ANAPLASMOSIS UPDATE

First, what is Anaplasmosis? This is a disease of cattle caused by an organism called Anaplasma marginale. This organism is a rickettsia, half way between the viruses and the bacteria. It is susceptible to tetracyclines, unlike viruses. The disease, anaplasmosis, is caused when the infected cattle react to the agent and destroy their own infected red blood cells. This reaction causes a severe anemia.

Which cattle are susceptible to infection with A. marginale? All cattle are susceptible to infection by A. marginale. Also, deer, elk, and other ruminants are susceptible to becoming infected and can act as natural reservoirs of the agent. Cattle of any age can become infected; however, young cattle do not become ill, as will be explained later.

How do cattle become infected with the anaplasmosis agent? A number of ruminants, such as cattle, deer, and elk can be carriers of the anaplasmosis agent. These species can carry the agent all or most of their lives and serve as a reservoir for infection of other animals. The transfer of the agent from a carrier animal to a susceptible animal can occur by a number of routes. One of the most common ways is via ticks. In California, we have a number of ticks that transmit the anaplasmosis agent and are extremely effective at passing the agent to new, susceptible hosts. Additionally, any transmission of a small amount of blood from a carrier animal to a susceptible animal can transmit anaplasmosis. So insects such as horse flies are capable of transmission. An even larger culprit in this type of transmission is man. Ear-tagging instruments, tattoo tools, needles, ear implant tools, castrating instruments, dehorning instruments, etc., can all easily transmit the agent. So humans are also important in the spread of this disease.

What happens when a susceptible animal becomes infected? If the animal is a calf under the age of 12 months, virtually nothing is noticed. The calf undergoes an incubation period of about 45 to 90 days, has a very mild illness, which is rarely noticed, and becomes a carrier for life. Cattle that become infected between 1 and 2 years of age become ill after the incubation period, with severity increasing with age.

Cattle over 2 years of age become very ill and approximately 50% die unless treated. The older the animals and the better shape they are in -- the sicker they get! Usually, once the cattle become infected, and if they survive, they stay infected for life. They are what are called "immune carriers" -- they do not get sick, but act as a reservoir for other susceptible animals. Therefore, being an infected carrier protects the animal from becoming sick if re-infected.

What determines if a herd will have problems with anaplasmosis? The location of the herd is the main factor determining whether or not problems will occur. The cattle and deer that might be reservoirs and the ticks that naturally transmit the disease are the primary factors. For example, herds raised in the Central Valley of California on permanent pasture, with no ticks, no deer, and no carrier cattle, have essentially no risk of anaplasmosis. These cattle are free of the disease, have no immunity (unless vaccinated), and are totally susceptible to infection and disease. If these cattle are introduced to foothill pastures, especially during a bad tick year, they will become infected, get sick, and approximately 50% will die if not treated. When cattle are raised in the coastal foothills, Sierra foothills, and many mountain areas of California, they become infected early in life, have no clinical disease when infected (because they are young), and are "immune carriers." If new, susceptible cattle come into these areas, they are at risk. If these carrier cattle go to the valley pastures, they may act as sources of infection -- especially via blood transfer (dehorning instruments, ear taggers, horse fly transmission, etc.). Many cattle herds are between these two extremes, and it is common for a percentage of the adult animals to become infected and ill every year. These are herds that need to be vaccinated routinely to prevent losses. It is common for bulls that come from anaplasmosis-free areas to be very susceptible when introduced to herds where anaplasmosis is common. Remember, when bulls become infected and are successfully treated (do not die), they are often sterile for many months.

What can you do to prevent anaplasmosis in your herd? This depends on the risk of anaplasmosis in your operation. For those "valley" herds, the only real risk is introduction of carrier cattle and transfer of blood (dehorners, tattoo instruments, castration instruments, etc.) from the new cattle to your native, susceptible animals. For foothill or mountain herds, you have to be sure incoming cattle or bulls are from anaplasmosis areas or have been vaccinated. For herds intermediate in risk, you will want to review your vaccination program with your veterinarian.

