Histo – the short name for histoplasmosis – is a deceiver. It used to be thought rare.

Only 71 cases were known to doctors in the United States up to 1945. Today an estimated fifty million Americans are believed to have been infected with it.

Histoplasmosis used to be considered a fatal disease. Today, among the millions infected, there are very few fatalities.

Histoplasmosis is a masquerader. The "summer flu" that Midwesterners used to get often is now thought to he been histoplasmosis. The disease is not "catching" from someone who has it, as tuberculosis is – but many times it has been mistaken for TB, as well as other diseases.

What Causes Histoplasmosis?

Histoplasmosis is caused by a fungus (mold), an extremely simple form of plant life. (Other familiar fungi are mushrooms, yeast and mildew.) The particular fungus, or plantæ, that causes this disease is known as histoplasmosisplasma capsulatum. It is tiny and light enough toloat in the air when stirred up with dust.

Once it is breathed in, the fungus gets down into the lungs. In effect, it takes root there like a seed and continues to live. The tiny plants increase in number within the lungs simply by dividing themselves in two – over and over again.

Although histoplasmosis is not as uniformly serious as was once believed, it infects millions of people all over the country, many of them living in the Mississippi, Ohio, Missouri and other river valleys.

It took years of detective work and the patient tracking down of clues to unmask and identify histoplasmosis. There are still many mysteries about the disease, but certain facts are known.

Where Histoplasmosis is Found

Histoplasmosis has gone to town. It used to be considered a rural Midwestern disease. But it has been discovered recently in small towns and even cities in the East and other parts of the country.

Because the histoplasmosis seeds, called spores, are living things, they need certain conditions in which to flourish. There must be warmth, moisture, and preferably some darkness.

These conditions are found most often in accumulated droppings from chickens, pigeons, starlings, and other birds, as well as bats. Therefore, the place of infection for many people has often been old chicken houses, barns, belfries, pigeon lofts, caves and in parks under trees where many birds have roosted.

One outbreak of histoplasmosis involved a troop of Boy Scouts who had worked hard cleaning up an old city park in which many starlings roosted. The dank, damp undergrowth of the park was disturbed for the first time in years – and the boys breathed in a sufficient quantity of fungus-bearing dust to get the disease.

In one celebrated instance, a number of schoolchildren came down with what eventually was diagnosed as histoplasmosis. The source of the disease was painstakingly traced to a window of the schoolroom. Several weeks before a load of coal had been dumped under the window. The coal, it is believed, came from a mine in which the histoplasmosis fungus had grown.

Who Gets Histoplasmosis?

Most persons who come in contact with a heavy barrage of histoplasmosis spores are infected. But fortunately in most persons the infection produces no symptoms. Usually people do not even know they have been infected, but some do get sick.

Schoolchildren of both sexes are frequent victims. More men than women, however, get the disease as adults. Very young children and old men are the most susceptible to the generalized form of histoplasmosis that spreads from the lungs to other parts of the body.

What Happens Within the Lungs?

When the fungus-bearing dust is breathed in, the tiny histoplasmosis spores are carried into the bronchial tubes (the air passages in the lungs). Some of the spores eventually reach deep down into the very tiny air sacs of the lung – where the air we breathe in finally winds up before it is exhaled. Then various things happen.

In the air sacs some of the spores are arrested by wandering police cells called phagocytes. They are taken to the lungs’ lymph nodes, where they are trapped and held. But they may find the lymph nodes an excellent place in which to stay and multiply.

The lymph tissue reacts to this invasion. A sensitivity – actually an allergic reaction – develops. The area becomes inflamed. The tissues of the nodes may be damaged, as well as nearby lung cells. Scars and calcium deposits may form.

Others of the spores that reach the air sacs are attacked by the body’s defenses right there. As it does tuberculosis germs, the body walls up most of these spores in calcified tubercles. (On an X-ray these look just like the tubercles of tuberculosis.) The little plants in their calcium prison become starved for oxygen and nutrition. Though remaining in the body, they are harmless and cannot multiply.

Spores that escape these defenses may damage lung tissue and even form cavities – also much like those of tuberculosis.

But, unless the spore invasion is enormous in quantity, these various reactions actually do the patient little harm in by far the majority of cases. Some feel no symptoms at all, others suffer a brief and relatively mild illness. Only when the spores spread throughout the body – as happens only rarely – is there real trouble. The "disseminated" form of histoplasmosis is often fatal.

What Histoplasmosis Does

Depending on the number of spores the patient has taken in, the symptoms of histoplasmosis vary widely in intensity. The symptoms, when they appear, are usually almost identical with those of flu. Fever, tiredness, sometimes a slight cough or chest pains. Actually, histoplasmosis takes four possible forms:

Mild infection. This is often without symptoms. The patient may not ever know he has had it. It lasts from one to three days.

Acute lung infection. This is usually self-limiting and confined to the lungs. The patient feels fever, recurring chills, cough, chest pain and labored breathing. Even without treatment, this clears up in two weeks to three months.

Chronic lung infection. Looking much like TB on an X-ray, this form shows cavities, calcium nodules and other TB-like signs. Illness hangs on. Treatment, when indicated, usually helps.

Disseminated form. A large number of the fungus spores spreading outside the lungs mean more serious symptoms: loss of weight, extreme tiredness, anemia and weeks or months of convalescence. Without treatment, a great portion of these patients die within four to ten months after their exposure to the fungus. Fortunately, this is a rare form of the disease.

How Histoplasmosis is Diagnosed

There are both skin tests and blood tests that can reveal the presence of histoplasmosis infection and disease.

Histoplasmosis also shows up on chest x-rays, but since x-ray findings are almost indistinguishable from those of tuberculosis, this may be undependable. Healthy young men who once unknowingly had histoplasmosis were kept out of military service during World War II because their x-rays suggested extensive tuberculosis scars.

Today there are a variety of specific skin tests – and also tests in which the organisms are examined under the microscope – that differentiate other fungus diseases and tuberculosis from histoplasmosis.

Treatment

Most cases of histoplasmosis require little or no treatment. After their flu-like symptoms, patients recover of their own accord.

A drug, amphotericin B, has been found effective in the more severe cases of histoplasmosis. Its use requires hospitalization, however, because the drug must be introduced into the bloodstream almost daily for a period of weeks or months. Side effects have to be carefully monitored.

Surgery – removal of sections of the lung that are imbedded with histoplasmosis spores – may sometimes be indicated when there has been extensive damage.

Prevention

Simple avoidance – of caves, belfries, old chicken houses, and the like – is one possible way to escape histoplasmosis. But this may well be impossible, particularly for people in rural areas. And even if a real effort were made to stay away from places of suspected infection, there are so many areas of unknown infection that avoidance of histoplasmosis would seem to be almost a matter of luck.

Here are a few simple rules that might – just might – help to prevent histoplasmosis or cut down its severity:

• Keep farm buildings as clean and dry as possible. Before sweeping them out, wet down the floor to prevent dust from rising.
• Always wet down chicken droppings before cleaning out chicken houses.
• Keep storm cellars clean and dry.
• Take care of minor illnesses and try to stay in as good general health as possible.