Brucellosis Updates and Information

As of October 1, 2021, California no longer requires brucellosis vaccination for beef breed heifers entering or moving within the state. However, beef breed heifers six months of age and older, entering California, are still required to have official identification. The brucellosis vaccination requirement for dairy breed heifers four months of age and older remains and is still in effect.

In addition, Brucella ovis testing requirement for rams entering California going direct to slaughter have been removed.


Brucellosis, also known as contagious abortion or Bang’s disease, is a contagious disease of livestock that also affects humans. In humans, it is known as undulant fever because of the intermittent fever that may accompany infection. It is one of the most serious diseases of livestock due to its ability to spread rapidly and cause significant reproductive losses in animals, and its zoonotic potential.


The disease is caused by a group of bacteria of the genus Brucella. Within this group there are several species of concern in livestock: Brucella suis, which predominately affects swine and reindeer, but can also affect cattle and bison; Brucella melitensis, the most important species in small ruminants, is not present in the United States (U.S.) but is common in Mexico; Brucella ovis affects sheep, and can cause infertility in rams; and Brucella abortus, which is the most common cause of brucellosis and mainly affects cattle.

In cattle, the disease usually localizes in the reproductive organs and the udder. Bacteria are shed in milk or leave the body with the aborted fetus, placenta, or with any discharges from the reproductive tract of an infected animal. Brucellosis is commonly transmitted by direct contact, but can also be transmitted to animals that come into contact with a contaminated environment. Aborted fetuses, placental membranes and/or fluids, and the vaginal discharge that persists for several weeks after an animal has aborted all carry the bacteria. A herd owner buying replacement cattle that have been infected or exposed prior to purchase can transmit the disease between herds.

A national eradication program has left most of the U.S. free of bovine brucellosis; however, a reservoir remains in the Greater Yellowstone Area, particularly in elk and bison, and spillover transmission does occur to domestic cattle herds.


The incubation period in cattle is quite variable, with abortions and stillbirths occurring two weeks to five months after infection. Cattle may be infected as calves but not show any signs of infection until they abort. Infected animals usually develop a positive reaction to the test within 30-60 days after infection, although some may not develop a positive reaction for several months.


There is no sure way to detect infected cattle by their appearance. The most obvious signs in female cattle are abortion, birth of weak or stillborn calves, and vaginal discharge.

Not all infected cows abort, but those that do usually abort between the fifth and seventh month of pregnancy. Even though their calves may appear healthy, infected cows can continue to harbor and discharge infectious organisms. Other signs include an apparent lowering of fertility with poor conception rates, retained placenta with resulting uterine infection, and decreased lactation.


Three surveillance procedures are used to detect infection in cattle: Market Cattle Identification (MCI) program blood samples at slaughter, Brucellosis Ring Test (BRT) performed on milk samples, and brucellosis blood testing done on animals for movement or change of ownership by private practitioners.

The primary surveillance method is a blood test from a sample of cattle more than two-years-old at slaughter (MCI program). Numbered tags or backtags are placed on the shoulders of all cattle being marketed. Blood samples are collected at packing plants according to the National Brucellosis Surveillance Plan. If a sample reacts to the test, it is traced by the backtag number to the owner of the herd from which the animal originated. The owner is contacted by a State or Federal animal health official to arrange for an investigation that may involve testing the entire herd. The key to the MCI program is proper identification of all animals so they can be traced to their herds of origin. Backtags and other man-made identification devices are collected and sent to a diagnostic laboratory along with matching blood samples to aid in identifying ownership of reactors.

A second surveillance method is a screening milk test called the BRT. If there is suspicion from a live animal or slaughter sample test, a small sample obtained from the creamery or farm milk tank can be tested for evidence of brucellosis. Milk from each cow in the herd is included in the sample taken for testing. All positive herds are investigated.

The final surveillance method is a blood sample taken from a live animal by an accredited veterinarian for the purpose of private sales, change of ownership, interstate movement, herd certification or show, at the expense of the owner. Brucellosis testing must be done at a CDFA or USDA approved laboratory.


Currently, there is a cooperative State-Federal brucellosis eradication program to eliminate the disease from the U.S. livestock population. Like other animal disease eradication efforts, success of the program depends on the participation of livestock producers. The program's Uniform Methods and Rules (2003) set forth the minimum standards for states to achieve eradication. States are designated brucellosis free when no cattle or bison are found to be infected for 12 consecutive months. California has been brucellosis free since 1997.

The disease may be avoided by employing effective sanitation and management practices. Replacement animals should be obtained from brucellosis free herds and free areas. Cattle may be tested when purchased and retested after a 30-60 day isolation period during which they are kept separate from the remainder of the herd. This will allow detection of animals that were in the incubation stage when acquired (although infected heifers may not test positive until after they abort/calve). Heifers may be vaccinated when they are 4-12 months old. At this time, a tattoo is applied in the right ear – official identification must be applied at the time of vaccination if none is existing.

Human Health

Brucellosis in humans, also known as undulant fever, is a serious disease. It can present as non-specific, flu-like illness lasting two to four weeks. Some symptoms persist or reoccur over longer periods of time, and may never go away. Other signs can include fatigue and headaches, followed by high fever, chills, drenching sweats, joint pain, backache, and loss of weight and appetite. Death does not often occur, but the complications from the disease can be severe. Rarely, if ever, does a human contract the disease from another human.

Only 115 cases of human brucellosis were reported in the U.S. in 2010 (CDC Brucellosis Surveillance). California had the highest number of reported cases that year (26). Primary sources of human infection are occupational exposure (farmers, ranches, veterinarians, packing plant workers, etc.) and consumption of imported unpasteurized dairy products; people also may become infected during travel to countries where disease is more prevalent. There is no danger from eating cooked meat or properly pasteurized dairy products because normal cooking temperatures kill the disease-causing bacteria.

Consuming only pasteurized dairy products can reduce the likelihood of infection. People handling or exposed to livestock can prevent infection and spread by disinfecting areas likely to become contaminated and keeping them clean (e.g. animal maternity pens and equipment), wearing appropriate personal protective equipment such as sturdy rubber or plastic gloves when assisting cows calving or animals that abort, and scrubbing well with soap and water after all contact with animals. Practices to prevent cuts and contamination of cuts and eyes with bodily fluids of animals are recommended. Exercise care in handling and disposing of placenta, discharges or aborted fetuses and avoid contact with tissues that could be infected.

Visit the CDC website for more information on brucellosis in people.

For Veterinarians

California has a mandatory calfhood vaccination program – all dairy heifers above 4 months of age must be vaccinated for any change of ownership or can only be sold directly for slaughter or to a registered feedlot for feeding to slaughter. Spayed heifers, steers, and bulls are exempt from this regulation. Veterinarians must be licensed and accredited and have a valid contract with CDFA to vaccinate calves against brucellosis in California. To become a contract veterinarian, please contact your district office.

For Contract Veterinarians Vaccinating Calves against Brucellosis: General Instructions

Additional Resources:
Ordering Brucellosis Vaccine

To order Brucellosis vaccine, a contract veterinarian may access the on-line system login page with a standard internet connection and browser at The order placement will require entry of a valid credit or debit card number. If a veterinarian declines to pay for the Brucellosis vaccine using a credit or debit card, a check may be used. Be advised, purchases made using a check can take more than two weeks and shipments cannot be expedited.