Learn About Histoplasmosis
Histoplasmosis is an infection caused by the fungus Histoplasma capsulatum. This infection is very common in the states surrounding the Ohio and Mississippi river valleys.
- Histoplasmosis is the most common of the three major endemic (limited to specific geographical areas) fungal infections of North America.
- Histoplasmosis is usually mild and self-limited in otherwise healthy individuals.
- Patients with deficient immunity tend to develop severe forms of histoplasmosis that can be life threatening.
- Smokers and patients who suffer from emphysema develop a chronic and progressive form of histoplasmosis that requires long courses of treatment.
What is Histoplasmosis?
Histoplasmosis is an infection caused by the fungus Histoplasma capsulatum. Histoplasmosis is the most common of the three major endemic fungal infections of North America. The other two are blastomycosis and coccidioidomycosis. These fungal infections are considered endemic because they follow distinct geographic distributions that are determined by soil and climate conditions optimal for their growth. The vast majority of histoplasmosis occurs in the states surrounding the Ohio and Mississippi river valleys, covering a large area of Midwestern United States. Few cases have been reported outside of this general area in the recent years, including in the northern plains and southeastern United States. Histoplasmosis is also common in Latin America and Africa.
How Histoplasmosis Affects Your Body
Histoplasmosis is acquired by inhaling aerosolized infectious fungal spores of Histoplasma. These spores are usually aerosolized by activities that disturb the earth such as digging, demolishing old buildings, and cutting down old trees. Most infections occur as outbreaks related to large construction projects. Others are related to recreational activities such as spelunking in bat infested caves. Once inhaled, the spores can cause a lung infection (pneumonia), which, if not controlled by a robust immune system, can spread throughout the body and cause disseminated disease, the most severe and life threatening form of histoplasmosis.
Activities and Exposures Linked to the Acquisition of Histoplasmosis
Sites likely to contain Histoplasma or activities likely to cause exposure to Histoplasma include:
- Caves – spelunking
- Chicken coops – cleaning, demolitions and use of bird droppings in gardens
- Bird roost – excavation
- Prison grounds and school yards – cleaning and routine activities
- Decayed wood pile – cutting and transporting the wood
- Dead trees – cutting wood and recreation
- Old buildings – demolition, remodeling, cleaning
How Serious is Histoplasmosis?
Disease manifestation and severity of histoplasmosis depend on three factors; the degree of exposure to the fungus, the immune status of the patient, and the health condition of the patient’s lungs. Most histoplasmosis infections are mild and self-limiting and often asymptomatic as they occur in otherwise healthy individuals. The infections can be severe if the exposure is heavy or the immune system of the infected individual is weak. In these cases histoplasmosis can cause respiratory failure and shock.
Symptoms, Causes, and Risk Factors for Histoplasmosis
Healthy individuals who contract histoplasmosis generally experience few symptoms, and if they become ill, recover quickly on their own. In contrast, histoplasmosis can be life-threatening in patients with weakened immunity, such as those with acquired immune deficiency syndrome (AIDS) and those receiving immunosuppressive medications.
The three common symptomatic forms of histoplasmosis that require antifungal therapy are:
- Acute histoplasmosis
- Chronic cavitary histoplasmosis
- Disseminated histoplasmosis
Other manifestation of histoplasmosis including lung nodules and fibrosing mediastinitis represent sequelae that manifest well after the infection is controlled and the infectious fungus is killed by the immune system. These manifestations require no antifungal therapy.
What Are The Symptoms of Acute Histoplasmosis?
Acute histoplasmosis manifests 2-4 weeks after exposure or earlier if the exposure is heavy. The most common symptoms of acute histoplasmosis are:
- Fever and chills, flu-like illness
- Muscle pain
- Loss of appetite
- Shortness of breath
- Dry cough
- Chest pain
Most symptoms resolve in a few weeks. If the exposure is very heavy, patient can progress to develop respiratory failure, requiring mechanical ventilation and care in an intensive care unit.
What Are The Symptoms of Chronic Histoplasmosis?
Patients with emphysema often develop and indolent and slowly progressive form of histoplasmosis that resembles tuberculosis clinically, except that is not contagious. The most common symptoms of chronic histoplasmosis are:
- Cough that is productive of thick yellow sputum
- Shortness of breath
- Feeling run-down or tired
- Fevers that is low grade and night sweats
- Weight loss
If left untreated, chronic histoplasmosis can progress with enlarging lung cavities, loss of lung function, and overall clinical deterioration.
What Are The Symptoms of Disseminated Histoplasmosis?
Individuals with depressed immunity are not able to control the initial infection with Histoplasma and as a result the infection progresses and spreads outside the lungs and throughout the body, affecting multiple organs and causing the severe illness called disseminated histoplasmosis. The most common symptoms of disseminated histoplasmosis are:
- Fever and chills, flu-like illness
- Shortness of breath– severe leading to respiratory failure
- Drop in blood pressure and shock
- Cough and chest pain
- Enlarged spleen and liver
- Gastrointestinal bleeding
- Ulcerations in the mouth and lip
- Bone marrow failure with decreased white and red blood cells
Disseminated histoplasmosis is life-threatening unless suspected and diagnosed in a timely fashion, ensuring rapid initiation of effective antifungal therapy and supportive intensive care.
What Are Risk Factors for Disseminated Histoplasmosis?
