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Topic Number: 16

From: WLewis6373@aol.com
Date: Sat, 15 Aug 1998 19:24:27 EDT
To: cavers@ditell.com
Subject: Recurrent Histo


To Gill Ediger and other commentators, Hi!
Perhaps some of your questions can be answered.

Immunity to histo is usually established about 30 days after exposure with
positive skin and blood tests. This immunity fades over a period of years.
It is not like TB that gives a lifetime immunity. Reexposure has
demonstrated  a rapid rise in titer in a few individuals in whom it was
measured.

The skin test becomes negative first. At the Texas Old Timers, CDC
found that 30% of volunteers were (falsely) negative. This points up the
inability of the present test sera to pick up all cases. You are one of
the 30%. You are immune whether the test confirms it or not.

If you do not cave for the next ten years, you may lose most of your
immunity. If you get an immuno-suppressive disease, you are again
susceptible. If you take chemical or radiation treatments that suppress
your immunity, you may get generalized histo and it may cause your demise.


Some of the early AIDS deaths were from overwhelming histo. It seems
likely that the calcified nodules seen on x-ray in the spleen and lungs do
harbor live histo cells for long periods. In  this, they may be similar to
the Ghon Complex in TB. Starvation or debilitating illness may take the
calcium from these nodules. I do not think you are referring to these
cases.

Many of the cases of chronic cavitation of the lungs with negative
tuberculin tests found in TB Sanitariums years ago turned out to be histo.
I do not think that these cases have ever been adequately explained.
Reinfection has been considered, but remains a hypothetical cause.
Certainly, most cases of reinfection do not go on to advanced, chronic
disease.

There are different strains of histo. In particular there is a strain with
larger spores in west Africa. If there is s medical  study associating a
certain strain with increased virulence, I am not aware of it.

We should be aware of North American Blastomycosis. It has been
associated with  moist northern campsites, beaver dams, fence posts
of cattle pens, etc.,in widely scattered locations. It is associated with
animals and.perhaps with animal dander. The Costa Rico Report associated
it with caves.

Other lung fungi are associated with storage and handling of our major
food crops, especially in silos. World wide exposure comes with almost all
of the crops furnishing natural fibers and sugar cane. Each has its own
name for the illness of workers inhaling the dust, especially in closed
spaces.

The speed of onset of histo has been questioned. The earliest onset I
found seems to have been 3 days and caused death in that young laborer.
The lung  air space was obliterated by a massive inflammatory response of
lung tissues. In fatal cases, the organism has been recovered from the
bronchial tree and the blood stream. Onset may occur in 30 days or longer
but these cases, in general, seem to have been more mild. The usual onset
in cavers seems to be 10 to 14 days after the initial exposure, often
after they have returned home. Some late cases may have come from exposure
to dust on objects from the cave, equipment, coveralls, artifacts, etc.

Thanks for sharing your experiences. We learn about the epidemiology of
this disease from your careful observations.

Warren Lewis. M.D. (retired)