Histoplasmosis: Description, Causes and Risk Factors: HistoplasmosisHistoplasmosis is an infectious disease caused by inhaling the spores of a fungus called Histoplasma capsulatum (A dimorphic fungus species of worldwide distribution that causes histoplasmosis in humans and other mammals; its ascomycetous state is Ajellomyces capsulatum. The organism's natural habitat is soil fertilized with bird and bat droppings, where it grows as a mold, fragments of which, following inhalation, produce the primary pulmonary infection; within the mammalian host tissues, inhaled mycelial fragments grow as uninuclear yeasts that reproduce by budding. This parasitic form may also be induced in the laboratory by culturing the mycelial phase at 37°C on a blood-enriched medium; growth reverts to the mycelial form when the temperature is below 37°C. Histoplasma capsulatum var. duboisii causes a clinically distinct disease, African histoplasmosis, in which large yeast cells with thicker walls are found in tissues, in contrast to the small yeast cells of Histoplasma capsulatum var. farciminosum, which causes epizootic lymphangitis). Histoplasmosis is not contagious; it cannot be transmitted from an infected person or animal to someone else. H. capsulatum is a dimorphic fungus, which means it has two forms. It is a mold (mycelial phase) in soil at ambient temperatures, and after being inhaled by humans or animals, it produces a yeast phase when spores undergo genetic, biochemical, and physical alterations. Spores of H. capsulatum are oval and have two sizes. Macroconidia (large spores) have diameters ranging from 8 to 15 micrometers (?m), and microconidia (small spores) range from 2 to 5 ?m in diameter. Yeast cells of H. capsulatum have oval to round shapes and diameters ranging from 1 to 5 ?m. The infection enters the body through the lungs. Histoplasma fungus grows as a mold in the soil, and infection results from breathing in airborne particles. Soil contaminated with bird or bat droppings may have a higher concentration of histoplasma. People who are risks for exposure to H. capsulatum spores may include: Gardener.
  • Heating and air-conditioning system installer or service person.
  • Microbiology laboratory worker.
  • Pest control worker.
  • Restorer of historic or abandoned buildings.
  • Roofer.
  • Spelunker (cave explorer).
  • Bridge inspector or painter.
  • Chimney cleaner.
  • Construction worker.
  • Demolition worker.
  • Farmer.
Histoplasmosis occurs in wide areas of the Americas, eastern Asia, Africa and Australia. It is rare in Europe. Rates increase in children zero to fifteen years of age, the chronic pulmonary form more prevalent in males. Histoplasmosis can also occur in animals (e.g., dogs, cats, cattle, horses and foxes) with a clinical picture similar to that of humans. Symptoms: Symptoms usually appear within three to 17 days after exposure; the average is 10 days.This may be shorter if the exposure is greater. Histoplasmosis primarily affects a person's lungs, and its symptoms vary greatly. The vast majority of infected people are asymptomatic (have no apparent ill effects), or they experience symptoms so mild they do not seek medical attention and may not even realize that their illness was histoplasmosis.If symptoms do occur, they will usually start within 3 to 17 days after exposure, with an average of 10 days.Histoplasmosis can appear as a mild, flu-like respiratory illness and has a combination of symptoms, including malaise (a general ill feeling), fever, chest pain, dry or nonproductive cough, headache, loss of appetite, shortness of breath, joint and muscle pains, chills, and hoarseness. Diagnosis: Histoplasmosis can be diagnosed by identifyingH. capsulatum in clinical samples of a symptomatic person's tissues or secretions, testing the patient's blood serum for antibodies to the microorganism, and testing urine, serum, or other body fluids forH. capsulatum antigen.On occasion, diagnosis may require a transbronchial biopsy. Culturing clinical specimens is a standard method of microbial identification, but the culturing process for isolating H. capsulatum is costly and time-consuming.To complicate matters, positive results are seldom obtained during the acute stage of the illness, except from clinical specimens from patients with disseminated histoplasmosis.However, research advances in polymerase chain reaction technology have resulted in methods that provide rapid, first-line detection and prospective identification of H capsulatum in clinical samples. Serologic evidence is often the prime factor in the diagnosis of histoplasmosis.Rapid and accurate determination of serologic test results depends on the proper collection, storage, and shipment of serum specimens. Thus, following guidelines established for these activities is essential. Because of their convenience, availability, and utility, the most widely accepted serologic tests are the immunodiffusion test and the complement-fixation test.Serologic test results are useful when positive. However, sometimes test results are negative even when a person is sick with histoplasmosis, a situation that arises especially in patients with weakened immune systems. Other Tests May Include: Skin biopsy.
  • Blood, urine, or sputum tests to look for signs of histoplasmosis infection.
  • Chest CT scan.
  • Chest x-ray.
  • Spinal tap to look for signs of infection in cerebrospinalfluid (CSF).
Treatment: Treatment with appropriate nonsteroidal anti-inflammatory medication and/or oral antifungal medication. The main treatment for histoplasmosis is antifungal drugs. Amphotericin B, itraconazole, and ketoconazole are the usual treatments. Antifungals may be given through a vein, depending on the form or stage of disease. In some cases, long-term treatment with antifungal drugs may be needed. Supportive therapy as indicated, especially in cases with immunosuppression or disseminated illness present. Preventive Measures: Excluding a colony of bats or a flock of birds from a building.
  • Posting health risk warnings.
  • Communicating health risks to workers.
  • Controlling aerosolized dust when removing bat or bird manure from a building.
  • Disinfecting contaminated material.
  • Disposing of waste.
  • Controlling aerosolized dust during construction, excavation, and demolition.
  • Wearing personal protective equipment.
  • Assigned protection factors.
  • Powered air-purifying respirators with hood, helmet, or loose-fitting facepiece and continuous-flow, supplied-air respirators with hood or helmet.
  • Air-purifying, full-facepiece respirators; powered air-purifying respirators with half-facepiece or full facepiece; and continuous-flow, supplied-air respirators with half-facepiece or full facepiece.
  • Pressure-demand, supplied-air respirators with full facepiece.
NOTE: The above information is for processing purpose. The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.


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