What vaccines are available? In California we currently have two vaccine options. The first is a live vaccine, called Anavac®, available from Poultry Health Laboratories. It is safe and effective when given to young cattle (4 to 11 months of age). The cattle become infected with the vaccine strain of Anaplasma and are "immune carriers." This method of preventing disease is basically a controlled infection. If this vaccine (Anavac®) is given to older cattle, they will become sick and could die, just as with the natural disease. Vaccination of mature bulls with Anavac® can cause death loss or infertility.

Recently, an investigational vaccine has become available for use in California. This investigational vaccine is a killed vaccine and when the cattle are vaccinated, they develop enough immunity to prevent illness when they become infected. This vaccine does not protect against infection by the anaplasma organism. When the vaccinated cattle are infected by the Anaplasma marginale organism under field conditions, they go through a normal incubation period of about 45-90 days, have a slight drop in their red blood cell count, and remain normal in appearance. These vaccinated cattle do not become ill; but they do carry the field strain Anaplasma organism after they become infected.

Most infected cattle then carry the organism for their entire life. They are "immune carriers". That is to say, they are "immune" to becoming sick from the agent; but are carriers of the agent. If you were to take a small amount of blood from one of these "immune carriers" and put it into a susceptible cow, that cow would become infected and sick.

These two vaccines are very important. If you purchase bulls or heifers for replacements this fall, be sure these cattle are protected. If the cattle were vaccinated with the live vaccine (Anavac®) as calves and not fed tetracyclines in the feedlot, they will be immune carriers and safe from getting sick. If they were fed tetracyclines (a common procedure for bulls being grown in a feedlot), they will lose their immunity after 1-2 years if they do not become re-infected. If the cattle are over a year of age, be sure they were vaccinated with two doses of the killed investigational vaccine. They should be protected against becoming ill when naturally infected on your ranch.

Where can you buy these vaccines? The live vaccine, Anavac®, is available through Poultry Health Laboratories, in Davis, California. Their phone number is (530) 753-5881. It must be shipped on dry ice or in liquid nitrogen and costs about $3.00 per dose plus shipping. There are often advertisements in the California Cattlemen’s Association magazine for this product. The killed, investigational vaccine is available through California Woolgrowers Association, at (916) 444-8122. This vaccine costs about $6.50 per dose and is shipped via normal refrigeration.

As you can see from this brief discussion, anaplasmosis is a very complicated disease, and the need to vaccinate will vary from herd to herd. Particularly important is the protection of susceptible cattle coming into an “anaplasmosis area.” Make sure when you buy bulls or replacement heifers that they are protected. Either they should be raised in anaplasmosis areas or they should be vaccinated to be protected. This is doubly important for bulls, because if they get sick and don’t die, they can be sterile. Talk this problem over with your veterinarian in detail. You won’t make any small mistakes when dealing with anaplasmosis in California!

Infectious bovine keratoconjunctivitis (IBK), commonly known as pinkeye, is a serious disease in California beef cattle, affecting more than 90 percent of calves in some herds. IBK causes red, teary eyes, and ocular ulcers. The infection suppresses appetite and weight gain, resulting in economic loss. Healed infections leave scarring, which rarely leads to total blindness but affects the value of purebred breeding animals and those intended for the show ring.

The infectious agent is the bacterium Moraxella bovis. Cattle older than one year become quite resistant to IBK but often harbor the bacterium in their tears and nasal secretions. The disease is often spread by the face fly, which is MOST abundant from midsummer to early autumn. An other factor influencing the seasonal occurrence of pinkeye is a large number of young, susceptible cattle in the herd.

M. bovis can be treated with a number of antibiotics. Most treatment recommendations, however, are based on anecdotal field observations. Over several years, Dr. George conducted scientifically controlled trials to find the most cost-effective way to treat pinkeye. Recently, he also tested a vaccine candidate for IBK developed in his laboratory.

While the laboratory work was carried out at the Davis campus, the Sierra Foothill Research and Extension Center was chosen for the field work because pinkeye is endemic among the SFREC cattle, affecting most of the weaning calves each year. While this high incidence is not welcomed by management, it provided an excellent research opportunity.

