Histoplasmosis (also known as reticuloendothelial zygomycosis) is a systemic infectious disease. Systemic means that the whole body can be affected, not just specific organs.
Histoplasmosis is caused by the fungus Histoplasma capsulatum. The fungus is dimorphic, i.e. it can exist in two forms: As a yeast fungus and as a mycelium (filamentous fungal mass).
Histoplasmosis is triggered when spores of the mycelial form of the fungus enter the alveoli through the air we breathe. The immune system recognizes the spores as invaders and begins to fight them with macrophages ("giant phagocytes"). Macrophages ingest the fungal spores, but the spores then develop into the yeast form within 15 to 18 hours.
Normally, the body can successfully fight histoplasmosis because the cells of the immune system destroy the traces of yeast. However, if the load of Histoplasma capsulatum is particularly high, the body's defenses may not be sufficient. As a result, symptomatic histoplasmosis develops.
The causative fungus Histoplasma capsulatum was first described by Samuel Darling in 1906. In 1932, Katharine Dodd and Edna Tompkins made the first diagnosis of histoplasmosis in an infant. Since then, histoplasmosis has been diagnosed all over the world.
The disease is particularly common in valleys with high temperatures and in Central Africa. A major outbreak usually occurs when a group of people travel to certain regions and become infected.
Most infections occur by inhaling the spores in places where the fungus grows in large numbers. Such places are, for example
- Caves where bats live,
- bird cages,
- chicken coops and
- all places where large quantities of bird dung accumulate.
Unfortunately, the spores can remain in the soil for years. When the soil breaks down into dust, the pathogens are particularly easy to pick up through the air.
Histoplasmosis can also affect other mammals such as dogs or cats. Animals and humans affected by histoplasmosis mainly show symptoms similar to pneumonia.
The disease is not transmissible, neither from animals to humans nor from humans to humans. However, a rare exception concerns transplanted organs, which can carry the fungal infection.
Histoplasmosis can be divided into various forms. These include, among others
- acute pulmonary histoplasmosis: can proceed with or without symptoms (symptomatic or asymptomatic) which can be symptomatic and asymptomatic,
- chronic pulmonary histoplasmosis: Causes chronic lung symptoms,
- ocular histoplasmosis syndrome: affects the ability to see,
- progressive disseminated histoplasmosis: causes injuries and inflammation in the mouth and throat,
- subacute progressive disseminated histoplasmosis: has serious effects on the central nervous system, the brain or the skin.
Around 90 percent of infections with Histoplasma capsulatum do not cause any symptoms. Sometimes small scars can be seen on X-rays of the lungs in asymptomatic patients.
Symptomatic patients with histoplasmosis often develop
- dry cough,
- chills,
- fever,
- weakness,
- sweating attacks and
- severe stomach pain
Symptoms begin to appear approximately 3 to 14 days after contact with the fungus.
If the histoplasmosis progresses further, symptoms may include
and vision problems.
One sign of an exacerbation of histoplasmosis is spotty areas, which can be seen on x-rays. They usually appear in the lower part of the lungs.

Histoplasmosis as spots in the lungs, visible in the CT image © DOUGLAS | AdobeStock
Other symptoms are mainly experienced by people with a weakened immune system:
- Encephalopathy,
- headaches,
- injuries in the mouth and
- cramps
In rare cases, histoplasmosis can be life-threatening.
The reliable diagnosis of histoplasmosis can be difficult. Many bacterial and fungal diseases have similar symptoms to histoplasmosis. These include, for example
In fact, before 1932, many patients with histoplasmosis were misdiagnosed with tuberculosis. Even today, accurate diagnosis remains a challenge. If the patient has visited areas at risk or the places described above, the doctor must be told! This can be decisive evidence for the correct diagnosis.
Growing a fungal culture
One method for the reliable detection of Histoplasma capsulatum is to create a fungal culture. A previously taken saliva, blood or tissue sample is applied to a culture medium. If the fungus grows, the diagnosis is confirmed.
However, in chronic histoplasmosis, the cultures only develop in around 60 percent of cases. In acute cases, they only develop in 15 percent of cases.
In addition, it can take 2 to 12 weeks for the cultures to develop. This time is lost for targeted treatment. However, acute progressive disseminated histoplasmosis can lead to death within a few weeks.
