Blastomycosis overview On the Web
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Blastomycosis is a fungal infection caused by the organism Blastomyces dermatitidis. It is endemic in portions of the Mississippi river and Ohio river basins and around the Great Lakes in North America, and causes clinical symptoms such as fever, productive cough and myalgia. The symptoms, develop between 3 to 15 weeks after exposure. Majority of the cases are self-limiting with out any progression. Antifungals are used to treat if symptoms persist for more than 4 weeks. Prognosis is good depending on the immune status of the individual.
Blastomycosis was first described in detail by Thomas Casper Gilchrist in 1894.
Infection occurs by inhalation of the conidia from its natural soil habitat. It has an average incubation period of 3 weeks to 3 months after exposure. Once inhaled, they multiply in lungs and initiate neutrophilic response with subsequent cell-mediated immune response leading to suppurative tissue destruction in lungs, and may disseminate through blood and lymphatics to other organs including skin, bone, genitourinary tract, and brain. The characteristic histopathological findings on sputum microscopy is the multi nucleated yeast form (budding).
Differentiating Blastomycosis from other Diseases
Blastomycosis presents as a mild flu-like illness and needs to be differentiated from other fungal disorders like coccidioidomycosis, histoplasmosis, aspergillosis, pneumocystis pneumoniasandporotrichosis.
Epidemiology and Demographics
Blastomycosis is endemic in the Mississippi river and Ohio river basins and around the Great Lakes in United States.The annual incidence is less than 1 case per 100,000 people in Mississippi, Louisiana, Kentucky, and Arkansas.
The risk factors are not well established for the acquisition of blastomycosis even in endemic areas. However, studies point out the role of moist soil rich in organic debris as a source of transmission.
According to the centers for disease control and prevention screening for blastomycosis is not recommended.
Natural History, Complications and Prognosis
Blastomycosis is a granulomatous disease entity, that can produce a wide range of signs and symptoms, but in most cases, it is a mild illness. The symptoms include fever, productive cough, hemoptysis and weight loss. If left untreated, a significant proportion of these cases may further disseminate to other body parts, most commonly to skin, followed by bone and joint, genitourinary system and other sites in the body (Nervous systemlandymphatics). The route of spread is most commonly either hematogenous or lymphatic. Prognosis of the individual depends on the immune status of the individual and treatment, usually good in immunocompetent patients with treatment, on contrast prognosis is poor in patients even with treatment in immuno-compromised individuals. Complications that may develop with blastomycosis include cutaneous involvement can cause large sores with pus (abscesses), osteomyelitis from bone involvement, prostatitis and epididymo-orchitis in males and tubo-ovarian abscess in females have been reported, disease recurrence.
History and symptoms
Symptoms of blastomycosis depends on the immune status of the individual, it presents as a flu-like illness with fever, chills, myalgia, headache, and a nonproductive cough which resolves within days in immunocompetent patients or as an acute illness resembling bacterial pneumonia, with symptoms of high fever, chills, a productive cough, and pleuritis in immunocompromised individuals. Blastomycosis can affect other organs through hematogenous spread or lymphatics which includes skin, bone, genitourinary tract and brain. Skin lesions, usually appear as ulcerated lesions and bone lesions can lead to osteomyelitis.
Blastomycosis is a primary disease of lung, but it may also affect other organs like skinbandone. Adetailed physical examination can guide towards the diagnosis. Lung examination findings include dullness to percussion, and creased fremitus. Signs of pleuritic involvement such as pleuritic chest pain and pleural rub may be found.
No radiographic findings are absolutely diagnostic of blastomycosis. Once suspected, the diagnosis of blastomycosis can usually be confirmed by demonstration of the characteristic broad-based budding organisms in sputum or tissues by KOH prep, cytology, or histology.
The findings on X-ray are not consistent or highly specific. Alveolar infiltrates may be present but are not localized to a particular lobe. Consolidations with or without cavitations, small pleural effusion's are relatively common. Sometimes, pulmonary nodules simulating tuberculosis or cancers may be present. Mediastinal lymph node enlargement is not a consistent finding but may be found occasionally.
The mainstay of treatment is antifungals. As per the current guidelines given by the Infectious Diseases Society of America, the appropriate regimen must be guided by the clinical form and severity of disease, as well as the immune status of patient and toxicity of antifungal agents. Only asymptomatic infections are left untreated, otherwise, all cases need therapy. Itraconazole given orally is the treatment of choice for most forms of the disease. Cure rates are high, and the treatment over a period of months is usually well tolerated. Amphotericin B is considerably more toxic, and is usually reserved for critically ill patients and those with central nervous system disease.
- Immuno-competent patient. (Non-Life threatening infection): Drug of choice in this cases is usually Itraconazole or Lipid Amphotericin B. Alternatively, daily fluconazole or ketaconazole may also be used.
- Immunocompetent patient. (Life-threatening infection): Pulmonary cases - These warrant treatment primarily with Lipid Amphotericin B or Deoxycholate Amphotericin B. Once the condition has been stabilized the patient may be switched to oral Itraconazole therapy. Disseminated cases - Drug of choice is same, however, patients nontolerant to Amphotericin B can be treated with fluconazole or Itraconazole.
- Immunocompromised patients: All patients warrant treatment with Lipid Amphotericin B as the drug of choice and Itraconazole once the disease has shown clinical improvement.
Avoiding travel to areas where the infection is known to occur may help prevent exposure to the fungus, but this may not always be possible.
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