Blastomycosis is a disease from the group of systemic mycoses that occurs with primary lung damage and hematogenous dissemination of fungal infection into internal organs, bones and skin. Disease can occur in various forms: pulmonary (bronchopneumonia), skin (rash, skin ulcers, subcutaneous abscesses), bone (osteomyelitis, arthritis), genitourinary (prostatitis, epididymitis), etc. The diagnosis is confirmed by isolating the pathogen – the fungus Blastomyces dermatitidis by microscopy, culture examination, biopsy. Therapy is carried out with antifungal drugs (itraconazole, amphotericin B); drainage and sanitation of abscesses may be indicated.
Various types are described in the medical literature: North American (Gilkraist’s disease), South American (paracoccidioidosis), European (cryptococcosis) and keloid (Lobo’s disease), of which the North American type has the greatest prevalence. North American blastomycosis is a fungal disease characterized by a polysystemic lesion with the development of purulent granulomatous processes in the lungs, skin, skeleton, and genitourinary tract. Blastomycosis is common in the USA and Canada; in the form of sporadic cases it occurs in Latin America, Africa, Europe, Australia, India. During epidemic outbreaks of the incidence of blastomycosis, children and young people under 20 are more susceptible. The issues of treatment and prevention of blastomycosis are at the junction of various clinical disciplines: mycology, pulmonology, dermatology, urology, etc.
North American blastomycosis is caused by the dimorphic (two-phase) saprophytic fungus Blastomyces dermatitidi, which lives in the soil. The fungus enters the human body by airborne dust when inhaling fungal spores with dust particles. The main ways of spreading the pathogen in the body include hematogenic and lymphogenic. Sexual transmission of blastomycosis is possible. The causative agent of blastomycosis can exist in two forms: mycelial and yeast. In the mycelial form, the fungus exists at a temperature below 30 ° C, and in the affected organism (at t 37 ° C) it passes into the yeast phase.
Once in the lungs, the microconidia of the fungus enter the yeast phase and cause the development of primary infiltrative foci of inflammation. At later stages, granulomas with areas of suppuration and necrosis form in the foci. The lesion of the skin and internal organs is secondary and occurs as a result of infection from the lungs. Concomitant diseases contribute to the development of blastomycosis: diabetes mellitus, tuberculosis, blood diseases, immunodeficiency conditions (for example, HIV infection). Risk groups for the incidence of blastomycosis include gardeners, agricultural workers and other people who often come into contact with soil containing blastomycete spores, as well as people living in endemic areas.
There are the following clinical forms of blastomycosis: pulmonary, cutaneous, bone, genitourinary and others (lesions of the central nervous system, pericardium, liver, spleen, thyroid gland, adrenal glands). Systemic (disseminated) blastomycosis can develop years after primary lung damage.
The pulmonary form of blastomycosis accounts for 60-90% of all cases of fungal infection and proceeds in the form of bronchopneumonia. The incubation period takes 30-45 days on average. The onset of the disease is acute or subacute; in the initial period, intoxication syndrome prevails: subfebrile or febrile temperature, chills, muscle and joint pain. Less often, blastomycosis develops from the very beginning as primary chronic, without pronounced clinical symptoms. He is worried about cough (dry at first, then with purulent sputum), hemoptysis, chest pain, shortness of breath. With an objective examination, wheezing, pleural friction noise are heard; radiologically, upper lobe infiltrates are detected, sometimes cavities. For others, patients with pulmonary blastomycosis are not contagious.
Among extrapulmonary lesions, the cutaneous form of blastomycosis is most common (40-80% of cases). Cutaneous blastomycosis occurs with vesicular-papular or papular-pustular rashes, which transform into ulcerative defects covered with abundant granulations. The ulceration that is separated from the sites is bloody or purulent. Ulcers can spread to the mucous membrane of the oral cavity, pharynx and larynx. The healing of ulcers occurs with the formation of a thin soft scar. Subcutaneous abscesses may form.
The bone form accounts for 25-50% of cases of extrapulmonary blastomycosis. It occurs mainly in the form of osteomyelitis of long tubular bones, spine, ribs. Abscesses of surrounding soft tissues, fistula passages, arthritis of nearby joints often form in the affected area.
The genitourinary form of blastomycosis (10-30% of cases) is more often diagnosed in men. The clinical picture corresponds to orchitis, epididymitis, prostatitis; hematuria and pyuria may be noted. Infection of women with genitourinary blastomycosis occurs sexually and is rare. With disseminated blastomycosis, internal organs may be affected with the development of liver abscesses, pericarditis, adrenal insufficiency, etc. When the central nervous system is involved, brain abscesses and meningitis occur.
First of all, blastomycosis should be suspected in patients who arrived from endemic areas and have signs of lung, skin, bone, and genitourinary system damage. Therefore, in addition to narrow specialists (pulmonologist, dermatologist, urologist, etc.), infectious disease specialists and mycologists should be involved in the examination of such patients.
The diagnosis of blastomycosis is confirmed when B. dermatitidi is detected in biological material: sputum, purulent discharge from fistulas and abscesses, urine, liquor, biopsy material. Microscopic examination and microbiological seeding are most often used. To obtain samples of the material, puncture of abscesses and aspiration of their contents, excision tissue biopsy are performed. Serological diagnosis of blastomycosis is carried out by methods of ELISA, RSC, RIA. Skin-allergic tests with blastomycin have low sensitivity and specificity. In order to detect changes in internal organs, additional instrumental studies are carried out: chest X-ray, osteoscintigraphy, CT of the brain and spine.
Pulmonary blastomycosis should be differentiated from other chronic lung lesions: bacterial pneumonia, tuberculosis, neoplasms and lung abscesses, pleural empyema, pulmonary aspergillosis, histoplasmosis. With the cutaneous form, pyoderma, other dermatomycoses, squamous cell skin cancer should be excluded. Genitourinary blastomycosis should be distinguished from bacterial prostatitis and orchiepididymitis, prostate cancer, syphilis. Bone blastomycosis requires differential diagnosis with bone tuberculosis and bacterial osteomyelitis.
Acute pulmonary blastomycosis can result in recovery without special treatment. In all other cases, antifungal therapy is the basis for the treatment of various forms of blastomycosis. In the mild course of the disease, itraconazole or ketoconazole is prescribed orally for 6 months; in severe cases, amphotericin is administered intravenously. According to indications, antifungal therapy is supplemented by surgical methods – drainage of the pleural cavity, opening of skin abscesses, necrectomy, etc.
Adequate and timely therapy of localized forms of blastomycosis makes it possible to achieve recovery in 90% of cases. With disseminated forms in the absence of treatment, the probability of a fatal outcome is high. In order to avoid infection with blastomycosis, it is recommended to observe the rules of personal hygiene, respiratory protection when loosening the soil and carrying out other agricultural work in a disadvantaged area, the use of barrier methods of contraception in case of accidental sexual contact.