Horse Diseases Paul R Earl Facultad de Ciencias Biol

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Horse DiseasesPaul R EarlFacultad de
Ciencias BiológicasUniversidad Autónoma de Nuevo
LeónSan Nicolás, NL, Mexico
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Major infectious diseases are discussed, along
with heaves which is an allergy. Colic is caused
by the endotoxins of intestinal bacteria in some
cases, and in many others by abrupt dietary
changes, obstructions or gas. Nonetheless, the
major cause of colic is damage to the circulation
of the intestinal wall by bloodworms.Most of
these diseases like pneumonia in foals relate
more to raising young horses on farms than to
infections in adult work or racing horses.
However, encephalitis viruses can kill many
adults in somewhat unpredictable outbreaks. West
Nile Virus is the 2004 threat, but much
vaccinated against.
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An effective disease control program with some
emphasis on prevention is part of a total
management for proper health, nutrition,
reproduction, growth and performance. Such a
program would contain the control of intestinal
parasites, administration of several vaccines and
other such concerns given here, but briefly.The
eradication of horse diseases lies in the distant
future. Meanwhile, better understanding of the
role of vaccination is encouraged.
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ColicGet that horse up and
walking. He got casted, because he was rolling
because of abdominal pain. Casted means that he
was trapped against the stall wall and could not
get up. He could not get his legs under him.
Pull him off the wall by the tail or halter.
Pain has many possible causes like endotoxins
from intestinal bacterial infections. The central
symptom of colic is pain. Therefore treat the
pain with analgesics or tranquilizers.
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The cause of colic might be inadequate
blood circulation in the intestinal
wall.Bacterial endotoxins may interfere with
the synthesis or effects of inflammatory
mediators that in turn affect 1/ Pain,
2/ Fever, 3/ Increased pulse, 4/
Reduced tissue perfusion, 5/ Inhibition of
intestinal motility, 6/ Expansion of
intravascular fluid volume, 7/ Depression,
8/
Hemoconcentration and 9/ Leukopenia.
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EtiologyMany cases of colic
involve bacterial endotoxins. Something has
caused the loss of the integrity of the gut, and
the vascularization of the intestinal wall.
Expect several possible causes, not one that is
easily identified. Once it is established that an
infection is active, longacting IV terramycin or
another choice of antibiotics can supply
appropriate treatment. More, the fundamental and
physiological basis of the colic have not been
treated. What are emboli?
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DiagnosisSigns of painful
distress such as sweating are obvious. The horse
may evince colic by pawing with the forelegs, but
impatient yet normal horses may paw the ground.
Rolling on the ground is the strong sign of
colic. Fever may be part of colic along with
endotoxicosis. Normal resting pulse rate is 36
beats/minute. The respiration rate is 8-16
breaths/minute.
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TreatmentExcellent prompt
responses follow the injection of a painkiller
like flunixin meglumine at 1.1 mg/kg IV, IM or
less 1-3 times through 24
hours.Another good painkiller is chloral
hydrate administered as a 12 solution IV slowly
(over 5 min) or orally. The dose can be 22 mg/kg
IV (10 g for 450-kg horse). Administration
through a catheter is ideal because it can cause
a severe perivascular reaction. The onset of
action is 15-20 min when administered IV. The
duration of action is up to 12 h.
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PreventionGood grass-based forage,
clean water and the control of
parasitic roundworms should be enough to prevent
most colic. Grains and concentrates seem less
important than the hay. However, if a racehorse
is not eating up, overexcercise is the likely
cause, and new problems even including colic and
certainly including lameness can follow by
pushing the horse passed its natural limits. The
racehorse pushed passed his limits will go off
his feed of oats. Still, fatigue or the like is
rarely involved in colic.
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TetanusThe microbe Clostridium tetani
is responsible for causing the muscle rigidity
often seen in tetanus, more commonly known as
lockjaw. The organism is found in most soils and
enters an animals body through dirty, neglected
wounds and especially via punctures. The exotoxin
which C. tetani produces binds to the nerves at
the site of the injury and then travels to the
spinal cord and brain.
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EtiologyTetanus is caused by
anaerobic (no oxygen) clostridrial bacteria,
everpresent Clostridium tetani which produces
spores that live in the soil. It is often a fatal
disease via the production of toxins. However,
tetanus often associated with deep wounds is
controlable with antibiotics. Rusty nails, barbed
wire and other hazards that produce cuts can lead
to seriously threatening tetanus for all mammals.
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DiagnosisA stiff gait, rigid
extremities, a sawhorse stance, not eating and
overreaction to sounds are signs of tetanus. They
appear about 2 weeks to a month following
infection, but can be seen earlier depending upon
the amount of toxin produced. The toxin prevents
muscles from relaxing. Once a muscle has
contracted as in closing the jaw, it cannot
return to its original relaxed state, thus
creating always observed rigidity. Death results
from either an inability to breath or due to
seizures.The toxins demyelinize nerves (myelin
is the insulation, the covering of nerves),
resulting in dysfunction shown as stiff muscles.

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TreatmentA variety of antibiotics
like terramycin can successfully treat the
infections, but not damage already done by
toxin.Antitoxin IM or IV can be given to
neutralize toxin. Note that oid means like. Then
toxoid is like (modified) toxin.
