by WLJ
Rushing water, stagnant ponds, or even the dry stages after wet periods
can lead to outbreaks of livestock disease. Mosquitoes and biting flies,
capable of carrying and transmitting diseases, thrive in the damp
weather, and naturally-occurring anthrax can take a toll on livestock
and wildlife when pastures dry after prolonged wet periods.
Horse owners should take precautions against mosquito-transmitted
diseases by having their animals vaccinated against West Nile Virus and
the reportable diseases Eastern and Western Equine Encephalitis. “If you
wait until cases of ‘sleeping sickness’ occur in your area, you may have
waited too long to vaccinate,” said Dr. Bob Hillman, Texas state
veterinarian and head of the Texas Animal Health Commission (TAHC), the
state’s livestock and poultry health regulatory agency.
“You need time for the vaccine to do its job, which is to build the
animal’s immunity to a particular disease,” he said. “Vaccine can
provide the best disease protection possible, but it’s also crucial to
keep up with booster shots, as recommended by the vaccine
manufacturer or your private veterinary
practitioner. In 2006, 111 horses were confirmed to have West Nile Virus
in Texas. So far this year, the disease has been confirmed in one horse,
located in Willacy County.”
Three cases of Potomac Horse Fever, which is not a regulatory disease,
have been confirmed in Kerr County by the Texas Veterinary Medical
Diagnostic Laboratory. Potomac Horse Fever, first detected in Maryland
in l979, is not typically found in Texas. Clinical cases usually are
found near rivers, streams, ponds or canals. The infection involves tiny
flukes that are parasites of water snails. The flukes hatch their
offspring into the water, and these are then picked up by aquatic
insects that molt into flying insects, including caddis flies and
mayflies. Horses can become exposed to Potomac Horse Fever when they eat
or drink anything contaminated with the insects.
Kerr County equine veterinarians are urging all owners to call their
practitioner if equine animals exhibit signs of Potomac Horse Fever,
which can include a reluctance to eat, fever, diarrhea, colic or
inflammation around the hoof. Treatment includes antibiotics and
supportive care.
Biting flies can mechanically transmit equine infectious anemia (EIA),
sometimes called “swamp fever.” This incurable disease, for which no
approved vaccine exists in the U.S., is a regulatory disease. TAHC
regulations require horses and other equine animals to have a negative
test for EIA within the previous 12 months before entering the state, or
going to events, assemblies, trail rides, undergoing change of
ownership, or entering a breeding farm. The most commonly known test for
EIA is the “Coggins” blood test. The incidence of EIA has dropped
dramatically since l997 when 750 equine animals in Texas were found to
be infected. Since January 2007, only 29 infected animals have been
detected.
“EIA-infected horses can develop severe anemia, fever and swelling. In
severe cases, EIA can kill the animals, but many times, the infected
animal has few signs of disease,” noted Hillman. “Prevent EIA
transmission by avoiding blood-to-blood contact between infected and
‘clean’ equine animals. Disinfect medical instruments and tack, and
control flies. Biting flies carry blood from one animal to the next on
their mouthparts, and they play a key role in the mechanical
transmission of EIA.”
Infected equines must be maintained at least 200 yards away from other
equine animals, euthanized, or sent to slaughter.
“In the past, untested equine animals could be sold for slaughter
through a livestock market. At the slaughter plant, blood samples were
collected and sent for laboratory testing. Now that Texas equine
slaughter plants have been closed, we can not ensure that horses moving
to plants in other states or countries are tested. Therefore, we are
requiring all horses to have a current EIA test, even when being sold
for slaughter,” said Hillman.
Rain, followed by hot weather can coax the invisible bacteria Bacillus
anthracis to the surface, a situation that has occurred on a ranch in
Tom Green County where 17 head of cattle and a number of white-tailed
deer have died. “Anthrax in Texas occurs nearly every year, and it is a
reportable disease to the TAHC. If we know an outbreak is occurring, we
can let ranchers in the area know that it’s time to vaccinate their
livestock. There is no preventive treatment for wildlife,” said Hillman.
Anthrax naturally occurs worldwide and in many states of the U.S.
Disease outbreaks have been reported in Minnesota, South Dakota and
Canada this year. When an anthrax-infected animal dies and isn’t
properly burned, the bacteria will infiltrate the soil and lie dormant
(but not spread) for many years. Under ideal weather and soil
conditions—a cool, wet spring, followed by a hot, dry spell—the bacteria
will resurface on grass and forage. The disease cycle starts again when
another animal ingests the resurfaced anthrax bacteria.
TAHC regulations require that an infected animal’s carcass, manure and
bedding be incinerated. This prevents wild animals from being exposed to
the disease, and it kills the bacteria, preventing another site where
the anthrax bacteria can resurface. Hillman urged ranchers to wear
gloves and long sleeves when preparing the burn site and to avoid moving
the carcasses, if possible. Exposure to anthrax carcasses could cause a
handler to develop a black skin lesion that requires prompt medical
treatment.
“There is no need for vacationers or hunters to worry about naturally
occurring anthrax. Just don’t touch or handle sick or dead animals, and
don’t pick up bones or shed antlers. We usually advise hunters not to
hunt feral or wild swine in the area during an anthrax outbreak. Feral
swine may root around carcasses of anthrax-killed animals, becoming
exposed to the bacteria but not contracting the disease.”
Hillman advised swimmers to avoid ponds or streams if dead animals are
nearby. The same advice goes for pets, too. By the time hunting season
starts, he said, cool weather usually puts an end to anthrax cases.
“Always harvest only healthy-looking animals, and, as a routine
practice, wear gloves when processing meat,” he said.
“In Texas, it is often ‘feast or famine,’ drought or flood,” said
Hillman. “With each of the conditions, there are concerns about
livestock health. So, while ranchers enjoy the lush grasses the rains
have produced, they may have to control pests to lower disease risks.
However, I don’t know many ranchers who would choose last year’s drought
over some extra vigilance this year.”
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