are the cause of brucellosis, which is a zoonosis transmitted by ingesting contaminated food (such as unpasteurized milk products), direct contact with an infected animal, or inhalation of aerosols.

After exposure to Brucella, humans generally have a two- to four-week latency period before exhibiting symptoms, which include acute undulating fever (>90% of all cases), headache, arthralgia (>50%), night sweats, fatigue, and anorexia.

[7] Later complications may include arthritis or epididymo-orchitis, spondylitis, neurobrucellosis, liver abscess formation, and endocarditis, the latter potentially fatal.

People may also be infected by inhalation of contaminated dust or aerosols, and as such, the CDC has labeled Brucella species as highly weaponizable.

Human and animal brucellosis share the persistence of the bacteria in tissues of the mononuclear phagocyte system, including the spleen, liver, lymph nodes, and bone marrow.

Maraston, assistant surgeon in the British Army in Malta, gave the first accurate description of the disease he called "Mediterranean gastric remittent fever".

E. Bang, a Danish veterinarian, described the intracellular pathogen causing abortion in cattle in 1897, and named it Bacillus abortus.

[10] In humans, the disease is acquired from unpasteurised milk and products or undercooked meat (consumers), laboratory inhalation (lab workers), accidental skin penetration or abrasion (farmers, slaughterhouse workers, and veterinarians), and (rarely) conjunctival contact, blood transfusion, transplacental, and person-to-person.

Though variable, symptoms can also include these clinical signs: headache, weakness, arthralgia, depression, weight loss, fatigue, and liver dysfunction.

[14] Congenitally infected infants can exhibit low birth weight, failure to thrive, jaundice, hepatomegaly, splenomegaly, respiratory difficulty, and general signs of sepsis (fever, vomiting).

[13] Brucella species are small, Gram-negative, facultative coccobacilli, most lacking a capsule, endospores, or native plasmids.

[18] The gastrointestinal tract is affected in about 70% of cases, including anorexia, abdominal pain, vomiting, diarrhea, constipation, hepatomegaly, and splenomegaly.

The skeletal system is affected in 20–60% of cases, including arthritis (hip, knee, and ankle), spondylitis, osteomyelitis, and sacroiliitis (most common).

Neurological symptoms include meningitis, encephalitis, radiculopathy, peripheral neuropathy, intracerebral abscesses, and acute or chronic neck rigidity (<50%), and the cerebrospinal fluid can show lymphocytic pleocytosis, low sugar, increased protein, positive bacterial culture (<50%), and agglutination (positive in >95%).

Prolonged incubation (up to six weeks) may be required, as they are slow-growing, but on modern automated machines, the cultures often show positive results within 7 days.

Polymerase chain reaction (PCR) shows promise for rapid diagnosis of Brucella species in human blood specimens.

Demonstration of a four-fold or greater increase or decrease in agglutinating antibodies over four to 12 weeks provides even stronger evidence for the diagnosis.

Recent investigations on the use of FBAT have however illustrated its high inaccuracy in proper diagnosis, highlighting the difficulty of brucellosis control in low-income settings.

Prevention[21] now includes: As regions endemic with Brucella primarily are low-income environments, approaching proper control of brucellosis remains a challenge.

[22] No clinical trials exist to be relied on as a guide for optimal treatment, but an at least six-week course of rifampicin or gentamicin and doxycycline twice daily is the combination most often used, and appears to be efficacious;[20][24][25][26] the advantage of this regimen is that it is oral medication with no injections; however, a high rate of side effects (nausea, vomiting, loss of appetite) has also been reported.

Local dispensaries dealing first-hand with brucellosis are occasionally also not aware on how to treat properly, highlighting the need for reevaluation on implementation of international treatment regimes.

[28] Drugs with effects against Brucella include tetracyclines, aminoglycosides (streptomycin, [since 1947], gentamicin, netilmicin), rifampicin, quinolones (ciprofloxacin), and third-generation cephalosporins.

Although the disease progression of brucellosis in modern times may make it seem unlikely, it was at least one agent in what may have been a multicomponent plague, along with Salmonella enterica serovar Typhi or another pathogen, or possibly the ancestral versions of Brucella were more lethal.

[citation needed] The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN).