Bovine brucellosis, also known as contagious abortion or Bang’s disease, is a bacterial infection impacting livestock and, in some instances, human health. It has historically challenged agricultural economies and remains a concern globally.
What is Bovine Brucellosis?
Bovine brucellosis is a contagious disease primarily caused by the bacterium Brucella abortus. This bacterium can survive and multiply inside host cells. While B. abortus is the main cause in cattle, other Brucella species like B. melitensis and B. suis can also affect cattle globally.
The disease predominantly affects cattle, but it can also infect other animals, including bison, elk, swine, horses, goats, and sheep. The bacteria localize in the reproductive organs and udders of infected animals. Infected animals may appear healthy yet still harbor and spread the bacteria.
How Does Brucellosis Spread?
Brucellosis spreads through direct contact with infected animals or their contaminated discharges. High concentrations of the bacteria are found in aborted fetuses, placental membranes, and uterine fluids after an infected animal has calved or aborted. Other animals can contract the infection by licking these materials or the genital areas of infected cows.
Indirect transmission occurs when cattle ingest contaminated feed or water. The bacteria can survive in the environment for several months, particularly in cool, moist conditions. Transmission through milk from infected animals is another route of spread.
The Impact of Brucellosis on Animals and People
In animals, brucellosis leads to reproductive problems. Common signs in livestock include abortions, usually between the fifth and seventh months of pregnancy, and the birth of weak or stillborn calves. Cows may also experience reduced milk production, infertility, and retained afterbirths leading to uterine infections. In male animals, inflammation of the testes (orchitis) and epididymides can occur. Economic losses for livestock producers stem from these reproductive failures, decreased milk yield, and the costs of treatment and culling.
Brucellosis is a zoonotic disease, meaning it can spread from animals to humans, where it is often called “undulant fever.” Humans contract the disease through direct contact with infected animals or their tissues, or by consuming unpasteurized dairy products. Symptoms in humans include fever, sweats, malaise, headaches, muscle pain, and joint pain, which may come and go for months or years. More severe complications can involve infections of the central nervous system, spleen, liver, and heart.
Managing and Eradicating Brucellosis
Managing and eradicating brucellosis involves a multi-faceted approach. Diagnosis relies on blood tests and milk ring tests to identify infected animals and herds. The milk ring test detects antibodies in bulk milk samples, indicating potential infection within a dairy herd. While sensitive for screening, it may not detect very small numbers of infected animals in large herds.
Prevention and control strategies include vaccination programs, primarily for calves, using vaccines like RB51. This vaccine is administered to non-pregnant female cattle, usually between four and twelve months of age, to prevent infection and abortion caused by Brucella abortus. Infected animals are culled to prevent further spread within a herd. Strict biosecurity measures, such as isolating new animals and restricting movement of potentially exposed animals, are also implemented.
Progress has been made in eradicating brucellosis in domestic livestock populations in many countries, including the United States. The U.S. national eradication program, which began in 1934, has dramatically reduced the disease’s prevalence in cattle. However, the disease persists in some wildlife populations, such as bison and elk in the Greater Yellowstone Area, posing an ongoing risk of spillover to domestic livestock. Public health measures, like the pasteurization of dairy products, remain important for preventing human infections.