Pinkeye vaccination study questions its effectiveness

With summer around the corner, pinkeye treatment will be an issue many cow-calf producers may have to deal with.

Studies from the United States have estimated that 17 percent of beef cattle herds are infected annually with pinkeye. Cattle with pinkeye (or conjunctivitis) will have an inflammation of the soft tissues surrounding the eye and eyelids. In addition, the clear surface of the eye or cornea may also be affected by creating a cloudy surface or even an ulcer. Infected cattle will have reddening of the eyeball and swelling of the inner lining of the eyelid. They may also have an increased sensitivity to sunlight and may squint or close their eyes in bright sunlight.

In most cases, there will be a discharge from the eye and excessive tearing. In many cases, you can pick these animals out from a distance by noticing the fan-shaped stain of tears and discharge on the side of their faces.

The most common cause of pinkeye is a bacteria known as Moraxella bovis. Recently, another related bacterial species known as Moraxella bovoculi has also been identified as a potential cause. Certain animals can become carriers of these bacteria and harbour the infection from year to year and spread it within herds.

The face fly has been identified as one of the means of spreading the bacteria from one animal to another. Tall grass or dusty conditions may predispose the eyes to infection by causing eye irritations. Cattle with a lack of pigmentation in their eyelids may also be predisposed to pinkeye.

Summer is the season for pinkeye because all of the risk factors are present: dust, sunlight, face flies and tall grass.

Dealing with a substantial outbreak can be frustrating. The difficulty of treating cattle on pasture and the challenges with identifying cases early in the course of disease can be daunting. A commercial vaccine against Moraxella bovis does exist and many producers who experience pinkeye outbreaks often inquire about whether or not the vaccine is effective.

In the August 2017 edition of the Journal of the American Veterinary Medical Association, a paper was published on a clinical trial evaluating the commercial pinkeye vaccine.

The study was carried out at the Iowa State University cow-calf research unit. The herd had a long history of pinkeye outbreaks, which made it an ideal site for a clinical trial evaluating the vaccine.

Anecdotally, we often hear of herds in Western Canada that have similar ongoing issues with pinkeye outbreaks. Unfortunately, we don’t completely understand why a particular herd continues to have yearly problems, while other herds only sporadically have pinkeye infections. It may have to do with a particular strain of the bacteria or particular animals that are carriers.

In the Iowa State trial, 214 calves received either the commercial pinkeye vaccine or a placebo injection of saline. Spring-born calves were enrolled in early July at the time of processing and were followed throughout the grazing season until weaning time.

Farm personnel were unaware which calves were given the vaccine and which received the placebo. Pinkeye was detected in 59.6 percent of the control calves that received the saline injection and in 59.1 percent of the vaccinated calves. Obviously, the rate of pinkeye treatments was virtually identical in the two groups and there was also no difference in average daily gain between the vaccinated and unvaccinated calves.

The results of this trial suggest that the commercial pinkeye vaccine was not effective in reducing the number of cases of pinkeye in these spring-born calves.

This is consistent with previous studies, which have shown that pinkeye vaccines do not provide strong protection. It should be noted that the commercial pinkeye vaccines do not contain antigens against the bacteria Moraxella bovoculi, which has been hypothesized as a cause of infections as well.

In this Iowa State herd, Moraxella bovoculi had been isolated previously and perhaps that is one of the reasons that the vaccine did not provide protection.

This trial is one example of the kind of research we need to provide evidence about the effectiveness of vaccines or treatments in veterinary medicine. The vaccine treatment was randomized and the farm personnel were blinded as to the status of the calves. These are important research components and are necessary for a valid trial.

It looks like we have more work to do before we have an effective vaccine available for pinkeye. The current scientific evidence would suggest that pinkeye vaccines will not provide complete protection against this frustrating disease.

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