Bovine RB-51 brucellosis case confirmed in Larimer County

Bovine RB-51 brucellosis case confirmed in Larimer County

The following was distributed to Colorado veterinarians by the Colorado State Veterinarian’s Office on October 9, 2020. Click here to sign up to receive immediate updates from the Colorado State Veterinarian’s Office.

The Colorado Department of Agriculture has confirmed a case of Brucellosis RB-51 strain in a cow on a raw milk dairy in Larimer County. The owner of the dairy submitted milk samples to CSU Veterinary Diagnostic Laboratory for routine Somatic Cell Count (SCC) testing. The SCC count from one cow was elevated; culture was completed and Brucella spp. was isolated. The samples were forwarded to USDA National Veterinary Services Laboratory and were identified as Brucella abortus RB-51 isolate.

Additional samples from the positive cow were collected by a regulatory veterinarian and have been submitted to NVSL for additional confirmatory testing.

The Colorado Department of Agriculture (CDA) and the Colorado Department of Public Health and Environment (CDPHE) are completing a joint investigation for this case. An epidemiologic investigation is being completed to determine the risk for the rest of the herd which will inform decisions as we move forward, including testing of cohort animals and implementation of a herd plan.

To date, no cases of human illness associated with this raw milk dairy have been reported to public health, however the investigation is ongoing.

The owner has voluntarily suspended distribution of raw milk until the investigation is complete.

Brucellosis vaccination

Veterinarians should work with producers to determine when Brucellosis vaccination is appropriate for herd management. The Brucellosis official calfhood vaccination will not prevent most animal vaccinates from getting infected. The goal of vaccination is to prevent abortions and shedding to prevent transmission in the herd. Given that B. abortus is now geographically limited to the Greater Yellowstone Area in wildlife, the need for routine vaccination of calves has decreased.

There is no requirement to vaccinate dairy or beef heifers in the state of Colorado; vaccines are typically administered to improve marketability of heifers and meet import requirements for other states.

The RB51 strain vaccine must be administered by an accredited veterinarian or by a State or Federal animal health official.  It is currently licensed for use in non-pregnant female cattle 4 to 12 months of age. Vaccinated calves (official calfhood vaccinates) must be identified with official identification and a vaccination tattoo placed in the right ear. The tattoo is comprised of an “R” to distinguish animals vaccinated with RB51, followed by a shield, and the digit of the last year of vaccination. All vaccinations must be recorded on form VS 4-26.

The vaccine strain is typically cleared within three days of vaccination and is not present in nasal secretions, saliva, or urine. As a modified live vaccine, in rare cases, vaccinated animals may not clear the vaccine promptly and can shed the vaccinate strain in milk or other secretions. Because strain RB51 can be shed in the milk of vaccinated animals, all milk or milk products consumed from vaccinated animals should be pasteurized for food safety purposes.

Strain RB51 is pathogenic in humans. Since 2017, three cases of RB51 infection in humans have been detected and all were linked to raw milk consumption.  Veterinarians that work with raw milk dairies should inform producers that vaccinated animals present a public health risk.


USDA Facts about Brucellosis:

USDA Factsheet:

USDA RB-51 Info Sheet:

CDC Risks from Unpasteurized Dairy Products:

CDC Raw Milk Questions and Answers: