What is Histoplasmosis?
Histoplasmosis is an infection caused by the mold Histoplasma capsulatum. The mold is found in the soil in many parts of the world and is spread by inhalation of spores. The spores convert into small budding cells that are engulfed by a type of white blood cell in the lungs. The mold cells reproduce and are spread to other parts of the body through the blood.
The infection may occur in any individual exposed to spores but tends to be more aggressive in people who are exposed to large quantities of the spores (such as those who have traveled to disease-endemic areas) or in individuals whose resistance to infection has been lowered (immunocompromised). Other individuals who are at risk include those who harbor birds or fowl in endemic areas. The infection is often without symptoms.
Other forms include acute histoplasmosis, a self-limited upper respiratory tract infection that frequently occurs in epidemics, progressive disseminated histoplasmosis, which is a multi-organ disease, or a chronic progressive histoplasmosis, a chronic pulmonary (respiratory) disease in which holes (cavities) are developed in the lung tissue.
In individuals with compromised immunity (such as HIV) the symptoms resemble sepsis (presence of microorganisms or their toxic products in the bloodstream) and may cause shock, respiratory complications, liver and kidney failure, and breakdown of skeletal muscle (rhabdomyolysis). Histoplasmosis most often occurs in the central and southern US and in parts of South America, the Far East, and Africa. In severe or untreated cases, the disease may be fatal.
How is it diagnosed?
History: The individual has usually been exposed to an area contaminated with bird or bat droppings. This may occur normally in endemic areas such as the Ohio valley. History may also include coexisting medical conditions that weaken (suppress) the body's normal defense system (immunity). Symptoms may be masked or absent. Symptomatic infection with mild flu-like illness may last one to four days. Moderately severe infections may show symptoms of fever, chest pains, cough, and aching joints, lasting five to fifteen days. The disease may take a more severe form and spread throughout the body. Symptoms include fever, shortness of breath, loss of weight, and mouth ulcers. This illness may last one week to six months.
Physical exam: Mild infections resemble upper respiratory infections. In progressive disease, ulcers of the mucous membranes in the mouth and throat may be present. Palpation (examining with the hands) may reveal enlarged lymph nodes, spleen and/or liver. In the severely immunocompromised, symptoms include fever and multiple organ involvement.
Tests: Diagnosis is confirmed by culture and isolation of the organism. For progressive or chronic infections, blood and bone marrow samples may be used to culture the organism. H. capsulatum can also be obtained from biopsy of infected organs. A more rapid presumptive diagnosis can be made by visualization of the fungus (with special stains) through a microscope. Blood tests are important adjuncts (additional procedures) in the diagnosis of histoplasmosis. The most commonly used are complement fixation and immunodiffusion assays, which detect antibodies to the histoplasmosis fungus.
X-ray findings during acute infection are variable and nonspecific. Moderately severe infections may be recognized as an atypical pneumonia on x-rays. Diagnostic tests may be performed to rule out complications or coexisting conditions. A complete blood count (CBC), hemoglobin or hematocrit can rule out anemia. Liver and kidney function tests can rule out impending failure. In individuals with HIV infection, bacteremia (bacteria in the blood) should be ruled out. A urine antigen test is very helpful in the diagnosis and follow-up of histoplasmosis in individuals with HIV infection. Skin test reactivity may persist for years following infection and is generally not useful for diagnosis without x-ray confirmation.
How is Histoplasmosis treated?
Histoplasmosis is treated with antifungal drugs. Treatment is for two weeks and may need to be extended up to six months for more severe cases. Individuals with HIV-related histoplasmosis may require lifelong suppressive treatment.
- For mild cases, no medicine is usually necessary.
- For more severe cases, antifungal drugs will be prescribed. Some must be given intravenously.
- For AIDS patients with histoplasmosis, chronic therapy with antifungal medication will be necessary.
- You may use non-prescription drugs, such as acetaminophen or aspirin, to relieve pain.
- Stay in bed until fever, pain and shortness of breath disappear for at least 48 hours. Then resume your normal activities gradually. Many people are fatigued and weak after recovery. Don't expect too much too soon.
- Avoid potential high-risk exposures.
What might complicate it?
The infection will be complicated by the presence of medical conditions that impair the immunity. Older individuals with chronic obstructive lung disease often develop more progressive infections that invade other organs.
With treatment, the prognosis for the infection is good. Acute or mild cases will have very good recovery. Progressive or chronic infections may become fatal if left untreated. With treatment, these infections may be controlled with minimal organ damage. Individuals with AIDS require lifelong therapy.
Histoplasmosis resembles a variety of upper respiratory illnesses and may show similar x-ray (radiologic) patterns. The severity of respiratory symptoms and biopsy of infected tissues may differentiate the infecting organism. Chronic cavitary histoplasmosis should be differentiated from pulmonary tuberculosis.
Mycologist, infectious disease specialist, radiologist, internist, neurologist and pulmonary disease specialist.
Seek Medical Attention
- You or a family member has symptoms of histoplasmosis.
- The following occur during treatment:
- Weight loss continues.
- Fever rises to 101°F (38.3° C) orally.
- Diarrhea is uncontrollable.
- Severe headache and stiff neck occur.
Last updated 20 December 2015