Blastomycosis

Blastomycosis is an infection that occurs by inhaling spores of 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 found in nature. That it is a dimorphic fungus implies that in its life cycle it takes the form of yeast and mycelium:

• First, yeast form with buds in the tissues.
• Second, mycelium forms on the ground and wood.

This type of fungus appears mainly 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 say, to dogs and cats.

Pathogeny

When you breathe in the spores, they travel to the lungs. Therefore, the immune system is activated. The spores can damage the bronchi and spread throughout the lung. However, if the individual’s defenses are not affected, this infection resolves without presenting any symptoms.

Instead, because it is a dimorphic fungus, the spores can transform into yeast in tissues thanks to body temperature. This causes them to have resistance to phagocytosis. As a consequence, they reproduce in the lower lobes, with suppurative changes and granuloma formation.

Once it affects the lung, it  can affect other organs, mainly bones and skin. On the other hand, when contagion is by skin inoculation, a reddened area or erythema called chancre or primary complex appears, which can evolve into granulomatous lesions on the skin.

Clinic

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

Pulmonary blastomycosis

50% are asymptomatic and only 1 to 5% present symptoms, the severity of which depends on the immune status of the patient. When they appear, the symptoms are similar to pneumonia:

• First of all, cough.
• Second, mild fever.
• Finally, dyspnea or shortness of breath.

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

• Acute blastomycosis

This has very marked pulmonary symptoms associated with fatigue, sweating and weight loss. It can be seriously complicated 2-3 weeks after infection.

• Chronic blastomycosis

In it appears a calcification of the pulmonary lesions, invasion of the pleura and sometimes of the thoracic wall.

Primary cutaneous blastomycosis

Primary cutaneous blastomycosis is a rare form of infection .  The location depends on the inoculation, mainly on the face and extremities.

Two weeks after inoculation of the fungus, a reddened lesion appears. The evolution of the primary complex will form elevated and larger lesions with involvement of the regional lymph nodes.

Sometimes the lesions ulcerate or become warty. They tend to spontaneously heal without treatment.

Disseminated blastomycosis

Rare entity produced by the dissemination of the fungus from the pulmonary focus to other organs via the bloodstream. The main conditions are cutaneous (it must be differentiated from primary cutaneous blastomycosis) and bone:

• Secondary cutaneous blastomycosis: This is sometimes the first clinical manifestation of the infection.
  • A small raised lesion appears that evolves into a red-purplish 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 meninges, brain, genitourinary tract, and prostate.

Diagnosis of blastomycosis

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

• On the one hand, radiological tests:  X-rays, computed tomography or magnetic resonance imaging. Useful in lung and bone involvement.
• On the other hand, a direct examination of the fungus.

• There are also immunological tests.
• Biopsy (useful in cutaneous blatomycosis).
• Serology.
• Lastly, cultivation.

Treatment

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

The most commonly used drugs are itraconazole, fluconazole and amphotericin B. Generally, when the infection is mild or moderate, itraconazole is preferred. However, in the presence of more serious life-threatening infections, intravenous amphotericin B is used.

In conclusion

Blastomycosis is a lung disease that can become complicated and seriously affect other organs. In the event of any symptoms, a specialist should be consulted to assess the diagnosis and possible treatment.