Brucellosis vaccine
The brucellosis vaccine, specifically the Brucella abortus RB51 vaccine, is an attenuated live bacterial vaccine designed for use in cattle, with no equivalent vaccine available for humans. Licensed conditionally by the U.S. Food and Drug Administration in 1996, the vaccine aims to prevent brucellosis—a zoonotic disease caused by different species of the Brucella bacteria, primarily affecting livestock but potentially transmittable to humans through consumption of contaminated animal products or contact with infected tissues. The RB51 strain is favored because it poses a lower risk of severe disease in both cattle and humans compared to other strains, and it allows for accurate differentiation between vaccinated and infected animals during testing.
Immunization efforts began in 1941, and the vaccine received full approval in 2003, being utilized across forty-nine states and additional territories. While the RB51 vaccine reduces the prevalence of the disease among cattle, it is not without risks; exposure to the vaccine can still pose health threats to humans, with potential symptoms ranging from mild to chronic. Individuals who suspect they have been exposed to the RB51 strain should seek medical guidance, especially if they exhibit symptoms such as fever, joint pain, or malaise. The development and use of this vaccine reflect ongoing efforts to manage brucellosis and protect both animal and public health.
Brucellosis vaccine
- ALSO KNOWN AS: Brucella abortus RB51 vaccine
Definition
The brucellosis vaccine (also known as the Brucella abortus RB51 vaccine) is an attenuated live bacterial vaccine for cattle. There is no brucellosis vaccine for humans.
The vaccine, which was licensed conditionally by the US Food and Drug Administration in 1996 for cattle, is a strain of live bacterium. RB51 is preferred because it is less likely to cause severe disease in cattle or humans than are other strains of B. abortus. B. abortus distinguishes serologically vaccinated animals from infected animals and does not cause false-positive reactions on standard brucellosis serologic tests.
Immunization
Cattle immunizations against brucellosis started in 1941. The RB51 immunization denotes a safer immunization both for cattle and for the veterinarians administering it. The vaccine received full approval in 2003. B. abortus RB51 vaccine is used in forty-nine states and in Puerto Rico and the U.S. Virgin Islands.
Pathology
Brucellosis is a zoonotic infectious disease caused by the bacteria of the genus Brucella. Although it is mostly a disease among livestock, it can be transmitted from animals to humans through human ingestion of undercooked meat and unpasteurized dairy products from infected animals and through handling infected animal tissue. Three species of Brucella cause the most concern: B. abortus, principally affecting cattle and bison, but may also infect goats, sheep, and other livestock; B. suis, principally affecting swine and reindeer but also dogs, horses, cattle and bison; and B. melitensis, principally affecting goats but also cattle, dogs, and even fish.
Pathogenicity
Brucellae are aerobic gram-negative coccobacilli that produce urease and that catalyze nitrite to nitrate. They have a lipopolysaccharide coat that is much less pyrogenic than other gram-negative organisms, which accounts for the rare presence of high fever in brucellosis. Brucellae can enter the human body through breaks in the skin and through mucous membranes, conjunctiva, and the respiratory and gastrointestinal tracts. Ingestion most often occurs by way of contact with or by ingestion of unpasteurized milk; meat products often have a low bacterial load. Percutaneous needle-stick exposure, conjunctival exposure through eye splash, and inhalation are the most common transmission routes in the United States.
Various Brucella species affect sheep, goats, cattle, deer, elk, pigs, dogs, and several other animals. Humans become infected by coming in contact with animals or animal products that are contaminated with the Brucella bacterium.
Impact
The RB51 vaccine was developed as a less pathogenic strain, but it retains pathogenicity for humans; exposure can still pose a human health risk. Identified forms of exposure include needle sticks, eye and wound splashes, and exposure to infected material. In a series of exposures reported to the Centers for Disease Control and Prevention, persons developed local symptoms of brucellosis infection; of those who became ill, most exhibited some systemic symptoms.
Routine serologic testing for brucellosis is not effective in monitoring for infection. Broader symptoms resulting from exposure to RB51 should be passively monitored for six months from the last exposure.
Acute symptoms of infection include fever, chills, headache, low back pain, joint pain, malaise, and occasional diarrhea. Subacute symptoms include malaise, muscle pain, headache, neck pain, fever, and sweating. Chronic symptoms include anorexia, weight loss, abdominal pain, joint pain, headache, backache, weakness, irritability, insomnia, depression, and constipation. Persons who believe they have been exposed to RB51 and who develop symptoms should consult a doctor or other healthcare provider.
Bibliography
Ashford, David A., et al. “Adverse Events in Humans Associated with Accidental Exposure to the Livestock Brucellosis Vaccine RB51.” Vaccine 3, no. 22 (September 3, 2004): 3435-3439.
Berkelman, Ruth L. “Human Illness Associated with Use of Veterinary Vaccines.” Clinical Infectious Diseases 37, no. 3 (August 1, 2003): 407-414.
Franco, M. P., et al. “Human Brucellosis.” Lancet Infectious Diseases 7 (2007): 775.
"Veterinary Guidance for Brucellosis." Centers for Disease Control, 18 Apr. 2024, www.cdc.gov/brucellosis/hcp/animals/index.html. Accessed 3 Feb. 2025.