Histoplasmosis
Basic Information
Histoplasmosis is a fungal infection that affects the lungs and respiratory system. A person can acquire histoplasmosis if they inhale air which contains the spores of the fungus Histoplasma capsulatum. This fungus is typically found in soil that has been contaminated by bird or bat droppings, but it can also be encountered in chicken coops, barns, belfries, caves or attics where birds or bats may have lived and roosted. In most cases, exposure occurs when an area containing Histoplasma capsulatum is disturbed in some way, sending the fungal spores into the air. Possible instances when this can happen include gardening, excavating sites, remodeling old homes, cleaning chicken coops, or exploring caves. While histoplasmosis can not be spread from person to person, it commonly occurs as a group outbreak if a number of people are simultaneously exposed to a Histoplasma fungus-contaminated area. In some cases, winds can carry the airborne fungal spores several miles, causing people who were never near the contaminated area to become infected. The Histoplasma capsulatum fungus is especially prevalent in the American mid-west, the Caribbean, and Central and South America.
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.
Symptoms
In episodes of histoplasmosis where the infected person has a healthy immune system, there are often no symptoms. This is referred to as "acute self-limited histoplasmosis". If the person does develop symptoms, they are most often flu-like in nature, such as fever, cough, fatigue and chest pain. Symptoms usually appear ten days after exposure, and subside without treatment after a few weeks. When symptoms disappear, it is unusual for there to be long-term ill effects.
It is important to realize that the severity of the symptoms depends on the duration of exposure and the immune system of the person. A person climbing around for a long time in a Histoplasma capsulatum-contaminated cave will develop a much worse case than a person who walked quickly through a similarly contaminated field. Also, someone with AIDS would develop a much more severe illness than a healthy person, even if both persons were exposed to the fungal spores for the same amount of time.
While histoplasmosis is generally a mild infection that goes away on its own (why it is called "self-limiting"), 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.
"Disseminated histoplasmosis" refers to histoplasmosis when it affects an immunosuppressed person and spreads outside the lungs to other body parts. When histoplasmosis spreads, it can affect bone marrow, the liver, the spleen, the lymph nodes, the mouth, the intestines, the 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 disfunction; typically an infection in the form of meningitis
- granulomas; masses that appear in the lymph nodes
Also, 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
- nightsweats
- 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 death.
Diagnosis/Treatment
When an infected person goes to the doctor, the doctor will ask about the person's symptoms. It is critically important for the doctor to know if the person has recently been in an area where the fungus is endemic. Once the doctor suspects histoplasmosis, there are a number of tests that can be used to confirm the diagnosis.
Even though it is not conclusive, a doctor may employ an X-ray examination. In most cases the fungal germs cause abnormal growths that can show up on a chest X-ray.
A more precise diagnostic method would be a biopsy during which specimens from the bone marrow, lung, lymph nodes, and liver are taken and tested. A diagnosis can also be made by identifying the fungus in either a blood, urine or phlegm sample.
In cases where the person is HIV-positive and it is suspected that they have disseminated histoplasmosis, bone marrow biopsies, peripheral blood smears, lymph node biopsies, bronchoalveolar lavage fluid samples, radioimmunoassays, transbronchial biopsies, and biopsies of cutaneous lesions are all effective as diagnostic tools. Evaluation of the bone marrow is typically the most conclusive test for diagnosing disseminated histoplasmosis.
Blood and urine tests can be used to determine whether or not the body is producing the antibodies and antigens that would be present in a person combating histoplasmosis. In most cases, however, these kinds of tests are neither sensitive enough nor specific enough to be used for a conclusive diagnosis.
There is no treatment for episodes of acute self-limiting histoplasmosis when the person has a normal immune system. In almost all cases the symptoms will subside on their own within a few weeks and there are not usually any long term ill effects. However, 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.
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. It is taken orally. The length of time a person has to 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, the doctor will prescribe Amphotericin B. Most patients take Amphotericin B for four to twelve weeks, and in ninety percent of the 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. Recurrences of disseminated histoplasmosis are rare in persons who do not have any underlying diseases once they go through one cycle of Amphotericin B treatment. A major problem with regard to the use of Amphotericin B is the possible side effects involved. These include nausea, loss of appetite, chills, fever, muscle aches, possible kidney damage, anemia, and fatigue.
Because the spores are airborne, prevention can be difficult. It is important to avoid areas where there is a prevalence of bird or bat droppings. An important thing to consider is that bird droppings, unlike bat droppings, do not carry the fungus. With bird droppings, the fungus develops if the waste is allowed to decompose over time. Thus, it might be a good idea to frequently clean out spaces such as barns and chicken coops in order to reduce the possibility of exposure. If a person must work near a potentially contaminated site, they should wear an air filtration mask and soak the dirt thoroughly with water before disturbing it. They should also warn others to avoid the site while work is being done there. At the same time, it is important to be cautious when exploring caves. A critical thing to consider is that people with underlying immune disorders, particularly people who are HIV-positive, should avoid these kinds of activities in areas where the fungus is endemic at all costs.