on 22-Jul-2021 (Thu)

Brucellosis (also known as 'undulant fever,' 'Mediterranean fever,' or 'Malta fever') is a zoonotic infection transmitted to humans from infected animals (cattle, sheep, goats, camels, pigs, or other animals) by ingestion of food products (such as unpasteurized dairy products) or by contact with tissue or fluids. It is the most common zoonosis worldwide and is an important public health problem in many developing countries [1-3].

Endemic areas for brucellosis include countries of the Mediterranean basin, Middle East, Central Asia, China, the Indian subcontinent, sub-Saharan Africa, and parts of Mexico and Central and South America (table 1) [4,5].

Brucellosis has been reported among wildlife in some regions [14]. In Australia and the United States, Brucella suis has been observed in approximately 20 percent of feral swine, and infection among hunters has been described [15-17].

Consumption of unpasteurized dairy products (especially raw milk, soft cheese, butter, and ice cream) is the most common means of transmission [1,18-20]. Hard cheese, yogurt, and sour milk are less hazardous, since fermentation takes place

Consumption of raw or undercooked muscle tissue or organ meat (such as liver and spleen) are less common modes of transmission [1].

Brucellosis is an occupational disease in shepherds, abattoir workers, veterinarians, dairy-industry professionals, and laboratory personnel (including laboratory workers handling Brucella cultures and as well as workers preparing brucellosis vaccines for animal use)

Rare cases of human-to-human transmission due to blood transfusion, tissue transplantation, breastfeeding, sexual contact, congenital transmission, and nosocomial infection have been described [22-25].

Four Brucella species can cause human disease: B. melitensis (isolated from small ruminants such as sheep and goats, as well as camels), B. abortus (isolated from cattle), B. suis (isolated from swine), and B. canis (isolated from dogs).

Worldwide, most human cases are caused by B. melitensis [1]

In general, human infection due to B. melitensis and B. suis is more virulent than human infection due to B. abortus or B. canis [2,28,29]

Two additional Brucella species, B. pinipedialis and B. ceti, have been isolated from marine mammals and detected as sporadic human pathogens [31-33]. Other relatively new species include B. microti (isolated from wildlife animals), B. papionis (isolated from baboons), B. inopinata (isolated from a human breast implant wound), and B. vulpis (isolated from red foxes) [34-37]. B. neotomae (desert wood rats) and B. ovis (sheep) are not pathogenic to humans.

Brucellae are small, nonmotile, facultative intracellular aerobic rods, 0.5 to 0.7 micron in diameter and 0.6 to 1.5 micron in length [38,39]. Gram staining demonstrates single, tiny, gram-negative coccobacilli [40].

Most strains require complex media for growth, which may be improved by adding serum or blood [40]. The optimum growth temperature is 35 to 37°C. Some biovars of B. abortus and B. suis require supplementary carbon dioxide [41]. Colonies are usually raised, convex, and 0.5 to 1.0 mm in diameter with a smooth, shiny surface [40].

The biphasic technique requires 6 weeks of incubation; the yield is variable (40 to 90 percent in acute disease versus 5 to 20 percent in chronic, focal, and complicated disease) [42]. Most blood cultures are positive between 7 and 21 days [43]; subcultures should be performed for at least 4 weeks [1].

The semiautomatic blood culture systems (Bactec and BacTAlert) shorten the detection time considerably; the presence of Brucella can be detected by the third day of incubation [2,10,44,45]. With automated blood culture systems, most isolates are recovered in one week; there is no need to incubate bottles longer than two weeks [42,46]. Cultures of other fluids or tissues (other than blood) may take up to three weeks to grow on plated media.

Brucella organisms can survive up to two days in milk at 8°C, up to three weeks in frozen meat, and up to three months in goat cheese. Brucellae shed in animal excretions may remain viable for >40 days if the soil is damp. The organisms are sensitive to heat, ionizing radiation, most commonly used disinfectants, and pasteurization [41,47,48].

