Histoplasmosis is an infectious disease caused by inhaling the microscopic spores of the fungus Histoplasma capsulatum. The disease exists in three forms. Acute or primary histoplasmosis causes flulike symptoms. Most people who are infected recover without medical intervention. Chronic histoplasmosis affects the lungs and can be fatal. Disseminated histoplasmosis affects many organ systems in the body and is often fatal, especially to people with acquired immunodeficiency syndrome (AIDS ).
Histoplasmosis is an airborne infection. The spores that cause this disease are found in soil that has been contaminated with bird or bat droppings. In the United States, the disease is most common in eastern and midwestern states and is widespread in the upper Mississippi, Ohio, Missouri, and St. Lawrence river valleys. Sometimes histoplasmosis is called Ohio Valley disease, Central Mississippi River Valley disease, Appalachian Mountain disease, Darling's disease, or Histoplasma capsulatum infection.
Anyone can get histoplasmosis, but people who come in contact with bird and bat excrement are more likely to be infected. This includes farmers, gardeners, bridge inspectors and painters, roofers, chimney cleaners, demolition and construction workers, people installing or servicing heating and air conditioning units, people restoring old or abandoned buildings, and people who explore caves.
The very young and the elderly, especially if they have a pre-existing lung disease or are heavy smokers, are more likely to develop symptoms that are more severe. People who have a weakened immune system, either from diseases such as AIDS or leukemia, or as the result of medications they take (corticosteroids, chemotherapy drugs), are more likely to develop chronic or disseminated histoplasmosis.
Causes and symptoms
When the spores of H. capsulatum are inhaled, they lodge in the lungs where they divide and cause lesions. This is known as acute or primary histoplasmosis. It is not contagious.
Many otherwise healthy people show no symptoms of infection at all. When symptoms do occur, they appear 3-17 days after exposure (average time is 10 days). The symptoms are usually mild and resemble those of a cold or flu; fever, dry cough, enlarged lymph glands, tiredness, and a general feeling of ill health. A small number of people develop bronchopneumonia. About 95% of people who are infected either experience no symptoms or have symptoms that clear up spontaneously. These people then have partial immunity to re-infection.
In some people, the spores that cause the disease continue to live in the lungs. In about 5% of people who are infected, usually those with chronic lung disease, diabetes mellitis, or weakened immune systems, the disease progresses to chronic histoplasmosis. This can take months or years. Symptoms of chronic histoplasmosis resemble those of tuberculosis. Cavities form in the lung tissue, parts of the lung may collapse, and the lungs fill with fluid. Chronic histoplasmosis is a serious disease that can result in death.
The rarest form of histoplasmosis is disseminated histoplasmosis. Disseminated histoplasmosis is seen almost exclusively in patients with AIDS or other immune defects. In disseminated histoplasmosis the infection may move to the spleen, liver, bone marrow, or adrenal glands. Symptoms include a worsening of those found in chronic histoplasmosis, as well as weight loss, diarrhea, the development of open sores in the mouth and nose, and enlargement of the spleen, liver, and adrenal gland.
A simple skin test similar to that given for tuberculosis will tell if a person has previously been infected by the fungus H. capsulatum. Chest x rays often show lung damage caused by the fungus, but do not lead to a definitive diagnosis because the damage caused by other diseases has a similar appearance on the x ray. Diagnosis of chronic or disseminated histoplasmosis can be made by culturing a sample of sputum or other body fluids in the laboratory to isolate the fungus. The urine, blood serum, washings from the lungs, or cerebrospinal fluid can all be tested for the presence of an antigen produced in response to the infection. Most cases of primary histoplasmosis go undiagnosed.
Acute primary histoplasmosis generally requires no treatment other than rest. Non-prescription drugs such as acetaminophen (Tylenol) may be used to treat pain and relieve fever. Avoiding smoke and using a cool air humidifier may ease chest pain.
