Histoplasmosis

Histoplasmosis is a lung infection caused by breathing in tiny fungal spores, often found in soil contaminated with bird or bat droppings. Most people who breathe in these spores never get sick or have very mild symptoms that clear up on their own. However, it can cause serious illness, especially in those with weakened immune systems.

What is Histoplasmosis?

Histoplasmosis is a lung infection caused by a fungus called Histoplasma capsulatum. This fungus lives in soil, especially where there are large amounts of bird or bat droppings. People get histoplasmosis by breathing in microscopic spores (tiny reproductive particles) of the fungus, which then settle in the lungs and can cause illness.

The Histoplasma fungus is common in certain parts of the world, particularly in the central and eastern United States, especially in the Ohio and Mississippi River valleys. It can also be found in parts of Central and South America, Africa, Asia, and Australia. When soil containing the fungus is disturbed, such as during excavation, demolition, or cleaning chicken coops, the spores become airborne. Breathing in these spores is the only way to get the infection. It is not contagious and cannot spread from person to person. Once inhaled, the spores travel to the lungs. In most healthy people, their immune system (the body's defense against infection) quickly fights off the fungus, and they may not even know they were exposed. For others, especially those with weakened immune systems, the infection can become more severe.

Symptoms

Many people infected with histoplasmosis have no symptoms or very mild, flu-like symptoms that go away on their own without treatment. When symptoms do appear, they usually start 3 to 17 days after exposure to the fungus. The type and severity of symptoms depend on how many spores were inhaled and the strength of a person's immune system.

Acute histoplasmosis is the most common form and often causes flu-like symptoms. These can include fever, chills, headache, muscle aches, cough, and chest pain. Fatigue (extreme tiredness) is also common. These symptoms typically resolve within a few weeks to a few months. Chronic histoplasmosis is a long-lasting form that mainly affects the lungs. It often resembles tuberculosis and can cause symptoms like cough, shortness of breath, fever, night sweats, and weight loss. This form usually affects people with underlying lung diseases, such as emphysema. Disseminated histoplasmosis is the most severe form. It occurs when the infection spreads from the lungs to other parts of the body, such as the skin, liver, spleen, bone marrow, and central nervous system (brain and spinal cord). This form is rare but can be life-threatening if not treated. Symptoms vary widely depending on which organs are affected but can include skin lesions, mouth sores, enlarged liver or spleen, and blood abnormalities. It primarily affects infants, young children, and people with severely weakened immune systems.

Causes & risk factors

Histoplasmosis is caused by inhaling spores from the Histoplasma capsulatum fungus, which thrives in soil enriched by bird or bat droppings. While anyone can be exposed, certain factors increase the risk of developing severe illness. These include having a weakened immune system, being very young or very old, or having existing lung conditions.

The primary cause is exposure to airborne Histoplasma spores. Activities that disturb contaminated soil can release these spores into the air. Examples include farming, construction, demolition, landscaping, caving, cleaning or renovating old buildings, and exploring areas with large bird or bat populations. The most significant risk factor for developing severe histoplasmosis is a weakened immune system. Conditions that suppress the immune system include HIV/AIDS, organ transplantation, cancer (especially leukemia or lymphoma), and certain medications like corticosteroids or TNF-alpha inhibitors (used for autoimmune diseases). Infants and young children, whose immune systems are still developing, are also at higher risk for severe or disseminated disease. Similarly, older adults, particularly those over 55, may have a less robust immune response, making them more vulnerable to serious infection. People with chronic lung diseases, such as emphysema or chronic obstructive pulmonary disease (COPD), are more likely to develop chronic pulmonary histoplasmosis.

How it's diagnosed

Diagnosing histoplasmosis can be challenging because its symptoms often mimic other conditions, like the flu or tuberculosis. Doctors typically use a combination of tests, including blood or urine tests to detect fungal antigens (substances released by the fungus) or antibodies (proteins made by the immune system), and imaging tests like chest X-rays or CT scans to look for lung changes.

A doctor will start by asking about your symptoms, medical history, and any potential exposure to areas where Histoplasma is common. They will also perform a physical exam. Specific laboratory tests are crucial for diagnosis. Antigen tests detect parts of the fungus in blood or urine samples. These tests are particularly useful for diagnosing severe or disseminated histoplasmosis and for monitoring treatment effectiveness. Antibody tests look for your body's immune response to the fungus, indicating past or present infection. In some cases, a doctor may need to collect a tissue sample (biopsy) from an affected area, such as the lungs, skin, or bone marrow, to grow the fungus in a lab (culture) or examine it under a microscope. Sputum (mucus coughed up from the lungs) cultures can also be performed. Imaging tests, such as a chest X-ray or computed tomography (CT) scan, can reveal characteristic patterns in the lungs, like nodules or infiltrates, which suggest a fungal infection.

