Histoplasmosis Causes, Types, Symptoms, Diagnosis, Treatment, Prevention, Complications

Histoplasmosis Causes, Types, Symptoms, Diagnosis, Treatment, Prevention, Complications


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What is histoplasmosis?


Histoplasmosis is a disease, usually affecting the lungs, caused by the Histoplasma capsulatum fungus. Although many people that are or have been infected with H. capsulatum do not appear ill, some people in the acute phase of the disease have a dry cough, fever, and chest pains and do feel ill. There are several types of histoplasmosis (acute, chronic, and disseminated, all with subtypes).

H. capsulatum was first described by Samuel Darling in 1906 within human tissue cells (histiocytes). In 1932, Katharine Dodd and Edna Tompkins made the first diagnosis of histoplasmosis in an infant. Since the 1930s, H. capsulatum has been found worldwide, but the majority of cases are found in river valleys in temperate regions of the world and in equatorial Africa (in Africa, H. capsulatum has a variant thick-walled yeast form termed H. duboisii). Often an outbreak occurs in a group of people after a visit to a certain area like a cave that contains bat droppings. In the U.S., histoplasmosis is endemic in the Ohio, Missouri, and Mississippi river valleys.

Infection with histoplasmosis is asymptomatic in approximately 95% of cases. Most patients with histoplasmosis recover uneventfully without therapy; in the case of chronic pulmonary disease, protracted courses of antifungal treatment may be necessary. Lifelong treatment may be required in the presence of immunosuppression (eg, AIDS)

Disseminated histoplasmosis in an HIV-infected patient is an AIDS-defining illness. In acute pulmonary histoplasmosis the course is usually benign, symptoms mild, and treatment unnecessary. Pulmonary histoplasmosis may require antifungal treatment if symptoms last for more than 4 weeks or if symptoms are moderately severe to severe

Some patients fail to clear their initial infection and develop chronic pulmonary histoplasmosis. A subset of these patients has chronic cavitary disease. Underlying lung disease (eg, chronic obstructive pulmonary disease [COPD]) predisposes to chronic pulmonary histoplasmosis. In general, without antifungal treatment this form of the disease progresses and pulmonary function deteriorates

Disseminated histoplasmosis may occur in the setting of immunosuppression, or in those at the extremes of age. Mortality without treatment is very high but can be greatly reduced by antifungal therapy
Central nervous system (CNS) histoplasmosis can manifest as meningitis, focal brain or spinal cord lesions, cerebrovascular accident, or diffuse encephalitis. It tends to be fatal if left untreated

Histoplasmosis is the most common endemic fungal infection diagnosed in the U.S. with about 250,000 new cases per year. H. capsulatum can occur in high concentrations in some sources (for example, bird and bat feces). Histoplasmosis has also been named Ohio River Valley fever and bird-fancier's disease. Histoplasmosis can affect other mammals like dogs and cats, but these animals do not transfer the disease to humans or to other animals. Dogs, cats, and other mammals develop symptoms mainly due to lung infections with H. capsulatum that mimic human histoplasmosis.

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Causes and risk factors of Histoplasmosis



  • Histoplasmosis typically results from exposure during activities that disturb soil harboring the organism, generating aerosols of spores
  • Examples of so-called microfoci of histoplasmosis include the following: caves, chicken coops, bird roosts, school yards, prison grounds, decayed wood piles, dead trees, contaminated chimneys, and old buildings
  • Activities that are associated with acquisition of histoplasmosis include spelunking (caving, pot holing), cleaning, demolition, use of bird droppings as fertilizer, excavation, and camping
  • Living in an endemic area predisposes to histoplasmosis
  • Pre-existing lung disease (eg, COPD) and cigarette use predispose to chronic pulmonary histoplasmosis
  • Those who are immunosuppressed, or who are at the extremes of age, are predisposed to symptomatic disseminated histoplasmosis
You can get histoplasmosis more than once. However, the first infection is generally the most severe. The fungus doesn’t spread from one person to another. It’s not contagious.


Are there different types of histoplasmosis?


Histoplasmosis has three major types of disease, and these three have other subtypes included in them. They are summarized with their subtypes as follows:

Acute


Acute, or short-term, histoplasmosis is typically mild. It rarely leads to complications.
The Centers for Disease Control and Prevention (CDC) estimate that between 50 and 80 percent of people who live in areas where the fungus is common have been exposed (CDC). Many of them probably did not have any symptoms of infection.

Chronic


Chronic, or long-term, histoplasmosis occurs far less often than the acute form. In rare cases, it can spread throughout the body. This disseminated form of histoplasmosis is considered life-threatening, unless treated.

