In early stages it is indistinguishable from T.B. Histoplasmosis Histoplasmosis is a dimorphic fungi i.e. it grows in two forms myeclia and yeast. It grows as mycelia forms, producing spores at 25degC on sabroud's agar and at 37degC it grows as a yeast form. This dimorphism plays a pa in human infection i.e. in their natural habitat (the soil) they grow us mycelia and release spores into the air. These spores are inhaled by humans and at the human temperature of 37degC they grow as yeast cells (Hyphae). Histoplasmosis resembles tuberculosis in ceain ways Like T.B. histoplasma infection is acquired by inhalation. Histoplasmosis is acquired by inhalation of dust paicles contaminated with bird or bat dropings that contain small spores (microconidia), the infectious form of the fungus. The clinical presentation and morphological lesions of histoplasmosis also strikingly resemble those of tuberculosis I. A self limited and often latent primary pulnionan' involvement which may result in coin lesions on chest radiography. 2. Chronic, progressive secondary lung disease which is localized to the lung apices and cause cough, fever and night sweats. 3. Localized lesions in extrapulmonary sites including mediastinum, adrenals, liver or meninges. 4. Widely disseminated involvement paicularly in immunosuppressed individual. An impoant distinguishing point in histoplasma infection is that it is never transmitted from 'non to ratan. Diagnosis of Histoplasma infection Fungal culture remains the gold standard diagnostic test for histoplasmosis. However, culture results may not be known for upto I months. Staining of the biopsy material also yields diagnostic results. Serological diagnosis is useful in self limited pulmonary infection, however at least 1 month is required for the production of antibodies.