With cattle producers restocking herds in certain parts of Texas following drought, experts are urging ranchers to be mindful of bovine anaplasmosis, an infectious disease that can be transmitted among cattle by blood.
“Due to sustained drought in Texas, many cattle operations
have been downsized or depopulated,” said Dr. Tom Hairgrove, Texas
A&M AgriLife Extension Service program coordinator for livestock and
food systems in College Station. “With restocking beginning on some
operations, carrier cattle from areas where infection is common could be
problematic.”
Hairgrove and Dr. Pete Teel, Texas A&M AgriLife
Research entomologist at College Station, provided a briefing to faculty
members recently in the department of animal science at Texas A&M
University.
Cattle can become infected with bovine anaplasmosis through transfer of red blood cells, Hairgrove said.
“Horse flies and deer flies are mechanical carriers and the
infected blood on their mouth parts is the only way they can spread the
disease,” he explained. “Contaminated ear tagging instruments, needles
and surgical instruments used while working cattle also can be a cause
of transmission. Thoroughly clean instruments and change needles between
cows.”
Biological vectors such as ticks can also be carriers. Teel
said two Dermacentor ticks – the winter tick and the American dog tick –
may serve as both vectors and reservoirs to sustain the disease in
Texas.
“The winter tick attacks cattle and other large animals
such as deer and horses from October to April,” Teel said. “They feed
as larvae, nymphs and adult ticks on the same host, but may be groomed
off as bloodfed-nymphs which molt to adults and then attach to another
host. If the initial host is an infected cow, and the second is not,
transmission of the anaplasma agent may occur.
“The American dog tick attacks a wide variety of animals
and feeds separately on three hosts, one for larvae, nymphs and adults,
respectively.
“Small-, medium- and large-sized animals are included,
often in a progressive fashion,” Teel said. “However, cattle are known
to be attacked by nymphs, which fall off when blood-fed to become adult
ticks. The adult ticks can then transmit the agent acquired as a nymph
to a non-infected cow. Spring and summer are the primary seasons of
activity for the American dog tick. Thus, ticks are a year-round risk
for transmission of the anaplasma agent.”
For ranchers, the potential for the disease is greater when
co-mingling non-infected cattle with those that carry the disease. Such
an example is when ranchers introduce purchased cattle to those in an
existing herd, the purchased cattle could be carriers – on the flip
side, introducing non-carrier cattle into a carrier herd could also be
problematic,” Hairgrove said.
Cattle that survive initial infection become lifetime carriers of the infection and are important to disease epidemiology.
“Red blood cells have a 160-day lifespan and newly
developed erythrocytes must be continually infected to maintain
persistent infection,” Hairgrove said. “Although all ages of cattle can
become infected, the disease is usually not apparent in animals less
than a year of age. Disease is more prevalent in cattle more than three
to four years of age.”
There are preventive aids that ranchers can use.
“Ranchers should use strict adherence to sanitation
procedures when using needles, surgical instruments, ear taggers, etc.,”
Hairgrove said.
As an additional preventive measure, strategically feed
Tetracycline during the vector season, he said. Beef producers can
consult with their local veterinarian for additional control measures.
Overall, Hairgrove stressed there is not a widespread
problem with the disease, but ranchers should become educated about
bovine anaplasmosis.
“We are not saying the sky is falling, but if you have
cattle that are carriers and then you start co-mingling cattle with
those that aren’t infected, that’s when you have problems,” Hairgrove
said.
