Summer has ended and fall is here, which means it is time for cattlemen to watch their herds for signs of anaplasmosis. This disease, which appears most often in the fall months, can be devastating to some herds if not treated properly or in a timely manner.
Anaplasma marginale is a parasitic organism that is transmitted through blood transfer by biting insects and ticks, and surgical instruments such as needles. In one study, a needle was used in an infected steer and then reused in the next 10 animals. That needle transmitted Anaplasma marginale to six of the next 10 cattle.
Dr. Meredyth Jones, assistant professor at the Texas A&M College of Veterinary Medicine and Biomedical Sciences Large Animal Hospital, explained that the organism attaches to red blood cells, which the body then removes, causing cattle to become anemic.
Anaplasmosis appears often in the fall season because symptoms surface about 21-45 days after infection, typically after the busy biting fly season of late summer. Cattlemen in southern states need to be particularly cautious because it appears most frequently south of Kansas.
“Many times cattle can be infected and show no signs of illness,” said Jones. “But during the fall months, if we are called on to examine a sickly, weak cow – anaplasmosis is high on our list of culprits.”
In the acute phase of infection cattle appear weak, “down,” and generically sick due to anemia. Affected cattle may also exhibit white or yellow mucous membranes (such as eyes, muzzles, udders, and vulvas). These mucous membranes will appear white due to the lack of red blood cells, or yellow because of the pigments released as red blood cells are broken down and removed from the body. Some cattle may even exhibit signs of aggressiveness. This aggressive behavior is caused by lack of oxygen to the brain.
“Because they are weak, they tend to resort to a ‘fight’ rather than ‘flight’ response,” Jones said.
Anaplasmosis also appears in a chronic form caused by a moderate level of anemia. Cattle lose weight over time which can cause abortions in pregnant cows. The blood of infected cows in both phases will be thin in consistency, almost watery, when examined.
“For a clinical diagnosis, veterinarians will commonly test a cow’s blood for anaplasmosis with a blood smear,” Jones said. “We can actually see the organism attached to the margin of red blood cells with a microscope.”