Histoplasmosis is a severe disease of the lungs caused by a fungus, Histoplasma capsulatum. Symptoms resemble the flu. This disease is also known as Darling’s disease, named after American physician Samuel Taylor Darling. Other names for this disease are Ohio Valley disease, Central Mississippi River Valley disease, Appalachian Mountain disease and Histoplasma capsulatum infection.
Young children, infants and the elderly are most likely to develop more sever symptoms. People who have a weakened immune system due to leukemia, chemotherapy, AIDS or steroid therapy are more likely to develop disseminated or chronic histoplasmosis. The fungus spores are in soil that has been infested or polluted with bird or bat droppings.
People who are exposed to soil have a greater chance of getting this disease. Infection occurs when the spores are inhaled or ingested.
Histoplasmosis is a spectrum illness ranging from mild to life-threatening. Symptoms of the disease, when they appear, develop three to seventeen days after exposure to the fungus. There are four common types of histoplasmosis: asymptomatic primary histoplasmosis, acute symptomatic pulmonary histoplasmosis, disseminated pulmonary histoplasmosis and chronic pulmonary histoplasmosis.
Asymptomatic primary histoplasmosis usually presents no symptoms in infected people. The only indicator of a past infection may be a small scar on the lung. X-rays and imaging would be used in this case to determine that the scaring is not cancerous.
Acute symptomatic pulmonary histoplasmosis occurs when individuals have a concentrated exposure to the fungus H. capsulatum. The severity of the disease depends on the amount of fungus spores that are inhaled. Reactions that occur from this infection range from a mild sick feeling to a serious condition. Symptoms are fever, dry cough, headache, chest pains, sweats, weight loss and chills. These symptoms occur because the immune system responds to the fungus with inflammation. Arthritis can occur, thought more commonly in women than in men. Erythema nodosuma, a type of skin rash that develops on the shin is another symptom.
Sever acute pulmonary syndrome can occur in people who have inhaled vast amounts of the fungus. In this case breathing become difficult and the lungs are deprived of a significant amount of oxygen. Acute pulmonary histoplasmosis is often referred to as spelunker’s lung because it occurs after exposure to large amounts of bat droppings, which are usually found in caves.
Disseminated histoplasmosis occurs mainly in infants and individuals with suppressed or damaged immune systems. This form of histoplasmosis can affect any part of the body such as the eyes, bone marrow, skin, liver, intestinal tract and adrenal glands. Symptoms depend on the organs infected. Symptoms can be meningitis, adrenal insufficiency, ulcers of the mouth, intestinal tract or tongue, pericarditis, pneumonia or anemia. Disseminated histoplasmosis that is not treated is often fatal.
Chronic pulmonary histoplasmosis affects people with pre-existing lung disease such as emphysema. Symptoms are night sweats, fever, fatigue, and a cough that includes bloody sputum. Because this disease is chronic, if untreated it can cause permanent debilitating lung damage.
The average time period for symptoms to occur is ten days. Most people infected do not display symptoms.
Diagnosis first includes a medical history of the individual. This disease can be challenging to diagnose because it mimics many other conditions. There are a few tests to detect the fungus: culture, stain, serology and skin test.
A fungal culture it the optimum test for confirming the diagnosis. A small amount of blood, tissue from the lymph nodes or lungs, sputum or bone marrow is set in a medium that encourages fungal growth. The culture is then checked for the fungus, H. capsulatum. The culture however, takes two to four weeks to grow. This test is not recommended in suspected cases of disseminated histoplasmosis because of the severity and potential fatality of the disease.
A fungal stain involves the microscopic examination of tissue that has been stained with a special dye. A positive test result is 100% accurate and can be determined in minutes. The challenge is obtaining a sputum sample from the lungs that contains enough fungus and obtaining tissue from other sites involves invasive procedures.
Serology examines the blood for antigens and antibodies. Antigens are substances the body creates as an immune response. Antibodies are proteins that the body creates in response to antigens. This test is a fast and accurate determinant of disseminated, chronic or mild histoplasmosis. Unfortunately results can be a false-negative, if patients have a damaged immune system or have been infected with another fungus.
A skin test involves injecting the histoplasmosis antigen in small amounts just under the skin of the forearm. The test takes 48 hours. A positive result does not mean that the infection is active, only that the individual has been exposed.
Other tests may be ordered depending on the symptoms of the individual, such as CT scans, chest X-rays and bronchoscopy. A chest X-ray is used to assess lung damage. A CT scan is used to detect complications in other organs. A bronchoscopy is used to biopsy tissue from the lungs for culturing. This also provides physicians with a bird’s eye view of the lungs and possible inflammation and damage.
A mild case usually requires no treatment. If symptoms are severe or the patient has chronic or disseminated histoplasmosis, then treatment with an antifungal medication is necessary. The drug and length of treatment depend on the type of disease, general health of the patient and the seriousness of the symptoms.
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