Pinkeye in cattle: A challenging disease
Pinkeye causes millions of dollars in loss each year for producers, due to poor weight gains, prices docked because of eye damage or blindness, calves cut back at sale time, etc. Stockmen generally try to prevent pinkeye outbreaks, but often this proves to be a frustrating task.
Dr. Annette O’Connor, Iowa State University, said that Moraxella bovis is generally considered to be the bacteria most commonly associated with pinkeye. ”However, there are other organisms that can be involved. Merely having M. bovis in the eye isn’t enough to cause the disease.” There must be trauma to the eye to enable these bacteria to establish an infection.
M. bovis tends to be just in the conjunctiva (the delicate membrane that lines the eyelids and exposed surface of the white of the eye), in the lubricating fluid. Unless there is trauma to the eye, the bacteria can’t bind to the cornea,” she said. Some of the things suspected of causing trauma include high levels of ultraviolet light, tall grasses that cut or scrape the eye while the animal grazes, dusty or windy conditions and face flies.
“Other flies like horn flies and stable flies may be involved also. Pinkeye cases usually peak in summer — probably because there are a lot of flies, the grass is long, weather is usually dry and dusty, and there’s a lot of ultraviolet light. Infection with other agents such as mycoplasmas and infectious bovine rhinotracheitis (IBR) can cause lower resistance in the eye and cattle are more likely to get pinkeye,” O’Connor said.
There are several ways to try to prevent pinkeye. “One way is to try to prevent situations where trauma occurs. Reduce the dust, clip the grass, provide shade, control the 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.”
“Regarding face flies, it’s hard to adequately control them. Unlike horn flies (that spend almost all their time on the host animal) face flies don’t spend much time on cattle. At any one time there may be only 5% to 10% of the face fly population on the cows; the rest of the flies are out in the pasture. And when they’re on the cattle, they don’t stay there long — just long enough to feed on eye secretions and go back to where they were. So they are not exposed to the pesticide that much. Our control measures are often not very effective,” O’Connor said.
“Some of these methods may work on some farms but not others,” she said. “On one farm the problem might be dust and the rancher institutes a fly control program, 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.”
A frequently used preventative practice is vaccination. The goal of vaccinating is to boost immune response to the causative organism. “Everything has happened to cause the disease; the M.bovis is there, trauma has occurred, and the pathology is started — and you’re hoping the immune response will protect the animal,” O’Conner said. “The results with vaccination tend to be variable, however.”
“The main reason is that we are not really sure which antigens we need to put in the vaccine to make it effective. M. bovis binds to the eye by means of tiny pili.” These are filament-like appendages of certain bacteria, and they contain some of the antigenic properties of the bacteria.
“If the vaccine contains pilus antigens it is thought to be more effective. The problem is that apparently the pilus antigens change more rapidly than the vaccines can be changed. Most of the vaccines contain several pilus antigens, but they have to go through all the 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 the M. bovis has that particular pilus antigen, it will probably work,” she said. However, if the pilus antigens change, the vaccine may not work.
“If the antigens change, or another pilus antigen is introduced to the farm with new cattle or flies, there may be a little bit of cross protection, but not much. This may be why most of the preventative practices tend to fail — they are either impossible to accomplish, or the technology is not up to the job.”
She said that the third type of preventative is treatment. “We don’t usually think of treatment as a preventative practice, but if we can’t prevent the disease from occurring, if we intervene and treat early, before the disease becomes really severe, then we can limit the impact of the pinkeye on production parameters like weaning weight.” We may also save an eye that would otherwise become scarred or permanently damaged.
“Producers often think they failed because they had to treat an animal, but if they understand the disease they realize why they sometimes can’t prevent it,” she said. “If they view aggressive treatment as a way to limit the impact of the disease, that’s also successful.” By treating early, you may help minimize spread of the disease (via face flies, from animal to animal).
Pinkeye is easily spread. “If you get the cattle in to treat some of them, and run them all through the chute, you are creating an environment in which all the calves will be more susceptible,” O’Conner said. “You may increase the transmission of the disease through the herd, unless you bring the affected one in by itself to treat. You need to make sure you are not the cause of transferring it. 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 fly, the spreader. When treating pinkeye, try to limit that impact.”
Some producers say they treated their herd and the pinkeye outbreak got worse. When you look at the way this disease occurs and is thought to be spread, 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.
“There are many reasons that prevention methods fail,” she said. “Vaccination might work one year but not the next, for instance.”
