AQHA Magazine September / October 2020 | Page 18

PG.16
AQHA VET NEWS
TETANUS
A CRUEL, EASILY - PREVENTED DISEASE©
ARTICLE BY: DR JENNIFER STEWART - BVSC BSC PHD EQUINE VETERINARIAN AND CONSULTANT NUTRITIONIST
Tetanus is not uncommon in unvaccinated horses.
Most cases end with the death of the horse.
At first glance, tetanus and botulism appear
unrelated as the symptoms are opposite
- spastic paralysis in tetanus and flaccid
paralysis in botulism. Both however
are caused by nerve toxins produced by
clostridial bacteria that interfere with normal muscle
contractions, have a worldwide distribution, affect nearly
all species, have a high death rate and have been known
for centuries - and still occur today. An early description of
tetanus was made by Hippocrates in the 5th century BC -
around 2500 years ago. In 1884, the cause was identified. In
1924 the first vaccine was produced and in 1932 vaccination
to protect horses from the toxin began.
are 600 times more resistant to tetanus than horses. Based on
the amount of toxin required to produce lethal disease, horses
are one of the most susceptible species.
When growing in soil, Cl. tetani is rod-shaped and has flagella
that give it sluggish mobility. As it matures and produces
spores, it enlarges at one end - resembling a drumstick. (Figure 1).
Tetanus is caused by toxins produced by a bacteria called
Clostridium tetani which has an almost universal distribution
in nature. It is found in human and animal manure, hay dust,
soil and also on clothing and skin contaminated with soil or
manure. It has also been identified in mud dredged from the
bottom of Lake Geneva, the Dead Sea, ship bilge water and
gun-wads. The toxin, 1mg (ie 1/1000 of a gram) of which can
kill 100 million mice, has been used on poison arrows where it
was obtained from burrows of large crabs.
Horses, guinea pigs, goats, monkeys, mice, sheep and humans
are highly sensitive to tetanus toxin, cattle dogs, and cats less
so, and birds are resistant - due in part to the inability of the
toxin to penetrate and bind to their nervous system. Cats are
around 10 times more resistant to infection than dogs and dogs
(Figure 1)
The spores are incredibly resistant to destruction – surviving
extreme environmental conditions, withstanding anti-septics
and killed only by boiling for at least four hours or autoclaving
at 115°C. The organism does not grow in normal tissue, but
when the skin is breached, tissue underneath gets damaged
and dies. This creates a perfect environment for the bacteria to
grow and multiply. The growing bacteria release a neurotoxin
that enters the blood stream and binds to nerves, causing
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