Brucellae are taken up by local tissue lymphocytes, enter the circulation via regional lymph nodes, and seed throughout the body, with tropism for the reticuloendothelial system

The incubation period (from acquisition to clinical manifestations) is usually two to four weeks; occasionally, it may be as long as several months [ 1,18].

Brucellosis typically presents with insidious onset of fever, malaise, night sweats (associated with a strong, peculiar, moldy odor), and arthralgias (table 3) [1,20]

The fever pattern is variable; it may be spiking and accompanied by rigors, or may be relapsing, mild, or protracted. Additional symptoms may include weight loss, arthralgia, low back pain, headache, dizziness, anorexia, dyspepsia, abdominal pain, cough, and depression [ 1,10]. Physical findings are variable and nonspecific; hepatomegaly, splenomegaly, and/or lymphadenopathy may be observed.

The clinical manifestations of brucellosis in patients with HIV infection are the same as in patients without HIV infection [49].

Complications of brucellosis include infection involving one or more focal sites; the likelihood of focal involvement ranges from 6 to 92 percent and is usually about 30 percent [20,50-54]. Complications of brucellosis occur more frequently in adults than in children [55,56].

Osteoarticular disease is the most common form of focal brucellosis; it occurs in up to 70 percent of patients with brucellosis [55,57-59]. Forms include peripheral arthritis, sacroiliitis, and spondylitis.

The sacroiliac (up to 80 percent of those with osteoarticular disease) and spinal joints (up to 54 percent) are the most commonly affected sites [ 60]

Peripheral arthritis and sacroiliitis occur in the context of acute disease. Peripheral arthritis usually involves the knees, hips, and ankles [ 57,58,61].

Spondylitis is a serious complication of brucellosis; it is more prevalent in older patients and patients with prolonged illness prior to treatment [57]. The lumbar vertebrae are involved more frequently than the thoracic and cervical vertebrae, and associated paravertebral, epidural, and psoas abscesses have been described [62-64]

Genitourinary involvement is the second most common form of focal brucellosis; it occurs in up to 8 percent of cases [42].

Additional manifestations include cystitis, interstitial nephritis, glomerulonephritis, and renal abscess [ 19].

In one study including more than 240 pregnant women with brucellosis, the obstetric complication rate was 14 percent; spontaneous abortion was the most common complication (6 percent of cases) [67].

Neurologic involvement occurs in up to 5 percent of cases [42]. Manifestations include meningitis (acute or chronic), encephalitis, brain abscess, myelitis, radiculitis, and/or neuritis (with involvement of cranial or peripheral nerves) [18,19,41].

Cardiovascular involvement occurs in up to 3 percent of cases [42]; it may include endocarditis, myocarditis, pericarditis, endarteritis [68], thrombophlebitis, and/or mycotic aneurysm of the aorta or ventricles.

Pulmonary involvement occurs in up to 2 percent of cases [42]. Bronchitis, interstitial pneumonitis, lobar pneumonia, lung nodules, pleural effusion, hilar lymphadenopathy, empyema, or abscesses may be observed [52,69-71].

Ocular involvement is rare; uveitis is the most common form. Other manifestations include keratoconjunctivitis, corneal ulcers, iridocyclitis, nummular keratitis, choroiditis, optic neuritis, papilledema, and endophthalmitis [72].

Dermatologic manifestations occur in up to 10 percent of cases. Findings may include macular, maculopapular, scarlatiniform, papulonodular, and erythema nodosum-like eruptions, ulcerations, petechiae, purpura, granulomatous vasculitis, and abscesses [41,52,73].

Chronic brucellosis refers to patients with clinical manifestations for more than one year after the diagnosis of brucellosis is established [10,74]. Chronic brucellosis is characterized by localized infection (generally spondylitis, osteomyelitis, tissue abscess, or uveitis) in patients with objective evidence of infection (elevated antibody titers and/or recovery of brucellae from blood or tissues).

The rate of relapse following treatment is 5 to 15 percent [75]. Relapse usually occurs within the first six months following completion of treatment, but may occur up to 12 months later [76-78].

In a multivariate model for predicting relapse, independent predictors included temperature ≥38.3°C, duration of symptoms <10 days prior to treatment, and positive blood cultures at baseline [79].

