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Histoplasmosis

Definition


Disease: Histoplasmosis Histoplasmosis
Category: Respiratory diseases
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Disease Definition:

In case a person works in or around soil that contains a fungus called Histoplasma capsulatum, he/she may get histoplasmosis, which is transmitted through airborne spores that people breathe into their lungs.
People who are especially at risk for histoplasmosis are construction workers, people who have contact with bird or bat droppings, landscapers and farmers.

Most people with histoplasmosis aren't aware that they have the infection because they never develop signs and symptoms. However, histoplasmosis could be serious for some people, especially infants and people with compromised immune systems.

Even for the most severe forms of histoplasmosis, effective treatments are available. However, these therapies could cause serious side effects and they usually involve extensive hospital stays. For this reason, people with compromised immune systems should avoid exposure to histoplasmosis.

Work Group:


Prepared by: Scientific Section

Symptoms, Causes

Symptoms:

Ranging from mild to life-threatening, there are several types of histoplasmosis. Although the most benign form doesn’t cause any signs or symptoms, serious problems throughout the body and in the lungs could be caused by severe infections. Usually, when signs and symptoms occur, they appear three to seventeen days after initial exposure.

MILD TO MODERATE CASES:

Asymptomatic primary histoplasmosis:
The most common form of histoplasmosis is asymptomatic primary histoplasmosis, which doesn't cause any signs or symptoms in otherwise healthy people who become infected. Small scars in the lungs could be the only sign of infection. In that case, special radiologic testing can usually confirm that nodules aren't cancerous.

Acute symptomatic pulmonary histoplasmosis:
Usually, this form of the disease occurs in otherwise healthy people who have had intense exposure to H. capsulatum. Reactions could range from a brief period of not feeling well to serious illness because the severity of the disease depends on the number of inhaled fungus spores. Some of the usual signs and symptoms of this form may include:

 

  • Sweats
  • Chills
  • Headache
  • Chest pain
  • Fever
  • Weight loss
  • Dry cough


In some cases, weeks or months after the initial infection, the patient may develop arthritis or pericarditis, which is the inflammation of the sac that surrounds the heart. These problems aren't a sign that the infection has spread outside the lungs. They develop because the patient's immune system responds to the fungus with an unusual amount of inflammation.

On the other hand, when people inhale a large number of spores, they may develop severe acute pulmonary syndrome, which is a potentially life-threatening syndrome that makes breathing difficult. Because acute pulmonary syndrome usually occurs after intense exposure to bat excrement stirred up by explorers in caves, it is also called spelunker's lung.

MODERATE TO SEVERE CASES:

Chronic pulmonary histoplasmosis:
People with an underlying lung disease such as emphysema usually develop this form of histoplasmosis. When this disease is left untreated, it could progress to disabling lung problems. This disease is chronic and is most common in white, middle-aged men. Some of its signs and symptoms may include:

 

  • Night sweats
  • Fatigue
  • A cough that may bring up blood
  • Fever


Disseminated histoplasmosis:
This disease could affect nearly any part of the body, including the eyes, bone marrow, intestinal tract, liver, adrenal glands and skin. It usually occurs in infants and people whose immune system is compromised. In most cases, when disseminated histoplasmosis is left untreated, it becomes fatal. Based on the affected organs, people with this form of the disease could develop:

 

  • Meningitis
  • Anemia
  • Ulcers of the mouth, tongue or intestinal tract
  • Pericarditis
  • Adrenal insufficiency
  • Pneumonia

Causes:

The temperate regions of the world are where hisoplasma capsulatum is primarily found. This fungus is especially common in chicken and pigeon coops, old barns, parks and caves because it thrives in damp soil that's rich in organic material, particularly the droppings from birds and bats.

The body temperature of birds is too high, that's why they can't be infected with histoplasmosis, however, they could carry H. capsulatum on their feathers; additionally, their droppings support the growth of the fungus. Canaries, parakeets and other birds that are usually kept as pets aren't affected. On the other hand, bats have a lower body temperature and can be infected; however, someone can't contract this disease from a bat or from another person.

When someone inhales the reproductive cells (spores) of the fungus, he/she develops histoplasmosis. These spores are extremely light, and when dirt or other contaminated material is disturbed, they float into the air. Because of this, the disease usually occurs in people living near construction sites, as well as landscapers, spelunkers, farmers and construction workers.

LUNGS AND HISTOPLASMOSIS:
The spores of H. capsulatum could easily enter the lungs and settle in the small air sacs because they are microscopic in size. In the air sacs, the spores will be trapped by macrophages, which are immune system cells that attack foreign organisms. The spores will be carried by the macrophages to lymph nodes in the chest, where they will continue to multiply. Scarring, inflammation and calcium deposits could be caused by this. The lymph nodes could become so enlarged in cases of heavy infection that they obstruct the lungs' airways or the esophagus.

