As in most other domesticated species in the
world, as well as in
humans, vaccination is an
important part of health
management and disease
prevention. Prevention and
protection from disease is
almost always far superior
than treatment of the problem.
Disease verses protection question can be affected by many factors. The
actual immunity or defense
mechanisms of the host (in
this case, the horse), how
strong is it? Nutrition and
body conditions affect the
host's ability to resist disease. Age, previous infections, presence of other disease and of course,
whether or not vaccinations have been given for
specific problems all have
a say on host immunity.
Environment also plays a
role in several ways.
Specific diseases exist in
certain areas or certain
types of environments,
contact with other horses
and sanitation or management conditions. The type
or pathogen involved is
another contributing factor. How virulent (how
infectious) and the actual
number of disease organisms present are important.
When considering types
of vaccination for your
horse, one must consider
all of the following. The
risk of exposure, chance of
infection and the consequences of infection are
important to know. The
safety and efficacy of a
particular vaccine are
other considerations.
Passive immunity is
obtained by foals in the
colostrum from mares, and
this gives foals protection
from everything the mother has antibodies against
for the first three months of life. Active immunity occurs when a disease organism or a vaccine challenges a horse's immune system. In a good preventive health management program, active vaccination of horses should begin at about three months of age. Killed vaccines are most commonly used, but some live or
modified live vaccines are
needed as well. Protection
occurs two weeks after
vaccination and boosters
are needed four weeks
after the first vaccine in
young horses.
Here in the Maritimes,
horses have different
needs than in other areas
of North America and the
following are some of the
more important diseases
they should be protected
from.
Tetanus or lock jaw most common in humans
and horses, is caused by
clostridium tetani. These
spores live in the soil and
feces and this is a worldwide problem. Infection
most commonly occurs by
contamination of wounds or
punctures to hooves.
Treatment is usually futile
and death is usually the
end result. The tetanus
toxoid vaccine has been
available since the 1930's,
and is very effective in
preventing the disease.
Aged horses need annual
vaccination, while foals
can start three months,
followed by four and 12
month boosters.
Rabies is a virus that
invades the brain of all
species in the world.
Frequently, rabies is
transmitted by wildlife
bites or aerosol spray from
animals like foxes, skunks,
racoons or bats. Rabies is
100 per cent fatal and
poses a serious risk to people. In southwestern
Ontario, rabies hits the
horse population from 60-
100 times per year. On
P.E.I., there have only
been two reported cases of
the dumb form of rabies in
foxes about five to six
years ago, while Nova
Scotia has reported several
forms of bat rabies. New Brunswick has recently presented racoon rabies near the U.S. border.
Rabies vaccinations are readily available, but to date, no efficacy studies have been done on horses. The risk is low here in our region, but if you have ever been involved with rabies in horses as I have, then I would strongly recommend annual vaccination. Young horses should
start at five months and
one year of age.
The respiratory viruses
are constantly sticking
their heads up in all of
North America, usually
here just before some big
stake races. Late spring or
early summer, early fall
just after the annual yearling sales and late fall,
after the Harrisburg Sale
are the usual time of epidemics here at Maritime
tracks. Equine influenza is
the most common form isolated here, but equine herpes virus
(rhinoneumonitis) also
occurs here. Mixed infections are not uncommon.
Equine influenza causes
mild to moderate lower
respiratory disease, which
usually lasts 5-14 days. The
"virus", as it is affectionately called, is often not
the major problem, but
rather the secondary complications that occur.
These would include bacterial tracheobronchitis
(lung infection), pharyngeal lymphoid hyperplasia
(throat infection or pimples), allergic bronchitis,
pneumonia, pleuritis, displacement of soft palate or
exercise-induced pulmonary hemorrhage (lung
bleeder). Flu virus is
transmitted by direct contact and aerosol which is
exacerbated by the transient horse population
moving all over the place
to race, etc. Horses less
than three years of age are
almost always the only
ones affected. Aged horses
rarely would obtain this
virus. Obviously, a great
loss of training and racing
time happens and often
whole stables or even
whole racetracks are
affected.
Traditional vaccines
available offer only short
term or incomplete protection primarily because of
strain differences. If given
every two months to two
and three-year-olds at high
risk, they do however
reduce the frequency,
severity and duration of
the disease. A newly released intra nasal vaccine called Flu Avert, is a modified live vaccine called Flu Avert, is a modified live vaccine delivered through the nose and supposedly, a single dose will have greater than six months protection.
Equine Herpes Virus-1 and EHV-4(Rhinoneumonitis) not only causes respiratory disease with similar signs in young horses, but it also
can cause abortion in
mares (often abortion
storms) or a paralytic
form can cause temporary
or permanent paralysis in
horses. Risk factors are
similar to influenza, but
EHV is an upper respiratory problem. Some of the
secondary problems listed
for influenza would be the
same for EHV. EHV-1 is
the cause of abortion, and
vaccination at three, five,
seven and nine months of
pregnancy with a killed
vaccine, like Pneumobort-
K, offers good protection.
EHV-1 and EHV-4 cause
respiratory problems and,
again, vaccines offer only
short term or incomplete
protection and should be
given bi-monthly. This
vaccine can cause a mild
transient fever for a day,
or two.
The four conditions listed above are the most
common problems vaccinated for in the
Maritimes, but there are
other considerations, especially if your horse is
being transported to certain areas of the United
States.
Eastern and Western
Equine Encephalomyelitis
is commonly reported in
the southern U.S., but is
uncommon in Canada.
Annual spring vaccinations are usually effective.
Strangles is a highly
contagious bacterial infection that affects upper respiratory tracts and often
other areas of the body,
primarily in weanlings
and yearlings. Death does
occur in 5-10 per cent of
reported cases. This bacteria, streptococcus equi,
can survive in environments for six months, and
is transmitted by nasal
discharge and ruptured
abscesses, and can
become endemic on some
breeding farms. There are
no definitive studies concluded yet, but anecdotal
evidence suggests that
both the intramuscular
and intra nasal vaccines
are ineffective, and the
latter can possibly induce
disease on a farm.
Potomac horse fever
(PHF) can cause sever
diarrhea and death, and
has occured in the
American east coast and
midwest, as well as in
Ontario and Quebec, but
has not yet been reported
in the Maritimes. An
Ehrlichial bacteria is the
causitive agent, but transmission is unknown. Tick
may be involved. Recent
studies suggests that currently available vaccines
are not effective and since
the risk of disease is low,
vaccination is not recommended.
In the future, increased
use of modified live vaccines is likely to occur
along with the use of new
adjuvants or carriers.
DNA vaccine studies are
currently underway in
horses and these may
offer better protection for
some of the diseases that
currently are difficult to
vaccinate successfully for.
The following summary
table would apply to
Maritime horses only.
