Histoplasmosis

Definition
Histoplasmosis is an infection caused by a fungus called Histoplasma capsulatum. Histoplasmosis is also known as Ohio Valley disease, Central Mississippi Valley disease, Appalachian Mountain disease and Darling's disease. The infection usually affects the lungs, but sometimes it spreads to other parts of the body.

Causes/associated factors
The histoplasma fungus thrives in soil and decaying or other material contaminated by bird or bat droppings. Contaminated areas may include caves, chicken coops, barns, pigeon lofts, old buildings, attics and basements, as well as moist areas under bridges and near streams.
In the United States, histoplasmosis is most common in the Central and Eastern states, particularly along the Ohio, Mississippi, Tennessee, Missouri and St. Lawrence River valleys, as well as the Rio Grande. Often, people living in these areas have had the infection. If you contract histoplasmosis, you may develop partial immunity to the infection. Partial immunity makes you less susceptible to future infections, as well as partially protected from the ill effects of the infection if you contract it a second time.

Certain occupations and hobbies make exposure to the fungus more likely, including:

construction or demolition work
cave exploration
roofing and chimney cleaning
heating and air conditioning installation or service
restoration of old or abandoned buildings
pest control
microbiology lab activities
bridge inspection or painting
farming or gardening

Transmission
You can contract histoplasmosis by inhaling dirt or dust that contains fungus spores. (The spores are released into the air when contaminated soil is disturbed by such factors as wind or construction activities.) The infection does not spread through person-to-person or animal contact.
The incubation period (time from exposure until symptoms appear) ranges from three to 21 days, but symptoms typically appear within 14 days. The incubation period tends to be shorter if you're exposed to a large quantity of spores, and it may be longer if you've developed partial immunity through a previous infection.


Signs/symptoms
Most people with mild cases of histoplasmosis don't have any symptoms. For others, symptoms are so mild that a visit to the doctor is not necessary. How ill you become may vary depending on how many spores you inhaled, your age and your susceptibility to this disease.
Histoplasmosis occurs in three forms:

Acute pulmonary histoplasmosis (APH)
A primary acute infection involves the lungs and may resemble the flu. This type of histoplasmosis typically clears up within one to two weeks, but a prolonged illness may last up to four weeks. Symptoms are usually vague and may include:

fever
nonproductive cough (no sputum)
a general feeling of discomfort
chills
muscle and/or joint aches
headache
chest pain that's usually not affected by coughing or deep breathing
skin rash
in severe cases, shortness of breath
Chronic pulmonary histoplasmosis (CPH)
A chronic lung infection is most common in men and those who have a chronic lung disease, such as emphysema. This type of histoplasmosis develops over the course of months or years and resembles mild tuberculosis. Symptoms may include:

fever
night sweats
a general feeling of discomfort
hemoptysis (coughing up blood)
cough that produces sputum
shortness of breath that progressively worsens
weight loss
Progressive disseminated histoplasmosis (PDH)
When histoplasmosis spreads to various organs, it's known as a disseminated infection. People with weak immune systems who are exposed to the histoplasma fungus -- such as people who have AIDS or cancer, those undergoing chemotherapy or long-term steroid therapy, or those taking drugs that suppress the immune system -- have a higher risk of developing disseminated histoplasmosis. It's also more likely to develop in children younger than age 1 and adult males in their 60s and 70s. If left untreated, a disseminated infection can be fatal.

Symptoms may include:

fever
chills
a general feeling of discomfort
weight loss
swollen lymph nodes
enlarged liver and spleen
sores in the mouth
gastrointestinal ulcers (sores)
anemia (a condition marked by a decreased level of red blood cells or hemoglobin, a protein that contains iron)
low white blood cell count (the blood cells that fight infection)
low platelet count (the cells that help blood to clot)

Diagnosis
Your doctor will do a physical exam and will also ask about your medical history, including possible exposure to the histoplasma fungus. You may need a chest X-ray and skin tests. Your doctor may also take swabs from any mouth sores and samples of blood, urine and sputum for lab analysis. If the diagnosis still isn't certain, your doctor may recommend a biopsy (obtain a tissue sample for further examination) of your liver, bone marrow, cerebrospinal fluid, lymph nodes, lungs or other involved areas.


Treatment
Mild cases of histoplasmosis typically resolve without treatment. Your doctor will prescribe an antifungal medication (and sometimes hospitalization) if you have severe symptoms or develop a chronic or disseminated infection. Examples of antifungal medications for the treatment of histoplasmosis include amphotericin B, itraconazole and and fluconazole. These medications can interact with several other medications, including those available without a prescription. Discuss all medications you take with your doctor.

Complications
Serious or prolonged cases of histoplasmosis may lead to various complications. During the acute infection, for example, the lymph nodes in the chest may become enlarged and cause pressure on surrounding organs. This can result in:
obstruction of the trachea (the windpipe), bronchi (the tubes that connect the trachea to the lungs) or esophagus (the tube that connects the throat and stomach)
pericarditis (inflammation of the membrane surrounding the heart)
superior vena cava syndrome (obstruction of blood return to the heart)
If the infection spreads to other organs, it may lead to:

heart valve damage
meningitis (inflammation of the membranes surrounding the brain or spinal cord)
damage to the adrenal glands (the glands that maintain normal levels of hormones in the blood)
bleeding from ulcers in the gastrointestinal tract
sores on the mucous membranes of the mouth, pharynx (the passageway for air from the nasal cavity to the larynx or voice box and food from the mouth to the esophagus), larynx (voice box) or lower gastrointestinal tract
Rarely, young adults who have been exposed to histoplasmosis but have no history of symptoms may develop vision loss. This type of histoplasmosis is believed to be caused when the fungal spores spread from the lungs to the eye.


Pregnancy-specific information
If you develop histoplasmosis during pregnancy, there appear to be no harmful effects for your baby. Severe infections during pregnancy have been successfully treated with antifungal medication.

Senior-specific information
Again, the risk of developing a disseminated infection is higher for men in their 60s and 70s.

Prevention
To prevent histoplasmosis, stay away from areas that are likely to have bird or bat droppings. Decrease your risk of inhaling fungal spores by spraying a mist of water over possibly contaminated areas before disturbing them. Additional dust suppression techniques are often used in excavation areas, such as air filtration systems in construction equipment. Wear a face mask, gloves and disposable clothing if you'll be exposed to potentially contaminated soil or dust. For certain people who have AIDS, antifungal medication may be recommended to prevent infection.