Anaplasmosis in Cattle – A Problem for the Fall Season

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."

In the acute phase, anaplasmosis can be quite fatal if not treated properly. Jones explained that ill cattle need to be treated with great care because the stress of working and handling cattle can be fatal if the disease is advanced.

"If you suspect a cow of being infected, don't chase her with horses or dogs if you can help it. You really need to handle them delicately to reduce their stress as much as possible," Jones said.

The most common treatment for the disease is the use of tetracycline antibiotics. Improvement in cattle's symptoms can be seen within a few days, but it takes between two to four weeks to see a significant recovery of red blood cell numbers.

As with most diseases, preventing the disease in the first place is ideal. Jones recommended using fly tags, rubs, and pour-on insect repellents to keep biting insects and ticks at bay. She also suggested changing needles between each cow when vaccinating or administering medicines. Another option is to put chlortetracycline in the feed at a low level to kill the organism before it can replicate and attach to red blood cells.

Unlike many diseases, which attack young and elderly populations, middle-aged cattle are most affected by anaplasmosis. In fact, most catastrophic cases occur in cattle between six and eight years of age. Younger cattle are better able to regenerate red blood cells and recover, often developing immunity. Therefore Jones recommends that cattlemen pay particular attention to their adult cows and bulls as the season progresses, watching for symptoms characteristic of anaplasmosis.

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