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Pinkeye (infectious
bovine keratoconjunctivitis) causes high losses annually for
cattlemen—due to poor weight gains, cost of drugs and labor in
treating infections, prices docked because of eye damage or
blindness, calves cut back at sale time. Seedstock producers
don’t want pinkeye scars on bulls or replacement females.
Stockmen generally try to prevent pinkeye outbreaks in their
herds, but often this proves to be a frustrating challenge.
Dr. Richard Randle,
College of Veterinary Medicine, University of Missouri, says
dealing with pinkeye is complicated by the fact there are
several causes of eye lesions in cattle that are all lumped
together and called pinkeye; a number of things can create signs
similar to those of infectious pinkeye—including eye injuries,
and IBR (“rednose”). A number of pinkeye “outbreaks” are
actually due to IBR when cattle herds do not have adequate
immunity to this viral disease. The success of treatment or
vaccination for pinkeye can be varied, as a result.
The most common
cause of pinkeye, however is Moraxella bovis, a bacterium that
can invade the eye if there are any scratches or irritation that
open the way for it to enter the tissues. “In most cases eye
lesions result from spread of contaminated eye material from an
infected eye to a non-infected animal, and this can happen in
several ways. Obviously, fly control is a big part of pinkeye
control,” says Randle.
Solid colored
cattle with dark skin around the eyes have traditionally been
thought to have less pinkeye, but this isn’t true. “The color of
the skin around the eye, and the related irritation from
ultraviolet light is a factor, but because of the variety of
agents out there that cause eye lesions, there are a lot of
things that make it to where color is not a big factor in
whether or not an animal will get pinkeye,” he says.
Dr. Annette
O’Connor, Iowa State University, says Moraxella bovis is
generally considered the bacterium commonly associated with
pinkeye, but other organisms can be involved. “Just having M.
bovis in the eye isn’t enough to cause pinkeye in cattle. There
must be trauma to the eye to enable bacteria to establish an
infection. M. bovis tends to stay in the lubricating fluid of
the conjunctiva (delicate membrane lining the eyelids and the
exposed surface of the white of the eye). Unless there is trauma
to the eye, the bacteria can’t bind to the cornea and cause the
disease,” she says. Things that cause trauma include high levels
of ultraviolet light, infections by viruses and mycoplasmas,
plant pollens, tall grasses that scrape or cut the eye while the
animal grazes, dusty feed, dusty or windy conditions, and face
flies.
“Other flies like
horn flies and stable flies may be involved also. The disease
incidence usually peaks in summer—probably because there are a
lot of flies, the grass is long, it’s usually dry and dusty, and
there’s a lot of ultraviolet light. All these things occur in
summer and conditions are right for trauma to occur to the eye.
There is also evidence that infection with other agents such as
mycoplasmas and infectious bovine rhinotracheitis (IBR) can
affect the eye,” says O’Connor.
Prevention
There are several ways to try to prevent pinkeye, such as
preventing situations where trauma occurs. “Reduce dust, clip
grass, provide shade, control flies, etc. But these practices
are not always effective. It’s difficult to control dust, almost
impossible to control UV light, and on some properties it’s
impossible to keep the pastures clipped,” says O’Connor. There’s
no one thing alone that is totally effective in prevention or
treatment. It’s a multi-faceted approach—doing a number of
things together to try to minimize the effect.
“Some of these
methods may work on some farms, while others won’t. On one farm
the problem might be dust: the rancher starts a fly control
program that’s effective, but it’s not the main cause of the eye
trauma. On one farm it might be dust and on another it might be
long grass. So that’s why you see variable responses to
management practices,” explains O’Connor.
Vaccination
The other most frequently used preventative practice is
vaccination. There are several brands of pinkeye vaccine
available. The goal of vaccinating is to boost the animals’
immune response to the causative organism. “You are hoping the
animal’s immune response will protect it. Results with
vaccination tend to be variable, however,” says O’Connor.
We don’t always
know what antigens to put in the vaccine to make it effective,
she says. M. bovis binds to the eye by means of filament-like
appendages called pili, and these contain some of the antigenic
properties of the bacteria. “If a vaccine contains pilus
antigens it’s thought to be more effective. But pilus antigens
change more rapidly than vaccines can be changed. Most vaccines
contain several pilus antigens, but they have to go through
tests to show efficacy, etc. before being accepted for use. Then
when they finally get on the market, if they are used on a farm
where M. bovis has that particular pilus antigen, it will
probably work,” says O’Connor. However, if the pillus antigens
change, the vaccine may not work.
“We don’t know how
this happens. Perhaps the antigens change, or another pilus
antigen is introduced to the farm from new cattle or flies.
There is some cross protection, but not much,” she says.
