– Dr. Michelle Arnold, UK Veterinary Diagnostic Laboratory
Figure 1: Anaplama marginale organisms (small purple dots) in the red blood cells (larger pink circles)
What is Anaplasmosis? Anaplasmosis is a disease caused by Anaplasma marginale, a bacterial organism that invades cattle red blood cells (Figure 1) and causes severe anemia, often resulting in death. In Kentucky, the disease affects adult cattle, typically in the fall of the year with most cases occurring from late September through the first 1-2 weeks of November.
What are the symptoms of anaplasmosis? This organism causes anemia in adult cattle which means there is an abnormally low number of red blood cells circulating in the bloodstream. Lack of red blood cells results in oxygen deprivation to the vital organs, but symptoms are not noticed until 40-50% of red blood cells are destroyed. Infected cattle will show signs of weakness, lagging behind the herd, staggering, rapid breathing and sometimes foaming from the mouth. Affected cattle quit eating, have a fever and may appear to rapidly lose weight. Most become very aggressive due to lack of oxygen to the brain. Mucous membranes will appear pale early in the course of disease and progressively turn yellow in color due to jaundice. Death can be sudden, especially with exercise, or cattle may be found dead with no prior symptoms. Typically, several adult animals in a herd will die within a short (1-2 week) span of time. Pregnant cows that survive will often abort their calves.
Do all cattle with anaplasmosis show these same symptoms of disease? No. Younger cattle, especially less than 6 months old, rarely exhibit signs of disease due to rapid and active production of new red blood cells (RBCs) in growing calves. Symptoms of anaplasmosis in animals from 6 months to 2 years of age are usually mild and may be misdiagnosed as pneumonia because both conditions include fever and increased respiratory rate but most will recover. Older animals (> 2 years old and up) are at elevated risk for disease and death, especially if under stress such as calving or in early lactation. Others can mount an effective immune response without obvious signs of sickness.
How do you treat an animal showing signs of Anaplasmosis? Treatment with antibiotics is essential for survival if showing signs of disease. A single subcutaneous injection of long-acting oxytetracycline at 22 mg/kg of body weight (BW) or 10 mg/lb BW will often stop the progression of anemia by slowing replication of the Anaplasma organism, allowing the immune system to take over and save the animal. Another option is Baytril® 100-CA1, the first fluoroquinolone antibiotic conditionally approved by the FDA for the treatment of clinical anaplasmosis associated with Anaplasma marginale in all classes of beef cattle except beef calves less than 2 months of age and beef bulls intended for breeding (any age). However, be aware that severely affected cattle may die due to stress when walked to the barn or going through the working chute. In an outbreak situation, it is recommended to treat all adult cattle in the herd with injectable oxytetracycline (for example, LA-200®, LA-300®), then begin feeding chlortetracycline (CTC) at the control dose (0.5-2 mg CTC/lb BW/head/day) in medicated mineral or feed throughout the rest of the vector (fly) season which ends around November 1st. Many medicated free-choice mineral mixes are now available for anaplasmosis control. Alternatively, hand feeding Aureomycin® daily in feed to deliver 0.5 mg/ lb BW/head/day will also control active infection.
If an animal survives the initial infection, then what? Will they get it again? If an animal (regardless of age) becomes infected with Anaplasma marginale and survives, that animal will become a “carrier” of the organism for life. As carriers, they are never sick again due to Anaplasmosis but serve as reservoirs or a source of infection for other uninfected animals. Infected bulls that survive may be infertile for up to a year while pregnant cows that survive almost always abort during recovery from infection. Recovery takes at least 2-3 months to rebuild red blood cells and regain lost weight.
How is Anaplasmosis spread? Anaplasmosis is considered a “tick-borne” disease because they can spread the organism through feeding on cattle. Although ticks are important for this organism to survive and spread, transmission can be by any method that moves affected red blood cells from infected to susceptible cattle. In addition to ticks, the Anaplasma organism may be spread by biting insects (mosquitoes, horse flies, stable flies) and/or using blood-contaminated tools such as dehorners, ear taggers, castration tools, and implant guns without disinfection between animals. Probably the most common way it is transmitted is using the same hypodermic needle on multiple animals when administering vaccines to the herd. Once infected, there is a 3-10 weeklong incubation period before the animal develops signs of a problem. Transmission may also be from cow to calf while pregnant although little is known about when this takes place in gestation.
