Brucellosis clues

by Cat Urbigkit

Livestock producers must be vigilant in maintaining separation of their cattle herds and elk and bison, both in time and space.

That's the message delivered by Wyoming State Veterinarian Dr. Jim Logan at the Wyoming Brucellosis Coordination Team's first meeting, which was held in Pinedale last week.

Brucellosis is a chronic disease that often causes infected animals to abort their fetuses. But abortion isn't the only major symptom that a herd is infected with brucellosis. Other characteristics associated with brucellosis are orchitis and arthritis, infertility, retained placenta and latency syndrome, which also occurs in bulls. With latency syndrome, a heifer calf exposed to brucellosis at calfhood may test free of the disease until after she has had her second calf.

"It hides in some individuals," Logan said.

The incubation period for brucellosis ranges between a few weeks to a few months or even years, so a negative test for the disease isn't a guarantee. Infected animals are life-long carriers, so infected livestock must be destroyed. Logan noted that since brucellosis is associated with the reproductive tract, heifers and pregnant cows are more susceptible to the disease than other cattle.

With a disease this complicated, Logan recommends livestock producers implement several prevention measures: temporal and spatial separation from bison and elk; management; surveillance; and vaccination of both calves and adults.

Logan cautioned that vaccination is only 60-80 percent effective, so this measure alone will not provide protection for cattle herds.

Logan noted that there have been seven brucellosis cases in Wyoming cattle herds in the last 40 years, and all were isolated to one herd per incident. All were shown to be from contact with infected wildlife.

Wyoming recently lost its brucellosis class-free status for its livestock herds, now being classified as a Class A state in which testing is required for movement and change of ownership. Only Texas and Wyoming have this classification, with Missouri recently achieving its class-free status.

Big Piney cattleman Bill Barney, in the audience at last week's meeting, addressed the group about the two states and their Class A status, noting it's hardly a fair comparison when it comes to economic impacts.

"Feed - Texas has an abundance of feed for finishing cattle; Wyoming does not," Barney said. "Feedlots - Texas has an abundance of feedlots; Wyoming does not. Wyoming doesn't even have one USDA-classified small packing plant, let alone mid-size or large."

Barney concluded: "Whereas Texas is a net importer of live cattle and exporter of finished product, we have to export everything that we grow. So while brucellosis Class A status is an inconvenience or an irritation for Texas, it's a matter of serious economic consequence for us. For practical purposes, we are the only one."

While Wyoming's cattle herds continue to test free of brucellosis, bison and elk populations in western Wyoming serve as a reservoir for the disease and pose a risk of transmission to livestock herds, as Logan described in the seven previous cases. Seropositive rates are 50 percent in bison and 28 percent in local elk populations, Logan said. Spreading the disease from animal to animal is more likely in high-density populations.

Logan said that generally, cattle are more at risk of disease transmission from bison than they are from elk because bison behavior more closely resembles cattle behavior. But in Wyoming, the greatest risk to cattle is from infected elk, Logan said, due to the number of elk and elk feedgrounds, which are often located in close proximity to ranches.

The potential for the spread of brucellosis beyond wildlife in the Greater Yellowstone region is real, Logan said. He added that wildlife health and populations could be affected as well.

Wyoming's new Brucellosis Coordination Task Force needs to be ready to make tough decisions and take tough actions for the betterment of Wyoming's future, Logan said.

The task force is charged with examining: transmission of the disease, both short-term and long-term; human health; protocol for the next outbreak; and reduction and elimination of brucellosis in elk.

Human health is an issue, according to Dr. Carl Musgrave of the Wyoming Department of Health. There are one or two cases of human brucellosis per year in Wyoming, Musgrave said, with about 200 cases nationally and 500,000 cases worldwide per year. Ranchers, veterinarians, hunters, butchers and others who may come into contact with infected animals are most at risk of transmitting the disease.