NEWSLETTER ARTICLES

Livestock and Natural Resources

MANAGEMENT OF PINKEYE
IN BEEF CATTLE
by Wayne Jensen

At the Beef Cattle Health Symposium in March this year, Dr. Lisle George, DVM in the Department of Medicine and Epidemiology at the School of Veterinary Medicine at UC Davis, reported on his work on treatment of cattle with pinkeye. As the warmer, drier months of the year approach, this information may be useful, should your cattle experience "pinkeye."

Dr. George suggests the prevention and control of pinkeye in beef cattle is relatively difficult. Reasons for these difficulties include the conditions where the cattle are raised, the gathering and restraining of cattle for treatment, and the large number of cattle that can be affected at any one time.

Although difficult to control, if left untreated the incidence of pinkeye can increase in the herd, especially in young cattle. This can lead to reduced weight gain, scarred eyes, and potential losses from buyer resistance to cattle with "bad" eyes. Even with treatment, there are the extra costs for those cattle with pinkeye. These costs result from the labor required to gather, handle, and treat the affected cattle, and the cost and the amount of the drug used in the treatment.

Methods that have been proposed to limit the effects of pinkeye include genetic selection of resistant animals, face fly control, vaccination for both IBR , the agent most commonly associated with this condition, and the "blitz" treatment of cattle with oxytetracycline.

There are certain breeds which are thought to be resistant to this condition, and those which are more susceptible. Cattle with Bos indicus breeding are supposedly naturally resistant, and the English breeds, Bos taurus, are more susceptible.

Face flies feed on secretions from the eye and nostrils of cattle. If present, M. bovis is shed in the secretions (tearing) from the eye-infected animal and can be spread by face flies to healthy cattle. While difficult to control, face fly populations can be reduced with insecticides.

Moraxella bovis can also be spread by humans. When working on the eyes of infected cattle, care should be taken to not infect the eyes of other cattle. Good sanitation practices should be used. After treating or checking the eyes of an animal with pinkeye, hands should be washed before checking the eyes of another animal. This can reduce the spread of the disease.

A vaccination program may work, but it will only be effective if the vaccine contains the same strain of Moraxella bovis affecting your cattle this year. I understand this vaccine may be effective one year but not the next. Check with your veterinarian about this practice before you decide to vaccinate.

From his experience, Dr. George suggests the most effective and least intrusive method for control of pinkeye is the large scale or "blitz" treatment of cattle with an effective antibiotic. He recommends this approach whenever 10% of the cattle become affected with pinkeye. However, not all antibiotics are effective against this organism.

Moraxella bovis is resistant to tylosin. Treatments containing tylan, such as puffer bottles of tylan sulfa, probably have limited effectiveness in the treatment of pinkeye.

His work with repetitive injections with penicillin G in the eye of infected cattle is effective. However, this therapy must continue each day until the ulcer on the cornea is healed. He suggested the lack of treatment duration to be the likely cause of failure when using this therapy.

The most promising, cost-effective antibiotic therapy for pinkeye was oxytetracycline (LA-200), according to Dr. George. Following label directions, infected cattle received two injections with a 48-hour interval between each injection. This treatment had a similar response compared to a daily subconjunctival injection of penicillin G.

Based on his work, Dr. George suggests this therapy should be considered in the control of pinkeye because of the ease of administration of oxytetracycline compared to repeated subconjunctival injection of other antibiotics, its effectiveness with fewer treatments, and its availability to producers.

While pinkeye is not a fatal disease, and affected cattle will eventually recover, Dr. George recommends animals should be treated early to shorten the duration and intensity of the disease, and to reduce the pain and suffering they will experience.

Recently I had the opportunity to experience an external parasite that used me as a host. Shortly after that experience, I received the following information from Dr. Nancy Hinkle, Veterinary Entomologist at UC Riverside, and I thought this would be of interest to those of you who work where you are exposed to ticks.

This could be a "good" tick year. Warm, wet springs that yield lush vegetation to support wild mammal populations typically produce increased tick numbers. This increases the likelihood that you and your dogs will encounter these parasites.

There are two types of ticks that commonly affect livestock and other species of animals including humans. They are classified as either hard-bodied or soft-bodied types. Examples of soft-bodied ticks include the well- known Pajahuello Tick and the Spinose Ear Tick. Hard- bodied ticks include the Winter Tick, Pacific Coast Tick, and Western Black-legged Tick.

All ticks have four life stages: egg, six-legged larva or seed tick, nymph and adult. The latter two stages are eight-legged. The life cycle and the period of time for blood-feeding on the host are variable for each species.

After a female tick has fed for a few days, it drops off to mature and lay several thousand eggs. Small, newly-hatched seed ticks feed on rodents and other small animals. When mature, they climb onto low-growing vegetation typically along trails, in a "host-seeking" position. As an animal passes by, brushing the vegetation, the tick responds to host cues (warmth, moisture, and carbon dioxide) and grasps onto the host. It frequently moves to an unexposed site before inserting its mouthparts into the skin. Because the tick takes a day or two to secrete a feeding tube before it can begin to suck blood, daily tick checks (visual and manual examination of the entire body for presence of ticks) can prevent feeding.