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PreventionTwo products
are available for protecting horses against
tetanus. These are tetanus antitoxin and tetanus
toxoid. Tetanus antitoxin gives immediate but
short lived protection. It is given to horses not
previously vaccinated that have a wound or to
newborn foals from unvaccinated mares. It will
impart passive immunity a short while. Tetanus
toxoid gives long-acting protection, taking 2
weeks for antibodies to develop. This vaccine is
given as 2 shots, one month apart, followed by a
yearly booster. Foals can be given the vaccine
beginning at 3 months of age. Pregnant mares
should be given the vaccine one month before
foaling.
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StranglesThe symptoms are severe,
complications are common and at present there is
no effective vaccine for the disease. Antibiotics
such as penicillin can control and eliminate
strangles best if the disease is detected early.
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EtiologyStrangles is caused
by Streptococcus equi, group C, which is a highly
contagious purulent lymphadenitis and
pharyngitis. However, other strectococci are also
involved S. equi, S. zooepidemicus, S.
dysgalactiae subspecies equisimilis and S.
pneumoniae capsule Type III. Some horses become
longterm asymptomatic carriers. Vaccines are
available in the form of injectable extracts or
as live, attenuated organisms given intranasally.
However, their use is somewhat controversial and
indicated for horses at risk.
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DiagnosisSwelling and
infection of the throat region with fever and a
cough. The horse may be unwilling to eat. There
is often a nasal discharge, which may be serous
or mucoid initially and later purulent.Abscesses
may form in the retropharyngeal or mandibular
lymph nodes, in this area, 10-14 days after
initial signs. Persistent drainage from the
submandibular or pharyngeal areas can occur.
Cranial nerve dysfunction may occur in cases of
retropharyngeal abscesses affecting the recurrent
laryngeal nerve. Both PCR and ELISA have been
tries with S. equi.
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TreatmentVancomycin, clindamycin,
levofloxin, tetracycline (tetramycin) and of
course penicillin will control strangles.
Penicillin G or tetramycin can be given most
easily in the feed, but this is not done. It is
not in the tradition !
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PreventionWe have a very common
disease and immune carriers. Then foals rather
than adults are the problem. Prevention could be
through vaccination, BUT the results of research
are poor. Can be given nasally. Strangles like
many horse diseases can be eradicated of course,
but the reality is far in the future.
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ParasitesRoundworms are SO COMMON and
SO DAMAGING that they should be much better
controlled. WHY NOT ? Because MANY owners and
trainers think parasites are a normal part of
horse life WITHOUT knowing about the ferocious
damage.The strongyle group of equine roundworms
includes large and small strongyles. They are the
most important internal parasites of horses
because they are the most common and because of
the type of damage the immature stages do to the
horse. These worms are called bloodworms.
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The 3 large strongyles are 1/ Strongylus vulgaris
(bloodworm or redworm), 2/
S. edentatus and 3/ S. equinus.
Small strongyles have more than 40 species
and are called cyathostomes. Larvas develop
from eggs in a week or so. They are surrounded by
protective sheaths. The infective third stage
larvas migrate up and down blades of grasses,
waiting to be eaten by a friendly horse.
Ingested larvas migrate through the intestinal
wall into the arteries.
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The larvas of another large strongyle,
2/ S. edentatus, localize in the cecal
or the portal veins and cause perivascular
thickening. The liver becomes swollen, looks
bluish-red and has the white larvae embedded
under its capsule. Prolonged infestation causes
chronic fibrosis, tending to lead to
peritonitis and adhesions. The third large
strongyle, 3/ S. equinus, produces submucosal
cysts in the liver, pancreas and intestine. Small
strongyles (cyathostomes) cause less harmful
reactions.
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DiagnosisBloodworms are
diagnosed from feces with a qualitative flotation
method in a centrifuge. A quantitative procedure
is the Stoll or McMaster technique, which uses a
counting chamber to sum eggs/g of manure.
With the 6-11 month prepatent period (egg to
mature adult) for large strongyles, infections
will not be evident until weanling or later.
Transound scanning andradiographic arteriography
are diagnostic tools that complement rectal
palpation. Acute horses can have fever, poor
appetite, rapid weight loss, depression, lethargy
and colic.
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Treatment Ivermectin liquid
and doximectin gel are most excellent dewormers
that knock out bot fly larvas. So does
milbemycin. Many anthelmintics are active against
large and small strongyles. Benzimidazole (e.g.,
fenbendazole) among very many dewormers works
well. Migrating larvas can be treated effectively
with thiabendazole or fenbendazole daily for 5
days, 2 doses of oxfendazole on alternate days or
ivermectin. Fecal examinations will help.
Start deworming foals at 2 months of age every 2
months for the first year. Deworm adults 4 times
a year.
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PreventionSanitation, no crowding
and good management offer the best control of
roundworms. Disinfection of the environment,
particularly water tanks and feeders, decreases
the horse's exposure to any infective larvae.
Fecal samples taken say twice a year or before
and after treatment will guage the effectiveness
of dewormers. Deparasitizing will vastly reduce
the number of nematode eggs in the pasture.