Patients with an intact immune system who develop chronic histoplasmosis are treated with the drug ketoconazole (Nizoral) or amphotericin B (Fungizone). Patients with suppressed immune systems are treated with amphotericin B, which is given intravenously. Because of its potentially toxic side effects, hospitalization is often required. The patient may also receive other drugs to minimize the side effects of the amphotericin B.
Patients with AIDS must continue to take the drug itraconazole (Sporonox) orally for the rest of their lives in order to prevent a relapse. If the patient can not tolerate itraconazole, the drug fluconazole (Diflucan) can be substituted.
In non-immunocompromised patients, alternative therapies can be very successful. Alternative treatment for fungal infections focuses on creating an environment where the fungus cannot survive. This is accomplished by maintaining good health and eating a diet low in dairy products, sugars, including honey and fruit juice, and foods like beer that contain yeast. This is complemented by a diet high in raw food. Supplements of antioxidant vitamins C, E, and A, along with B complex, may also be added to the diet. Lactobacillus acidophilus and Bifidobacteria will replenish the good bacteria in the intestines. Antifungal herbs, like garlic, can be consumed in relatively large does and for an extended period of time in order to be most effective.
Most people recover from primary histoplasmosis in a few weeks without medical intervention. Patients with chronic histoplasmosis who are treated with antifungal drugs generally recover rapidly if they do not have an underlying serious disease. When left untreated, or if serious disease is present, histoplasmosis can be fatal.
AIDS patients with disseminated histoplasmosis vary in their response to amphotericin B, depending on their general health and how well they tolerate the side effects of the drug. Treatment often suppresses the infection temporarily, but patients with AIDS are always in danger of a relapse and must continue to take medication for the rest of their lives to keep the infection at bay. New combinations of therapies and new drugs are constantly being evaluated, making hard statistics on prognosis difficult to come by. AIDS patients have problems with multiple opportunistic infections, making it difficult to isolate death rates due to any one particular fungal infection.
Since the spores of H. capsulatum are so widespread, it is almost impossible to prevent exposure in endemic areas. Dust suppression measures when working with contaminated soil may help limit exposure. Individuals who are at risk of developing the more severe forms of the disease should avoid situations where they will be exposed to bat and bird droppings.
Acidophilus— The bacteria Lactobacillus acidophilus, usually found in yogurt.
Adrenal gland— A pair of organs located above the kidneys. The outer tissue of the gland produces the hormones epinephrine (adrenaline) and norepinephrine, while the inner tissue produces several steroid hormones.
Antigen— A foreign protein to which the body reacts by making antibodies.
Bifidobacteria— A group of bacteria normally present in the intestine. Commercial supplements are available.
Corticosteroids— A group of hormones produced naturally by the adrenal gland or manufactured synthetically. They are often used to treat inflammation. Examples include cortisone and prednisone.
Histoplasmosis: Protecting Workers at Risk. Centers for Disease Control and Prevention. 〈http://www.cdc.gov/niosh/97146eng.html〉.
National Institute for Occupational Safety and Health. Cincinnati, Ohio. (800) 356-4674.
Histoplasmosis: Protecting Workers at Risk. Centers for Disease Control and Prevention. 〈http://www.cdc.gov/niosh/97146eng.html〉.
Histoplasmosis is a disease caused by a mycotic (fungal) infection of Histoplasma capsulatum fungal spores. The infection develops when fungal spores are inhaled, and the resulting disease affects the lungs. The fungus is found globally and is endemic (occurs normally) in some areas of America. The key factor about these spores is their resilience in the environment and their ability to become airborne when the ground is disturbed. Those at risk of disease are people exposed to contaminated soils, caves, and bat and bird housings. The disease is not transmissible between humans.
In the majority of cases, infection will not result in disease, but in severe cases, persons with histoplasmosis may present with chronic tuberculosis-like symptoms. People with existing immune system problems are at an increased risk of the disease spreading to other organs of the body, which can be potentially fatal if untreated. Treatment commonly includes anti-fungal medication.
