Brucellosis

Disease/Disorder

Also known as: Malta fever, undulant fever

Anatomy or system affected: Brain, heart, joints, liver, musculoskeletal system, nervous system, reproductive system, spine, spleen

Definition: A bacterial infection transmitted to humans from infected livestock and wildlife that is usually acquired from unpasteurized dairy products.

Key terms:

antibiotics: drugs that inhibit or kill bacteria and are used to treat bacterial infections

chronic: a disease of long duration, typically several weeks, months, or years

pasteurization: a method first described by the French scientist Louis Pasteur for killing bacteria in food and beverages

relapse: the recurrence of signs and symptoms after they have subsided or ceased

vaccine: a substance, usually injected, that stimulates the immune system to protect the body against a specific infectious disease

zoonotic: an infection of animals that can be transmitted to humans

Information on Brucellosis

Causes: Bacterial infection; consumption of unpasteurized dairy products from infected animals; contact with infected livestock or wildlife

Symptoms: Recurrent fever, headache, muscle, back, and joint pain, arthritis, fatigue

Duration: Several weeks or chronic

Treatments: Antibiotics

Causes and Symptoms

Brucellosis is a zoonotic disease, an infection that humans acquire from infected animals. Brucellosis is caused by Brucella bacteria transmitted to humans from cattle, sheep, goats, elk, bison, caribou (reindeer), and wild pigs. The bacteria have been found in porpoises, harbor seals, some types of whales, and dogs. Most human cases are acquired by consuming unpasteurized milk, cheese, and other dairy products. People working in microbiology labs, slaughterhouses, and meat-packing plants get brucellosis by inhaling airborne droplets contaminated with the bacteria. The bacteria also enter the body through contact with wounds and mucous membranes (eyes, nose, and mouth). Veterinarians and hunters are exposed to brucellosis in this way. Person-to-person transmission is rare, as is transmission by breast milk, transplant, and transfusion (blood donation). Transmission by sexual contact has not been documented.

After ingestion, inhalation, or contact, the bacteria move into the blood. Brucella do not remain in the blood for long; they invade a variety of human cells, which protects the bacteria from the immune system. Once in the blood, the bacteria enter white blood cells called neutrophils. The neutrophils normally seek out, ingest, and destroy bacteria. However, Brucella enter neutrophils and remain alive because the bacteria produce substances that inhibit the immune functions of neutrophils. The infected neutrophils enter the lymphatic system, a network of vessels that filters tissue fluids (called lymph when inside the vessels) and returns them to the circulatory system. In this way, Brucella spread throughout the body and invade cells of nearly every organ system. The bacteria infect the liver, spleen, kidneys, joints, breasts, and central nervous system. Reproduction of the bacteria in these organs causes tissue damage, and triggers the characteristic signs and symptoms of brucellosis.

Symptoms arise days to months following exposure to Brucella. The first symptoms resemble a severe flu-like illness, and include fever, headache, fatigue, malaise (a feeling of ill health), anorexia (loss of appetite), and pain in muscles, back, and joints. These symptoms are caused by the immune system's response to the infection. However, the immune response to these bacteria is ineffective because most of the bacteria reside inside the body's cells. Fever and symptoms often decline during infection. However, bacterial reproduction kills cells, which release the bacteria, inducing another wave of fever and symptoms. Brucellosis has been called undulant fever for these returning fevers. If untreated, the disease progresses and becomes chronic. A chronic infection lasts many weeks or months, perhaps years.

Chronic infection is characterized by recurrent fevers and relapses. A relapse is the return of signs and symptoms. Chronic brucellosis is associated with arthritis, inflammation of joints, and spondylitis, inflammation of the joints between bones of the spinal column. Arthritis and spondylitis are painful and disabling. Endocarditis, inflammation of the inner lining of the heart, is a particularly dangerous aspect of chronic brucellosis. In addition, brucellosis affects the nervous system, causing encephalitis, inflammation of the brain, and meningitis, inflammation of membranes surrounding the brain and spinal cord. Encephalitis and meningitis are serious complications of brucellosis. The bacteria cause swelling in other organs, including the liver, spleen, testes, epididymis (tubes that carry sperm from the testes), and scrotum. Some patients experience chronic fatigue and depression. Brucellosis is rarely fatal, resulting in death in probably less than 2 percent of cases in the United States. Most fatalities are related to endocarditis or severe neurologic disease (meningitis or encephalitis).

Infected animals exhibit no external signs of disease. Infected livestock such as cattle, goats, sheep, and domestic bison may abort spontaneously or produce weak offspring. Reduced milk production is associated with infection, but can be caused by other diseases and disorders. Fortunately, brucellosis has been nearly eradicated from domestic livestock in the United States.

Treatment and Therapy

Most cases of brucellosis turn out well. However, early diagnosis and treatment are important for making full recovery and preventing serious, disabling complications associated with chronic, relapsing disease. Diagnosis is based on the symptoms, laboratory tests, and a history of recent activities, such as travel abroad, that may have resulted in exposure to brucellosis. Brucellosis is well controlled in US livestock and outbreaks of brucellosis among humans are unexpected. In 2014 there were only ninety-two human cases in the United States. Most brucellosis cases in the United States are acquired through consumption of unpasteurized dairy products from countries such as Mexico, whether imported or consumed while abroad. An outbreak in the United States is so unlikely that any brucellosis outbreak is investigated as a possible bioterrorist event. Thus, given a history of exposure, and symptoms consistent with brucellosis, laboratory tests confirm the presence of an ongoing infection.

