Anaplasmosis and your herd

ANAPLASMOSIS Staying ahead of a costly problem for California’s cattle producers

by Gaby Maier, DVM, PhD, DACVPM, Extension Veterinarian for Beef Cattle Herd Health & Production, UC Davis and Josh Davy, UC Livestock/Range Advisor, Tehama, Glenn and Colusa counties

Anaplasma marginale is a blood parasite that targets red blood cells of ruminants including cattle. Anaplasmosis is the disease caused by the organism, estimated to cost the U.S. cattle industry several hundred million dollars annually, and one of the most important cattle diseases throughout the world. The name Anaplasma stems from the Greek words an (“without”) and plasma (“shape”) describing an organism that appears to have little substance to it. “Marginale” means – you guessed it – marginal, so we are talking about a small organism living “on the edge”, in this case on the outer edge of red blood cells. It falls in the order Rickettsiae, which belong to the bacteria, but similar to viruses it needs other cells to live and can’t survive outside an animal for long.

Transmission between cattle occurs via several species of ticks. In California, Dermacentor aka the dog tick is most commonly responsible for transmission. Mechanical transmission of small amounts of blood through instruments such as taggers, hypodermic needles, tattooers or through blood-sucking insects like biting flies is also possible. Once infected, disease in cattle develops within 7 to 60 days depending on the infective dose. The body recognizes the intruder and destroys infected red blood cells. This process causes fever, anemia, lethargy, abortion and death in cattle. The disease can easily be confused with respiratory disease because cattle may have a fever and breathe harder. Since red blood cells get destroyed during the disease, there are fewer of them picking up oxygen in the lungs, which cattle try to compensate for by breathing faster. It is like going from sea level to a 10,000-foot mountain and realizing the air is pretty thin and getting out of breath easily.

Some telltales that cattle have the disease include the color of mucous membranes, like the inside of the mouth, that may appear pale or yellow, incoordination, and/or a cow’s behavior. With insufficient oxygen supply to the body including the brain, changes in behavior occur. Often cattle are simply found dead and a necropsy by a veterinarian will lead to diagnosis. Affected cattle can become aggressive and may attack an approaching person so proceed with caution if you suspect anaplasmosis in a cow or bull. Stress, such as a gather, can exacerbate the disease causing death. If anaplasmosis is suspected as the culprit causing aggression, it may be better to leave animals where they are. 54 California Cattleman September2020 Although not BQA approved, antibiotic treatment with a dart gun may be less stressful than a long walk to the corral or roping in this particular instance.

Besides cattle, blacktail and mule deer, water buffalo, American bison and bighorn sheep can also become infected and act as reservoirs although disease is most severe in cattle. Cattle that survive the infection likely stay infected for life, i.e. they eventually replenish their red blood cells, but the organism survives at low levels in their body. The good news is that recovered cattle are usually protected from future anaplasmosis disease; the bad news is that survivors can become quite debilitated with loss of body condition, decreased fertility and their calves can have reduced weaning weights.

Age at infection determines the severity of disease where young animals less than six months of age rarely are affected by the infection, while older cattle, especially those over two years of age are much more likely to become very sick and die. Sick cattle can be treated with antibiotics or blood transfusions and may survive. However, treatment works best in the early phases of the disease and the stress of restraint can kill the animal once the disease has progressed. Anaplasma marginale does not cause disease in people, but there are other Rickettsiae that infect humans through tick bites, e.g. Rocky Mountain spotted fever. Removing ticks as soon as possible helps prevent tickborne disease in people.

HOW CAN YOU PROTECT YOUR HERD FROM ANAPLASMOSIS?

The herd status determines how Anaplasma should be managed. Herds that do not come into contact with infected ticks, infected wildlife or infected cattle, for example in the Central Valley on permanent pasture, have little risk for disease. For such naïve herds, the biggest risks for an anaplasmosis outbreak are either movement to an endemic area or introduction of a carrier animal. If such a herd needs to be moved to an area that is suspected to harbor Anaplasma, vaccination of all adult cattle before movement is the best option. For incoming cattle to a naïve herd, a negative blood test should be a prerequisite for introduction. Introducing a positive animal to a negative herd could start the spread of disease and could result in multiple losses.

On the other hand, if the herd is in a known endemic area, cattle at the highest risk of disease are unexposed additions to the herd, for example a breeding bull that comes from an Anaplasma-free herd. These animals have a high chance of becoming sick from anaplasmosis when they join the herd. The best ways to prevent this from happening is to purchase bulls that test positive or that have been vaccinated.

In endemic areas, deliberate exposure of young animals to pastures that are thought to harbor ticks that transmit Anaplasma is a common way to address the disease. A study from 2013 that followed a commercial beef herd in California from March through September showed that the percent of infected replacement heifers rose from 19 to 69 percent and from 41 to 92 percent in two groups of heifers during the study period. In mature cows, 90 percent tested positive initially and 95 percent at the end of the study showing that it is possible to manage Anaplasmosis through deliberate exposure in this herd, but other situations may be different.