Anyone who lives in an endemic area may develop a mild, self-limited infection with Histoplasma. The fungus usually remains in the body and never causes a problem, but if the immune system becomes depressed, it may become active again. The following may depress the immune system and can lead to active and severe histoplasmosis:
- Recipients of solid organ transplant
- Immunosuppressive medications
- TNF blockers such as infliximab
- Corticosteroids such as prednisone
- Anti-rejection medications such as mycophenolate and azathioprine
- Extremes of age
When to See Your Doctor?
If you live in the Midwestern United States, have been exposed to activities that can cause histoplasmosis, or your immune system is weak and you are manifesting symptoms of respiratory tract infection, you should contact your doctor.
Diagnosing and Treating Histoplasmosis
It is important to get your questions about histoplasmosis answered by a healthcare professional.
What to Expect When You Discuss histoplasmosis with Your Health-care Provider
- If you have signs and symptoms of severe or chronic histoplasmosis
- If you should be treated with antifungal therapy and for how long
- If you should get tested for potential predisposing diseases such as emphysema and HIV infection
How is Acute Histoplasmosis Diagnosed?
Health-care providers diagnose acute histoplasmosis by asking patients questions about potential exposure and compatible symptoms and findings of physical examination. They also order tests to confirm the diagnosis of acute histoplasmosis. These tests include a blood test for Histoplasma antibodies and antigen. The antibody test might be negative if done early after the infection. Antibody tests might be repeated after few weeks later to confirm the diagnosis. The antigen can also be negative if the infection is mild.
How is Chronic Histoplasmosis Diagnosed?
Healthcare providers suspect chronic histoplasmosis in patients with underlying emphysema who develop a chronic infections resembling tuberculosis with source exposure consistent with that of histoplasmosis. A chest x-ray is often done and shows a cavity in the upper lung zones filled with fluid. Histoplasma antibody tests are usually positive and sputum cultures usually grow Histoplasma.
How is Disseminated Histoplasmosis Diagnosed?
Rapid diagnosis of disseminated histoplasmsosis is absolutely essential to ensuring early initiation of effective antifungal therapy and good outcome. Histoplasma antigen and bronchoalveolar lavage done by bronchoscopy are the most effective and widely used methods to secure an accurate and timely diagnosis of disseminated histoplasmosis. These tests are done when disseminated histoplasmosis is suspected in a severely ill patient with depressed immunity and who resides in the endemic area or had a compatible exposure.
How is Acute Histoplasmosis Treated?
Most acute histoplasmosis cases resolve themselves after few weeks of illness. If symptoms are disabling or last beyond 4 weeks antifungal therapy is recommended. The treatment of choice is oral itraconazole given for twelve weeks. Patients with severe acute histoplasmosis leading to respiratory failure are treated initially with intravenous amphotericin B for one to two weeks followed by oral itraconazole given for twelve weeks.
How is Chronic Histoplasmosis Treated?
Chronic histoplasmosis is treated with oral itraconazole for 12 to 18 months until resolution of symptoms and radiographic abnormalities.
How is Disseminated Histoplasmosis Treated?
In addition to critical care therapies with mechanical ventilation and other modalities to support the patient, disseminated histoplasmosis is treated initially with intravenous amphotericin B for two weeks followed by oral itraconazole given for twelve months. In addition the underlying immunosuppression needs to be reversed by using antiretroviral medications in the case of HIV infection and AIDS and stopping the immunosuppressive medications that predisposed the patient to the disseminated infections.
Living with Histoplasmosis
As long as the diagnosis is made and antifungal therapy started in a timely fashion, histoplasmosis can be effectively treated with the currently available therapies.
What to Expect From Histoplasmosis
- Needing to miss school or work for a few weeks because of symptoms
- Needing to have a chest x-ray or chest CT and blood test to diagnose histoplasmosis
- Possible need for bronchoscopy, a procedure performed under sedation by lung doctors (pulmonologists) to directly inspect the bronchi with a flexible camera and collect sample by bronchoalveolar lavage
- Needing to take antifungal therapies for prolonged periods of time
- Repeating chest x-ray and blood test to ensure resolution of the infection of antifungal therapy
Currently available therapies are usually very effective in treating histoplasmosis as long as the diagnosis is made and treatment started in a timely fashion. Patients usually make a good recovery after completing the treatment course and reversing the underlying immune suppression that might have predisposed to the infection such as AIDS or use of immunosuppressing medications.
For more information about the epidemiology and management of histoplasmosis please visit the CDC website at http://www.cdc.gov/fungal/diseases/histoplasmosis/
Questions to Ask Your Doctor about Acute Bronchitis and Bronchiectasis
Suggested Questions for Your Doctor about Histoplasmosis:
- What caused me to have histoplasmosis and do I have any underlying lung disease or immune deficiency that predisposed me to histoplasmosis?
- Could I give this infection to friends and my family members? (The answer is “No.”)
- Do I need to get a chest x-ray or chest CT? (Most of the time, the answer is “Yes.”)
- Will antifungal therapy make me feel better? (Most of the time, the answer is “yes.”)
- Is Histoplasmosis treatable and is the therapy effective? (The answer is usually “Yes”)
- How long will it take to recover from my infection with histoplasmosis? (The answer is most of the acute symptoms of fever and shortness of breath will resolve within weeks of therapy but one might have lingering symptoms of fatigue and chest pains for months after the initial diagnosis and treatment of histoplasmosis)
Chadi A. Hage, MD, FCCP
Date Last Reviewed