NEWSLETTER ARTICLES
Livestock and Natural Resources

Most livestock producers on the Central Coast are familiar with this disease, and probably have had first-hand experience with anaplasmosis with vaccination programs or treatment of cattle. However, there have been some recent changes regarding the prevention of anaplasmosis which you need to know. My thanks to Dr. John Maas, Extension Veterinarian, UC Davis, for the information in this article.

To begin with, what is anaplasmosis? It is a disease of cattle caused by an organism called Anaplasma marginale. This organism is a rickettsia, half-way between a virus and a bacteria. It is susceptible to tetracyclines. The organism is an obligate parasite, which means it cannot be grown in the laboratory. The disease is caused when infected cattle react to the organism, and their body removes its own infected red blood cells. This causes a severe anemia.

Which cattle are susceptible to infection with A. marginale? All cattle are susceptible to infection by A. marginale.

Recently, you may have attempted to purchase vaccines to prevent anaplasmosis and discovered they are no longer available. Since the first of the year, the two U.S. companies that manufactured and marketed vaccines for the prevention of anaplasmosis nationwide have decided not to continue making these vaccines. The first anaplasmosis vaccine manufactured for cattle in the United States was made by Fort Dodge and was called Anaplaz®. More recently, Mallinkrodt (later Schering-Plough) marketed a vaccine called Plazvax®. Both of these vaccines protect against anaplasmosis by similar mechanisms.

The vaccines contain the organism, Anaplasma marginale, which is harvested from infected cattle. The organism is killed and processed to make an effective vaccine. When the cattle are vaccinated, their immune system responds to the vaccine antigen.The cattle develop enough immunity to prevent illness when they become infected.

The vaccines do not prevent 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 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.

How do cattle naturally become infected with the anaplasmosis agent? A number of ruminant animals such as cattle, deer, and elk can be carriers of the anaplasmosis agent. These species can carry the agent most or all of their lives. They serve as a reservoir for infection of other animals and in this way, the organism perpetuates itself. 

The transfer of the agent from a carrier animal to a susceptible animal can occur by a number of routes. One common way is via ticks. In California, we have a number of ticks that transmit the anaplasma agent. All of these ticks pass the agent from one life stage to the next (most tick species have four life stages).

Some of our common ticks pass the agent to the next generation of ticks via the egg (transovarial transmission). So these ticks 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. Insects such as horse flies, are also 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. 

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 animal and the better shape they are in, the sicker they get!  Usually, once the cattle become infected, they stay infected for life. They are "immune carriers." They do not get sick, but act as a reservoir for other susceptible animals.

When does anaplasmosis cause problems? The short answer is, "When older (more than 2 years of age) cattle become infected." However, for cattle raised in the central California Valley on permanent pasture, with no ticks, no deer, and no carrier cattle there is essentially no risk of anaplasmosis. These cattle are free of the disease, have no immunity (unless vaccinated), and are totally susceptible. 

If these cattle are introduced to foothill pastures, especially during a bad tick year, they are very much at risk for becoming infected and becoming ill or dying. When cattle are raised in the coastal foothills or the mountains of California, they often become infected early in life, have no clinical disease, and are "immune carriers." If new, susceptible cattle come into these areas, they are definitely at risk. If these carrier cattle go to the valley pastures, they may act as sources of infection, especially via blood transfer.

Many cattle herds are between these two extremes, and it is common for a few to many cattle to become infected and become ill every year. These are the herds that need to vaccinate routinely to prevent losses. It is common for bulls that come from anaplasmosis-free areas to be very susceptible when introduced into herds where anaplasmosis is common.

It is easy to see why these two vaccines were very important for many ranches. Without killed vaccines, many operations may have to "let nature take its course." This may get a little costly! 

In California, we do have another alternative. We have a vaccine called Anavac®. This vaccine is a modified live vaccine. It is safe and effective when given to young cattle. They 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 adult cattle, they will become sick and could die, just as with the natural disease. Therefore, use of this vaccine cannot be undertaken lightly.

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." This is doubly important for bulls, because if they get sick and don’t die, they can be sterile for up to a year. Vaccination of mature bulls with Anavac® can cause tremendous losses. Hopefully, one or both of these companies will begin to produce vaccine again and by the time you read this article the problem will be solved. If not, talk this problem over with your veterinarian in detail. You don’t want to make any small mistakes when dealing with this disease in California!

