What is brucellosis?
Brucellosis is in infectious disease caused by bacteria in the genus Brucella. Brucella are aerobic, gram-negative coccobacilli. Brucellosis is a zoonotic infection (meaning the disease occurs mainly in animals but is occasionally transferred to humans). Brucellosis has been known by various names such as Mediterranean fever, Malta fever, undulant fever, Crimean fever, Bang's disease, and gastric remittent fever. Brucellosis is found in North-American wild animals (elk, bison) and is occasionally found in domesticated animals (cattle, pigs, sheep, and goats). The major species of the genus Brucella that cause the disease are B. melitensis, B. suis, B. abortus, and B. canis; these are associated with sheep, pigs, cattle, and dogs respectively. The most pathogenic (likely to cause disease) species are B. melitensis and B. suis.
Brucellosis was thought to be first described by Hippocrates and the Romans more than 2,000 years ago. In 1887, Dr. David Bruce isolated the organisms from patients who were living on the island of Malta (hence the name Malta fever). The disease was eventually named after Dr. Bruce (brucellosis). The disease has been found worldwide, and high-risk areas include the Mediterranean countries, South and Central America, Eastern Europe, Africa, Asia, the Middle East, and the Caribbean. Fortunately, there are only about 100-200 people infected per year in the United States. California and Texas have the highest infection rates.
Strains of highly pathogenic Brucella have been considered to be used as a biological weapon because the organisms can be aerosolized and then easily inhaled.
What causes brucellosis?
The cause of brucellosis is bacterial. Brucella bacteria can enter the human body through mucous membranes, breaks in the skin, the respiratory tract, gastrointestinal tract, and even the conjunctiva. Unfortunately, these organisms can survive reasonably well within the body's cells, including different types of cells. These bacteria can be transported within the human cells via the lymphatic system or in the bloodstream to other organs. Any organ system can be involved, and both localized and systemic (body-wide) infections may occur. The bacteria can also replicate inside host cells and then be released when the cell dies. These bacteria go on to spread the infection to other human cells.
The most common way individuals become infected with brucellosis is by eating or drinking unpasteurized or raw dairy products. If animals like sheep, goats, buffalo, cows, or camels are infected with Brucella, the milk they produce is contaminated with the bacteria. Another way that brucellosis spreads to humans is by inhalation of the bacteria. Although this risk is generally associated with people who work in laboratories studying Brucella organisms, it is possible that people working in meat-processing areas could be exposed to the bacteria by inhalation of droplets from contaminated meat (cattle, sheep). The bacteria can also infect humans through breaks in the skin or through the mucous membranes. Commonly infected animals that are hunted that may contain Brucella are caribou, moose, wild hogs (feral hogs), elk, and bison. Person-to-person transmission of brucellosis is rare but may occur during sex, blood transfusions, transplacental transfer, or even in contact with menstrual blood.
According to the U.S. Centers for Disease Control and Prevention (CDC), brucellosis is only weakly contagious because person-to-person spread of brucellosis is rare. Unfortunately, people can easily get the disease from eating or drinking unpasteurized or raw dairy products and can even become infected by inhaling aerosolized bacteria or become infected through breaks in the skin or mucous membranes.
Brucellosis is contagious as long as living bacteria are present in domestic and wild animals and/or their secretions, including milk products. In addition, the bacteria have been documented to survive in the environment for up to two years under favorable conditions (darkness, cold temperatures, and relatively high CO2 concentrations) and still cause disease.
What are the symptoms of brucellosis?
Brucellosis can cause a wide range of symptoms. Some symptoms appear early while others may develop over a long time period. Initial or early symptoms may include
- pain in the muscles, joints, and/or abdomen,
- pain in the back,
- loss of appetite,
- weight loss,
- headache, and/or
- swollen lymph nodes.
Over time, the fevers may become recurrent with night sweats, joint pain may worsen, and organ swelling may occur in the heart, testicles, liver, and/or spleen, resulting in decreased functioning of these organs. Some people will develop a skin rash and/or micro-abscesses (subcutaneous granulomas) in the skin. In addition, patients may have chronic fatigue, depression, and neurologic symptoms. It takes about two to four weeks (latent period) after initial exposure for most people to start showing symptoms.
The incubation period (time between infection and the development of the disease) for brucellosis is considered to be highly variable, with a range of five days to five months, with a few patients reporting incubation periods as long as a year; the average incubation period is about two to four weeks.
Diagnosis of brucellosis
Although the patient's primary-care provider (including internists and family practitioners) can treat brucellosis, it is not unusual to consult infectious-disease specialists, neurologists, rheumatologists, and specialists in travel medicine about treatment and/or prevention of this disease. In severe infections, other specialists may be consulted (for example, urologists, obstetrician-gynecologists [for infected pregnant patients]) depending on the organ system most altered.
Brucellosis is diagnosed preliminarily by the patient's history of exposure to likely sources of Brucella bacteria and the patient's clinical symptoms. Confirmation of the diagnosis is made by culturing Brucella bacteria from the patient. In addition, there are serological tests for the organisms done on the patient's blood specimens. These tests look for IgM or IgG antibodies directed against the bacteria. However, the CDC recommends that these tests be confirmed by a Brucella-specific agglutination test, a specific test that is usually run by a specialty laboratory. These tests help differentiate brucellosis from leptospirosis, malaria, tularemia, and other diseases that may produce similar symptoms.
What are the treatments for brucellosis?
According to the CDC, doxycycline (Vibramycin, Oracea, Adoxa, Atridox) and rifampin (Rifadin) are the recommended antibiotics, taken in combination, for a minimum of six to eight weeks to treat infected patients. This long treatment time is due to the organism's ability to survive inside human cells; consequently, the CDC recommends that a firm diagnosis be established before long-term antibiotic treatment is begun. Individuals who are immunosuppressed and pregnant patients, in most cases, should be treated in consultation with an infectious-disease specialist.
There are many home remedies listed on the Internet for brucellosis. A few examples include colloidal silver, garlic, a spice termed Origanum syriacum, mixtures of essential oils, and many others. Scientific evidence is lacking about the effectiveness of these remedies. Patients should discuss with their doctors any remedies before using them.
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What is the prognosis for brucellosis?
In general, the prognosis for patients infected with Brucella is very good. If individuals are treated appropriately within the first few months of symptom onset, they are curable with antibiotics and usually don't develop chronic disease. The symptoms usually improve and are completely gone within about two to six months. However, the prognosis is poor in people who develop organ changes or complications such as heart damage, neurological, or genitourinary problems caused by chronic Brucella infection. The mortality (death) rate is low for brucellosis (about 0.4%-2%).
Is it possible to prevent brucellosis?
It is possible to prevent or reduce the chances of developing brucellosis. Simple methods such as avoiding known infected animals, never drinking unpasteurized milk, and, if associating with potentially infected animals, wearing gloves and/or a mask reduces the chances of infection.
Because brucellosis is mainly a disease involving livestock, vaccines have been developed that are effective for cattle, sheep, and goats. Unfortunately, there is no vaccine available for use in humans.
United States. Centers for Disease Control and Prevention. "Brucellosis." Nov. 2, 2021. <https://www.cdc.gov/brucellosis/index.html>.
United States. Centers for Disease Control and Prevention. "Travelers' Health: Brucellosis." June 24, 2019. <http://wwwnc.cdc.gov/travel/yellowbook/2016/infectious-diseases-related-to-travel/brucellosis>.
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