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ARS dairy scientist Albert Guidry credits cooperation
among ARS, state universities, dairy producers, and industry for
the success of the Staphylococcus aureus vaccine against
mastitis.
(K9144-1)
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Al Guidry is looking for a herd of
willing heifers.
He could use about 1,000 of these adolescent cows to test a new vaccine against
the toughest form of mastitis—the kind caused by Staphylococcus
aureus. Current commercial vaccines immunize against two staph strains that
cause only about 40 percent of staph-induced mastitis cases in the United
States, slightly more in Europe. And antibiotics are ineffective against staph
because the bacteria have become resistant, or they have holed up in regions of
the gland where the drugs can't reach.
So Guidry, a dairy scientist at the Beltsville (Maryland) Agricultural Research
Center, went looking for the missing links. He screened 44 percent of the U.S.
dairy herd to find the serotypes responsible for the other 60 percent of
staph-related mastitis cases.
Collaborator Ali I. Fattom, with the biotechnology company Nabi in Rockville,
Maryland, had what Guidry was looking for: a single serotype of S.
aureus—called 336. Fattom, who is involved in developing a human
vaccine against staph, knew that 336 accounts for only about 10 to 12 percent
of human staph infections. In U.S. cows, however, it's responsible for 50 to 60
percent.
The result of this collaboration is a trivalent vaccine containing 336 together
with the other two staph strains known to cause mastitis. Whether or not the
new vaccine will prevent mastitis still needs to be proved. But it can cure
it—even a good percentage of the most recalcitrant cases—when
combined with antibiotics. That's according to tests being led by another of
Guidry's longtime colleagues, Michigan State University veterinary scientist
Phil M. Sears.
Sears had been looking for a way to boost the bovine immune system, hoping that
a more vigorous immune response combined with antibiotics would control chronic
mastitis. And he had good results. When he isolated the causative S.
aureus strain from a dairy herd, killed it, then injected it back into the
infected cows a few weeks before administering antibiotics, he cured more than
half.
But isolating the causative agent from each herd is too cumbersome for
commercial use. The trivalent vaccine appears to solve this problem.
"It applies to all herds, and it's a purer, cleaner preparation,"
says Guidry. When Sears tested it in commercial dairy cows, it proved to be as
effective as his herd-specific vaccine, curing 55 to 60 percent of infected
cows.
Because of these promising results, Sears is confident the vaccine will protect
heifers from infection. "I don't have any doubt," he says, noting
that the vaccine cleared staph infections in about 10 percent of infected
cows—even before he administered antibiotics. And it cleared 7 of the 9
cases in the Beltsville herd with the administration of antibiotics, Guidry
adds.
Nabi and ARS are jointly applying for a
patent covering the new vaccine. The company will look for a partner with
channels in the agricultural arena to fund further studies and market it.
Before the vaccine can go to market, its ability to prevent infection needs
additional validation, says Guidry.
He figures that will require several years and a whole lot of heifers.—By
Judy
McBride, Agricultural Research Service Information Staff.
This research is part of Animal Health, an ARS National Program (#103)
described on the World Wide Web at http://www.nps.ars.usda.gov.
Albert J. Guidry is with the
USDA-ARS Immunology and Disease
Resistance Laboratory, 10300 Baltimore Ave., Bldg. 173, Room 105,
Beltsville, MD 20705-2350; phone (301) 504-8285, fax (301) 504-9498. |
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