In the setting of Brucella arthritis, the synovial fluid white blood cell count is usually ≤15,000 cells/microL (lymphocyte-predominant) [83-86]. The organism can be grown in synovial fluid [86-88].

Laboratory findings of brucellosis may include elevated transaminases and hematologic abnormalities including anemia, leukopenia or leukocytosis with relative lymphocytosis, and thrombocytopenia (table 3)

Measurement of the cerebrospinal fluid (CSF) adenosine deaminase (ADA) level may be a useful adjunctive test for diagnosis of central nervous system brucellosis [92]. However, elevated CSF ADA levels may also be observed in the setting of tuberculosis and other infections, and there is no clear threshold to distinguish neurobrucellosis from meningitis caused by other infectious agents [93,94].

In the setting of brucellosis with neurologic involvement, cerebrospinal fluid findings include a pleocytosis (10 to 200 white blood cells, predominantly mononuclear cells), mild to moderately elevated protein levels (mean 330±490 mg/dL in one study [89]), and hypoglycorrhachia [90,91].

Brucellosis should be suspected in patients with relevant signs and symptoms (fever, malaise, night sweats, and arthralgia) in the setting of relevant epidemiologic exposure (consumption of unpasteurized dairy products, animal exposure in an endemic area, and/or occupational exposure).

A definitive diagnosis of brucellosis may be made via either of the following [3,86,97-99]:

● Culture of the organism from blood, body fluids (urine, CSF, synovial fluid, and pleural fluid), or tissue (such as bone marrow or liver biopsy)

● A fourfold or greater rise in Brucella antibody titer between acute and convalescent phase serum specimens obtained ≥2 weeks apart

A presumptive diagnosis of brucellosis may be made via either of the following [3]:

● Brucella total antibody titer ≥1:160 by standard tube agglutination test (SAT) in serum specimen obtained after onset of symptoms

● Detection of Brucella DNA in a clinical specimen by polymerase chain reaction assay

For patients with suspected brucellosis, blood cultures and serologic testing should be performed. In addition, laboratory studies including complete blood count and liver function tests should be obtained.

For patients with negative blood cultures and negative serologic studies, further investigation should be guided by the clinical presentation, tailored to individual circumstances. As an example, patients with signs and symptoms of osteoarticular disease warrant synovial fluid analysis and radiographic imaging.

Patients with neurologic manifestations warrant lumbar puncture; this procedure usually does not enable definitive diagnosis but may be useful to distinguish brucellosis from other causes of disease.

If the above evaluation is unrevealing, bone marrow biopsy for culture and histopathology is warranted [1,41]. If bone marrow evaluation is not diagnostic and there is evidence for liver involvement (based on liver function tests and/or radiographic imaging), liver biopsy is warranted.

Culture — The sensitivity of blood culture for diagnosis of brucellosis is 15 to 70 percent [100].

Blood cultures are often negative in the setting of chronic disease [2].

Bone marrow culture is more sensitive than blood culture and is considered the gold standard for diagnosis of brucellosis [1]. In one study including 50 patients diagnosed with brucellosis, bone marrow culture was positive in 92 percent of cases [101]. Bone marrow culture has a shorter time to detection than blood culture, and its sensitivity is not diminished by prior antibiotic use [101].

Tests that may be most useful for patients with complicated and/or chronic infection include the 2-mercaptoethanol (2-ME) agglutination test, the immunocapture agglutination (Brucellacapt) test, and the indirect Coombs test.

A variety of serologic methods that enable antibody detection against lipopolysaccharide or other antigens have been used for diagnosis of brucellosis. The most common tests are SAT and enzyme-linked immunosorbent assays (ELISAs). Additional tests include screening tests (Rose Bengal agglutination test and the immunochromatographic lateral flow assay)

In acute disease, any of the assays may be positive; in chronic, complicated, or focal disease, SAT may be negative while 2-ME, Brucellacapt, Coombs, and ELISA IgG may be positive.