In most cases, the infection clears on its own without treatment, and the person doesnot develop any noticeable signs or symptoms.

However, the spores could enter a person's bloodstream and travel to other parts of the body if the immune system isn't able to eliminate the spores. In this case, the person could develop a variety of severe problems, which if not diagnosed and treated quickly, could become fatal.

Complications

Complications:

A number of serious complications could be caused by histoplasmosis even in people who are otherwise healthy. However, the potential problems are usually life-threatening in infants, people with compromised immune systems and older adults.

Some of the complications of acute and chronic pulmonary histoplasmosis may include:

Enlarged lymph nodes:
Histoplasmosis usually affects the lymph nodes in the central part of the chest. This region lies between the lungs and contains the trachea, esophagus, heart and many small lymph nodes. In a small percentage of people with acute pulmonary histoplasmosis, the lymph nodes could become large enough that they obstruct the esophagus or airways, making it difficult to swallow or breathe. In some cases, the pulmonary arteries and veins, which are the large blood vessels in the lungs, could also become blocked.

Pericarditis:
This complication is the inflammation of the pericardium, which is the sac that surrounds the heart. Normally, this sac should contain a small amount of fluid. However, that amount could increase when the pericardium becomes inflamed, which could interfere with the heart's ability to pump blood efficiently. Instead of being caused by the infection of the pericardium itself, when pericarditis occurs as a complication of histoplasmosis, it results from the inflammation in the nearby lymph nodes.

Fibrosing mediastinitis:
When the adjoining structures are invaded and blocked by scar tissue from lymph nodes, fibrosing mediastinitis occurs. This is a rare but severe complication of histoplasmosis, which occurs later in the course of the disease. Usually, its signs and symptoms don't appear until the disease is quite advanced, and they may include chest pain, breathlessness and a cough that brings up blood. This complication could be life-threatening in case structures in both lungs are affected.

Arthritis:
One of the common complications of acute pulmonary histoplasmosis is joint inflammation, which usually occurs in conjunction with a skin rash (erythema nodosum). Women are much more likely to be affected by this complication than men. Usually, arthritis clears on its own or after a brief course of NSAIDs, despite the fact that it may persist for months.

COMPLICATIONS OF DISSEMINATED HISTOPLASMOSIS:
Almost any organ system in the body could be affected by disseminated histoplasmosis, which could cause a number of serious and potentially fatal complications. Some of those complications may be:

Meningitis:
Meningitis could be life threatening. It is the infection and inflammation of the membranes or meninges and fluid, called the cerebrospinal fluid that surrounds the brain and spinal cord. The first signs and symptoms of this disease are a high fever, severe headache and vomiting. This disease usually strikes suddenly, and as it progresses, the brain becomes swollen and may begin to bleed. When meningitis occurs as a complication of histoplasmosis, it usually develops in people whose immune systems are compromised, but in some cases, it could also develop in people who are otherwise healthy. In a small percentage of cases, meningitis is fatal.

Adrenal insufficiency:
The hormones that give instructions to virtually every organ and tissue in the body are produced by the adrenal glands, which are located just above the kidneys. Some serious and potentially life-threatening complications could occur in case the glands don't provide enough of these hormones. Untreated Addison's disease, which is adrenal insufficiency, is fatal.

Treatments:

Usually, if someone has a mild case of acute histoplasmosis, treatment won't be necessary. However, a person will most likely need treatment with one or more antifungal medications in case their symptoms are severe, or if they have the chronic or disseminated forms of the disease. The type of the illness, its severity and the patient's overall health will determine the specific drug and the length of treatment. Amphotericin B and itraconazole are two examples of antifungal medications that are commonly used.

Usually, the initial treatment of choice for people with disseminated histoplasmosis or severe disease is one of the several formulations of amphotericin B. However, depending on how the patient's condition improves, he/she will be switched to itraconazole within a few days to a few weeks because these drugs could be toxic to the kidneys and must be administered intravenously. In case a person has severe respiratory disease and difficulty maintaining oxygen levels in their bloodstream, they may also be given corticosteroids initially.

In mild cases of disseminated hitoplasmosis as well as in chronic pulmonary disease, itraconazole alone could be effective. Itraconazole could be taken in pill form and it has fewer side effects, however, it doesn't work as quickly as amphotericin B. The patient may experience headache, dizziness, nausea, vomiting or diarrhea while using this medication, but over time, these symptoms usually go away. The patient should be closely monitored during treatment in case they have a history of liver or kidney problems, or another lung disease.

Someone may be prescribed fluconazole, which is another antifungal drug, in case he/she is not a candidate for itraconazole or if they can't tolerate the medication. However, a person is more likely to experience a relapse with fluconazole, and it isn't as effective as itraconazole.

Prognosis:

Not Available

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