For this reason , appropriate treatment must be administered immediately on suspicion - without waiting for the results.
Serological tests
There are a number of serological tests. These tests look for antigens or antibodies in the blood, urine or spinal cord. These are formed when the immune system has had contact with Histoplasma capsulatum.
These tests can provide largely accurate results. They are particularly successful in chronic, symptomatic and progressive histoplasmosis (75 to 90 percent). However, it takes up to three weeks to detect only a small number of acute cases (15 percent). In addition, the test procedures can be falsified by other pathogens.
However, in places with an increased incidence of histoplasmosis, these tests can be a sufficient indication. Early treatment can then begin.
Further diagnostic procedures
There are other procedures that may help the doctor to diagnose histoplasmosis. These include
- A count of the blood cells in a sample,
- X-rays of the lungs,
- computed tomography(CT),
- echocardiogram and
- tests to determine the level of alkaline phosphatase in the blood - this is elevated in those affected.
A surgeon may need to be consulted to perform a biopsy.
Specialists in infectious diseases and pulmonary medicine usuallyspecialize in the treatment of histoplasmosis.
Antifungal treatment is not an option for patients with
- asymptomatic histoplasmosis or
- acute local inflammation.
Patients survive histoplasmosis on their own within a few weeks.
If the symptoms persist for a month or longer, treatment with
- Itraconazole,
- ketoconazole or
- amphotericin B
may be successful.
Treatment with itraconazole or amphotericin B is probably necessary if
- the central nervous system is affected
- the patient is suffering from other diseases, or
- his immune system is suppressed and he is suffering from severe advanced disseminated histoplasmosis.
The duration of treatment and the dosages depend on the patient.
Some new azole-added drugs may be successful in cases that do not respond to any other therapy.
In some cases of histoplasmosis, surgery may be necessary. Surgical techniques include
- pericardiocentesis or
- pericardial window surgery.
Both techniques have been developed to drain fluid that is pressing on the heart.
Also
- an ectomy of lesions in the lungs,
- an operation on lymph nodes or
- of the heart
may also be necessary if the histoplasmosis has had a corresponding effect on the body.
Around 90 percent of people with histoplasmosis recover completely without further complications. In some cases, small scarring appears in the lungs.
As the severity of histoplasmosis increases, so does the risk of complications.
- Pleural effusions or
- pericarditis (inflammation of the pericardium)
occur in 5 percent of acute, symptomatic histoplasmosis. A further 5 percent of those affected suffer rheumatological problems such as
- arthritis,
- erythema nodosum or
- coccardial erythema.
Around 90 percent of patients with chronic pulmonary histoplasmosis develop
Some patients suffer inflammation of the adrenal glands. This may be associated with Cushing's syndrome (increased cortisol levels due to obesity).
Other patients develop ocular histoplasmosis syndrome. In this case, the fungus enters the blood vessels of the retina via the lungs. This is followed by inflammation of the retina, which can subsequently lead to scarring. This can result in visual impairment or even partial blindness.
Patients with acute progressive disseminated histoplasmosis can develop problems with the central nervous system. This can lead to
lead to heart problems.
People with this form of histoplasmosis require immediate treatment. Otherwise, histoplasmosis leads to death within a few weeks.
Histoplasma capsulatum can be found anywhere where a lot of bird droppings accumulate. Construction pits are also a breeding ground for the fungus. As the spores are very resistant, they remain in the soil when it disintegrates into dust.
People with a weak immune system have an increased risk of contracting histoplasmosis. They should avoid such danger spots.
There is no vaccine for histoplasmosis. However, most people produce sufficient antibodies against the infection to regenerate. However, this is not sufficient protection against re-infection with histoplasmosis.
Around 90 percent of those affected do not develop any symptoms. A further 5 to 7 percent show symptoms but recover completely.
Only a few cases of histoplasmosis progress to such an extent that they have long-term or even life-threatening consequences. In many cases, those affected by such serious histoplasmosis are already pre-disposed. For example, they have a weakened immune system.
Those affected by chronic pulmonary histoplasmosis can suffer from impaired lung function.
Progressive desseminated histoplasmosis can lead to death within a few weeks if left untreated. However, even with appropriate treatment of this histoplasmosis, relapses can occur and long-term treatment may be necessary.