The sensitivity and specificity of SAT are high (95 and 100 percent, respectively, in one study) [103]

SAT may not be used for diagnosis of B. canis infection; B. canis serology should be requested specifically if brucellosis is suspected but the SAT is negative, or if there is clinical suspicion for B. canis infection [44,104].

There are a number of disadvantages associated with serologic tests. Cross-reactivity with other bacteria is a problem with standard tube agglutination; cross-reacting organisms include Francisella tularensis, Yersinia enterocolitica, Escherichia coli, Salmonella urbana, Vibrio cholerae, and others [1,110].

The interpretation of serologic tests can be difficult in the setting of chronic infection, reinfection, relapse, and in endemic areas where a high proportion of the population has antibodies against brucellosis [70].

Thus far, development of molecular testing for diagnosis of brucellosis is promising, but this is not yet a routine diagnostic tool [18,115-118]. All Brucella 16S rRNA gene sequences have been determined to be identical; therefore, 16S rRNA gene sequencing is useful for genus identification, but cannot be used for species identification [118].

For evaluation of spondylitis, magnetic resonance imaging is the preferred imaging study; other modalities include plain radiography, computed tomography (CT), and bone scintigraphy [60,119]. The Pons sign (a step-like erosion of the anterosuperior vertebral margin) is a characteristic manifestation [120].

For patients with brucellosis who present with fever of uncertain etiology and undergo CT scan, hepatosplenic disease with localized calcification may be observed (image 1) [121].

Bone marrow biopsy and liver biopsy may demonstrate noncaseating granulomas (consisting of epithelioid cells, polymorphonuclear leukocytes, lymphocytes, and some giant cells) in the setting of infection due to B. melitensis and B. abortus; in B. melitensis infection, the granulomata are very small. B. suis infection is often accompanied by chronic abscess formation [41].

Fungal infection – Fungal infections (eg, histoplasmosis, blastomycosis) may be associated with granulomatous disease.

Brucellosis is one of the most frequent laboratory-acquired infections. 5 In addition, brucellosis is classified as a category B biological weapon by the Centers for Disease Control and Prevention (CDC) owing to the ease of facilitated transmission. 6

Brucellosis is one of the earliest known diseases. Throughout history the disease has taken many different names, including Mediterranean, Maltese, or Crimean fever and Bang disease. It was named undulant fever after 1913 and then brucellosis, the name used today, from 1940 onward. 7,8

David Bruce, a military surgeon, isolated brucellae from the spleens of the patients in Malta between 1886 and 1887. The bacterium was named Micrococcus melitensis after isolation. A Danish doctor, Bang, later proved that the principal cause of abortion in bovines was a miniscule bacillus that he named Bacillus abortus. 6 In 1914 Traum isolated the bacteria from the aborted fetuses of pigs and gave the name Bacterium abortus suis.

In reference to Bruce’s name, the bacterium was renamed under Brucella as Brucella melitensis, Brucella abortus, and Brucella suis in the 1920s.

Brucella spp. are small, gram-negative, nonmotile, non–spore-forming, intracellular-reproducing, aerobic coccobacilli with a size of 0.6 to 1.5 μm in length and 0.5 to 0.7 μm in width.

lthough most Brucella spp. reproduce in aerobic conditions, B. abortus and B. suis are micro- aerophilic and require 5% to 10% carbon dioxide . 12

The cytoplasmic, peri- plasmic, and outer membrane structural proteins bear antigenic features and are recognized by the immune system. 17

The lipopolysac- charide layer on the cell wall shows endotoxic activity. The O-chain polysaccharide on the lipopolysaccharide layer has a significant role in the bacterial virulence. The three epitopes on the O-chain, named A, M, and C, can vary according to their species.

The bacterium survives for 6 weeks at 4°C in cream, 30 days in ice cream, and 15 to 100 days in fresh cheese. 20,21 Boiling and pasteurizing the milk kill the bacterium.

Brucellae also die when the milk goes sour or lactic acid fermentation occurs. It is safe to consume cheese after 60 to 90 days. The bacterium is also sensitive to heating, ionized radiation, and disinfectants. 22,23