An Introduction to Histoplasmosis for Arizona Cavers

James B

The purpose of this note is to provide background information on histoplasmosis or "histo" for novice Arizona cavers. I am not a doctor. While the information below was gleaned from scientific literature and my own experience as a patient, if you have questions about the prevention, diagnosis, and treatment of histoplasmosis, I have three pieces of advice: 1. See your doctor. 2. See your doctor. 3. SEE YOUR DOCTOR!

I have not included citations to the literature. Sources of further information are listed at the end.

Causal organism and where it lives: Histoplasma capsulatum causes the North American form of histoplasmosis or "histo." This fungus grows well in high-nitrogen soils rich in organic matter, including those enriched with droppings from chickens, bats, blackbirds, pigeons, starlings, and other animals. Of these, bat guano is considered the greatest hazard. Bats themselves carry the disease; birds apparently do not. Bird droppings might need to compost with soil before they can support growth of H. capsulatum, while the organism is able to grow in fresh bat guano. People can encounter high concentrations of Histoplasma spores when they stir up sediments in enclosed spaces, such as chicken coops, attics, barns, caves, and tree cavities.

In the United States, "histo" is most common in the eastern and central states, especially in river valleys. In some areas, such as the valleys of the Ohio, Missouri, and Mississippi Rivers, the fungus is abundant and widespread, and tests with histoplasmin show that many humans have developed sensitivity to H. capsulatum. This includes people who have no history of close contact with bird or bat roosts. In one area of Kansas City, more than 80 percent of the population becomes histoplasmin-positive by age 20. A well-documented outbreak in Indiana in the late 1970s affected more than 100,000 people.

Except for the Rio Grande Valley, Histoplasma is comparatively less abundant in the Southwest. In Texas and New Mexico, in the great cave roosts of the Mexican Free-tailed Bat, Tadarida brasiliensis, spelunkers and researchers have contracted "histo" after disturbing guano deposits.

Here in Arizona, Histoplasma is apparently less common, and its distribution seems to be patchy. Still, detection by sampling and culture of cave soil is difficult. While the risk of "histo" might not be high in all Arizona caves, I do not know of any way to predict which caves will house this organism. Some Arizona bats create guano deposits in the smallest caves and rock shelters. Caution is always appropriate.

Route of entry into the body: Inhalation of airborne spores causes "histo" in humans and dogs. Higher doses and/or longer exposure can cause more serious cases. The disease is not communicable from person to person.

People at risk: Children and the elderly might be more susceptible to infection than healthy young adults. People with weakened immune systems are at increased risk of contracting the disease, including those taking corticosteroids, those on immunosuppression after transplants, and those with acquired immunodeficiency syndrome (AIDS). Sadly, in recent years, "histo" has become a killer of people with AIDS.

Prevention: No vaccine is commercially available, though several have been investigated. Prevention centers on avoiding inhalation of spores.

Many cavers who contract histoplasmosis report having inhaled large doses of cave dust. I came down with it after digging in loose guano deposits in Jamaican caves. We were young and reckless, and we wore no protection against spores. If you blow your nose and produce lots of cave dirt in your mucus, stop and think hard about your caving habits. While most cases are benign and self-limiting, "histo" can be serious, even grave.

Take-home message on prevention and early detection: Spelunkers should strive to minimize the generation and inhalation of airborne spores. For your own sake, and for the sake of your fellow cavers, try to avoid stirring up guano or dirt as you move through a cave. When in doubt, wear a respirator approved for excluding the spores of Histoplasma, or stay out of the cave. If you become ill after exploring a cave, especially if you develop the symptoms described below, be sure to tell your doctor about your activities.

Clinical presentation, diagnosis, and treatment: Tens of millions of people in the United States are thought to have been infected with this fungus at some time in their lives. Most humans with demonstrable antibodies to Histoplasma have experienced no symptoms at all, or they have endured a mild illness with full recovery. That is, in the great majority of cases, exposure to the fungus caused no untoward clinical effects, or at most a self-limiting, flu-like illness. Some authorities estimate that prior to the advent of AIDS, approximately 95 percent of histoplasmosis cases were benign.

Be alert for the symptoms of the "primary acute form" of the disease. Incubation from exposure to illness varies from roughly 3 to 17 days (average approximately 10 days to two weeks). Symptoms vary, and can include headache, fever, fatigue, chest pain, loss of appetite, a dry cough, joint pain, red lumps on the skin of the extremities, and other symptoms. Many cases resemble influenza or other respiratory infections. While the flu typically lasts about one week, a "histo" attack can hang on for weeks. Most cases of "histo" resolve without specific treatment with antifungal agents. Recovery from a mild case can confer partial resistance to future attacks, but do not count on it. Some individuals develop serious hypersensitivity reactions upon repeat exposure.

This is speculative, but given that our Grotto includes many experienced, globe-trotting cavers, it would not surprise me if histoplasmin skin tests show that most of us have been exposed to Histoplasma.

I will not frighten you by giving detailed descriptions of the more serious, even fatal forms of histoplasmosis. Adverse sequelae include damage to the lungs and eyes, and dissemination into other organs. One man I know lost his eyesight to the point where he could no longer drive an automobile. The cause was not entirely clear, but damage to his retinas appeared to be related to his well-documented histoplasmosis. As a follow-up to my own primary attack, which was not all that bad, I have my eyes examined every year or two, and I have a chest x-ray every ten years or so.

Diagnosis is by direct culture of the organism from the patient's tissues, sputum, or urine. Chest x-rays and studies of circulating antibodies are often helpful, as well. Physicians use care to differentiate "histo" from other fungal infections (mycoses) of humans, including blastomycosis and coccidioidomycosis (or Valley Fever). Valley Fever is relatively abundant here in Arizona, especially among desert dwellers. To complicate matters further, advanced "histo" can mimic tuberculosis, and it can co-occur with other diseases, including Valley Fever and tuberculosis.

If indicated, a physician might prescribe oral itraconazole, or, in more serious cases, intravenous Amphotericin B. Both have been shown to be effective in treating histoplasmosis, and, as with all drugs, both have side effects, especially Amphotericin B. New therapies are under development.

Sources of further information: Consult your doctor and your local health department. America's leading authority on public-health issues arising from histoplasmosis is the National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, Georgia. Their phone number is (404) 639-3158. You can find NCID on the Net at www.cdc.gov/ncidod/ncid/ncid.htm .

The following is a direct quote from NIOSH's web page on histoplasmosis: "Recommended work practices and guidance on the selection of respirators and other items of personal protective equipment for protecting workers are described in a booklet developed by the National Institute for Occupational Safety and Health (NIOSH) and the National Center for Infectious Diseases (NCID). A free copy of Histoplasmosis: Protecting Workers at Risk is available from NIOSH by calling (800) 356-4674 and requesting publication number 97-146. The text of this 20-page booklet is available through the NIOSH Internet home page: www.cdc.gov/niosh/homepage.html  (Click on "NIOSH publications"), or directly at www.cdc.gov/niosh/97-146.html ."

Remember: Avoid breathing dust, especially if bats have roosted in the cave. When in doubt, SEE YOUR DOCTOR. ^*^

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