Last week, the Washington State Department of Agriculture (WSDA) discovered a dairy cow had been sent to slaughter infected with the bacteria that causes tuberculosis in both cattle and humans. That discovery launched an investigation into the presence of additional bovine tuberculosis at both the cow’s most recent dairy and the dairy it had been purchased from a year ago. On Friday, state and federal agriculture officials did not find any evidence of tuberculosis in the cattle at the cow’s former dairy, located in Snohomish County, WSDA communications director Hector Castro told Food Safety News. A team of seven veterinarians from the WSDA and the U.S. Department of Agriculture first tested the farm’s 20 dairy cows, and then the remainder of the farm’s cattle — roughly 300 heads — which are kept separately from the dairy cows. Within the last year, the Snohomish County farm has transitioned from selling milk for pasteurization to selling raw milk. The farm’s owner voluntarily halted all milk sales until agriculture officials could test the herd, as tuberculosis can be passed to humans through raw milk. Now the investigation has turned to the Grant County dairy that most recently owned the cow. On Friday, investigators completed the first phase of testing that herd, which involves injecting each cow with an antigen that produces a bump on the skin. Investigators will wait 72 hours before returning on Monday to check for any cattle that might still have the bump, which would suggest a tuberculosis infection. “We’re hopefully going to know a lot more next week in terms of the possible source of this infection,” Castro said. The Grant County dairy only produces milk that is pasteurized before sale, eliminating the risk of tuberculosis transmission to humans. Regardless, until the WSDA completes its investigation, the department has restricted the dairy from moving cattle off its premises or selling any milk for raw consumption. The infection discovered last week was the first case of bovine tuberculosis in Washington since 1988. According to a WSDA press release, the federal government began a bovine tuberculosis eradication program in 1917 that has virtually eliminated the disease in the U.S. To comply with state law, raw milk cows must annually test negative for Brucellosis, Tuberculosis, Q Fever, and a number of other diseases. New animals must be tested within 30 days prior to entering the herd.