Histoplasmosis is a fungal infection. It can occur in people with healthy and suppressed immune systems. In people with healthy immune systems, it usually does not cause noticeable symptoms, although some people experience flu-like symptoms and mild respiratory problems. In people with suppressed immune systems, it can cause more serious problems, including respiratory distress, kidney and liver failure, and brain damage.
Histoplasmosis is caused by the Histoplasma capsulatum. This fungus is predominantly found in the central United States, especially in the Mississippi and Ohio River areas, the Caribbean, and South America. The infection usually begins in the lungs but can spread to other parts of the body and cause a wide range of symptoms, particularly in people with compromised immune systems. People who were infected with H. capsulatum when their immune systems were healthy can develop histoplasmosis years later if their immune systems become compromised.
People can become infected with H. capsulatum upon breathing in soil or dust contaminated with bird droppings that contain the fungus. HIV-positive people with CD4 cells below 150 are at the highest risk of developing either mild or severe histoplasmosis after breathing in the fungus. However, histoplasmosis is not considered to be a common disease among people with AIDS, including those who live in the central United States where H. capsulatum is most common.
What are the symptoms and how is it diagnosed?
Most people who are infected with H. capsulatum do not experience any symptoms of disease. If the infection causes active disease, symptoms can include fever, weight loss, skin lesions, breathing difficulties, chest pain, nonproductive (dry) cough, anemia, and enlargement of the liver, spleen, and lymph nodes. The higher the CD4 cell count, the more likely it is that histoplasmosis will only involve the lungs; the lower the CD4 cell count, the more likely it is that H. capsulatum will cause disease in other parts of the body, including the central nervous system (meningitis). More rarely, people can experience shock and multiple organ failure.
The most effective way to diagnosis this infection is to collect sputum (phlegm), blood, or bone marrow samples. Once these fluids have been collected, a laboratory will attempt to grow the fungus in test tubes or to look for the fungus under a microscope. It is also possible to look for a H. capsulatum antigen—a key fragment of the fungus—in blood and urine samples.
How is it treated?
People with healthy immune systems who are diagnosed with histoplasmosis don't necessarily require treatment, as the symptoms are usually mild and clear up on their own. For people with compromised immune systems, histoplasmosis can be progressive and life threatening and, as a result, often requires treatment.
Treatment depends on the severity of disease. In patients with moderate to severe disease, liposomal amphotericin B (either Ambisome, Abelcet or Amphotec) is given every day through an IV line, usually while staying in a hospital. IV treatment is continued for at least two weeks or until the patient is feeling better.
If the patient has meningitis, the dose of liposomal amphotericin B is usually increased and continued for four to six weeks.
In patients with less severe histoplasmosis, oral itraconazole (Sporanox) may be all that's needed—at a dose of 200 mg three times daily for three days followed by 200 mg twice daily thereafter. The liquid version of Sporanox is preferred because it is better absorbed by the body and has fewer interactions with food.
After histoplasmosis is successfully treated, liposomal amphotericin B is discontinued and Sporanox is started or continued. This is necessary to help prevent the histoplasmosis from recurring. Oral Sporanox is continued for as long as the CD4 count remains below 150—it can be discontinued if the CD4 count remains above this level for at least six months.
A syndrome—called immune reconstitution inflammatory syndrome (IRIS)—where antiretroviral treatment can actually exacerbate the symptoms of an opportunistic infection due to a strengthened immune response, has not been commonly reported with histoplasmosis.
Can it be prevented?
Because H. capsulatum can be found in dirt and soil—particularly in central parts of the United States—it is very difficult to prevent coming into contact with the fungus. Moreover, H. capsulatum can live in a person's body for many months or possibly years before it causes disease, depending on the health of the person's immune system.
If your CD4 cell count is below 150, you should take care when engaging in certain activities—or avoid them altogether—if you live in central parts of the United States or other parts of the world where H. capsulatum is prevalent. For example, it's a good idea to wear a mouth and nose guard/mask if dust is created while working with surface soil, or cleaning chicken coops, disturbing soil beneath bird-roosting sites, or exploring caves.
Because histoplasmosis is more likely to occur in HIV-positive people with compromised immune systems, a good way to help prevent it from occurring is to keep the immune system healthy, such as by using antiretroviral drugs, reducing stress, eating right, and getting plenty of rest. Sporanox, at a dose of 200 mg a day, is a possible preventive treatment for HIV-positive people with fewer than 150 CD4 cells who are at high risk for H. capsulatum infection because of their work or residence in a high-prevalence area—Sporanox can be discontinued when the person's CD4 count remains above 150 for at least six months.
Are there any experimental treatments?
If clinical trials for HIV-positive patients with histoplasmosis are being conducted, they will most likely be listed on ClinicalTrials.gov, a site run by the U.S. National Institutes of Health. The site has information about all HIV-related clinical studies in the United States. For more info, you can call their toll-free number at 1-800-HIV-0440 (1-800-448-0440) or email firstname.lastname@example.org.
Last Revised: January 18, 2016