Histoplasmosis – an infectious fungal disease

Histoplasmosis is an infectious disease caused by the mycete Histoplasma capsulatum . It occurs mainly in the lungs, but can sometimes spread throughout the body.

  • Histoplasmosis is acquired through the inhalation of fungal spores. 
  • Most patients have no symptoms but feel unwell, fever and cough, and sometimes difficulty breathing.
  • Sometimes the infection spreads, causing enlargement of the liver, spleen and lymph nodes and damage to other organs.
  • Diagnosis is based on culture of tissue and fluid samples.
  • The need for treatment with antifungal drugs depends on the severity of the infection.

Histoplasmosis is particularly common in the eastern and midwestern states of the United States, particularly along the Ohio and Mississippi river valleys, but can occur in the southern states and is also present in parts of Central and South America, Africa, Asia and Australia. Outbreaks associated with bat-dwelling caves have occurred in Florida, Texas, and Puerto Rico.

Fungi of the genus Histoplasma develop best in soil and dust contaminated with bird or bat droppings. Chicken farmers, construction workers, speleologists (people who like to explore caves) and others who work in contact with the soil are more likely to inhale the spores produced by Histoplasma. The risk of infection is greatest when the activity generates airborne spores (for example, the removal of trees or buildings on construction sites in areas where birds or bats live) or when exploring caves.

Most people who have contracted a Histoplasma infection do not have any symptoms. Inhaling large amounts of spores can cause serious illness.

Shapes

There are three main forms of histoplasmosis:

  • Acute pulmonary histoplasmosis: It is the initial stage of the infection. It occurs in the lungs and does not spread.
  • Progressive disseminated histoplasmosis: If the immune system is weakened or immature, the infection can spread through the blood from the lungs to other parts of the body, such as the brain, spinal cord, liver, spleen, lymph nodes, adrenals, digestive system, or bone marrow. This form rarely occurs in healthy adults. It usually occurs in babies or very young children who are malnourished or in people whose immune systems are weakened, such as those with AIDS or who are taking drugs that suppress the immune system, including corticosteroids ( Risk Factors for the Development of Fungal Infections ).
  • Chronic cavitary histoplasmosis: In this form, one or more gaps (cavities) gradually form in the lungs over several weeks. The infection does not spread from the lungs to other parts of the body.

Symptoms

Symptoms vary according to the form of the disease.

Acute pulmonary histoplasmosis

Symptoms usually appear 3-21 days after inhaling the spores. People get sick, develop fever and cough, and have a flu-like sensation. Symptoms usually disappear without any treatment within two weeks and rarely persist for more than six weeks.

People who inhale a lot of spores can develop pneumonia, experience severe dyspnea, and be ill for months.

Acute pulmonary histoplasmosis is very rarely fatal, but it can become severe in people with a weakened immune system (as in the case of AIDS patients).

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Progressive disseminated histoplasmosis

Symptoms are vague at first. A feeling of tiredness, weakness and general malaise may occur later. Symptoms can worsen very slowly or extremely quickly.

Pneumonia can develop but is rarely serious, except in AIDS patients. In rare cases, meningitis (inflammation of the tissues lining the brain and spinal cord) can develop , causing headache and stiff neck. Enlargement of the liver, spleen and lymph nodes may occur. Rarely, the infection causes ulcers to form in the mouth and intestines. Rarely, the adrenal glands are damaged, resulting in Addison’s disease .

Without treatment, this form is fatal in over 90% of people. Despite treatment, people with AIDS can experience rapid death.

Chronic cavitary histoplasmosis

This lung infection develops gradually over several weeks, causing cough and difficulty in breathing that progressively worsen. Symptoms include weight loss, night sweats, mild fever, and generalized malaise.

Most people recover without treatment within 2 to 6 months. However, breathing difficulties can continue to worsen and some people produce sputum with blood, sometimes abundant. Lung tissue is destroyed, forming scar tissue. Lung damage or bacterial superinfection can lead to death.

Diagnosis

  • Culture and examination of tissue or body fluid samples
  • Sometimes blood and urine tests
  • Chest X-ray

To diagnose histoplasmosis, doctors take samples of sputum, urine, blood, or oral ulcers (if any). Doctors can use a fiberoptic probe ( bronchoscope ) to take samples from the lungs. Or they may perform a biopsy to take samples from the liver, bone marrow, or lymph nodes. These samples are sent to the laboratory for culture tests. Urine and blood can be analyzed for proteins ( antigens ) released by the fungus. A test may be performed to identify the genetic material of the fungus (its DNA).

In addition, doctors do a chest X-ray to look for evidence of lung infection.

For some rare forms of the infection, the assistance of infectious disease specialists is required to make the diagnosis (and treatment).

Prognosis

Acute primary histoplasmosis almost always resolves without treatment. Chronic cavitary histoplasmosis can be fatal. Untreated progressive disseminated histoplasmosis has a mortality rate greater than 90%.

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Treatment

  • Antifungal drugs

Otherwise healthy people with acute pulmonary histoplasmosis rarely require drug treatment. However, if after a month the condition does not improve, itraconazole, administered orally, is often prescribed. If severe pneumonia develops, amphotericin B is given intravenously, followed by itraconazole.

L ‘ disseminated histoplasmosis progressive requires treatment. If the infection is severe, amphotericin B is given intravenously, followed by itraconazole orally. If the infection is mild, only itraconazole is used.

If people with AIDS develop histoplasmosis, they may need to take an antifungal drug (usually itraconazole) for the rest of their life. However, they may stop taking the antifungal medication if their CD4 count (amount of a particular type of white blood cell) rises and remains adequately high for at least six months.

In the case of chronic cavitary histoplasmosis , itraconazole or, for more serious infections, amphotericin B can eliminate the fungus. However, treatment cannot reverse the damage caused by the infection. Therefore, most people continue to have breathing problems, similar to those caused by chronic obstructive pulmonary disease . Hence, treatment must be undertaken as soon as possible to limit lung damage.

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