Brucella are rod-shaped bacteria that belong to the genus Brucella. They can cause the infectious disease brucellosis in humans.
What are brucellae?
Brucella belong to the gram-negative bacteria. Gram-negative bacteria can be stained red in the Gram stain. Unlike Gram-positive bacteria, they have an outer cell membrane in addition to a thin peptidoglycan layer of murein. This distinction plays a crucial role in selecting the right antibiotics for treatment. Until 1986, the genus Brucella was divided into different species. However, since the phylogenetic trees all showed some similarity, it was considered to combine the entire bacteria into the species Brucella melitensis. Currently, however, the phylum still divides into 10 subspecies. These include Brucella canis, Brucella abortus, Brucella melitensis, Brucella ovis, Brucella ceti, and Brucella suis. Human pathogens are the bacteria Brucella melitensis, Brucella suis, Brucella abortus, and Brucella canis.
Occurrence, distribution, and characteristics
Brucella are distributed worldwide. They live in the urinary and reproductive tract of sheep, pigs, cows, and also dogs. Endemic areas exist mainly on the Arabian Peninsula, in Asia, Africa, and in Central and South America. In Germany, cattle as well as sheep and goat populations are free of Brucella abortus and Brucella melitensis. In wild animals, however, the bacteria are still quite widespread. Therefore, infections occur again and again in Germany through imported animals or through transmission from wild animals to farm animals. Since there is a reporting obligation for brucellosis, quite precise figures are available. Four to five cases are reported per year. Most of these are imported. Turkey is by far the most common country of infection. Pathogen reservoirs are livestock and wild animals. Domestic wild boar, for example, is a pathogen reservoir for Brucella suis. Illnesses in humans are usually caused by the consumption of contaminated food. The bacteria can also be transmitted to humans through direct contact with infected animals. However, unpasteurized milk is the most significant source of infection for humans. Products made from unpasteurized milk also act as a source of infection. In principle, however, brucella can enter the body not only through the digestive tract, but also through the eye conjunctiva, the respiratory tract or injuries in the skin. In addition, brucellosis is one of the infectious diseases that are frequently acquired in the laboratory. Direct transmission from person to person, on the other hand, has hardly been observed. Only in isolated cases did infection occur after blood transfusions, breastfeeding, or sexual intercourse.
Diseases and symptoms
Brucella belong to the facultative intracellular pathogens. They enter the body and are then taken up by the phagocytes of the defense system when the immune system is functioning. This is how they reach the lymph nodes. From there, they enter the bloodstream via the lymph and can reach all organs via the bloodstream. The pathogens settle particularly frequently in the lympho-reticular organs such as the spleen, bone marrow or liver. The incubation period is between 5 and 60 days. The infectious disease can be distinguished between different courses. Around 90 percent of all infections are subclinical. They do not cause any symptoms in the patient and can only be diagnosed with the aid of antibody detection. Acute or subacute brucellosis, on the other hand, is characterized by fever, night sweats, chills and nausea. Characteristic of the disease is febris undulans, a wave-like fever. The fever persists for one to three weeks, followed by fever-free intervals. However, in the chronic form of brucellosis, the fever may persist for several months. Swelling of the liver or spleen is found in thirty percent of all patients. Infections of the bones and joints are also common. While in children it is mainly the sacroiliac joint that is affected, in adults the bacterial inflammations tend to show up in the area of the intervertebral discs. In two thirds of patients, the lumbar spine is affected. However, the inflammatory changes only become apparent on X-ray after two to eight weeks.The infection is associated with severe local pain and may also be accompanied by neurological abnormalities in the area of infection. In the course of brucellosis, however, other organs may also be affected. Thus, testicular inflammation, meningitis, pneumonia and inflammation of the heart valves may occur. If the lungs are affected, the granulomatous inflammatory foci can easily be confused with those of tuberculosis. Most acute courses of brucellosis heal spontaneously and without permanent damage. However, five percent of patients relapse. Relapses can occur up to two years after the initial illness. In addition to the healing, acute form, however, there is also the protracted chronic form of brucellosis. This is often accompanied by non-specific symptoms and psychological changes. These include depression, insomnia and emotional lability. Brucellosis is usually treated with antibiotics. The gold standard is two to three weeks of therapy with doxycycline and streptomycin. In chronic courses, treatment for six months may be required. However, recurrence can still occur even after therapy with antibiotics. Vaccinations against brucella are not performed in Germany. Although two live vaccines are available, they are used exclusively in veterinary medicine and not in human medicine.