Progressive disseminated histoplasmosis: 


chronic progressive disseminated histoplasmosis with oropharyngeal lesions or ulcers; subacute progressive disseminated histoplasmosis with intestinal, adrenal, cardiac or central nervous system (CNS) involvement; and acute progressive disseminated histoplasmosis with encephalopathy, meningitis, mass lesions and cutaneous (skin) lesions.

Symptoms of Histoplasmosis


Most people who are infected with this fungus have no symptoms. However, the risk of symptoms increases as you breathe in more spores. If you are going to have symptoms, they generally show up about 10 days after exposure.

Possible symptoms of  Histoplasmosis include:


  • fever
  • dry cough
  • chest pain
  • joint pain
  • red bumps on your lower legs

In severe cases, symptoms of Histoplasmosis may include:


  • sweating a lot
  • shortness of breath
  • coughing up blood

Widespread histoplasmosis causes inflammation and irritation. Symptoms of Histoplasmosis may include:


  • chest pain, caused by swelling around the heart
  • high fever
  • stiff neck and headaches, from swelling around the brain and spinal cord

Testing for and Diagnosing Histoplasmosis


If you have a mild case of histoplasmosis, you may never know that you were infected.

Testing for histoplasmosis is usually reserved for people who both have a severe infection and live or work in a high-risk area.

To confirm a diagnosis, your doctor might conduct blood or urine tests. These tests check for antibodies or other proteins that indicate prior contact with histoplasmosis. Your doctor might also take urine, sputum, or blood cultures to make an accurate diagnosis. However, it can take up to six weeks to get results.

You may need other tests, depending on what parts of your body are affected. Your doctor might take a biopsy (tissue sample) of your lung, liver, skin, or bone marrow. You might also need an X-ray or computerized tomography (CT) scan of your chest. The goal of these tests is to determine if additional treatments are needed to address any complications.

How is histoplasmosis treated?


For asymptomatic people or people with acute localized infection who are otherwise healthy, antifungal treatment is usually not recommended as these people have or will resolve the infection in about three weeks. If symptoms persist a month or more, itraconazole (Sporanox), ketoconazole (Nizoral) or amphotericin B (Fungizone, Amphocin) may be effective. If CNS involvement occurs, or if the person is compromised by other diseases or is immunocompromised and has severe histoplasmosis (progressive disseminated histoplasmosis), either itraconazole or amphotericin B is recommended. The lengths of time, dosing amounts, and dosing routes are usually individualized for the patient; consultations with both infectious disease and pulmonary specialists are recommended. Other new azole compound drugs may be effective in some difficult or unresponsive cases; the consultants could help select the appropriate new drug treatment.

Surgery has been used to treat some complications seen in some cases of histoplasmosis. Examples of surgical procedures include pericardiocentesis or a pericardial window procedure (both designed to remove fluid that compresses the heart) in the few patients that develop pericarditis; resection of cavitary lung lesions; excision of lymph nodes that compress pulmonary, vascular, or other structures; and replacement of damaged heart valves or other structures.

What are the complications seen with histoplasmosis?


The majority (about 90%) of people that are infected with H. capsulatum recover completely with no complications. A few cases may show small areas of lung scarring on chest X-rays. With progressive severity of the disease (chronic to disseminated), the complications become more numerous and disabling. Pleural effusions and pericarditis can develop in about 5% of acute symptomatic patients. Another 5% may develop rheumatologic problems like arthritis, erythema nodosum, or erythema multiforme. About 90% of patients with chronic pulmonary histoplasmosis develop cavitary lung lesions, and some may develop pulmonary fibrosis and dyspnea (shortness of breath), and some may get adrenal gland infections which may be rarely associated with Cushing's syndrome (elevated cortisol levels, causing upper body obesity and a rounded face). Others may develop ocular histoplasmosis syndrome in which H. capsulatum spreads from the lungs to the retinal blood vessels (choroid) which become inflamed (uveitis) and then develop fragile abnormal blood vessels. This area can form scar tissue and thus replace the retina's macular tissue, which results in partial blindness. Patients with acute progressive disseminated histoplasmosis may develop CNS problems that result in encephalopathy or seizures; adrenal insufficiency; or cardiac problems like valve failure, angina, and poor cardiac output. Acute progressive disseminated histoplasmosis, if not treated quickly and appropriately, can lead to death in a few weeks. Even with lifelong antifungal treatment, about 10%-20% of cases will relapse.

How Can I Prevent Histoplasmosis?


You can reduce your risk of infection by avoiding high-risk areas. These include:
  • construction sites
  • renovated buildings
  • caves
  • pigeon or chicken coops
If you can’t avoid high-risk areas, there are steps you can take to help keep spores from getting into the air. For example, spray sites with water before working or digging in them. Wear a respirator mask when there is a high risk of exposure to spores. Your employer is obligated to provide you with appropriate safety equipment if it’s needed to protect your health.