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Opportunistic Fungal Infections, Part 3: Cryptococcosis, Histoplasmosis, Coccidioidomycosis, and Emerging Mould Infections

Opportunistic Fungal Infections, Part 3: Cryptococcosis, Histoplasmosis, Coccidioidomycosis, and Emerging Mould Infections

Because of lapses in the immune system, immunocompromised hosts are at risk for infection with endemic fungi. Although infection is associated with exposure, it may represent reactivation of latent disease from exposure that occurred many years previously. When a patient presents with an infection suspected of being caused by an endemic fungus, it is of utmost importance to obtain a thorough history, including past and current places of residence, recent travel, and exposure to pets or other animals. Serological studies are often required to make the diagnosis.

It is also important to consider moulds other than Aspergillus species as the cause of fungal infections in immunocompromised hosts. Infections attributed to Zygomycetes and Fusarium and Scedosporium species are being reported with increased frequency. These infections clinically present in a manner similar to infections caused by Aspergillus species and often cannot be distinguished from aspergillosis on radiographic imaging or often on histological examination. Thus, culture is often required to confirm the diagnosis. In addition, currently available antifungal therapies have gaps in their coverage of some of these organisms, making identification all the more necessary.

CRYPTOCOCCOSIS

Cryptococcus neoformans is responsible for cryptococcosis. Infection is acquired by inhalation. Initial exposures to the yeast can lead to active symptomatic infection with local or disseminated disease or latent infection similar to that caused by Mycobacterium tuberculosis.1

Cryptococcosis has been described in patients with cancer who have impaired cell-mediated immunity or have received high-dose corticosteroid therapy. Donor organ- transmitted disease has been reported in patients who have received a lung2 or corneal transplant.3

The primary sites of infection are the lung and CNS. Infection can occur at other sites, including the skin, prostate, and eye. Most immunocompromised hosts will present with constitutional symptoms, including fever, malaise, cough, weight loss, or headaches. Chest radiographs may show alveolar or interstitial infiltrates that can be caused by other pathogens1 and thus make diagnosis challenging (Figure 1).

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