Some veterinarians take swabs from affected eyes to culture the causative organism, and make an autogenous vaccine for that herd, since there are often other organisms involved besides M. bovis. This may work for some herds, or work for a year or two, and you don’t know if the autogenous vaccine helped or not. “For instance, one year you may have a really bad pinkeye problem, and the next year it might be better, or it might be caused by something else. You may have had an incredibly dusty year, and the next year it rains,” she said.
If the changed conditions coincide with the year you made your autogenous vaccine, you may think the vaccine worked, but in reality it might be that 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 also only be effective for one particular year, and the next year new antigens are involved. Or, in the year that you vaccinated (and felt the vaccine was effective), maybe there was not going to be any pinkeye. Then maybe three years later you get an outbreak and wonder why the vaccine doesn’t work.
“There are many potential ways to get the disease, and also the pilus antigens keep changing. Another scenario might be that the autogenous vaccine did work, resulting in a decrease in pinkeye, but the next year a face fly or new cattle on the ranch brought in another strain of M. bovis with a different pilus antigen, and now your vaccine doesn’t work,” she said.
Her impression is that most people think that face flies are the principle cause of pinkeye, but pinkeye existed in the U.S. before we had face flies here. “Pinkeye was first identified in this country in the 1890s, and face flies didn’t enter the U.S. until 1952, from Nova Scotia, gradually moving south across the whole country. Incidence of the disease has increased with the spread of face fly populations. But at the same time, agriculture has intensified since 1952. There are so many changes in how people handle cattle now. We’re very sure that face flies contribute to the problem, but are not the only factors,” O’Connor said. She believes that veterinarians and cattle producers need to understand why preventative practices sometimes fail.
Dr. Phillip Kesterson, Zoetis Technical Service veterinarian, said part of the problem is that Moraxella bovis is not the only bacterium involved. “Another bacterium that plays a significant role is Moraxella bovicoli,” he said.
The current thinking is M. bovis is the primary pathogen and that M. bovicoli works as a co-pathogen. M. bovoculi is a very diverse bacterium with multiple virulence factors and we are continually discovering new things about it.
“When we look at bacteria that we culture from affected eyes, and the difference between those two strains, reports show that there is a 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 said.
There are vaccines available for pinkeye, for the M. bovis strain, but currently no fully-licensed vaccines for M. bovoculi. “There is a conditional licensed product now available for that M. bovoculi, but the main challenge with any vaccination strategy is matching the strain within the bottle to the strain in the cattle. This can be difficult because these bacteria seem to be able to change,” Kesterson said.
Ralph Walton DVM of Cross Street Veterinary Clinic in Tulare, Calif., works with cattle herds and utilizes autogenous vaccines created by Hygieia Laboratories in Woodland, Calif. “The advantage of an autogenous vaccine is that it’s made for the specific organism causing problems. The disadvantage is that it takes time to make it. You can’t just go to your farm supply store or veterinary clinic to buy some. We have to find the isolate, grow it, and make the vaccine,” he said.
“If the pinkeye outbreak starts in June, you are looking at August by the time you get the vaccine. So in some instances we may be talking about next year before it can really help us. When weather cools off in the fall and the flies go away, you won’t have much problem with new cases,” he said.
“This is the frustrating aspect, though the autogenous vaccine works as well or better than commercial vaccine, especially since it targets the specific pathogen in your herd.” If the commercial vaccine isn’t protecting the cattle, this gives another option.
Dr. Ken Vroman, a veterinarian in Fayette, Mo., has been using autogenous pinkeye vaccines for 27 years, created by Addison Labs in Fayette, Mo. “Vaccines are not a panacea; they go hand-in-hand with good management and seem to help, in most cases. Vaccination also seems to have an additive effect. When you go through a herd and give them all an autogenous vaccine for one or both bacteria strains, Moraxella bovis or M. bovoculi, you have better pinkeye control the second year that you use the vaccine. It’s like a booster; it seems like we need to build herd immunity,” he said.
“With a pinkeye vaccine, we have to determine whether to include Mycoplasma as well,” Vroman said. “The eye disease can be worse when this pathogen is involved.” He believes that a good autogenous vaccine is a tool that can be used after you address any management problems, and your veterinarian has helped you diagnose the disease — and come to the conclusion that the vaccine you are using isn’t effective for this particular pathogen. ❖
— Smith Thomas is a cattle rancher, horseman, freelance writer and book author, ranching with her husband near Salmon, Idaho. She can be reached at firstname.lastname@example.org.