On Friday, Montana state officials announced that a few thousand head of cattle had been quarantined, as a cow near the border of Yellowstone National Park has tested positive for brucellosis.
Brucellosis was first introduced into North America by infected livestock brought in by European settlers. It’s a zoonotic bacterial infection with forms that affect many different species of mammals, most notably humans, bison, elk, cattle, horses, pigs, sheep and goats.
In cattle, signs of brucellosis are limited. The disease presents itself most commonly with abortions and premature calf death.
According to the USDA, 6400 cases of human brucellosis were reported in 1947. Now, roughly 100 cases are reported annually to the Centers for Disease Control and Prevention. From a livestock perspective, annual losses in agriculture have decreased also, from more than $400 million in 1952 to less than $1 million today.
“We don’t like finding brucellosis-positive cows, but if it’s out there, we want to find it before cattle are shipped to market or out of state,” state veterinarian Marty Zaluski said in a release. “That’s why we have a program – we have to assure other states we’re doing everything we can to manage this endemic wildlife disease problem.”
In Canada, an eradication program was initiated for bovine brucellosis in the 1940s, and in 1985, the country was declared free of the disease. According to the Canadian Food Inspection Agency, the last known case occurred in 1989 in a cattle herd in Saskatchewan.
Livestock producers in the United States are encouraged to manage the disease on their farms by limiting exposure to the bacteria, whether this means maintaining a relatively closed herd, ensuring animals are purchased from facilities free of the disease, maintaining boundary fences, limiting exposure to other calving land and providing sanitary, adequate calving handling facilities.
Vaccines like B abortus Strain 19 and RB51 have been shown to increase resistance, but will not always prevent an animal from becoming infected. In Canada, vaccination is not permitted: a step necessary in keeping brucellosis-free status under the World Organization for Animal Health. (CFIA)
In areas where brucellosis has spread into domestic herds from wild animals such as elk and bison, management is more controversial. This is certainly true around Yellowstone National Park, where management includes hazing, capture, culling and vaccination of bison.
Genomics studies looking to identify certain genes for susceptibility have had conflicting results. One of the most recent studies, published in May, suggests certain bovine genotypes do appear more susceptible than others. And although several articles highlight the complexity of genetics in disease susceptibility, some remain optomisitic for the future of management through phenotypic and genomic selection.
As part of the epidemiological investigation to determine the infection source, producers in the immediate area will have to test their livestock.
Though Montana has found at least one infected animal in five of the last eight years, based on USDA regulations, it is not at risk of losing its Class Free status.
This post, written by Debra Murphy, originally appeared on Genome Alberta.