Blastomycosis overview

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]

Overview

Blastomycosis is a fungal infection caused by the organism Blastomyces dermatitidis. It is Endemic to portions of North America, and causes clinical symptoms similar to histoplasmosis. Only about half of people who have infection usually develop disease. The symptoms if at all, develop between 3 to 15 weeks after exposure and are similar to a flu like illness.

Historical Perspective

Blastomycosis was first described by Thomas Casper Gilchrist [2] in 1894 and sometimes goes by the eponym Gilchrist's disease [3]. It is also sometimes referred to as Chicago Disease.

Pathophysiology

Infection occurs by inhalation of the fungus from its natural soil habitat.It has an average incubation period of 3 weeks to 3 months after exposure.Once inhaled in the lungs, they multiply and the initial neutrophilic response and the subsequent cell-mediated immune response are manifested as a supperative tissue destruction seen in lungs, and may disseminate through the blood and lymphatics to other organs including the skin, bone, genitourinary tract, and brain.The histopathological findings are the multinucleated yeast form (budding).

Causes

Blastomycosis is a fungal infection caused by Blastomyces dermatitidis.

Differentiating Blastomycosis from other Diseases

Blastomycosis presents as a mild flu-like illness and needs to be differentiated from other fungal disorders that presents with similar complaints. These disorders have overlapping signs & symptoms that often need detailed history. Coccidioidomycosis, Histoplasmosis, Aspergillosis, Pneumocystis pneumonia, Sporotrichosis are the most important diseases to be considered in the differential.

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. Blastomycosis is also distributed internationally, cases are reported from Africa, India, Middle east, Mexco, Central and South America.

Risk Factors

The risk factors are not well established for the acquisition of blastomycosis in endemic areas. However, studies point out the role of moist soil rich in organic debris as a source of transmission. Immunosuppression also increases the risk of infection.

Screening

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 array of signs and symptoms, but is usually a mild illness in many cases. 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 system, lymphatics etc).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

Diagnosis

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 immunocomeptent patients or as an acute illness resembling bacterial pneumonia, with symptoms of high fever, chills, a productive cough, and pleuritis in immunocomprimised individuals. Blastomycosis can affect almost any other site such as liver, spleen, breast, lymph nodes etc, through hematogenous spread. Skin lesions, usually appear as ulcerated lesions and bone lesions can lead to osteomyelitis.

Physical examination

Blastomycosis is disease of lung ,but it can affect other organs like skin bone etc. A detailed physical examination can guide towards diagnosis. Lung examination findings include dullness to percussion, increased fremitus etc. Signs of pleuritic involvement such as chest pain and rub may be found.

Laboratory Findings

No clinical or radiographic abnormalities 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.

X-ray chest

The findings 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.

Treatment

Medical Therapy

As per the 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 treated, 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.

• Immuno-competent 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 non tolerant to Amphotericin B can be treated with fluconazole or Itraconazole.

• Immuno-compromised patients.
  • All patients warrant treatment with Lipid Amphotericin B as the drug of choice and Itraconazole once the disease has shown clinical improvement.

Primary Prevention

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.