Wednesday, August 22, 2018

PRO/AH/EDR> Anthrax: latent infection, comment

ANTHRAX: LATENT INFECTION, COMMENT
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Date: February 2018
Source: Canadian Veterinary Journal [summarized, Mod.MHJ, edited]
<https://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC5764212&blobtype=pdf>


Robert S. Gainer, 2018. Spore concentration and modified host
resistance as cause of anthrax outbreaks: A practitioner's
perspective. Canadian Veterinary Journal 59 (2):185-187.
<https://europepmc.org/backend/ptpmcrender.fcgi?accid=PMC5764212&blobtype=pdf>

[Abstracted, summarized - Mod.MHJ]:
Most of what is written about the cause of anthrax outbreaks is by
professional academics in the fields of microbiology, epidemiology,
and pathology. Little has been written by veterinary practitioners as
it is normally not part of their job. Academic contributions could be
closer to the actual fact and could be more useful if they recognized
a practitioner's humble experiential intuition.

Gainer is a large animal veterinarian in practice for over 30 years in
northern Alberta and southern Northwest Territories. He notes that
without the usual alkaline soil-storing spores acting as a source of
infection, the infection must be transmitted from host to host with
the infection able to exist in a latent state most of the time.
Anthrax develops as a peracute infection when the extremely oppressive
insect harassment during high summer reduces the populations'
resistance to low levels, and tabanid biting flies transmit the
bacteria.

In a 3-year study in the Selous National Park in Tanzania, anthrax was
suspected in the wildebeest by previous biologists and veterinarians,
but was not confirmed despite many submissions for culture and
histopathology. A Canadian pathologist, Bob Lewis, suggested he take
lab mice into the field and inject them with carcass fluids as soon as
possible. The mice that died were to be frozen for transport and
shipped to the closest diagnostic lab. Eight of 9 mice came back
positive for anthrax, and he stopped doing necropsies on carcasses
that may have been anthrax-infected. Of the 28 confirmed and suspect
field necropsies, none showed the macroscopic features considered to
be diagnostic of the disease at that time. Eventually, he noticed that
the retropharyngeal lymph nodes were enlarged in some, but not in all.
Mostly they differed little from the normal healthy animals we shot
and necropsied routinely for food and other purposes. At the same
time, 4/8 biologists with the project developed cutaneous anthrax
lesions on their hands. In his 30 years as a veterinarian in Alberta
and NW Territories, he has noted a similar pattern of apparently
healthy animals dead. In these Canadian regions, the summer heat and
fly stress was so stark, his hands would get covered in blood from his
horses.

--
Communicated by:
ProMED-mail
<promed@promedmail.org>

[We know that animals can acquire latent infections with _B.
anthracis_. It is well documented and would allow the pathogen to pass
successfully from one summer to the next when the latter summer heat
would reduce the innate resistance, the infection could break loose,
bring the animal down, and be a source of infection for a number of
other stock. A coincident plague of biting flies would exacerbate the
stress.

Logically, this latent infection may explain how the pathogen was
brought by sea in the 16th century from Andalusia in cattle destined
for the Spanish missions in New Spain. Not having barbed wire in the
16th century, the common grazing Plains bison would have become
infected, and, in their seasonal migrations, transferred it north and
eventually into the Wood bison herds in northern Alberta and North
West Territories, where it became and is still especially virulent. A
working Wood bison bull weighs 1135 Kg. while the mature Plains bison
bull is only some 910 Kg., and in any Wood bison outbreak, over 80% of
the deaths are of bulls. The extra virulence is needed to kill them.
After the widespread and almost total slaughter of bison in the 19th
century, anthrax had to be reintroduced into the western plains with
the trailed cattle from Texas.