Randle says, “In
terms of the vaccines available, there’s varied success with
those. Tryng to build a good immunity at the eye level is
difficult. The thing to understand about vaccine is that in a
lot of instances it won’t prevent an outbreak. But in the face
of an outbreak, vaccination can help by reducing severity of the
cases and maybe shortening the time period,” he says.
“In herds where we
have a severe eye problem that doesn’t respond to normal
therapy, an option is to take swabs from eyes and try to culture
the organism and determine what is actually going on. This can
help us redirect the therapy. In herds with severe problems it
may warrant trying to better determine the cause and see what
other agents may be responsible,” explains Randle.
Herd Health
Keeping good immunity to other diseases (such as IBR and BVD)
can help prevent pinkeye. Som viral diseases can hinder the
immune system and lead to higher incidence of other problems.
Dr. Robert Cope (Salmon, Idaho) has found that when ranchers
vaccinate calves with modified live IBR-BVD vaccine, this
dramatically reduces incidence of pinkeye, foot rot, diphtheria
and summer pneumonia in the calves.
IBR (infectious
bovine rhinotracheitis, or “red nose”) can also be mistaken for
pinkeye. Randle says, “IBR has an eye form and can cause runny
eyes and eye lesions that look very similar to infectious
pinkeye. Being a virus, IBR does not respond well to antibiotic
therapy. So some eye lesions may actually be an eye form of IBR.
This is a herpes virus, and herpes can cause ulcers. Once a body
is infected with herpes, it’s always infected--like a person
with recurring cold sores or shingles. Situations of stress
bring it on again. IBR vaccines are very effective at preventing
some of the respiratory or reproductive problems associated with
IBR, but not always effective at preventing the eye lesions.”
Total herd health
is very important, and this includes cattle management and
nutrition. There are many things involved in the pinkeye issue,
such as trace minerals and basic deficits in mineral content of
diet that can make a difference, according to Dr. Larry Letner,
at Harris, Missouri. In order to reduce pinkeye, he feels a
rancher needs to understand mineral content of the soil, grass
types, growing seasons, protein levels in forages, etc. In his
practice, Letner focuses on total herd health and principles of
management and nutrition before he starts with drugs and
vaccines. A lot of people start at the top with drugs, and then
finally get back to what some of the underlying causes might be,
he says.
Treatment
O’Connor says an important part of prevention is treatment. If
we intervene and treat early, before the disease becomes severe,
we can limit the impact of pinkeye on weaning weight, and may
also save an eye that would otherwise become scarred or
permanently damaged.
“People often think
they have failed because they had to treat an animal, but if
they understand the disease they will realize why they sometimes
can’t prevent it. If they view aggressive treatment as a way to
limit the impact of pinkeye, that’s also successful,” she says.
By treating early, you minimize spread of pinkeye (via face
flies, from animal to animal).
Pinkeye is easily
spread. “If you get the cattle in to treat a few and run them
all through the chute, you create an environment in which all
the calves will be more susceptible. You may increase
transmission of the disease through the herd, unless you can
bring the affected animal in by itself to treat. If you treat an
animal with pinkeye, make sure your hands are clean before you
touch the eyes of the next animal, or you’ll defeat the
purpose—you will be the spreader! It’s very important when
treating pinkeye, to try to limit that impact,” explains
O’Connor.
She has heard
producers say, “I treated the herd and the pinkeye outbreak got
worse!” It could certainly work that way. If you round up the
herd, put them in a dusty corral and run all the calves through
the chute, you might be making it possible for them all to get
pinkeye.
Cases of pinkeye
caught in early stages respond very well to treatment, but even
eyes that are badly ulcerated and blind will recover, with
proper treatment. Two things are important in treating
pinkeye--using an antibiotic to combat the infection, and
protecting the eye from dust, sunlight, flies and other
irritants while it heals. Cope says M. bovis is susceptible to
many of the more commonly used antibiotics, and some are
marketed as topical treatments for pinkeye. “Unfortunately, it
is difficult to maintain adequate levels of drugs applied
topically; they don’t stay in the eye long enough. Tears wash
the medication out of the eye within a few hours,” he says.
Ointments, powders, sprays or squirts must be repeated at least
twice daily to be effective.
“Normal cattle
produce up to an ounce of tears daily. Cattle affected by
pinkeye produce many times more tears than normal, which rapidly
wash away antibiotics on the surface of the eye,” explains Cope.
Antibiotics injected under the conjunctiva lining the inside of
the eyelid stay at the site longer, he says.
An antibiotic mixed
with dexamethazone is often used for this injection; it not only
lasts longer at the site than topical medication, but also
provides pain-killing anti-inflammatory relief. LA-200 has also
been shown to be beneficial, injected intramuscularly or
subcutaneously at a rate of 4.5 cc per 100 pounds of animal,
says Cope.