He devised four different trials testing different antibiotics and combination of antibiotics as well as different dosages and application methods. Each trial consisted of three groups of about 20 to 40 calves. Two groups received treatment, and the third group was left untreated as a control. Over the past three years, he also began a separate study with his experimental vaccine.

Treatments Studied

1) Oxytetracycline versus furazolidon Intramuscular injections of a long-acting oxytetracycline (LA-200, 20mg/kg body weight) 72 hours apart. A topical application of furazolidone spray daily for 3 days.

2) Penicillin G versus oxytetracycline/tetracycline Injecting Procaine penicillin G just beneath the thin layer of tissue on the surface of both eyeballs; repeated daily until healed.

Injecting oxytetracycline intramuscularly (LA-200, 20mg/kg body weight) on day 1 and 3; also feeding oxytetracycline (2 grams/calf daily) from day 4 to day 14. Re-treated if ulcers recurred or occurred in previously unaffected eye.

3) Penicillin G combined with dexamethasone Injecting procaine penicillin G (1 ml) with a fine needle through the skin of the upper eyelid so that a small "blip" was visible just under the tissue of the inner eyelid.

Injecting penicillin G the same way together with 1 ml dexamethasone.

4) Florfenicol Injecting florfenicol (Nuflor, 20 mg/kg body weight) intramuscularly on days 0 and 2.

Injecting one dose of florfenicol at 40 mg/kg on day 0.

2) Both penicillin and oxytetracycline /tetracycline combination were similarly effective in treating acute cases. Both treatments resulted in shorter healing times and decreased severity and extent of corneal ulcers over the controls. The tetracycline combination was more effective in preventing recurrences and new cases of the disease than the penicillin.

3) With or without dexamethasone, penicillin neither speeded healing nor reduced the size of corneal ulcers. Injecting the drugs through the upper eyelid seems to be ineffective.

4) Calves in both florfenicol treatment regimes healed faster and had fewer lesions and recurrences than controls.

Based on this work, Dr. George provided the following recommendations:
Injecting 20 mg/kg body weight of long-acting oxytetracycline intramuscularly is the most effective treatment for pinkeye. Two injections over a two- to three-day period are recommended. Long-acting oxytetracycline should be used sparingly in herds with endemic anaplasmosis because treated animals lose their immunity to anaplasmosis.

Intramuscular injections of oxytetracycline combined with 10 days of oral tetracycline can reduce the incidence of pinkeye for the entire summer. This long-lasting protection may be desirable in herds with very high incidence of the disease.

Procaine penicillin G is an effective treatment. When using this option, calves should be treated daily for at least 3 days. The penicillin should be injected directly under skin of the eyeball, not into the upper eyelid. Dexamethasone did not improve the effectiveness in our trial.

Florfenicol (at 40mg/kg once or 20mg/kg twice 24 hours apart) is an effective treatment option.

Vaccine Tests and Results
In his lab, Dr. George has isolated and purified a cellular factor (cytotoxin) from M. bovis that may stimulate an immune response and protect calves from infection with the bacterium. He combined the cytotoxin with three different adjuvants -- water-oil emulsion, immunostimulating complexes (ISCOMS) and aluminum hydroxide -- into experimental vaccines. Trials have proven the aluminum hydroxide preparation to be ineffective in protecting against pinkeye. At SFREC, the ISCOMS plus the toxin preparation yielded the lowest incidence of corneal ulcers and other clinical scores. Those ulcers that did appear to heal more rapidly after treatment (with oxytetracycline) than those in control animals. However, ISCOMS alone also protected at low levels. Calves vaccinated with the water-oil vaccine preparation had worse disease than the controls.

He reported that great progress was made during 1998-99 in his investigations of the M. bovis cytotoxin and its potential use in a vaccine. Specifically, he successfully cloned the M. bovis cytotoxin gene. The vaccine demonstrated effectiveness in lab tests with rabbits. Proposed research will specifically address whether the novel recombinant M. bovis cytotoxin vaccine can prevent/reduce the severity of IBK.