Many cattle producers think of anaplasmosis as horsefly disease – but Craig Payne said, beware the tick.
“Probably a more efficient transmitter of this blood parasite is going to be ticks,” Dr. Payne, a veterinarian with University of Missouri Extension, told Ozarks Farm & Neighbor. “Unlike the horsefly, the ticks actually serve as a site where this organism can go through some reproductive cycles and replicate, so they’re a way in which the population of the parasite increases.”
Anaplasmosis is caused by a Rickettsial parasite called Anaplasma marginale. It infects red blood cells, causing the body’s immune system to attack and destroy the cells faster than they can be regenerated; this causes the animal to become anemic, which eventually leads to systemwide oxygen deprivation and death. It can also be transmitted with an injection needle, or castration or dehorning equipment that hasn’t been sterilized.
Payne said the clinical signs of anaplasmosis are fairly easy to recognize, especially if you’ve seen them before. “The animals will become jaundiced, and you may see that yellow color show up around the whites of the eyes,” he said. “If it’s a white colored animal, sometimes producers will report seeing a yellow coloring of the udder and the teats, and if you’ve got hands-on access to the animal you can actually look at the mucous membranes of the vulva and see yellowing there.” The animal will also tend to run a fairly high fever, 104° or more, versus the normal 101-102°.
There are also behavioral signs; the animals appear depressed and, “as they get into the later stages of the disease and the anemia becomes worse, some animals, if the producer’s trying to take them to a facilities for examination or treatment, will become aggressive,” due to the oxygen deprivation, Payne said.
If clinical signs are apparent, the animal is typically treated with an injectable vaccine, but producers can also prevent the onset of anaplasmosis by administering a feed containing chlortetracycline. Payne said the antibiotic is available in mineral blocks and other forms, with a recommended feeding level of 2 mg/lb/day per head of cattle. That’s the high end of the anima’s needs, but “If you have some that are not consuming the supplement or the mineral block in adequate amounts, they may not be getting enough of the chlortetracycline to prevent the disease,” he said. There is also a conditionally licensed vaccine that’s been approved in Missouri but is fairly expensive, and Payne said Extension has not demonstrated either its efficacy or lack thereof.
Dr. Jeremy Powell, University of Arkansas Extension veterinarian, warned, “It’s not going to last that long in the animal,” he told OFN. The treatment vaccine is also potentially life-threatening if the animal is already anemic.
Powell recommended controlling the vectors with “fly tags or back rubs that contain insecticide, anything to control the number of biting insects and ticks that would be likely to spread the disease to cows.” In addition, wild ruminants are reservoirs of the disease, and supply the parasites that the insects carry to the cattle herd.
Infections usually occur in late summer or early fall when the flies and ticks are most active.
