What is histoplasmosis?
Histoplasmosis is a fungal infection caused by the fungus Histoplasma capsulatum, which grows in soil and material contaminated with bat and bird droppings. The fungus has been found in the droppings of domestic birds, such as chickens, starlings and other birds that often nest around the house.
The disease mainly affects the lungs with most patients often showing minimal or no symptoms.
What are the causes and risk factors for histoplasmosis?
Infection occurs by breathing in the spores that become airborne when contaminated soil is disturbed or from visiting a cave inhabited by bats. Humans and animals such as dogs, rats and cats may become infected. The disease is not transmitted from human-to-human or animal-to-human.
Histoplasmosis is a common disease throughout the world, occurring in temperate and tropical climates such as parts of the USA, Africa and Australasia. It has been widely studied in some regions of the USA where it is highly prevalent. The region often referred to as the 'Histo Belt' includes Arkansas, Kentucky, Tennessee, West Virginia as well as other areas of southeastern and central US. In certain areas, up to 90% of the adult population is infected with histoplasmosis.
Infants, young children, and older persons, particularly those with chronic lung disease are at increased risk for severe disease. Sometimes the infection may spread from the lungs to other organs (disseminated histoplasmosis). This is more commonly found in people with immunodeficiency such as those with cancer or acquired immune deficiency syndrome (AIDS).
What are the clinical features of histoplasmosis?
There are several clinical presentations of histoplasmosis.
|Acute pulmonary histoplasmosis (lung disease)
|Chronic pulmonary histoplasmosis
|Progressive disseminated histoplasmosis
|Ocular histoplasmosis syndrome (eye disease)
Cutaneous features of histoplasmosis
Skin lesions of histoplasmosis are varied and can be caused by an immune reaction to an acute pulmonary infection (the lesions do not have the fungus in them) or as a manifestation of disseminated histoplasmosis (the lesions are infected).
- Erythema nodosum presents with painful red plaques on the shins. This is due to an immunologic reaction and organisms cannot be obtained from this site.
- Erythema multiforme is a target or bull's eye type of skin reaction. This too is an immunologic reaction and organisms cannot be obtained from this site.
- Skin lesions appearing as papules, pustules and nodules may be found throughout the body and are caused by the fungus spreading to infect the skin. Biopsy of lesions often shows the fungus.
How is histoplasmosis diagnosed?
Laboratory and radiological studies are performed to confirm the diagnosis of histoplasmosis.
- Sputum cultures — positive yields found in 10–15% of patients with acute pulmonary histoplasmosis and 60% in patients with chronic pulmonary histoplasmosis
- Blood cultures — positive results were seen in 50–90% of patients with progressive disseminated histoplasmosis
- Serologic testing may indicate spreading of the disease
- Chest x-ray and CT scanning
- Tissue biopsy may show characteristic histopathology of histoplasmosis.
What is the treatment for histoplasmosis?
Most people infected with acute pulmonary histoplasmosis that have healthy immune systems and who are not experiencing any symptoms of the disease will recover spontaneously without any treatment. Otherwise healthy patients with mild symptoms need to be monitored. Patients with prolonged or severe pulmonary symptoms may require treatment with antifungal therapy. All cases of chronic pulmonary and disseminated histoplasmosis need to be treated with antifungal medications.
The antifungals ketoconazole and itraconazole are the drugs of choice to treat mildly symptomatic or prolonged acute pulmonary histoplasmosis. They are also useful in treating cutaneous or rheumatologic manifestations of the disease in patients with weakened immune systems.
Amphotericin B is the drug of choice for severe cases of acute pulmonary histoplasmosis, chronic pulmonary histoplasmosis and all forms of disseminated histoplasmosis. Chronic progressive disseminated disease may run a long course that lasts for years with long asymptomatic periods interspersed. Acute progressive disseminated disease may need life long treatment with antifungals to prevent relapses.