Histoplasmosis was first reported in the United States in 1926. It occurs worldwide and is endemic in some parts of the United States. It primarily affects the lungs, but in some cases spreads to other organs in the body. Histoplasmosis is also known as Darling's disease, Ohio River Valley Fever, Mississippi River Valley disease, and Appalachian Mountain disease.
Approximately 95% of people infected with this disease remain asymptomatic (without symptoms) or have symptoms that heal spontaneously; in most cases these people will develop partial immunity against re-infection. If symptoms do occur, they will usually develop within 3– 18 days. Acute symptomatic pulmonary histoplasmosis has a short duration, with possible symptoms including fever, chills, chest pain, and a non-productive cough.
Chronic pulmonary histoplasmosis presents with longer-lasting symptoms that are similar to tuberculosis: chest pain, loss of breath, coughing, sweating, and fever. Disseminated histoplasmosis is the most serious form of the disease; it is only common among immunosuppressed people and can be fatal if left untreated. In these cases, the disease spreads from the lungs to other organs, and symptoms include neck stiffness, skin lesions, and mouth sores.
Histoplasmosis is contracted by inhalation of the Histoplasma fungal spores, which thrive in damp, organically rich soil, and some animal droppings, such as those of birds and bats. Once these microscopic spores enter the lungs, they imbed in the small air sacs and trigger an immune reaction that, in serious cases, leads to inflammation, scarring, and calcium deposits on the lungs. The extent of histoplasmosis infection is dependent both on the number of spores inhaled and the immunity of the host.
Histoplasmosis is primarily located in the temperate regions of the world and is endemic in areas of America, including the south-eastern, mid-Atlantic, and central states of Arkansas, Kentucky, Missouri, Tennessee, West Virginia, Ohio, and Texas, as well as Central and South America. Most cases of the disease are sporadic, but point source outbreaks have been previously described.
The fungal spores are commonly found in fertile soils, caves, poultry houses, bird roosts, and areas harboring bats. The spores frequently become airborne when disturbed; are extremely resilient; and remain viable in the environment for long periods of time. In fact, plants fertilized with droppings may contain spores and produce infectious smoke when burned. This gives the spores the ability to transfer large distances from the initial source and still retain viability in causing disease.
WORDS TO KNOW
MYCOTIC: Mycotic means having to do with or caused by a fungus. Any medical condition caused by a fungus is a mycotic condition, also called a mycosis.
IMMUNOSUPPRESSION: A reduction of the ability of the immune system to recognize and respond to the presence of foreign material.
SPORE: A dormant form assumed by some bacteria, such as anthrax, that enable the bacterium to survive high temperatures, dryness, and lack of nourishment for long periods of time. Under proper conditions, the spore may revert to the actively multiplying form of the bacteria.
Due to the high prevalence of histoplasmosis fungi, infection is common, and 80% of people living in fungal rich areas of the United States could exhibit a positive skin test for the presence of histoplasmosis fungi. However, development of disease is rare and is only considered a risk to people with weakened immune systems, such as very young children, elderly people, organ transplant and chemotherapy patients, and persons with autoimmune disease. The ages of people affected range from children to adults, and there is no increased incidence among either sex, although chronic lung infections are more common in men than women.
Although quite infrequent, outbreaks of histoplasmosis have been previously described and generally result from a single event causing the disruption of a large area housing the fungus, such as construction, clearing, cleaning, and cave exploration. One such outbreak occurred in 2001 in Indiana and infected 523 school students. The cause of the outbreak was rototilling of a courtyard containing the fungus.
Histoplasmosis may present symptoms similar to other diseases, and as such, diagnosis is achieved through blood tests or laboratory culture. Generally, histoplasmosis fungal infections do not lead to the development of disease, and, even in mild cases, the disease usually resolves without treatment. When required in severe disease states, the most common treatment for histoplasmosis is anti-fungal medication. In most cases, previous infection will result in partial protection against reinfection.