If the proportion of infected drops below 50 percent, the danger of outbreaks seems to increase. Exposure of animals to the pathogen at the right time including the presence or absence of infected ticks or the use of needles or other instruments during processing will influence how well the herd becomes exposed. This method entails some unknowns and is therefore not without risk of failure if conditions in the environment change.

There is concern that treatment with oxytetracycline for any reason can render an already exposed animal back to a vulnerable state because the drug is effective against Anaplasma. However, if used at the labelled drug dose, multiple rounds are required to achieve killing of all organisms and is very unlikely to occur if only one or two doses are given. Use of CTCs (chlortetracycline) medicated feed products fed free choice are only approved for control of active infection of anaplasmosis and require a Veterinary Feed Directive (VFD).

WHAT ABOUT VACCINATION?

The only vaccine available at present is an experimental killed vaccine that can be purchased through the California Cattlemen’s Association. Unfortunately, the efficacy of the vaccine has never been tested in California, which means we do not actually know how well it is able to protect from disease. Given the cost of the vaccine, blanket vaccination of all animals in the herd can be expensive and it is unknown how well cattle are protected. As a killed vaccine, it requires a booster shot four weeks after the initial dose and yearly revaccination. Vaccinated animals will test positive on an antibody ELISA test, i.e. the test cannot distinguish between vaccinated and infected cattle. The Anaplasma polymerase chain reaction test, which tests for the presence of the pathogen’s DNA, will be negative in an animal that was vaccinated but never infected.

Anaplasmosis vaccines are difficult to make because of the biology of the organism and its immune evasion mechanisms and because of strain variability. In the Midwest, many different strains have been found within the same herd. One explanation for the abundance of strains in that region is the commingling of cattle from different parts of the country in feedlots of the Great Plains. We do not know what the predominant strains of Anaplasma in California are or whether we have a similar patchwork of strains than the midwestern states. Gaining this knowledge will be important in making sure future vaccines will be effective in California herds.

CURRENT RESEARCH

The Beef Cattle Herd Health and Production team at UC Davis has launched a survey that will be sent out to a sample of ranchers across the state to gather more

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A word from former CCA President Tom Talbot,

information on the current state of this important cattle DVM: “To my fellow beef cattle producers and beef disease in California. The researchers are trying to learn cattle veterinarians: Could you please take the time how familiar ranchers are with the disease, how to complete the questionnaire you recently received widespread it appears to be, whether the area where it regarding anaplasmosis. Information received from can be found is expanding, how it is managed and what this survey will help us to direct research and acquire the risk factors are for having cases of the disease in funding to hopefully better manage this costly and cattle. A companion survey of beef cattle veterinarians rapidly expanding disease.” is being conducted as well to complement the rancher survey. The results may help provide guidance into how to reduce the risk of disease in areas where Anaplasma is endemic or where the disease is newly SHOULD YOU ORDER THE emerging. ANAPLASMOSIS VACCINE?

It may alert ranchers that have been Anaplasmosis is an infectious parasitic disease in cattle, spread unaware of the disease to become primarily by ticks and blood sucking insects like mosquitoes. The more vigilant and look out for cases. killed anaplasmosis vaccine protects cows and bulls of any age from infection and requires a booster given 4 to 6 weeks after the In order to be able to assess what the initial vaccination. Find out below if you should order the vaccine! differences are between locations with and without the disease, both positive and negative herds are needed and are NO Do you own cattle? YES equally important.

Based on the results of the survey, blood samples from targeted herds will be collected to survey what strain types are circulating in California and You don’t need it, Do they graze in also to study factors such as what percentage of the herd needs to be but should still support the YES areas where Anaplasmosis NO positive in order to achieve herd California is a immunity and if there is correlation to Cattlemen’s problem? the strain type. The results may also be Association (Consult your local veterinarian to find out) important to assess how good future vaccine candidates will be at providing protection for California herds. Do you want to prevent the effects of the disease

There is interest in development including severe anemia, of a new vaccine for anaplasmosis and weakness, fever lack of Kansas State is at the forefront of that YES appetite, depression, NO type of research. One group at Kansas constipation, decreased State has evaluated the feasibility of ear implants for delivery of vaccine for anaplasmosis and have tested milk production, jaundice, abortion and possibly death? You don’t need to the use of combination adjuvants order it versus a single adjuvant in a challenge ORDER TODAY BY CALLING (916) 444-0845! experiment where the combination Available in 10 or 50 dose bottles resulted in diminished clinical signs in 10-40 doses: $8.50 per dose infected Holstein steers. It is important 50+ doses: $7.50 per dose to understand, however, that these are *10 dose minimum and $10 flat rate shipping SOLD ONLY TO CALIFORNIA CATTLEMEN’S ASSOCIATION MEMBERS early stages of vaccine development and a commercial product is still far in the future.