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Pinkeye Continues To Be A Head-Scratching Affair

We've all seen it. That white spot on a calf's eye that sticks out like a sore thumb in the cowherd. A quick scan of others includes a mental inventory of teary

We've all seen it. That white spot on a calf's eye that sticks out like a sore thumb in the cowherd. A quick scan of others includes a mental inventory of teary, cloudy or photosensitive eyes.

If there's only one or two cases, it's probably not the infectious kind, but if 5% of the herd has it, the safe money is on a bacterial-caused infectious bovine keratonconjuctivitis, better known as pinkeye. It's a longtime problem that continues to affect beef cattle; however, recent discoveries may lead to improved methods of prevention.

“Ten years ago, if you asked anyone the cause (of pinkeye), they'd have just said Moraxella bovis (M. bovis),” explains Annette O'Connor, Iowa State University College of Veterinary Medicine associate professor. “But we're not making much progress in vaccinating for it, and this may be because there are probably other organisms involved.”

Other possible pinkeye-causing bacteria are Moraxella ovis (M. ovis) and Moraxella bovoculi (M. bovoculi).

  • M. ovis – Scott McVey, DVM, University of Nebraska Veterinary Diagnostic Laboratory, says M. ovis is like a cousin to M. bovis, and he's starting to see more of it in the lab.

    “About 60% of our isolates from pinkeye are probably from M. ovis,” McVey says. In a given year, the Nebraska lab handles 75-100 isolates/year.

    However, O'Connor says no studies clearly show that M. ovis is a cause of pinkeye. She says it's exciting to learn if more than one organism is causing pinkeye so better vaccines can be designed.

    “People may think finding M. ovis means it's the problem, but just because its there doesn't mean it's the cause. I can go out and swab healthy cows and get M. ovis out of their eyes,” she says.

    McVey says M. ovis is present in the upper respiratory tract and eyes of animals and it may act as an “opportunist” once the corneal surface of the eye is damaged — as a result of flies, mechanical injuries from grass or UV light.

    M. ovis is much like other bacteria; if given an opportunity, a problem can sure flare up very quickly,” he says.

  • M. bovoculi – “I'm in the camp that doesn't believe in M. ovis (as a cause of cattle pinkeye),” says John Angelos, University of California-Davis School of Veterinary Medicine assistant professor. He points out that M. ovis originally came from a sheep with conjunctivitis. “I'm suspicious that what people have been calling M. ovis for a long time is probably M. bovoculi.”

    Angelos first isolated M. bovoculi in beef and dairy calves in Northern California while conducting an antibiotic-efficacy trial in 2002. “It was only after doing some pretty extensive bio-chemical testing and molecular characterization that we were able to show it was in fact different from M. ovis,” Angelos says.

    As with M. ovis, he says it's not known if M. bovoculi can cause pinkeye; it can be isolated from cattle without pinkeye, similar to what occurs with M. bovis.

    “It certainly has the toxin-genes that are related to the M. bovis toxin gene,” Angelos says.

    McVey agrees M. bovis is still a major player when it comes to pinkeye, and that vaccines geared towards this organism are generally effective. Unfortunately, there are no commercially available vaccines against M. ovis or M. bovoculi.

    One option is formulation of an autogenous vaccine custom-made from isolates in a specific herd. This summer, O'Connor and Angelos will work on separate projects studying the efficacy of autogenous vaccines and M. ovis and M. bovoculi.
Necessary or sufficient cause? In understanding how a disease works, researchers try to determine necessary and sufficient causes. A necessary cause is something that absolutely must be present for the disease to occur.

For example, to have smallpox, the smallpox virus must be present. Bovine respiratory disease, however, stems from pasteurella, haemophilus, bovine viral diarrhea, IBR or PI3.

“There's a multitude of organisms that by themselves could be the cause,” O'Connor says. Researchers like diseases that have necessary causes because the fastest way to control it is to control the necessary cause.

“We used to think that M. bovis was a necessary cause of pinkeye. So if we could just get the vaccine to work, all our problems would be solved,” O'Connor says. “If new studies do end up suggesting multiple organisms, such as M. ovis or M. bovoculi, can cause pinkeye, then for some producers this may explain why we're having problems controlling it.”

Sufficient causes are a bit more complicated. Just because the organism is sitting on the edge of the eye doesn't make it a sufficient cause of pinkeye. There needs to be another component.

