Keeping Cattle Fever Ticks Away From U.S.
Herds By Alfredo
August 23, 2002
Its been nearly 60 years since the United States rid
itself of cattle fever ticks that can transmit a serious livestock disease
known as bovine babesiosis. But despite being eradicated in the United States,
the ticks still persist in Mexican cattle, many of which cross the border for
A quarantine zone in south Texas along the Mexican border is
currently the only barrier to cattle fever ticks reentry into the United
States, where all cattle are susceptible to the disease the ticks carry.
To prevent a costly reinfestation, U.S.-bound animals are
dipped in coumaphos, an organophosphate pesticide that kills the
ticks. But some Mexican ticks have developed resistance to coumaphos and other
pesticides used in Mexico. So Agricultural
Research Service scientists at the
Livestock Insects Research Laboratory in Kerrville, Texas, have been
looking for ways to monitor resistance in Mexican ticks.
ARS physiologist Felix D. Guerrero and microbiologist John H.
Pruett have identified two independent mechanisms by which ticks become
resistant to pyrethroid pesticides still used in Mexico. And they have found
one strain of resistant Mexican tick possessing a gene that produces a large
amount of a specific esterase protein involved in the breakdown of pyrethroids.
Best of all, Guerrero and Pruett have shortened the time needed
to spot pyrethroid resistance in a specimen from six weeks to just one day.
Though pyrethroid resistance is becoming widespread, it's not found everywhere
in Mexico, so pyrethroids can still play a role in killing ticks and preventing
As their research has shifted focus to coumaphos resistance, the
two scientists have adapted a test that uses color to recognize resistant ticks
and can be performed on crushed tick larvae or dissected adult tick brains.
They are working to clone the tick genes involved in coumaphos resistance and
will develop rapid tests for detecting them.
ARS is the U.S. Department of
Agriculture's chief scientific research agency.