Brucellosis is not very common in the United States, where100 to 200 cases occur each year. But brucellosis can be very common in countries where animal disease control programs have not reduced the amount of disease among animals.

Brucellosis is an infectious disease caused by the bacteria of the genus Brucella. These bacteria are primarily passed among animals, and they cause disease in many different vertebrates. 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 these bacteria.

Fortunately, the combination of pasteurization of milk and progress in the eradication of the disease in livestock has resulted in substantially fewer human cases than in the past. Ninety-eight cases of human brucellosis were reported in 1997, a fraction of the 6,400 cases reported in 1947. Currently, about 80-100 cases of human brucellosis are reported annually. Many of those are people who have traveled internationally and ingested unpasteurized dairy products.

Brucellosis is diagnosed in a laboratory by finding Brucella organisms in samples of blood or bone marrow. Also, blood tests can be done to detect antibodies against the bacteria. If this method is used, two blood samples should be collected 2 weeks apart.

Yes, but treatment can be difficult. Doctors can prescribe effective antibiotics. Usually, doxycycline and rifampin are used in combination for 6 weeks to prevent reoccuring infection. Depending on the timing of treatment and severity of illness, recovery may take a few weeks to several months. Mortality is low (<2%), and is usually associated with endocarditis. These are live vaccines, and strain 19 is known to cause disease in humans.

Considering the damage done by the infection in animals—decreased milk production, weight loss in animals, loss of young, infertility, and lameness—it is a very serious disease of livestock. The rapidity with which it spreads and the fact that it is transmissible to humans makes it all the more serious.

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Direct person-to-person spread of brucellosis is extremely rare. Mothers who are breast-feeding may transmit the infection to their infants. Sexual transmission has also been reported. For both sexual and breast-feeding transmission, if the infant or person at risk is treated for brucellosis, their risk of becoming infected will probably be eliminated within 3 days. Although uncommon, transmission may also occur via contaminated tissue transplantation.

B. canis is the species of Brucella species that can infect dogs. This species has occasionally been transmitted to humans, but the vast majority of dog infections do not result in human illness. Although veterinarians exposed to blood of infected animals are at risk, pet owners are not considered to be at risk for infection. This is partly because it is unlikely that they will come in contact with blood, semen, or placenta of the dog.

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Humans are generally infected in one of three ways: eating or drinking something that is contaminated with Brucella, breathing in the organism (inhalation), or having the bacteria enter the body through skin wounds. The most common way to be infected is by eating or drinking contaminated milk products. When sheep, goats, cows, or camels are infected, their milk is contaminated with the bacteria.

Although RB51 was developed as a less pathogenic strain, it does retain pathogenicity for humans so exposures can pose a human health risk. Post-exposure prophylaxis should therefore be considered for persons with RB51 exposure. RB51 was derived by selection in rifampin-enriched media and is resistant to rifampin in vitro. Use of rifampin for post-exposure prophylaxis or treatment, a recommended choice for other pathogenic bacteria, will not be effective for RB51.

There is no effective way to detect infected animals by their appearance. The most obvious signs in pregnant animals are abortion or birth of weak calves. Milk production may be reduced from changes in the normal lactation period caused by abortions and delayed conceptions. Not all infected cows abort, but those that do usually abort between the fifth and seventh month of pregnancy.

Brucellosis is commonly transmitted to susceptible animals by direct contact with infected animals or with an environment that has been contaminated with discharges from infected animals. Aborted fetuses, placental membranes or fluids, and other vaginal discharges present after an infected animal has aborted or calved are all highly contaminated with infectious Brucella organisms.

Before 1934, control of brucellosis was limited mainly to individual herds. Today, there is a Cooperative State–Federal Brucellosis Eradication Program to eliminate the disease from the country. Like other animal disease eradication efforts, success of the program depends on the support and participation of livestock producers. The program's Uniform Methods and Rules set forth the minimum standards for States to achieve eradication.

There are a number of supplemental tests based on various characteristics of antibodies found in the blood and milk of infected animals. These tests are especially useful in identifying infected animals in problem herds and herds in which chronic brucellosis infection exists and from which infection is difficult to eliminate. Another diagnostic method involves culturing Brucella organisms from infected tissues, milk, or other body fluids, from aborted calves or fetal fluids and membranes.

vaccination. Replacement animals should be tested when purchased and retested after a 30- to 60-day isolation period during which they are kept separate from the remainder of the herd. These practices will allow detection of animals that were in the incubation period of the disease when acquired.

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Note: PEP recommendations for B. abortus RB51 (attenuated vaccine strain) differ from those for fully pathogenic Brucella spp. As RB51 was derived by selection in rifampin-enriched media and is resistant to rifampin in vitro, the use of rifampin for PEP or treatment will not be effective for RB51. Post-exposure prophylaxis for those at high risk of exposure should include doxycycline 100 mg orally twice daily for at least 21 days.

Brucellosis is transmitted to humans through contact with tissues or bodily fluids of animals infected with Brucella bacteria. Therefore, persons at highest risk for brucellosis are those who work with agricultural animals (e.g., cattle, pigs, sheep, and goats) that are infected, such as veterinarians and ranchers. Brucellosis also is spread by the ingestion of unpasteurized dairy products, causing a risk to persons who consume raw milk or cheeses made with raw milk.

USGS scientists are collaborating with university, State, and Federal groups on a number of studies. Ecological studies focus on forage availability, habitat use, and bison population dynamics. Brucellosis research includes examining the risk of transmission of the disease from wildlife to cattle, identification of exposed animals in the field, and the safety of vaccines to wildlife species.