Histoplasmosis is a fungal lung infection that is caused by the fungus Histoplasma capsulatum. It occurs when people inhale the mycelia form of the fungus and its spores. Most people who get Histoplasmosis do not actually even present any symptoms, they remain asymptomatic. Histoplasma capsulatum can be found in areas that have a high concentration of bat and bird droppings, caves, birdhouses, river valleys in temperate regions such as the Ohio river valley, and equatorial Africa. There are about a quarter of a million cases of Histoplasmosis in America a year and can also affect other mammals such as pets like cats and dogs, though humans cannot catch it from these animals.
What is Histoplasma capsulatum?
The fungus has two forms, the mycelia form that it is inhaled in and then a yeast form. When the spores and mycelia are inhaled they are carried to the lung alveoli where macrophages (cells from the immune system) will surround and engulf them. Inside the macrophages it changes to its yeast form after between 15 to 18 hours and it is then killed. If there are too many spores and mycelia for the immune system to deal with a form of Histoplasmosis can develop. The more fungus the person inhales the more likely they are to present symptoms of the Histoplasmosis infection.
Symptoms of Histoplasmosis
90% of cases are asymptomatic but some of those patients may reveal scars on the lung if they are given a chest x-ray. Those that show symptoms may include;
- dry cough
- abdominal pains
- weight loss
- chest pain
- loss or reduction of vision
- mouth ulcers
- sometimes, though rarely, death
Types of Histoplasmosis
There are three main types of Histoplasmosis and then within those three types are also further sub categories. The three main types are acute pulmonary histoplasmosis, chronic pulmonary histoplasmosis and progressive disseminated histoplasmosis.
Is Histoplasmosis contagious?
Histoplasmosis is not a fungal infection that is contagious from person to person like some others. In extremely rare circumstances a person receiving a transplanted lung may get the infection because the organ they received was infected. Histoplasmosis is caused by the inhalation of the fungus. An additional point to consider is that histoplasma capsulatum can live in soil for many years, and if that soil is dusty and dry you are more likely to breathe it in.
For many asymptomatic people their own immune system can deal with the infection. Fungal drugs that are used when there are symptoms include itraconazole, amphotericin B, ketoconazole and other azole drugs. Treatment depends on the type of Histoplasmosis the patient has and how severe the infection is. It is also affected by whether the patient has a weakened immune system from another illness or treatment. Sometimes surgery may be needed.
Although nearly all patients with Histoplasmosis recover fully, in rare cases there are complications that can last a lifetime, breathing problems, the need for anti-fungal treatment for the rest of your life, blindness or partial loss of vision to name a few.