A fungus which has filamentous growth at 25 degrees C and yeast growth at 37 degrees C. It is reported to be a human pathogen. It may be associated with birds.
Histoplasma sp is a fungus that is found in nature and one that has thermal dimorphic. It has its natural habitat in soil that has been contaminated with birds' droppings as well as bats excrements. It is commonly found in tropical areas although there are divergent views, some of which claim that it can be found all over the world. The Genus Histoplasma in which the Mold or fun belongs usually has only one species, which is the Histoplasma capsulatum, which then exists in two varieties namely Histoplasma capsulatum var. duboisii and Histoplasma capsulatum var. capsulatum. The teleomorph for the species is called Ajellomyces capsulatus.
Histoplasma sp is known to cause histoplasmosis, which is a disease that has a wide spectrum that range from mild pulmonary infection to chronic and fatal chronic illnesses. The lungs are especially infected due to the inhalation of conidia. The reticuloendothelial system (RES) is largely involved when the infection includes the Histyoplasma var. capsulatum dissemination. One might also find cases where Histoplasma capsulatum also gets involved although this is rare. Thyroid glands may also be involved by Histoplasma capsulatum although such an infection is rare as well.
Histoplasma capsulatum var. duboisii does not affect the lungs but it has a huge bearing on the bones and the lungs and it is the one responsible for African histoplasmosis. The nature of this infection makes even the healthy individuals get affected. The dissemination however comes to those who are no thoroughly immunized as well as the elderly. There are has been cases of chronic cavitary histoplasmosis in those individuals who have other pulmonary diseases.
Histoplasma capsulatum is a thermally dimorphic and this makes this fungus to attain a mold from 25 degrees Celsius and to attain the best form in temperatures revolving around 37 degrees Celsius. Whenever the fungus colonies are at 25 degrees, they tend to grow quite slowly and change from appearing a bit granular to attaining a cotton stature. The color that is initially white changes to brown as the fungus advances in age. One can also observe at the back a yellowish color that is almost turning to orange.
The features can be made more elaborate when observed on brain heart infusion sugar (BHIA) or the Sabouraud dextrose sugar because of their catalytic nature that allows the fungus to grow more efficiently. Temperatures at 37 degrees makes allows for the formation of yeast of yeast cells that are ovoid and narrow-shaped. Var.capsulatum however creates smaller yeasts as compared to those of var. duboisii.
The differentiation of Histoplasma capsulatum from the two genera is best achieved at the conversion of yeast phase at 37 degrees Celsius, which involves the hybridization of nucleic acid as well as specialized exoantigen testing. This also helps in the detection of antigen, which is also offers, an efficient way histoplasmosis diagnosis. It is also important to note that Chrysosporium does not have the ability to produce tuberculate macroconidia and neither does Sepedonium produce microaleuriconidia at any point.
Information on Histoplasma sp is still scant and therefore many of the anti fungal tests have not been widely conducted to test how this fungus works. There are medications that can help in inhibiting the fungus although there is a likelihood of resistance in many instances.