal wash sample from a dog with pulmonary blastomycosis.
Pyogranulomatous inflammation is evident Wright's-Giemsa stain; X magnification. Most dogs with ocular blastomycosis have concurrent lung, skin, or lymph node involvement, allowing cytologic diagnosis to be made based on samples collected less invasively from these tissues.
Vitreal aspirates and subretinal aspirates have been recommended in patients with only ocular involvement, but these techniques may threaten vision in an eye that is not already blind. Figure 6. Cytologic examination of a vitreal aspirate from a dog with ocular blastomycosis reveals pyogranulomatous inflammation and Blastomyces organisms Wright's-Giemsa stain; 50X.
Definitive diagnosis based on cerebrospinal fluid CSF analysis is rarely possible in dogs with blastomycosis involving the brain or spinal cord. When cytologic samples from infected tissues are not diagnostic yet you highly suspect blastomycosis, serologic testing may be performed. Dogs with blastomycosis produce antibodies directed against the Wisconsin-1 WI and A antigens of B.
Antibody titers may persist in cured animals, making it impossible to use agar gel immunodiffusion results to monitor response to therapy or disease recurrence. Recently, an enzyme immunoassay test to detect B. Cross-reactivity with other fungal agents especially Histoplasma capsulatum and a few nonspecific false positive results have been reported.
A few veterinary laboratories offer PCR-based diagnostic tests for fungal diseases. PCR promises increased sensitivity and speed of diagnosis compared with conventional diagnostic tests, but the utility of PCR in early diagnosis of canine blastomycosis has not been evaluated. Drugs most often recommended to treat dogs with blastomycosis are amphotericin B and the azole antifungals, including itraconazole, ketoconazole, fluconazole, and voriconazole.
Table 1 provides a summary of recommended dosages for commonly used antifungal agents. These drugs are not FDA-approved for veterinary use. Amphotericin B is a polyene antibiotic that binds ergosterol, an essential component of the fungal cell wall, thereby disrupting the cell wall and causing the organism's death. Amphotericin B's principal adverse effect is cumulative nephrotoxicosis, so monitor renal function before each dose.
The desoxycholate form of amphotericin B is most commonly administered as an intravenous infusion. Amphotericin B may be administered during the initial treatment of dogs with severe or rapidly progressive blastomycosis to improve the rate of recovery.
Combination therapy with amphotericin B and an azole antifungal allows for a decreased total dose of amphotericin B to be administered, potentially decreasing the potential for nephrotoxicity. A lipid-complexed formulation of amphotericin B has recently become available. This formulation, Abelcet The Liposome Company , is eight to 10 times less nephrotoxic than amphotericin B desoxycholate, allowing higher cumulative doses to be administered.
The azole antifungals ketoconazole, itraconazole, fluconazole, and voriconazole interfere with ergosterol synthesis. Itraconazole is the azole most often recommended for treating dogs with blastomycosis since it is as effective as amphotericin B but is associated with fewer adverse effects and can be administered orally. Peak plasma concentrations do not occur until six to 14 days after treatment is begun, resulting in some lag time before clinical response. Itraconazole is extensively bound to plasma proteins and is lipophilic, leading to good distribution throughout most tissues, but concentrations in urine and CSF are low.
Itraconazole does not cross the normal blood-brain, blood-prostate, or blood-ocular barrier, but infections with Blastomyces organisms at these sites often respond well to treatment with itraconazole, perhaps because of increased penetration of the drug when inflammation is present.
Asymptomatic increases in alanine transaminase ALT activity are common but should not prompt a change in therapy unless the dog exhibits anorexia, vomiting, or abdominal pain. Vasculitis resulting in ulcerative dermatitis or limb swelling develops in 7. Be sure to distinguish this drug reaction from a manifestation of cutaneous blastomycosis. Fluconazole is an azole antifungal that is minimally protein bound and highly water soluble, penetrating the blood-brain, blood-prostate, and blood-ocular barriers well and achieving high concentrations in urine, CSF, and ocular fluids.
Voriconazole is a derivative of fluconazole that has a broader spectrum of action, improving its efficacy against blastomycosis while maintaining wide tissue distribution and the ability to cross the blood-brain, blood-ocular, and blood-prostate barriers.
As such, this drug may be effective in treating CNS fungal infections including blastomycosis. Administer itraconazole or the other azoles for at least 60 days in all infected dogs, and continue for at least one month after all clinical and radiographic evidence of disease has resolved.
The likelihood of relapse is related to the severity of the initial lung disease, and it most often occurs within six months of therapy cessation. The two most important negative prognostic factors are CNS involvement and severe lung disease. Dogs with severe diffuse pulmonary blastomycosis often deteriorate during the first two or three days of treatment, perhaps related to an inflammatory response directed against dying organisms in the lungs.
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