| VIVO Infectious Diseases | Bacterial Diseases of Man and Animals |
Brucellosis in Humans
Human rucellosis is probably the most common zoonotically-acquired disease in the world. Global annual incidence of human infection has recently been estimated to be at least 2 million cases.
Humans are incidental or dead end hosts, and human-to-human transmission of Brucella is quite rare. Essentially all cases of brucellosis in humans are the result of contact with infected animals or by consumption of their products such as milk and milk products like cheese. Certainly, a number of countries have essentially eradicated infection in domestic livestock and have very low, mostly imported, cases of Brucellosis. However, in large regions of the world, brucellosis in livestock is common, so human infections are also common.
Clinical Disease
Human clinical brucellosis results most frequently from infection with B. melitensis, abortus, suis and canis. There are some differences in the virulence of these different species of Brucella but the clinical course is similar among them; B. melitensis is considered the most widespread and virulent species for humans. The key diagnostic challenge is that the symptoms of brucellosis are non-specific and very similar to several other infectious and even non-infectious diseases. Determining whether a given patient indeed suffers from brucellosis can start with patient history (e.g., assisting in birthing of a goat or drinking unpasteurized milk) but absolutely requires reliable diagnostics.
Brucellosis in humans is seen in several clinical forms:
- After initial infection, patients experience an acute phase of disease, characterized by intermittant fever, chills, sweating, fatique, and joint pain. to This acute phase is seen in roughly half of infected patients.
- The propensity for Brucella to be sequestered in phagocytic cells results in the common occurrance of persistent infections in which the patient continues to show disease, often intermittantly, for weeks or months. Clinical disease is highly variable. Common manifestations of such long term infection include disease of almost any system: bone and joints, nervous (neurobrucellosis), gastrointestinal, cardiovascular, liver, respiratory, and genitourinary. Abortion can occur after infection of pregnant women.
- Relapsing or recrudescent infection are not rare and are seen in patients that appear to be cured of their infection, but in which the infection is not totally elimnated.
Treatment
Brucellosis is not easy to treat. The most commonly recommended antibiotic therapy is a 6-week course of doxycycline, by itself or combined with rifampicin (in some countries rifampicin is restricted to patients with tuberculosis). Treatment with fluoroquinolones is an alternative therpay. Of increasing concern is isolation of antibiotic-resistant strains of Brucella and additional alternative therapies for brucellosis require investigation for efficacy.
Prevention and Control
With rare exceptions, humans acquire brucellosis by handling infected animals, especially during abortions or even live births, and consumption of dairy products from infected animals. As Demosthenes was reputed to advise when asked what was to be done about the decline of Athens, "don’t do what you are doing now.” More succinctly, if you live in regions where brucellosis is endemic among livestock:
- Wear gloves and, if possible a mask, and wash your hands well after helping animals give birth.
- Do not consume non-boiled or non-pasteurized milk or eat yogurt, cheese and other dairy products that have not been prepared from such heated milk. There are many reasons to not become part of the "raw milk" craze, brucellosis being just one example.
Another source of contracting brucellosis is at slaughter of infected animals or consumption of infected meat. Again, wear protective gear (mask, gloves) when slaughtering or performing a post-mortem examination on animals suspected of being infected, and cook meat from such animals well before consumption. Brucella are actually quite fragile bacteria and cooking meat or organs from infected animals readily kills the bacteria, eliminating the chance of infection by ingestion.
References
Laine CG, Johnson VE, Scott HM, Arenas-Gamboa AM. Global Estimate of Human Brucellosis Incidence. Emerg Infect Dis. 2023; 29:1789-1797.
Qureshi KA, Parvez A, Fahmy NA, Abdel Hady BH, Kumar S, et al. Brucellosis: epidemiology, pathogenesis, diagnosis and treatment-a comprehensive review. Ann Med. 2023; 55:2295398.
 Biology of Brucella and An Overview of Brucellosis |
Brucellosis in Ruminants  |
Updated April 2026. Send comments to Richard Bowen: rabowendvm@gmail.com