Treatment options

Most mild cases of histoplasmosis do not require specific treatment and resolve on their own. However, moderate to severe infections, or those affecting people with weakened immune systems, usually require antifungal medications. The type and duration of treatment depend on the severity and form of the infection, and it can range from a few weeks to over a year.

For mild cases in healthy individuals, doctors often recommend rest and symptom management, similar to treating a common cold or flu. The body's immune system is usually capable of clearing the infection without medication. When treatment is necessary, antifungal medications are used. The most common oral antifungal drug is itraconazole, which is often prescribed for several months, sometimes up to a year or more, depending on the infection's severity and location. Itraconazole works by stopping the fungus from growing. For severe cases, especially disseminated histoplasmosis or infections in people with severely weakened immune systems, intravenous (IV) amphotericin B may be used first. This powerful medication is given directly into a vein and works quickly to fight the infection. After initial treatment with amphotericin B, patients often switch to oral itraconazole for a longer period to ensure the infection is fully cleared and to prevent relapse. Your doctor will determine the best treatment plan for your specific situation.

Recovery & outlook

The outlook for histoplasmosis is generally good, especially for healthy individuals with mild infections who often recover completely without treatment. For those requiring medication, recovery can take several months, and it's crucial to complete the full course of antifungal drugs to prevent relapse. The prognosis is less favorable for severe disseminated cases, particularly in people with very weakened immune systems, but treatment significantly improves outcomes.

Most healthy people who develop acute histoplasmosis recover fully within a few weeks to a few months. Even without specific antifungal treatment, their immune system effectively clears the fungus. However, some people may experience lingering fatigue for a period after the acute symptoms resolve. For chronic pulmonary histoplasmosis, treatment with antifungal medications can significantly improve symptoms and lung function. However, some lung damage may be permanent, especially in individuals with pre-existing lung conditions. Regular follow-up with a doctor is important to monitor recovery and manage any long-term effects. Disseminated histoplasmosis is the most serious form, but with prompt and appropriate antifungal treatment, many people recover. Without treatment, severe disseminated histoplasmosis can be fatal, especially in infants and those with severely compromised immune systems. It is vital to adhere strictly to the prescribed medication regimen and attend all follow-up appointments to ensure the infection is fully eradicated and to prevent recurrence.

When to see a doctor

You should see a doctor if you develop flu-like symptoms, such as fever, cough, or muscle aches, especially if you live in or have recently traveled to an area where histoplasmosis is common and have been exposed to disturbed soil or bird/bat droppings. Seek immediate medical attention if you have a weakened immune system and develop any symptoms, or if symptoms worsen rapidly.

It is particularly important to seek medical advice if your symptoms are severe, do not improve within a few weeks, or if you experience shortness of breath, chest pain, or unexplained weight loss. These could be signs of a more serious form of histoplasmosis. If you have a known weakened immune system due to conditions like HIV/AIDS, cancer, or organ transplant, or if you are taking immunosuppressant medications, any new or worsening symptoms warrant immediate medical evaluation. In these individuals, histoplasmosis can progress rapidly and become life-threatening. Always consult a healthcare professional for diagnosis and treatment. They can determine if your symptoms are due to histoplasmosis or another condition and recommend the appropriate course of action. Do not attempt to self-diagnose or self-treat.

Frequently asked questions

How do people get histoplasmosis?

People get histoplasmosis by breathing in tiny spores from the Histoplasma capsulatum fungus. This fungus lives in soil, particularly where there are large amounts of bird or bat droppings. When this contaminated soil is disturbed, the spores become airborne and can be inhaled.

Is histoplasmosis contagious?

No, histoplasmosis is not contagious. It cannot spread from person to person, nor can it be transmitted from animals to people. Infection only occurs by inhaling the fungal spores directly from the environment.

Who is most at risk for severe histoplasmosis?

People with weakened immune systems are most at risk for severe histoplasmosis. This includes individuals with HIV/AIDS, cancer, organ transplant recipients, those taking immunosuppressant medications, infants, young children, and older adults (especially over 55).

How long does histoplasmosis last?

For healthy individuals, mild histoplasmosis symptoms usually clear up within a few weeks to a few months without specific treatment. For more severe or chronic forms, treatment with antifungal medications can last from several months to over a year.

Can histoplasmosis come back after treatment?

Yes, histoplasmosis can sometimes recur, especially in people with weakened immune systems or if the full course of antifungal medication is not completed. Doctors often recommend long-term follow-up and sometimes continued medication to prevent relapse in high-risk individuals.

Where is histoplasmosis most common?

Histoplasmosis is most common in the central and eastern United States, particularly in the Ohio and Mississippi River valleys. It is also found in parts of Central and South America, Africa, Asia, and Australia, wherever the Histoplasma fungus thrives in suitable soil conditions.

Sources

• MedlinePlus — Histoplasmosis
• Mayo Clinic — Histoplasmosis
• Cochrane Library — Histoplasmosis