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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
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
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
"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
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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