Anaplasmosis: 
(part 2: "current treatment and preventative measures")
John G. Kirkpatrick, DVM 
OSU College of Veterinary Medicine

Transmission: A. marginale, the parasite, may be transmitted both mechanically and biologically.  Mechanical transmission occurs by direct inoculation of infected red blood cells (RBCs) into susceptible cattle on blood contaminated surgical instruments (dehorners, castration instruments, and tattooing instruments), hypodermic needles, or on the mouth parts of biting flies and mosquitoes.  Dermacentor sp. or hard ticks are the natural biological vectors of anaplasmosis in the United States.  The natural mechanical and biologic vectors are usually seasonal and most outbreaks coincide or shortly follow these seasons. 

Mechanical transfer by contaminated needles or surgical instruments occurs when the transfer of infected RBCs from a carrier animal to susceptible animal within minutes.  When this form of transmission occurs there are usually several animals affected within a short time period.

Clinical signs: Clinical signs of anaplasmosis are related to the age of the animal.  Calves under 6 months of age become infected, rarely show clinical signs, and remain carriers.  Carrier animals seldom exhibit clinical signs when challenged with A. marginale later in life.  A carrier animal may or may not give a positive reaction to serologic tests for A. marginale.  A. Marginale bodies may or may not be demonstrated in the stained blood smear of the carrier animal.  However the carrier’s blood is infective for the susceptible animal.  Yearling to 18-month-old cattle will develop symptoms.  The clinical signs are mild and these animals become carriers.  In adults, signs are progressively severe; the animals will either die or become carriers. 

The incubation or prepatent period is 3 to 8 weeks and is the time between inoculation of the infectious agent and occurrence of A. marginale bodies in 1% of the RBCs.  The developmental stage is about 4 to 9 days and is the time when most of the characteristic signs of anaplasmosis appear.  During this phase from 10% to greater than 75% of the RBCs may be infected. 

Clinical signs in adult animals include depression, off feed, fever up to 107 degrees F., anemia or paleness and/or yellow mucous membranes, rapid respiration, urine may be yellowish in color, occasional belligerence, dehydration and constipation, and sudden death.  Most deaths occur in the later stages of the developmental stage or early convalescent stage.

The convalescent stage extends from the time it is evident, by blood smears, that the animal is positively responding to the anemia until normal blood values are attained (no longer anemic).   The animal that lives will enter into the carrier stage, remain a carrier, and serve as a reservoir of infection as long as it lives.

Treatment: Treatment of cattle with anaplasmosis is not without risk.  Any exertion, driving, loading into a trailer, or loading into a chute, of the severely anemic animal may cause its death.  Choosing to not treat the belligerent cow can be a wise decision as they often overexert resulting in their death.

Oxytetracycline (OTC) can be very effective in reducing the severity of the disease when administered during the early to mid-point of the developmental stage.  Your veterinarian may elect to give a blood transfusion depending on the degree of anemia and the perceived risks to the affected animal.

Prevention: Anaplasmosis is a herd problem and should be approached as such.  Outbreaks occur when there is no control program, anaplasmosis carriers and susceptible animals are present in the herd, and vectors (mechanical and / or biological) for transmission are present. 

Anaplasmosis control is based on preventing the transmission of infected RBCs from carrier animals to susceptible animals.  Strategic environmental management, insecticides and repellents, cleanliness of surgical instruments and changing of needles between animals must be in place to minimize disease transmission. 

OTC administered every 28 days beginning at the start of vector season and ending 60 days after the end of vector season will prevent clinical anaplasmosis.  The recommended dose is 6.6 to 11 mg / kg (3 to 5 mg / lb.) of body weight.  This would insure each animal received the proper amount of drug, but would be highly labor intensive.  It is necessary that individual needles be used for each animal. 

Chlortetracycline (CTC) consumed at the rate of 1.1 mg / kg (0.5 mg / lb.) body weight daily during vector season will prevent transmission of anaplasmosis. CTC may be administered in medicated feed; salt-mineral mixes offered free choice, and medicated blocks.  It is imperative that consumption levels are monitored.  Effectiveness is dependent on proper intake.  It may be necessary to maintain continuous year around feeding of CTC dependent on geographic location, carrier exposure, and vector exposure.  When continuous CTC medication is fed year-round, CTC consumption levels of 0.22 to 0.55 mg / kg (0.1 to 0.25 mg / lb.) have proven effective.  Your veterinarian should definitively diagnosis the disease and provide you with additional information to assist in treatment and prevention.

Insure that animals have easy access to medication.  Keep all medicated feed, salt-mineral mixes, and blocks out of direct sunlight and rain. 

The development of an efficacious anaplasmosis vaccine will prove to be of extreme economic benefit.  CTC feeding is expensive and inadequate consumption is ineffective.