The mild winter and early, wet spring in Oklahoma has been a blessing. However, insects that are vectors for the cattle disease anaplasmosis have also enjoyed the weather and are quite plentiful. Any blood-sucking insect can be a potential carrier of the disease. Ticks and horse flies are often the most common culprits. Cattle-working tools such as castration knives and vaccination needles are other methods of anaplasmosis transmission.
Anaplasmosis is an infectious disease of cattle caused by a rickettsia organism, Anaplasma marginale. This organism invades red blood cells, forming a small dot or marginal body and causes the infected cells to be removed from circulation, thereby initiating the clinical signs of anemia. 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 red blood cells. 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 red blood cells 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.
Be certain to visit with a large animal veterinarian about prevention of the disease in your herd and treatment of any infected animals. 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.