I, and many others, have tried and failed to recover viable anthrax
spores in the soil under and next to carcasses of confirmed white tail
deer deaths from anthrax. They are very sensitive to the anthrax
toxins and die with low titres. Where the spores persist on affected
Texas ranches has yet to be determined. Once a deer is dead, the
potential for blow fly contamination of nearby browse -- the deer's
favorite food, though they do also graze -- is available, and other
deer will be infected, if not also by biting flies. Maybe Bob's
hypothesis of cycles of latent infection may explain the persistence
of this disease in Texas white tails.

Bob has suggested an associated atypical-death reducing cause
recognition and a latent infection cycle exacerbated by seasonal
stress. These are hypotheses, and nature is illiterate and does what
it does. But, anyone needing a project for their graduate students
might want to explore these ideas. Retropharyngeal and mesenteric
lymph nodes could be collected from deer at dressing stations for
evidence of latent infections, and blood samples to check for antibody
status and proof of exposure. Logically, this should be done on
ranches where deer deaths from anthrax or not are known. Similarly,
are atypical deaths of uncertain cause more common in cattle herds
that have suffered from anthrax?

I have known Bob for a number of years. He is sound. There are a
number of his anthrax articles listed in the CVJ article. If you
should want to discuss this paper with Bob Gainer, his email is:
<gainer.bob@gmail.com>.

As an academic, albeit an epidemiologist and not a clinician, I would
like to comment that Bob may be describing hyperacute-stress deaths in
livestock and wildlife with latent _Bacillus anthracis_ infections and
not from latent _B. anthracis_ infections. Remember, more men die with
enlarged prostate glands than from prostate cancer. - Mod.MHJ]

[See Also:
2016
----
Anthrax - Canada: (AB) bovine
http://promedmail.org/post/20160419.4170484
2015
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Anthrax - Canada (10): (AB) bison, further confirmations
http://promedmail.org/post/20150824.3598790
Anthrax - Canada (09): (AB) bison
http://promedmail.org/post/20150823.3597470
Canada (08): (AB) bovine http://promedmail.org/post/20150816.3581348
Canada (06): (AB) bovine http://promedmail.org/post/20150730.3548199
Anthrax - Canada (04): (NT) bison, no new cases
http://promedmail.org/post/20150728.3543114
Anthrax - Canada (03): (NT) bison, conf
http://promedmail.org/post/20150723.3531387
Anthrax - Canada (02): (NT) bison, susp.
http://promedmail.org/post/20150715.3513428
Anthrax - Canada: (SK) bison
http://promedmail.org/post/20150710.3499232
2013
----
Anthrax, bison - Canada: (NT) estimated 2012 losses
http://promedmail.org/post/20130901.1917232
2012
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Anthrax, bison - Canada (08): (NT)
http://promedmail.org/post/20120814.1244145
Anthrax, bison - Canada (07): (NT)
http://promedmail.org/post/20120809.1237144
Anthrax, bison - Canada (06): (NT)
http://promedmail.org/post/20120803.1227788
Anthrax, bison - Canada (05): (NT)
http://promedmail.org/post/20120726.1216201
Anthrax, bison - Canada (04): (NT)
http://promedmail.org/post/20120711.1198108
Anthrax, bison - Canada (03): (NT)
http://promedmail.org/post/20120710.1196294
Anthrax, bison - Canada (02): (NT)
http://promedmail.org/post/20120709.1194889
Anthrax, bison - Canada (NT)
http://promedmail.org/post/20120706.1192749
2010
----
Anthrax, bison - Canada (16): (NT) MS, resolved
http://promedmail.org/post/20100913.3307
Anthrax, bison - Canada (15): (NT) MS, conf.
http://promedmail.org/post/20100901.3127
Anthrax, bison - Canada (14): (NT), WBNP conf.
http://promedmail.org/post/20100831.3108
Anthrax, bison - Canada (13): (NT), susp.
http://promedmail.org/post/20100821.2925
2007
----
Anthrax, bison - Canada (AB) http://promedmail.org/post/20070913.3030]
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