The current thinking is that M. bovis
is the primary pathogen and M. bovoculi
works as a co-pathogen.
“When we look at bacteria cultured
from affected eyes, and differences
between those two strains, reports
show higher incidence of M. bovoculi
in these cultures. This confounds our
thinking on what is actually causing
the disease, and how those two
pathogens work together,” he shares.
Several factors play a role. “In veterinary
medicine we talk about the epidemiological
triad - interaction between
the host, the pathogen and the environment,”.
Dr. Kesterson continues.
“These things overlap; genetic susceptibility
of the host, stress, comingling
with other cattle (some of which may
have pinkeye), environmental factors
such as dust, UV light exposure,
fl ies, mechanical irritation from rigid
forage plants/grass awns, along with
the pathogen effects. There might be
concurrent infections, and/or changing,
mutating forms of bacteria, new
serotypes, shedding of bacteria from
other animals in the group, etc. All
these things overlap to increase the
incidence or severity of this disease.”
Signs of pinkeye include sensitivity
to light (eye held shut), excessive
tears, a cloudy appearance or white
spots on the eye, or ulcerations. Left
untreated, some lesions become deep
and may lead to permanent scarring
and impaired vision or result in rupture
of the cornea and blindness.
“I don’t think people realize the
rapid onset of this disease. The central
corneal lesions in some cases can
appear as quickly as 10 to 12 hours
after infection begins. Some animals
have full-blown pinkeye within 24
hours. Thus, it becomes urgent to treat
the eye,” Dr. Kesterson recommends.
OTHER CAUSES OF
The fi rst thing we think of when we
see any of these signs is pinkeye, but
there are other causes of ocular irritation.
Environmental challenges include
dust, tall grass, or hay that includes
sharp seed-heads. There may be foreign
material such as cheatgrass seeds
caught underneath an eyelid, scraping
the cornea every time the animal blinks.
Fascinating Face Fly Fact: they like super fresh grass-origin manure (hey, who doesn’t?) -
they will lay their eggs in a cow patty deposited only 15 minutes earlier.
“Another possibility, when we see
a watery eye, is viral infection. The
most common virus that might cause
these signs is IBR (infectious bovine
rhinotracheitis). We must sort out all
possibilities, which include environmental
challenges, trapped foreign
bodies, other diseases, or true pinkeye,”
suggests Dr. Kesterson.
“When we examine the affected eye,
almost 100% of the time, lesions from
a trapped foreign body (caught under
the eyelid) will be on the periphery of
the eye (closer to the edge), whereas
pinkeye lesions are almost always
centrally located,” he says.
If the sensitive, watering eye is suspected
to be due to IBR, the producer
needs to talk with a veterinarian
about the other effects of this virus.
“This disease can cause respiratory and
reproductive issues; a watery eye may
be a signal for further investigation
and a discussion about vaccination
protocols to protect the herd,” Dr.
Treating pinkeye can be challenging.
There are only a few products labeled
for treating this disease, and producers
need to work with their veterinarian
to try to fi nd the most appropriate
treatment for their own situation.
“In practice, I was commonly asked
about benefi ts of injecting antibiotic
into the tissues surrounding the eye
(the conjunctivae), into the inner part
of the eyelid,” Dr. Kesterson recalls. “A
small amount of antibiotic like penicillin,
often mixed with a corticosteroid
(to help reduce pain and infl ammation)
was often injected into this tissue. A
study published in 1995 in the (Journal
of the American Veterinary Medical
Association) found there was no benefi t
to injecting any of the products they
evaluated. This procedure may have
risk for additional harm to the animal.”
Treatment for pinkeye should
include protection for the eye. When
Dr. Kesterson suffered a corneal
scratch himself, diagnosed by his
eye doctor, it was excruciating to be
outside in the sunlight. “Bright light
caused extreme pain. Just covering
the eye brought huge relief. An eye
patch for an affected animal is one of
the most important things you can
do for that animal,” he says.
In severe cases veterinarians sometimes
suture the third eyelid (nictitating
membrane) across the eye to protect
and nourish it. This is better than
suturing the eyelids together, which
might cause more irritation due to
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