Bovine Brucellosis and RB51 

What is Bovine Brucellosis? 

Bovine brucellosis is a serious and contagious livestock disease that has significant 

animal health and public health consequences. The bacteria that causes this disease, 

Brucella abortus, is known to cause abortions in cattle worldwide. Brucellosis usually 

spreads through contact with infected birthing tissues and fluids (e.g., placenta, aborted 

fetuses, fetal fluids, vaginal discharges). The bacteria can also be found in the milk, 

blood, urine and semen of infected animals. In humans, brucellosis causes symptoms 

including fatigue, recurrent fevers and arthritis, which can be serious and debilitating. If 

left untreated, its effects may become chronic. Farmers, ranchers, veterinarians and others 

that may come in close contact with infected animals during the birthing process or 

individuals who consume unpasteurized milk from infected animals are more vulnerable 

to getting this disease. 

Brucellosis Eradication 

USDA and its partners established a cooperative State/Federal Brucellosis Eradication 

Program more than 50 years ago to eliminate the disease from the United States. 

When the program began, brucellosis was widespread throughout U.S. livestock, but the 

eradication program offered dramatic results. In 1956, there were 124,000 affected herds 

in the United States. By 1992, this number had dropped to 700 herds. Today, the number 

of affected herds is in the single digits, with all 50 states, Puerto Rico and the U.S. Virgin 

Islands considered Brucellosis Class Free since July 2009. 

Because of their Class-Free status, States are not required to vaccinate against brucellosis. 

Each State decides whether vaccination is needed in their state although APHIS does 

encourage it in States with affected wildlife populations. 

Before the eradication program began, thousands of people each year became sick with 

brucellosis primarily through occupational exposure or those working directly with 

animals. Together with increased pasteurization of dairy products, the brucellosis 

eradication program greatly reduced the number of human cases. Renewed interest in 

consuming unpasteurized milk and milk products has led to an increase of human 

infections. 

 

Animal and Plant 

Health Inspection 

Service 
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Vaccination 

Vaccination was an important tool in the control, management and elimination of 

brucellosis, and is still used today as needed to manage the disease. In February 1996, 

APHIS licensed the Brucella abortus strain RB51 vaccine for use in cattle as part of the 

eradication effort, a safer replacement to the Brucella abortus strain 19 vaccine 

previously used. 

USDA does not require vaccination and it is voluntary. Strain RB51 vaccine must be 

administered by an accredited veterinarian or by a State or Federal animal health official. 

When animal health officials decide to vaccinate female calves, the calves must be 

vaccinated according to the label directions. This vaccine should not be given to pregnant 

animals. 

All vaccinated animals must be identified with the standard official USDA vaccination 

eartag and a vaccination tattoo identifying them as vaccinated with the RB51 vaccine and 

indicating the year that the animal was vaccinated. Animals are rarely vaccinated more 

than once. 

RB51 vaccine is considered safe and helps protect about 70-80 % of vaccinated cattle 

from becoming infected with brucellosis. The vaccine produces an immune response that 

increases the animal’s resistance to the disease. Vaccinated cattle can shed the vaccinestrain of the bacteria in their milk for a short period of time after vaccination, and in rare 

cases prolonged shedding has been detected. 

During the time when the vaccine is being shed, rare cases of human infection with RB51 

have been associated with drinking unpasteurized (raw) milk in the United States. 

Pasteurization kills the bacteria and keeps people from getting sick. To protect yourself 

and your family, consume only pasteurized milk and milk products. This is especially 

important for people with weakened immune systems or who are pregnant. RB51 can 

cause severe illness or miscarriages in humans. Doctors can treat patients infected by 

brucellosis with antibiotics, but it is resistant to rifampin and penicillin. 

There is no way to test for animals actively shedding the vaccine at either the herd or 

individual level. RB51 can be identified through Brucella milk culturing, a process that 

can take several days. Raw milk products do not have a long shelf life that allows for this 

kind of testing prior to sale or consumption. Pasteurization-- which kills RB51, other 

types of Brucella, and a variety of other disease-causing bacteria -- remains the best way 

to avoid illness. 

For More Information 

USDA, APHIS, VS, Cattle Health Staff, 4700 River Road, Riverdale, MD 20737 

(301) 851-3502 or VS.SPRS.CattleHealthCenter@aphis.usda.gov 

Information Sheet: Brucella abortus Strain RB51 Vaccine