Anaplasmosis Season

DR. ERIN LARIMORE

JACKSON, MO.
   The majority of anaplasmosis cases are reported in late summer and fall. Anaplasma marginale causes disease by infecting red blood cells. The infected blood cells are removed from the body by the immune system causing anemia. In mild cases, animals may have elevated temperature, depression, and pale mucous membranes. In severe cases, animals may have yellowing around the eyes, severe depression or nervousness, and eventually die. If herds are not monitored closely, the first sign may be dead animals.
   The disease progresses rapidly until the immune system kicks in or treatment is provided. Long acting injectable oxytetracycline is the antimicrobial used most often for treating Anaplasmosis. The recommended dose is 10mg per pound of body weight every 72 hours for a total of three to four treatments. This treatment only halts the development of the bacteria; the animal must still be able to mount an immune response and replace the red blood cells that were lost in order to recover. Early treatment with antibiotics increases the odds that an animal can respond to the disease challenge. ***Remember, oxytetracycline for treatment of Anaplasmosis is considered extra-label drug use and must be prescribed by the herd veterinarian!***
   Animals that recover from infection with Anaplasmosis become carriers. Carrier animals have life-long immunity and rarely show clinical disease again, but they do serve as a reservoir of the organism within herds. It was once believed that carrier animals could be eliminated with repeated doses of injectable oxytetracycline. New studies show that repeated injections are not effective at eliminating the carrier status of animals.
   There are three strategies to control Anaplasmosis: minimize transmission, feed antimicrobials (CTC), and vaccination. To minimize transmission means to control ticks and biting flies which transmit the disease through their bite. Transmission can also occur via blood contaminated equipment such as needles, dehorners, or castrating equipment. Needles should be changed between every animal and equipment disinfected to minimize the risk of Anaplasmosis transmission.
   Feeding chlortetracycline (CTC) is the only approved antimicrobial for control of Anaplasmosis. This needs to be fed during arthropod vector season which can span from March through November in this part of the country. Some approvals for feeding of CTC require it be hand fed daily. Be sure to read and follow the feeding directions on the label as to whether the product needs to be hand fed daily or can be offered free choice.
   The last method for control of Anaplasmosis is vaccination of animals. There is not a commercially licensed vaccine available, however, MO veterinarians can order an experimental vaccine that was developed at LSU. The vaccine has been deemed safe for animals, but no research has been done to demonstrate its effectiveness at preventing and controlling the disease. The general consensus of veterinarians using the vaccine in the state is that it reduces the number and severity of disease events where Anaplasmosis has been problematic.
   This time of year be suspicious of Anaplasmosis if cattle have fever, depression, poor appetite, constipation, yellow membranes, nervousness, or are dead. Information from MU Guide: Control of Anaplasmosis in Missouri. ∆
   DR. ERIN LARIMORE: Livestock Specialist, University of Missouri