How is Anaplasmosis diagnosed? If an animal is found dead and no more than 24 hours has passed since the time of death, the animal can be submitted to a veterinary diagnostic laboratory for necropsy or a veterinarian may perform a field necropsy to determine the cause of death. If an animal is alive and showing signs consistent with anaplasmosis, the UKVDL recommends a blood sample (both a red top and a purple top tube) be submitted for an accurate diagnosis. Whole blood (purple top tube) is needed for a complete blood count (CBC) to assess the degree of anemia, to potentially identify the organism in a blood smear and for a new PCR test now available to identify the Anaplasma DNA. The red top tube of blood is needed for a serum test (the Anaplasmosis cELISA) to detect antibodies indicating infection and/or carrier status. However, the serum test may be negative early in the disease process. Blood should be collected and transported to the lab as soon as possible (overnight ship with cold packs). Please visit the UKVDL web site for additional information at http://www.vdl.uky.edu
Is an effective vaccine available? Kentucky is among the list of states approved by the USDA for sale of the anaplasmosis vaccine marketed by University Products LLC of Baton Rouge, LA. Vaccination should keep animals from experiencing sickness and death but does not prevent infection and still allows development of the carrier state. The vaccine can be used during an outbreak and has been used in cows in all stages of pregnancy with no problems being reported. The recommendation is a two-dose regimen given 4 weeks apart with annual re-vaccination required. Immunity should develop within 7-10 days of the 2nd dose according to the manufacturer. Vaccination should ideally begin with yearlings. The downside to vaccination is that vaccinated animals will test positive for anaplasmosis which is unacceptable for most seedstock operations. More information may be found at: http://www.anaplasmosis.com/home.html
What is the best way to prevent problems due to Anaplasmosis? Preventing infection with Anaplasma marginale is difficult due to the large number of infected herds throughout the state, the frequent movement of cattle and the ease with which the organism is transmitted. In addition, antibiotic treatment and vaccinations do not prevent animals from becoming carriers. For these reasons, the goal is often to prevent disease and death loss when the herd is first exposed to the Anaplasma organism and as it spreads within the herd. One control option is to offer chlortetracycline (CTC) at the control dose of 0.5 mg-2mg/lb BW per head per day throughout the vector (fly) season to the herd (May-Nov). This is easily accomplished by purchasing a free-choice mineral with CTC added for anaplasmosis control. However, CTC intake varies greatly from cow-to-cow, so some eat too much and others not enough. Research has found it is equally effective to pulse feed CTC (offer CTC for 30 days, take a 30-day break then offer CTC for the next 30 days and so on) as to offer CTC continuously for control of the disease. To obtain CTC, a producer must have a written VFD from a licensed veterinarian to present to the feed store before purchase of the product. FDA states that “once a veterinarian has determined that anaplasmosis infection exists within a herd, whether or not clinical signs are apparent yet, he/she may write a VFD to direct the use of CTC for controlling the progression of the disease in that herd.” FDA leaves how to make this determination to the discretion of the veterinarian. How long to use the product is also left to the veterinarian’s discretion, based on his or her assessment of the disease risk. A VFD order can be issued for a maximum of 180-day duration of feeding; if needed for a longer period of time, a new VFD order must be written. On the actual VFD form for CTC, the veterinarian can only choose the #5 option for a free choice product. Remember, feeding CTC will not prevent disease if the animals are not consuming sufficient amounts so intake should be monitored. Even when feeding CTC throughout the vector season, some individual animals may still become infected and die if they do not eat enough. Using CTC or any feed additive in a manner not stated on the label is illegal and strictly prohibited for producers, veterinarians, and nutritionists. If unable to obtain a VFD or feeding CTC is not an option, vaccination is another possible control measure available that can work but is a bit pricey at $8-10 per dose. To reduce the cost, if willing to draw blood and submit for anaplasmosis testing, the vaccine can then be targeted for use in only the individuals who test negative for antibodies. Animals that test positive will not need vaccination nor CTC therapy. This Anaplasmosis cELISA blood test (currently $9 per test) can be run on the same blood sample used for pregnancy testing, too.
Will Anaplasmosis always be a problem for KY cattle herds? Maybe. The disease should reach a point of “endemic stability”, meaning nearly all the animals in herds have been exposed to the disease and are immune to its effects. However, studies have found that herds in traditionally endemic areas such as Florida are not necessarily full of positive animals. In other words, there is no way to know the status of your own herd (how many cows are carriers and how many are uninfected) unless you blood test. Any new additions to the herd purchased from areas of the US without anaplasmosis and brought to KY will be at higher risk of disease and should be tested to determine their status. Similarly, new purchased additions may be Anaplasmosis carriers and can infect cows in your herd if there are many negative cows. Bottom line is to test new purchases and work with your vet to determine next steps.
Will carrier cows and bulls always have Anaplasmosis? Should they be culled? Carriers in the herd are not necessarily bad even though they carry the organism in their blood cells. Once an animal is a carrier, it is protected from disease and will not develop anemia and die. However, carriers that consume a consistent, high dose of tetracycline over a prolonged period (called “chemosterilization”) may inadvertently clear the organism and are susceptible to re-infection and sickness/death in subsequent seasons. Attempting to clear the organism or eradicate the disease is usually limited to high value seedstock and those that require international movement. Consult your veterinarian for further information about testing and disease control recommendations for your area.
Example VFD Form for Free Choice CTC
Beef and Non-lactating Dairy Cattle: As an aid in control of active infection of anaplasmosis caused by Anaplasma marginale susceptible to chlortetracycline when delivered in a free-choice feed.
Drug Concentration:
- 8000 g/ton (to provide 0.5 to 2.0 mg/lb body weight/day) [Must use a FDA-approved proprietary formulation.]
- 6000 g/ton (to provide 0.5 to 2.0 mg/lb body weight/day) [Must use a FDA-approved proprietary formulation or formulation in 21 CFR 558.128(e)(6).]
- 5000 g/ton (to provide 0.5 to 2.0 mg/lb body weight/day) [Must use a FDA-approved proprietary formulation.]
- 700 g/ton (to provide 0.5 to 2.0 mg/lb body weight/day) [Must use a FDA-approved proprietary formulation.]