Histoplasmosis

Histoplasmosis is a disease caused by the fungus Histoplasma capsulatum.  Its symptoms vary greatly, but the disease primarily affects the lungs.  When other organs are affected, it is called disseminated histoplasmosis, which can be fatal if untreated.

Positive histoplasmin skin tests occur in as many as 80% of the people living in areas where H. capsulatum is common, such as the eastern and central U.S. Infants, young children, and older persons (in particular those with chronic lung disease) are at increased risk for severe disease.  Disseminated disease is more frequently seen in people with cancer or AIDS.

Causes and Development; Contributing Risk Factors

The H. capsulatum fungus grows in soil and material contaminated with bat or bird droppings, and is especially prevalent in the American mid-west, the Caribbean, and Central and South America.  Spores become airborne when contaminated soil is disturbed, and breathing the spores causes infection.  The disease is not infectious.

After the spores have been inhaled into the body, they develop into their pathogenic yeast form.  They can reproduce and spread through the blood, usually accumulating in the lungs.  A person with a strong immune system will develop a nearly complete lifelong immunity within two weeks of exposure.  The main factors that determine the course of the infection are the immune system of the infected person and the extent of exposure.  For this reason, people who are HIV positive are particularly at risk of a severe case of histoplasmosis if infected.

Past infection results in partial protection against ill effects if reinfected.

Signs and Symptoms

Most of those affected have no apparent ill effects, but if symptoms occur, they will start within 3 to 17 days of exposure; the average is 10 days.  The acute respiratory disease is characterized by respiratory symptoms, a general ill feeling, fever, chest pains, and a dry or nonproductive cough.  Distinct patterns may be seen on a chest X-ray.  Chronic lung disease resembles tuberculosis and can worsen over months or years.  The disseminated form is fatal unless treated.

Disseminated histoplasmosis usually affects an immunosuppressed person and spreads outside the lungs to other body parts.  When histoplasmosis spreads, it can affect bone marrow, the liver, spleen, lymph nodes, mouth, intestines, brain, and the adrenal glands.  Disseminated histoplasmosis can be fatal, but is extremely rare.  Symptoms of disseminated histoplasmosis include:

• high fever
• weight loss
• respiratory problems
• myelosuppression (such as anemia)
• hemosepsis
• gastrointestinal bleeding from focal, oral, or mucosal ulcers
• central nervous system dysfunction; typically an infection in the form of meningitis
• granulomas; masses that appear in the lymph nodes.

In addition, long-term smokers who have emphysema are more likely to acquire histoplasmosis than others, and often develop a chronic lung complication if infected.  When persons with emphysema inhale the fungal spore, they develop "chronic pulmonary histoplasmosis".  Symptoms of chronic pulmonary histoplasmosis include:

• a severe cough that can produce green or yellow phlegm
• chest pain
• weight loss
• night sweats
• fatigue
• loss of lung parenchyma

In most cases, symptoms last for several months and, if left untreated, can result in either permanently damaged lungs or even death.

There are instances when "acute self-limited histoplasmosis" can be more serious.  An infected person might experience muscle pain, joint pain, or irritating red lumps on the arms or legs.  If the person has had heavy exposure to the fungal spore, they may also develop bronchopneumonia or enlargement of the lymph glands within the lungs.  Also, some people develop an inflammation of the heart lining, a condition that is called "pericarditis".  If a person experiences either pericarditis or joint pain, there are medications that can be prescribed to reduce inflammation.

Treatment and Prevention

Antifungal medications are used to treat severe cases of acute histoplasmosis and all cases of chronic and disseminated disease.

When people have disseminated histoplasmosis, or have a mild infection but either have an underlying disease or are immunosuppressed, medication is necessary.  Typically, in cases that are not too severe, a doctor will prescribe Itraconozole, taken orally.  The length of time a person must take Itraconozole varies according to the severity of the infection.  It is usually effective and tolerable, although it can have negative side-effects when taken with other types of medication.

In cases that are more severe, a doctor might prescribe Amphotericin B, generally for 4-12 weeks.  In 90% of cases where Amphotericin B is used, the histoplasmosis infection is destroyed.  It is administered intravenously, something that many consider a drawback.  Many patients with immunosuppressed conditions, particularly people who are HIV-positive, must continue taking Amphotericin B for life in order to prevent a recurrence.  Itraconozole can also be used to prevent relapse.

Prognosis; Complications

Mild disease usually resolves without treatment.

While histoplasmosis is generally a mild infection that goes away on its own (the "self-limiting" form of the disease), it can progress into a dangerous and even fatal complication, particularly in individuals who have impaired immune systems.  Histoplasmosis can spread from the lungs to other body parts in cases where the infected person has AIDS, has leukemia, has recently had an organ transplantation, or has been using corticosteroids.  It can be particularly severe with HIV-infected persons.  In all of these cases, histoplasmosis can develop into a fatal condition unless treated.