When ‘Summer Pinkeye’ Strikes
Pinkeye – infectious bovine keratoconjunctivitis (IBK) – can impact the health and well-being of any bovine and is especially tough on calves this time of year.
Historically, pinkeye has been attributed to a corneal infection by the bacteria Moraxella bovis (M. bovis). Cattle are considered the primary reservoir of M. bovis, and infected carrier animals may harbor this organism year-round without showing any signs of eye problems. Once pinkeye begins in a herd, it is highly contagious and can spread rapidly by direct contact through nasal and ocular discharges and by vectors such as flies.
In recent years, researchers have also identified Moraxella bovoculi (M. bovoculi) and Mycoplasma bovoculi as potentially contributing to the problem, according to John Angelos, DVM, UC Davis School of Veterinary Medicine. Research has yet to confirm that these organisms actually cause corneal ulceration, a classic feature of pinkeye.
M. bovis has at least two known factors that are important for its ability to cause pinkeye: pili and cytotoxin. The bacteria stick to and embed in the eye via pili proteins. “These are hair-like projections that allow the bacteria to anchor to the corneal epithelial cells,” Angelos says.
There are seven different serogroups of M. bovis pili, which explains why pinkeye vaccine use in cattle sometimes seems to be a hit or miss proposition. Angelos notes that vaccines may work better in cases where vaccine immune responses cross-react with Moraxella strains present in a herd. The opposite is true as well.
Cytotoxin released by M. bovis lyses corneal epithelial cells causing ulcers to form. “It’s a toxin that pokes holes in corneal epithelial cell membranes, thereby causing destruction of the skin cells. However, M. bovis does not stop there. Once it's breached that layer of skin cells, it has a tendency to burrow even deeper into the inner layers of the cornea,” Angelos explains.
In the same manner, cytotoxin is also believed to be responsible for destroying white blood cells needed to fight eye infections. When white blood cells rupture, they may release enzymes that can further break down the cornea, making the disease worse.
“While this has not been proven, we think that it can increase corneal injury during pinkeye,” Angelos says.
Faster Diagnoses And Treatment Needed
There is no set time period from once the disease is noticed until it is a threat to the health of the eye, according to A. J. Tarpoff, Kansas State Extension beef veterinarian. The speed at which bacteria can damage the bovine eye highlights the need for quickly recognizing the problem and making decisions regarding treatment – especially if you opt to use antibiotics.
“As the disease progresses it develops an ulcer typically in the center of the eye,” Tarpoff says, in a university news release. “Either one or two things happen — it starts to heal, or it builds up pressure on the inside of the eye from the inflammation and possibly ruptures.”
Angelos says antibiotics are useful only if an active infection is underway, noting that oxytetracycline, tulathromycin and hypochlorous acid spray have label claims to treat pinkeye.
Extra-label drug use (ELDU) of florfenicol and ceftiofur for IBK has also been reported, according to Sandra Stuttgen, DVM and an associate professor with the University of Wisconsin Division of Extension.
Stuttgen reports that ELDU involving sub-conjunctival injections (often are sub-palpebral, placed under inner surface of the eye lid) using penicillin have anecdotal evidence of effectiveness. Sub-conjunctival/sub-palpebral injections have caused violative residues at slaughter markets, she cautions. Topical antibiotic ophthalmic ointments may also be helpful. See Stuttgen’s article Managing and Preventing Pinkeye.
If a case of IBK has already healed, Angelos warns against using antibiotics just because the eye looks abnormal. “If you see blood vessels covering the corneal scar the eye has already healed and antibiotics are not needed at this stage,” he says. “It’s important for producers to know that, because one of the most common reasons why cattle are given antibiotics is for pinkeye, and we want to reduce unnecessary antibiotic use as much as possible.”
Supportive Practices Can Help
Angelos encourages the use of an eye patch which can help speed the healing process. He cites recent research by Gaby Maier, UC Davis beef Extension Veterinarian, that shows corneal ulcer healing times were faster when using an eye patch.
“Don’t seal the patch all around the eye as you need to allow for drainage and air circulation,” Angelos advises. “Check the eye a couple times after you put the patch on. While that might mean additional labor, you shouldn’t just assume the eye is healing just because it has a patch covering it.”
Stuttgen adds that promptly isolating affected animals is important for controlling IBK and providing relief from sunlight aids in recovery. Stabling affected cattle, applying eye patches or suturing the eyelids are also beneficial, she says.
Use Disposable Gloves And Disinfectant
Pinkeye agents from eye fluid and discharge can easily cover hands, halters and instruments and help spread these agents between animals. Use of disposable gloves, needles and syringes can minimize that potential.
Stuttgen reminds veterinarians and producers treating pinkeye cases to not touch active lesions with bare hands. “Don’t touch your own face or body, and properly remove gloves and wash your hands after handling cattle with pinkeye,” she says.
Using a disinfectant on equipment such as halters or instruments (e.g., hemostats/forceps) used to remove foreign bodies is also a good idea to prevent spread of any infectious agents. Angelos says an inexpensive and effective disinfectant for that purpose is household bleach at a 1 to 10 dilution (mix 1 part household bleach to 9 parts water).
Be sure to rinse used equipment in cool water to remove all organic debris before cleaning the equipment with the bleach solution, so it performs to its best potential, Stuttgen adds.
“Finish with a clean water rinse, dry and store equipment in clean, dust-free containers,” she says. “Thoroughly clean, sanitize and dry halters and/or nose leads used while treating cattle with pinkeye.”
When Plant Awns Are At Fault
Sometimes what appears to be a case of pinkeye is actually an eye injury caused by foxtails or other plant awns acting as foreign bodies in the eye.
During examination, Angelos says you can usually differentiate between pinkeye and a foreign body acting as an eye irritant.
“With a classic case of pinkeye, you typically will see corneal cloudiness that begins in the center of the eye and moves outward,” he says. “Foxtails and other plant materials that become embedded in the recesses around the eye cause cloudiness that is typically on the edge of the cornea.”
If you find a plant awn like a foxtail, you can often use forceps to remove it. “They can be attached firmly, so you typically have to tug on them for removal. If they break apart, you may have to go fishing for them,” Angelos says.
To help locate these plant awns, you can use your thumb to push back on the eyeball as shown in this example (Note that the fingers do not touch the eyeball directly, just the skin of the upper eyelid while gently pressing inward on the eyeball with the thumb.). Typically, cattle need to be haltered when performing this type of exam. Once the plant awn is removed, the eye will usually heal on its own. Have the producer monitor it, however, to make sure no further action is needed.
If the animal is particularly valuable, you can also consider proactively using antibiotics. “I would try to make an assessment of how deep the scrape appears,” Angelos suggests. “If there's no evidence of blood vessels starting to grow in, you know it's a very early lesion, and it may heal on its own without further treatment. Ideally the eye should be checked in one to two days after removing a plant awn to make sure the eye is healing and not getting worse.”
If the eye appears worse, Angelos recommends using an antibiotic. Stuttgen adds that, “Veterinarians may also determine the need for antibiotics by gauging damage to the cornea using a fluorescent stain.”
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