Blood tests permit detection of antibodies to the bacteria. Antibodies are substances produced by white blood cells in response to infectious agents such as viruses and bacteria. The body produces antibodies that are specific for each type of infectious agent. Thus, the presence of antibodies for Brucella is a reliable sign of brucellosis. If the bacteria are present in the blood, the blood may be cultured in a microbiology lab. A blood culture applies a sample of blood to nutrients that promote the growth of bacteria. Once the bacteria grow they can be identified as Brucella. Because Brucella travel widely through the body, other body fluids and bone marrow can also be cultured. To determine if meningitis or encephalitis is related to brucellosis, cerebrospinal fluid is sampled and studied in the laboratory. Cerebrospinal fluid surrounds and protects the brain and spinal cord. The fluid is obtained by lumbar puncture, a procedure in which a needle is inserted between the vertebrae of the lower back to draw fluid into a syringe. Healthy cerebrospinal fluid contains no bacteria. An echocardiogram, an image of the heart's internal structure, detects signs of endocarditis.

Antibiotics are drugs that kill bacteria and these drugs are an effective treatment for brucellosis. Six weeks to several months of antibiotic therapy are required, depending on the severity of the infection. In many cases, people take a combination of two different antibiotics. Arthritis and spondylitis are treated with analgesics, medications that reduce pain. Meningitis and encephalitis are treated with drugs that suppress inflammation.

Brucellosis can be prevented by reducing the risk of exposure. Unpasteurized dairy products, including milk and cheese, should not be consumed, especially when traveling abroad. So-called “village cheeses,” usually made from goat and sheep milk, are known to carry brucellosis. Meat should always be fully cooked before serving. Workers in meat-packing and slaughterhouse facilities should follow their employer's and Occupational Safety Health Administration (OSHA) standards regarding safe handling of meat. These procedures may include the use of personal protective gear such as gloves and eye protection (to prevent splashes with contaminated fluids). Microbiology laboratory workers who study material contaminated with brucellosis bacteria should also follow similar precautions established by the laboratory employer and OSHA. Hunters should wear gloves to protect their hands when dressing game, especially elk, moose, and wild pigs. Game meat should be stored properly and cooked thoroughly before serving.

Perspective and Prospects

A Scottish physician, Sir David Bruce, first described the Brucella bacteria in 1887. Bruce made important discoveries about the disease among goats on the Mediterranean island of Malta, which is the source of this disease's former name, Malta fever.

Brucellosis once caused enormous losses in the US livestock industry. In 1952, reduced milk production and livestock losses cost the industry $400 million. Infected cattle and other livestock drove a relatively high rate of human brucellosis in the United States. As of 2013 brucellosis is uncommon in the United States, affecting about 100 people each year. The infection has become uncommon because of the Cooperative State Federal Brucellosis Eradication Program, begun in 1934. This program has nearly eradicated brucellosis among domestic livestock. In 1934 11.5 percent of cattle herds in the United States tested positive for brucellosis. As of 2000, only six herds tested positive, and they had a low infection rate of less than 0.25 percent.

Continued prevention of human infections depends on effective control of animal brucellosis. The disease is incurable in animals. Thus, control has relied on vaccination and herd screening, followed by removal and killing of infected animals. The vaccine is effective at preventing infection in cattle. However, it is less effective at preventing disease in domestic bison. Scientists are seeking an improved vaccine because bison can transmit the infection to cattle. Wildlife such as elk and bison in the Yellowstone area carry and can transmit brucellosis to domestic livestock. Control of brucellosis in wild elk and bison has proven to be difficult because these animals migrate and gather in large numbers near food during winter. Congregating elk and bison are more likely to spread the infection within a herd. More important, wild elk and bison can enter ranchland and expose domestic cattle and bison to infection. To prevent congregation of wild herds of elk and bison, the United States Animal Health Association recommends that wildlife managers stop the practice of feeding wild herds during the winter. However, most human cases of brucellosis in the United States do not occur in the states of Yellowstone (Montana, Wyoming, and Idaho): over half occur in California and Texas.

Worldwide, brucellosis is not well controlled in domestic and wild animals, which results in enormous economic losses and about 500,000 human infections each year. Brucellosis is most common in countries with underdeveloped public health or domestic animal health programs, and where pasteurization and animal vaccination is not systematically practiced. Most cases of brucellosis occur in countries around the Mediterranean Sea, Eastern Europe, Africa, Middle East, India, Latin America, and the Caribbean.Considerable effort has been focused on developing more effective vaccines to control the infection in domestic livestock.

Vaccines have been effective in the United States, even though several species of Brucella are known. Only a few species cause disease in humans. These include Brucella melitensis, B. suis, B. abortus, and B. canis. Of these, B. melitensis causes the most serious disease in humans. It is transmitted by sheep and goats and has been eradicated in the United States, although it continues to cause disease worldwide. B. suis infects pigs and occasionally infects hunters. B. abortus has been nearly eradicated in the United States, although it persists in wild elk and wild bison. B. canis infects dogs and is an uncommon cause of infection in veterinarians and dog breeders. B. ceti infects porpoises and whales, and B. pinnipediae infects harbor seals. These rarely cause disease in humans.

For Further Information:

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