Two cases of brucellosis found in Montana cows

Two cows from Gallatin and Madison counties have tested positive for brucellosis in the last two months, but the Montana Department of Livestock said it does not believe the cases represent an increased risk of an outbreak.

The department reported the first positive case on Jan. 5 and the second on Feb. 22. Both infected cows have since been killed, and epidemiological investigations are underway.

“These two cases are not related epidemiologically,” said state veterinarian Dr. Marty Zaluski. “We have averaged about one case per year since 2010, so the time proximity of the two cases this year does not represent an increased risk. It’s more of a coincidence, and not an indicator of increased transmission risk.”

The first infected cow was from a Madison County ranch. The ranch’s entire herd was tested in December, and at the time, the cow was identified as a “suspect” case. The case was later confirmed after the National Veterinary Services Laboratories tested tissue samples. The last time Madison County had a positive case was in 2019, Zaluski said.

“We have genetic information that shows the transmission is likely from wildlife from birth tissue, most likely from elk,” he said. “Nowadays, almost all of our documented cases were spread from calving product of elk to livestock.”

The second case was reported on Feb. 22 in Gallatin County, which has not had a positive case since 2010, Zaluski said. The department said the infected animal tested negative in 2021 but tested as a reactor during a voluntary herd test in January.

Brucellosis is a bacterial disease mainly found in cattle, elk and bison. The primary side-effect of the disease in those animals is miscarriages and stillbirths, Zaluski said. The disease can also cause undulant, or chronic, fever in rare cases among humans, he said.

Both cases were identified as a result of voluntary testing by the ranch owners, which Zaluski said is imperative to managing the disease.

“A high rate of testing, much of it voluntary, is the primary reason we continue to find affected herds rapidly,” Zaluski said in a press release announcing the Madison County case. “A robust testing program not only minimizes the impact to that operation but protects our state and our trading partners.”

The two cases in 2022 are among the 12 recorded since Montana established its Designated Surveillance Area in 2010. Parts of Park, Gallatin, Madison and Beaverhead counties make up the Designated Surveillance Area. There are around 450 herds of livestock in the surveillance area totaling more than 100,000 animals, Zaluski said.

The Greater Yellowstone Area is the country’s last known source of the disease, Zaluski said. And the department believes bison and elk in and around the park have carried the disease since the early 1900s.

Zaluski said the state had eradicated the disease several decades ago and received its Class Free Status in 1985. Between 1985 and 2006, there were no reported cases of the disease in Montana livestock, he said. But as infection rates in elk increased over the last 20 years, so did the spillover of infections to cattle, he said — leading to the state establishing the Designated Surveillance Area in 2010.

“(The spillover) created a lot of problems for cattle because brucellosis is a highly impactful disease as it relates to trade whether it’s interstate or international,” he said. “When we have these transmissions, we need to pursue them aggressively.”

As part of a multi-year targeted elk brucellosis surveillance project, the Department of Livestock and Montana Fish, Wildlife and Parks recently captured and tested elk from the Tobacco Root Mountains south of Whitehall for brucellosis. All 163 elk captured tested negative for the disease, according to a news release from the Department of Livestock.

When Montana lost its Class Free Status in 2008, Zaluski said the United States Department of Agriculture estimated it would cost the state between $7 million and $15 million stemming from testing costs and barriers for exporting cattle out of state. Now the state spends $2 million per year managing the disease, Zaluski said.

Before the state established the Designated Surveillance Area, if two or more affected herds were detected in two years, the state would have lost brucellosis Class Free Status. But with the surveillance area, affected herds are no longer subject to depopulation, and states can maintain Class Status, according to the department.