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Serology for Brucellosis

What is Serology for Brucellosis (the Brucella Antibody Test)?

Serology is the science dealing with blood serum and especially their immunological reactions and properties. Blood sent for “serology” means the serum will be tested for antibodies, antigens, and other immune system properties.

Antibodies are proteins made by the immune system. They help to destroy harmful bacteria, viruses, parasites, and fungi that invade our bodies. If antigens get into the body, they can cause a number of illnesses and diseases. One of these is brucellosis.

Antibodies are structured to target specific antigens. This is why serology not only helps determine whether a person has a current infection, but also what type of agent is responsible. The serologic test for brucellosis is often simply known as the “brucella antibody test.”

If antibodies for the Brucella bacteria are found, the person may currently have or have had brucellosis.

Overview of Brucellosis and Its Cause

The Bacteria

Brucellosis caused by a class of bacteria called Brucella. There are several strains of these bacteria that can lead to problems in humans. These are:

  • Brucella melitensis
  • Brucella abortus
  • Brucella suis
  • Brucella canis

The bacteria tend to be passed from animals to humans. Animals that can carry and transmit the Brucella bacteria include:

  • goats
  • sheep
  • cattle
  • camels
  • pigs
  • dogs (rarely)

Brucella is not transmitted to humans via casual contact such as touching. Eating the meat of infected animals is also extremely low-risk, as long as it is fully cooked.

Most cases of brucellosis are due to direct contact with the bodily fluids of infected animals. These include urine and blood. It can also be passed on by direct contact with the tissues, placentas, and aborted fetuses of infected animals.

Eating unpasteurized dairy products made from the milk of infected animals can also put you at risk.


Brucellosis can be either an acute (short-term) or chronic (long-term) infectious disease. Symptoms include:

  • muscle and joint pain
  • chills and/or profuse sweating
  • fever
  • fatigue and weakness
  • back pain
  • swollen glands

Purpose of a Serologic Test for Brucellosis

The bacteria that cause brucellosis are not passed easily from animals to humans. Also, many people do not come into contact with animals that normally carry Brucella. As a result, testing will likely be ordered when symptoms are present and the person was in a situation where infection could have occurred.

People at higher risk than the general population include farm workers and veterinarians. Slaughterhouse workers and meat inspectors also have a higher-than-average risk.

The Procedure for a Serologic Test for Brucellosis

If your doctor suspects you have brucellosis, you will need to provide a blood sample to be analyzed. This is not a complicated procedure, and should not cause any severe pain or discomfort. Your doctor (or another qualified healthcare professional) will insert a needle into a vein and collect a small amount of blood in a vial. It will then be analyzed in the lab. The test usually used to analyze your blood is called a Brucella agglutination test.

Understanding the Results of Serology for Brucellosis

Antibodies are produced in response to the brucella infection. Therefore, a person who was not exposed to Brucella should not have any antibodies for the bacteria in their blood. An absence of Brucella antibodies is classed as a normal result. If you do have these antibodies, it means you are or were likely infected with the bacteria.

False Positives and Other Concerns About Reliability

There are a few reasons why diagnosing an active Brucella infection can be challenging.

  • Some other types of bacteria can cause a false positive (i.e., testing positive for the presence of Brucella when it is, in fact, not present).
  • Some immunizations can cause a test to be positive when there is no infection.
  • A positive test does not always mean the person has a current infection. It could mean they were exposed to Brucella at some point in the past. It might also mean they have an immunity against this type of bacteria.
  • If a person was recently exposed to the Brucella antigen, there may be too few antibodies to be detected by the test.

More tests or follow-up testing may be needed to confirm or rule out brucellosis.

How Is Brucellosis Treated?

As with the vast majority of bacterial infections, brucellosis is treated with antibiotics. The duration of the treatment will depend on factors such as whether there are any complications. It is possible for people who have been treated to relapse. Symptoms can also persist for a long time, sometimes even years.

As a final note, it is important to keep in mind that brucellosis is very rare. In fact, there are only 100 to 200 cases each year in the entire United States (New York State Department of Health). If your doctor does suspect brucellosis, however, following up with testing and treatment is vital to raise the odds of a full recovery.

Content licensed from:

Written by: Krista O'Connell
Published on: Aug 15, 2012
Medically reviewed on: Jan 04, 2016: Mark LaFlamme, MD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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