Vaccine failure puzzles biologists
By The Associated Press - 5/31/04
Source: The Capital City's Newpapar Online
JACKSON, Wyo. (AP) — Biologists are puzzled why brucellosis exposure rates have spiked among some vaccinated elk.
Disease rates at the Greys River elk feedground have even exceeded the high rates of the 1970s, before the state began vaccinating elk against brucellosis, according to Brandon Scurlock, a biologist with the Wyoming Game and Fish Department.
‘‘To be honest, I have no way of explaining this,'' Scurlock told a recent forum in Pinedale on elk feedgrounds.
Controlling the disease, which can cause animals to abort, is important because it can be transmitted to cattle.
The detection of the disease in cattle caused Wyoming to lose its federal brucellosis-free status earlier this year. That in turn has led to laborious and costly testing requirements.
While feedgrounds help keep elk away from cattle by encouraging them to congregate, the same congregation helps spread disease.
About 25 percent of elk on all feedgrounds test positive for exposure to the disease — compared to less than 3 percent of other elk.
Vaccination at the Greys River feedground began in 1985. Brucellosis exposure dropped below 10 percent in the mid-1990s, down from 54 percent in the 1970s.
In 2000, however, rates jumped to 26 percent before hitting 54 percent the following year. This year, 59 percent of elk tested positive.
Biologists originally thought that a weak batch of vaccine given to some elk in 1998 was to blame for the brucellosis rates at the Greys River feedground.
But Scurlock said that theory is no longer plausible because disease rates should have dropped among the elk that have been vaccinated with the correct dosage since then.
He said more tests are needed to find out what is happening.