“The organism in the eye and a scratching of the eye from a fly are two things that are sufficient to cause the disease,” O'Connor explains.

Without realizing it, producers then try to reduce the other component of the cause such as controlling the fly population, clipping grass or breeding cattle for “hooded” eyes to prevent UV light damage.

These sufficient causes can vary within a herd, as well. For example, in a herd of 100 cows, 40 may get pinkeye. For half those cases, flies scratched the eye; the other half may have badly formed eyes. Furthermore, some may be infected with the M. ovis (if further studies suggest it's a cause) strain, others with M. bovis.

“If you're using a vaccine that only works against M. bovis, you're still going to have those other cases and it will look like your vaccine didn't work, but actually it did,” O'Connor says.

Some control tactics. Pinkeye can impact calf-weaning weights by 20-30 lbs., impact labor requirements during a busy time of year and cause great animal suffering. But the good news is that an explosion of pinkeye one year is frequently followed by minimal occurrences the next. Researchers aren't sure why; some think it's because producers are proactive the following year. Others speculate cows may have developed colostral antibodies.

Regardless, fly control and vaccination are the most common preventive practices producers implement, O'Connor says.

Because there are many M. bovis strain variations and other bacterial opportunists, Angelos says, “People need to pay attention to it. Start with something we know that works.”

He recommends using a commercially available standard M. bovis pinkeye vaccine first. If outbreaks persist, have a culture sample taken to see what's growing. From those results, he recommends vaccinating with an autogenous vaccine.

McVey says producers must keep a close watch on cattle in order to detect problems early. “By the time you get to the point of an ulcer on the cornea, obviously milky looking eyes and swollen tissue, it's too late,” McVey says.

But once there's a problem, antibiotics are a management option for clearing up pinkeye cases. “It shouldn't be seen as a failure to treat animals with antibiotics who have pinkeye, because we can intercede very quickly and limit the animal suffering,” O'Connor says.

Some standard recommendations. Angelos offers these systemic antibiotic recommendations for pinkeye treatment.

Note: If any antibiotic product is not labeled for pinkeye, you must obtain a prescription from your vet, as this constitutes an extra-label use of the product. Also, always observe the manufacturer-recommended pre-slaughter drug withdrawal periods.

  1. Long-acting tetracycline (BIO-MYCIN® 200 or Liquamycin® LA-200®)
    Dose: 4.5 ml/cwt.
    Route: Both products are labeled for subcutaneous (subQ) use, and such administration is recommended whenever possible, as they can be very irritating to tissues. In addition, BIO-MYCIN® 200 is also approved for intramuscular (IM) use.
    Frequency: Two injections 48-72 hours apart.
    Label: Both products are labeled for pinkeye and available without prescription. Follow label directions.
  2. NuFlor® (florfenicol)
    Dose: 3 ml/cwt.
    Route: IM.
    Frequency: Two injections 48 hours apart.
    Alternatively, NuFlor® can be used as single injection for longer action.
    Dose: 6 ml/cwt.
    Route: SubQ.
    Frequency: One treatment.
    Label: Not currently labeled for pinkeye; veterinarian's prescription is required.
  3. Excede® (ceftiofur)
    Dose: 1.5 ml/cwt.
    Route: SubQ at the base or middle third of the ear. With injection in the middle-third of the ear, inadvertent injection of the drug into an artery is possible, which is fatal. Dosing at the base of the ear is easier and safer; seek a veterinarian's training on proper administration. Video links for administration are available at: Click on “Excede for beef cattle,” then on “Administration.”
    Frequency: One injection provides therapy for 7-8 days.
    Label: Not currently labeled for pinkeye; veterinarian's prescription is required.
  4. DRAXXIN® (tulathromycin)
    Dose: 1.1 ml/cwt.
    Route: SubQ in the neck.
    Frequency: One injection.
    Label: Recently approved for pinkeye treatment; veterinarian's prescription is required.
Additional recommendations
  • Use disposable latex gloves in examining the eye; dispose of gloves after examination.
  • Disinfect halters or nose tongs used to restrain the animal.
  • Dispose of needles and syringes used to treat animals.
  • If patching the infected eye, don't seal the patch with glue all the way around — it needs air and drainage. Check under the patch within a week to monitor progress.