Awareness is a key factor in ensuring successful disease prevention, so before beginning a job or activity with a potential risk of exposure to the histoplasmosis fungi, it is important to investigate all of the potential risk factors involved. When working in areas carrying a high risk of making contact with the fungal spores, it is also important to wear appropriate protective clothing, such as disposable coveralls, to prevent transfer of the spores from the worksite and a dust mask that covers both the nose and the mouth to filters out all particles larger than 2 microns in size.
Due to the natural widespread occurrence of Histoplasma capsulatum, it would be virtually impossible to decontaminate all infected sites. Prevention is commonly achieved by minimizing the disruption of soils in affected areas in addition to limiting the exposure of persons to dust in contaminated environments. In areas where soil disruption is unavoidable, spraying infected areas thoroughly with water mist prior to beginning excavation reduces the number of aerosols produced.
Cases of chronic disease caused by histoplasmosis are on the rise, and are attributed mainly to the increasing number of persons living with HIV and weakened immune systems due to chemotherapy, organ transplant, or autoimmune disease. It has also been seen that immunosuppression later in life may also result in reactivation of quiescent infection born from earlier exposure. As the number of people living with immune disorders increases, scientists expect there will be a proportional increase in the prevalence of chronic histoplasmosis. For this reason, scientists consider histoplasmosis to be an emerging infectious disease.
Land use might also play a part in the resurgence of histoplasmosis. Development of lands traditionally used for farming in the nitrogen-rich belt of the central and Southern United States could also be a factor in the increased number of reported cases.
Scientists have learned that histoplasmosis infection can also lead to ocular histoplasmosis syndrome (OHS). OHS is a condition that damages blood vessels in the eyes and leads to impaired vision. It is thought that the fungal spores travel from the lungs to the eye and lodge in the blood vessels leading to the retina. This causes no initial damage to eyesight, although it does leave recognizable histo spots on the blood vessels. Vision loss can occur years after the initial infection. Detecting the histo spots can indicate future vision loss, and laser eye surgery can reduce the likelihood of vision loss by 50%. The National Eye Institute recommends that individuals that live in areas where histoplasmosis is endemic have their eyes checked regularly, and for medical practitioners to consider the presence of histo spots as an indication that vision loss may occur.
Awareness of this disease acts to minimize unnecessary exposure to contaminated areas and promote the use of protective equipment when required. The National Institute for Occupational Safety and Health, along with the Center for Disease Control and Prevention (CDC), engages in promotions geared to educate employers and workers about the risks and prevention strategies for histoplasmosis.
IN CONTEXT: REAL-WORLD RISKS
The Division of Bacterial and Mycotic Diseases, Centers for Disease Control and Prevention (CDC) list the following as “risk groups” for histoplasmosis:
- Persons in areas with endemic disease with exposures to accumulations of bird or bat droppings (e.g., construction or agricultural workers, spelunkers).
- High risk groups are immunocompromised persons (e.g., persons with cancer, transplant recipients, persons with HIV infection).
- No national surveillance exists.
Mandell, G.L., J.E. Bennett, and R. Dolin. Principles and Practice of Infectious Diseases, Vol. 2. Philadelphia, PA: Elsevier, 2005.
Chamany, S., et al. “A Large Histoplasmosis Outbreak Among High School Students in Indiana, 2001.” Pediatric Infectious Disease Journal. Vol. 23, no. 10 (2004): 909–914.
Directors of Health Promotion and Education. “Histoplasmosis.” 2005 <http://www.dhpe.org/infect/histo.html> (accessed February 23, 2007).
National Eye Institute. “Histoplasmosis.” December 2006 <http://www.nei.nih.gov/health/histoplasmosis/index.asp> (accessed February 23, 2007).