Ticks usually crawl on the host's body for a few hours before biting. Unattached ticks do not transmit disease. Ticks require several hours to become firmly attached and, if left undisturbed, feed for several days without moving. Disease is rarely transmitted within the first day or so. Also, when attached for only a short time they are easy to remove and there is less chance of secondary infection.

To remove a tick, use tweezers, grasping the tick as close to the skin as possible. Pull slowly and firmly, without twisting or crushing the tick. Squeezing the tick may result in the contents being injected through the mouthparts into your skin, increasing chance of infection. Similarly, irritating the tick with heat or chemicals may cause it to regurgitate. Treat the bite site with an antiseptic to avoid infection.

It is a good idea to retain the tick for identification. If the individual bitten by the tick subsequently develops symptoms of a tick-transmitted disease, the tick can be tested for determination of the causative agent. The tick may be placed in a self-sealing plastic bag and stored in the refrigerator for several weeks.

Be especially watchful for the first couple of weeks following a tick bite. If signs of illness such as flu-like symptoms, headache, fever, lack of balance, skin rashes, muscle or joint pain, or nausea develop, see a physician. The tick may then be sent to an appropriate laboratory for analysis to assist in disease diagnosis.

This leads me to a discussion of Lyme disease. What is it? Lyme disease is the most significant tick-transmitted disease in North America. There are an estimated 10,000 human cases annually in the US, with California averaging about 150 diagnosed cases per year.

The Lyme disease agent, Borrelia burgdorferi (a type of bacterium called a spirochete), is transmitted to humans by the Western black-legged tick, Ixodes pacificus. Throughout their range, these ticks are most prevalent during fall and winter. In nature, the disease is maintained by other tick species in a reservoir population consisting of various rodents, especially the dusky-footed woodrat (Neotoma fuscipes), kangaroo rat (Dipodomys californicus), and the deer mouse (Peromyscus maniculatus). These rodents are not made ill by the bacteria, allowing them to carry the disease and pass it along to ticks that feed on them.

Ixodes pacificus is a three-host tick, meaning that each feeding stage (i.e. larva, nymph, adult) requires one vertebrate blood meal for its development. Each stage attaches to a vertebrate host, feeds to repletion, detaches, drops from the host, and molts to the next stage. Typically, the larvae feed on small rodents, and thus pick up the Lyme disease spirochete. The next stage, the nymph, may feed on rodents (thus increasing its chance of being infected) or larger mammals. Adult ticks typically feed on large hosts such as dogs, deer, horses or humans.

The Western black-legged tick is active year-round in many areas of the state, but highest numbers are encountered from November to May, reflecting the species’ affinity for higher humidities. Ixodes pacificus has been collected in almost every California county, but is most prevalent along the coast and western range of the Sierras.

What are Lyme disease symptoms? Initially, Lyme disease produces symptoms similar to those of the flu, with muscle aches, low-grade fever, headaches, and general malaise. These symptoms usually go away within a few days. But months to years later more severe symptoms occur. If the Lyme disease bacteria migrate to the heart, chronic heart problems can result. If the bacteria move into the central nervous system, various mental problems can result, from memory loss to dementia or paralysis. The most common long-term Lyme disease consequence is joint involvement, producing severe arthritis, and swelling of the knees, elbows, or other joints.

Clinically, Lyme disease often (50-80% of cases) manifests itself as a skin lesion, popularly known as the "bull's-eye" rash, a red circle enclosing a lighter center which over a period of days expands in diameter. Initial symptoms include fever, fatigue and muscle aches. Subsequently, the joints, cardiovascular system, and central and peripheral nervous systems may be involved. Lyme arthritis is characterized by severe pain and swelling of the joints, typically occurring weeks to months following tick exposure. In rare cases vision and kidney function may be impaired.

Can Lyme disease be cured? If diagnosed and treated in time, Lyme disease can be cured by antibiotics. This is why it is important that any suspicious symptoms be brought to your physician's attention, especially if there is a history of previous tick exposure.

How can I protect myself? Avoid tick habitats. If an area supports populations of woodrats and kangaroo rats, it is suitable for Lyme disease ticks. Ticks live in leaf litter and duff, so don't sit on the ground in areas where ticks are found. If you're going to be out in tick-infested areas, use a repellent containing either DEET or permethrin (read and follow label instructions scrupulously). Ticks are more commonly found on the uphill side of mountain trails, so when walking in steep terrain, avoid brushing against vegetation along the uphill side of the path. When outdoors in the woods or grassland, tuck your pants inside your socks. Spray repellent on pants and socks. Check your body each evening, especially belly button, arm pits, crotch area, ears, and head for the presence of ticks. If you feel something crawling on your body, do not ignore it.

Lyme Disease has not been a major problem in this part of the state. Dr. Hinkle says there is a 1 in 20,721 chance of contracting this disease in Santa Barbara County and 1 in 28,838 chance in San Luis Obispo County. While these odds are low, this is a serious problem in other regions of the United States. A colleague of mine contracted Lyme Disease during a visit back east and became very ill from this disease. It is something to be aware of when you are in tick habitat.