Histoplasmosis (cont.)
How is histoplasmosis transmitted?
Histoplasmosis is not transmitted person to person except for a few rare
instances when a transplant patient has contracted histoplasmosis from a
transplanted organ. The large majority of cases occur when people inhale fungal
mycelia and spores, usually from a source where the fungus growth is enhanced.
Such sources or areas are in caves containing bat or bird droppings, chicken
coops, birdhouses, bird roosts, or soil contaminated with such droppings.
Unfortunately, H. capsulatum can survive in soil for years, and if the soil
becomes airborne (dust), inhalation of H. capsulatum-contaminated dust may lead
to histoplasmosis.
How is histoplasmosis diagnosed?
Definitive diagnosis of histoplasmosis can be complicated, especially if the
patient gives no history of exposure to areas contaminated with H. capsulatum.
Many bacterial and fungal infections can produce clinical findings that are
found with H. capsulatum infections (for example, granulomatous nodules found in
sarcoidosis and tuberculosis, or lung infiltrates seen on X-ray in coccidiodomycosis, blastomycosis, aspergillosis, and other lung infections). In
fact, before 1932, many patients with chronic pulmonary histoplasmosis were
diagnosed as having tuberculosis. Differentiating histoplasmosis from other lung
infections can still be a diagnostic challenge for clinicians.
Cultures of blood, sputum, or tissue biopsy samples can be cultured on media that
supports H. capsulatum growth. If H. capsulatum is cultured, the diagnosis is
confirmed. However, at best, cultures are positive in only about 60% of patients
with chronic pulmonary infections and are positive in only about 15% of acute
cases. Furthermore, it may take from two to 12 weeks for the fungus to grow enough
to be identified in culture, which could delay treatment especially in
progressive disseminated cases. Blood cultures range from 50%-90% positive in
progressive disseminated cases. Positive cultures for H. capsulatum definitively
diagnose histoplasmosis. Unfortunately, acute progressive disseminated
histoplasmosis, if not treated quickly and appropriately, can lead to death in a
few weeks. In suspected cases, treatment should begin immediately without
waiting on cultures to grow positive for H. capsulatum.
There are several types of serology tests (tests for antigens and antibodies)
that are used on blood, urine, and cerebral spinal fluid (CSF). They can give
fairly rapid results especially with symptomatic, chronic, or progressive
disseminated disease (75%-95% positive after six weeks) but take about three weeks to
be positive in a small number (about 15%) of acute cases. Unfortunately, the
reagents share some cross-reactivity with other fungal genera (for example,
Aspergillus, Blastomyces, and Coccidioides), so false-positive results can be
obtained. Further, these tests for H. capsulatum can be positive in people that
live in areas with endemic histoplasmosis and also can be positive in patients
that have inactive disease.
Stains (Giemsa stain or methenamine silver stain) of tissue samples, blood,
sputum, bone marrow, lymph node aspirates, and other fluids can allow
microscopic visualization of H. capsulatum. However, the accuracy of
identification depends on the experience of the observer as other organisms may
resemble H. capsulatum. Researchers suggest this method be backed up by other
tests such as serology and cultures.
Many other tests may be used to help the physician determine the extent of
infection by H. capsulatum. Examples are listed below:
- CBC or complete blood count: Low white blood cell counts can occur in chronic
progressive histoplasmosis.
- Chest X-rays can show lung changes (infiltrates, cavitations, and enlarged
lymph nodes) that may occur in chronic and acute progressive disseminated
histoplasmosis.
- CT scan may show bilateral adrenal gland involvement in subacute progressive
disseminated histoplasmosis.
- Echocardiography helps determine if heart valves are infected or if
pericarditis is present in acute pulmonary or progressive disseminated
histoplasmosis.
- Alkaline phosphatase levels in the blood are increased in chronic pulmonary
and acute progressive disseminated histoplasmosis.
Other tests and procedures may be done to help determine the diagnosis or extent
of infection; those listed above are the most common. Occasionally, a surgeon
may need to be consulted to obtain lung tissue, pleural fluid, or lymph node
biopsy for culture and microscopic evaluation to aid diagnosis.
- ketoconazole, Nizoral, Extina, Xolegel, Kuric - Learn about ketoconazole (Nizoral, Extina, Xolegel, Kuric), a drug used to treat a variety of fungal infections such as dandruff, jock itch, athlete's foot, and ringworm.
- Complete Blood Count (CBC) - A complete blood count (CBC) measures the concentration of white blood cells, red blood cells, and platelets in the blood and aids in the diagnosis of conditions and diseases such as anemia, malignancies, and immune disorders.
- Pneumonia - Learn pneumonia symptoms, causes, treatment, signs, diagnosis and types: viral and bacterial (Pneumocystis carinii, Klebsiella, Mycoplasma, Chlamydia pneumoniae).
Latest Medical News
Infectious Disease RSS