Blastomycosis is an infection that occurs by inhaling a fungus that mainly affects the lungs.  If it spreads it can affect the nervous system, bones and other organs.

The Blastomyces dermatitidis  is a dimorphic fungus present in nature. That it is a dimorphic fungus implies that in its life cycle it adopts the form of yeast and mycelium:

• Yeast form with buds in the tissues.
• Micello form on the ground and wood.

This type of fungus appears mostly in temperate and humid climates, near rivers or lakes and in wood. For this reason, it mainly affects rural workers, such as farmers and peasants. On the other hand this type of fungus also affects domestic mammals; that is, to dogs and cats.

Pathogeny

By inhaling the spores, they travel to the lungs. Therefore, the immune system is activated. Spores can cause lesions in the bronchi and spread throughout the lung. However, if the individual’s defenses are not affected, this infection resolves without presenting any symptomatology.

In contrast, because it is a dimorphic fungus, spores can be transformed into yeasts in tissues thanks to body temperature. This causes them to have resistance to phagocytosis. As a result, they reproduce in the lower lobes, with suppurative changes and formation of granulomas.

Once it affects the lung it can affect other organs, mainly bones and skin.  On the other hand when the infection is by cutaneous inoculation a reddened area appears (it is called erythema) called chancre or primary complex, which can evolve giving granulomatous lesions in the skin.

Clinic

The clinical forms are varied, the most common is pulmonary blastomycosis. Other less frequent variants with cutaneous blastomycosis and disseminated blascomycosis.

Pulmonary blastomycosis

50% are asymptomatic and only 1 to 5% have symptoms, whose severity depends on the patient’s immune status. When they appear, the symptoms are similar to pneumonia:

• Cough.
  • Purulent or hemoptoic sputum. The cough is accompanied by emission of mucus greenish and viscous when it is purulent and with traces of blood when it is hemoptoic.
• Slight fever.
• Shortness of breath or difficulty breathing

The evolution can lead to chest pain and more rarely, pleural effusion. The pulmonary lesions are variable , from small nodules to large areas of necrosis that severely compromise pulmonary function. Depending on its evolution, we can differentiate it into:

• Acute blastomycosis , which presents with very marked pulmonary symptoms associated with fatigue, sweating and weight loss. It can be complicated in an important way 2-3 weeks after infection.
• Chronic blastomycosis , in which there is a calcification of the lung lesions, invasion of the pleura and sometimes of the chest wall.

Primary cutaneous blastomycosis

Primary cutaneous blastomycosis is an uncommon form of Blastomyces dermatitidis infection  . The location depends on the inoculation, mainly on the face and extremities.

Two weeks after the inoculation of the fungus, an erythematous (reddened) lesion appears, called the primary complex or chancre, with involvement of the lymphatic vessels or lymphangitis. The evolution of the primary complex will form papulo-nodular lesions (elevated and larger) with involvement of the regional lymph nodes.

Disseminated blastomycosis

Rare entity produced by the dissemination of the fungus from the pulmonary focus to other organs by blood. The main affections are the cutaneous one (it is necessary to differentiate it from the primary cutaneous blastomycosis) and the bone one:

• Secondary cutaneous blastomycosis. It is the most common site of dissemination, sometimes it is the first clinical manifestation of the infection.
  
  • The lesions lack a defined location. A papule appears (small elevated lesion) that evolves into a red-violaceous nodule.
  • In evolution it tends to soften, forming ulcers or abscesses.
• Bony blastomycosis It mainly affects the vertebrae and ribs. The lesions will produce an inflammation of the periosteum (hard layer that covers the bones), with fibrosis and lysis of the bone.

Disseminated blastomycosis can affect almost all organs, including the common meninges, brain, genitourinary and prostate.

Diagnosis of blastomycosis

Diagnostic techniques will be based on demonstrating the existence of the fungus. There are different tests:

• Radiological tests. X-ray, computerized tomography or magnetic resonance. Useful in lung and bone affectation. In the case of pulmonary involvement, pulmonary condensates similar to those that appear in pneumonia will be observed.
• Direct examination of the fungus from flakes of damaged skin, sputum or bronchial lavage.
• Immunological tests
• Biopsy (useful in cutaneous blatomicosis).
• Serology.
• Culture.

Once the fungus has been determined, the treatment will consist in the use of antifungal drugs. The choice of one and the other, dose and duration of the treatment will depend on the symptomatology and degree of affectation of the patient.