Eyes generally heal
faster (and with less complications) if protected with eye
patches or sewing the eyelids shut. The latter has the advantage
of being more dependable for protecting the eye from bright
light, dust and flies (eye patches sometimes come loose or rub
off), and also keeps the eyelids immobile. There’s no blinking
to rub the protruding ulcer and keep irritating the inflamed
eye. The eye is also constantly bathed in its own tears, which
seems to have a healing effect. Keeping the eye stitched shut
for awhile keeps it from drying out; a seriously affected eye
has a tendency to bulge and prolapse--and become dried out,
which is a detriment to healing.
A twice-daily application of a topical pinkeye antibiotic may
work if infection is caught early, but if pinkeye has several
days’ start and the eye is already turning blue or ulcerating,
injecting the eyelid and protecting the eye for a couple of
weeks gives much better results. Cases detected and treated
early are less likely to develop complications (such as deep
ulceration and scarring, “bubble eye” and permanent damage), but
it is still important to treat eyes in late stages of pinkeye.
Treatment helps an eye heal faster and with less damage than if
you let the disease run its course, and will also eliminate
bacteria causing the infection—to ensure that the animal does
not continue to serve as a source of pinkeye for the rest of the
herd.
No Magic Bullet
Randle says, “In herds with outbreaks that appear to be pinkeye,
there are variations in effectiveness of treatment. We don’t
know for sure which agent is causing the problem in every case.
When dealing with M. bovis, early treatment with tetracycline is
very successful, given intramuscularly or subcutaneously.
Tetracycline in feed is a help in prevention, but levels in feed
are not high enough to be 100 percent effective.”
Some veterinarians
take swabs from affected eyes to culture the causative organism,
and make an autogenous vaccine for that herd, since there can be
other organisms involved besides M. bovis. O’Connor has never
seen any scientific literature that said this works, or doesn’t
work. “The individual farm would have to attest to whether it
worked, but this is incredibly difficult. For instance, one year
you may have a bad pinkeye problem, and the next year it might
be better, or it might be caused by something else. You may have
had a dusty year, and the next year it rains.”
If the changed
conditions happen to coincide with the year you made the
autogenous vaccine, you may think the vaccine worked, but in
reality it might be you had less pinkeye due to less dust, fewer
flies, or some other condition that changed so the eyes could
stay healthy. “The vaccine might only be effective one
particular year, and the next year new antigens are involved.
Or, in the year you vaccinated, maybe there was not going to be
any pinkeye anyway. Then maybe 3 years later you get an outbreak
and wonder why the vaccine doesn’t work. People don’t understand
why it seemed to work for 3 years and then suddenly didn’t
work,” she says.
“There are so many
potential ways to get the disease, and also the pilus antigens
are changing. The autogenous vaccine may work, and you see a
decrease in pinkeye, but the next year perhaps a face fly or new
cattle on the ranch bring in another strain of M. bovis with a
different pilus antigen, and now your vaccine doesn’t work.”
Many people are
sure that face flies are the cause of pinkeye, but as O’Connor
points out, pinkeye existed in the U.S. before we had face
flies. “Pinkeye was first identified in this country in the
1890’s, and face flies didn’t enter the U.S. until 1952 from
Nova Scotia, gradually moving south across the country.
Incidence of pinkeye has increased with spread of face flies.
They contribute to the problem, but they are not the only
factors.”
Randle says, “Many
of the things that might be potentially effective for prevention
are costly. So this creates a challenge in determining the most
appropriate thing to do, and it must be evaluated for each herd.
If an outbreak occurs, however, aggressiveness is always better
than waiting to see if it gets better. Having a plan of action
and moving to it early is what we recommend, and it should be a
multi-faceted approach, taking into account all the things that
play a role.”
The Disease
Ropert Cope, DVM, Salmon, Idaho says pinkeye incidence is
variable, but in some herds 45 percent of calves are affected
over the course of a summer. “Signs in calves include runny
eyes, squinting, and avoidance of bright light. These signs are
usually seen 3 to 5 days after infection. At that point, small
ulcers may be developing on the surface of the cornea. These
ulcers often enlarge to as much as one-half inch in diameter by
5 to 7 days after infection,” he says.
“If the ulcer is
due to trauma, such as a wound to the eye caused by a stick, the
ulcer will generally be off to one side of the cornea. An ulcer
caused by pinkeye will almost always be in the center. Blood
vessels grow toward the ulcer, finally reaching the center of it
by 14 to 16 days. Rupture of the eyeball is rare, but can occur
with severe infection or following trauma when a blind animal
runs into objects. Otherwise, the eyes of most infected cattle
heal within 60 days, but usually leave scar formations on the
cornea in the form of a white spot,” says Cope.
The normal cornea
can be damaged by light, viruses and/or M. bovis, resulting in
neutrophils gathering to combat the bacteria. Neutrophils are
white blood cells that ingest and destroy foreign cells. “The
neutorphils release enzymes that increase the size and depth of
the ulcer, allowing perforation of the cornea and prolapse of
the iris through the defect,” he explains. |