Wayne Jensen

It’s that time of year again. Fly populations are starting to increase. The two main problems are from horn flies that can decrease production and face flies carry the bacteria that cause Pinkeye. Horn flies can cause cattle to have decreased weight gains. They cause these losses by biting through the skin of the cattle and sucking fluids from underneath the skin. Face flies irritate the cattle’s eyes by using rasp-like mouth parts to stimulate tear production. The face flies feed off these excess tears. More importantly, the face flies carry the causative agent of Pinkeye, Moraxella bovis. This bacteria causes tremendous damage to the eye and also very large economic losses. So, one of the primary goals of face fly control is the prevention of Pinkeye.

To give you an idea how the population of these flies increases during the season, refer to the two graphs below. These represent the fly counts I made on the Ontiveros Ranch (Table 1) near Sisquoc and the Hayes Ranch (Table 2) near Lompoc over a period of 24 weeks in 1996. This study began in March and concluded at the end of October. The horn fly counts represent the counts on one side of the animal so if you double the numbers represented on the graphs you can get an indication of the number of these flies feeding on an animal every day. Face fly counts in this part of the state are relatively low but tend to remain constant throughout the season.

As an observation, on week 19, the Ontiveros cattle were sprayed with a product containing Permethrin and you can see the immediate reduction in horn flies numbers, then followed by an increase until numbers began to fall in October.

When developing a strategy to reduce these fly populations on your cattle, Drs. Hinkle and Maas provide the following information you should consider in your program. Both face flies and horn flies develop resistance to insecticides over time. For maximum prevention, it is advisable to switch the class of drug you use each year or two. If you used an organophosphate ear tag last year, use a pyrethroid ear tag this year. Additionally, if you plan to use a pyrethroid ear tag this year, use an organophosphate spray this year. Alternating the classes of drugs in this manner will increase the success of your preventive program.

Table 1.

Table 2.

It is also recommended that application of ear tags be delayed until the fly population is relatively high so that the possibility of them developing resistance is lowered. Sprays, back rubbers, face rubbers, and dust bags can be helpful in reducing the fly populations early in the season, before ear tag application. Then, as the fly populations increase, apply the fresh ear tags to achieve maximum benefit. Always follow the manufacturer’s label directions for ear tag application. If they call for two ear tags, use two ear tags! If they recommend ear tags for calves or if ear tags for calves are needed to prevent Pinkeye in the calves, use the tags in the calves. Remember, in the Fall, always remove the ear tags. If the ear tags are left in the cattle the flies that overwinter, particularly the face flies that overwinter will develop resistance to the drug you used and it will no longer be effective.

Face flies and horn flies lay their eggs in cow manure and the larvae only develop in cow manure. Therefore, some of the compounds that are fed or given in bolus form that kill the larvae in the manure pat can be very effective.

Examples of this include the slow release bolus with diflubenzuron (Vilgilanteâ). This compound is an insect growth regulator (IGR) which is safe and cross-resistance does not develop. Another IGR that is used in "feed through" products is methoprene. Other products are available that can kill the fly larvae when used as a "feed through."

Note: These materials are also effective in killing the larvae of dung beetles. Be aware if you have dung beetles present, they may be reduced or eliminated also. A number of years ago, I released three species of "dung" beetles in northern Santa Barbara County and two of the three are established. One species was observed in the manure of cattle on the Ontiveros Ranch, but I did not find them at the Hayes Ranch. How effective dung beetles are to help reduce fly populations is not well documented. Since the species I released remove relatively large quantities of manure underground in their life cycle, it is presumed there may be a benefit to maintaining their populations.

Some of the important items to keep in mind for fly control and pesticide use are: Plan ahead for insecticide and ear tag purchases. Fly season always comes, even if delayed by cool weather or rain.

Consult with your veterinarian regarding the active ingredient(s) in these products and the history of effectiveness in your cattle.

Always follow the label instructions, warnings, and precautions: these products can potentially be toxic to you, your children, pets, and others working with them around the chute.

Follow label withdrawal times and keep records of treatment dates, products, and lot numbers.

Dr. Nancy Hinkle, Extension Veterinary Entomologist at UC Riverside and Dr. John Maas Extension Veterinarian at UC Davis provided this timely information and also prepared the following list of the pesticides registered for use on beef cattle in California for 1999.