BRUCELLOSIS Sir David Bruce (1855-1931) British Army physician and microbiologist who discovered Micrococcus melitensis 1887, the organism isolated from the spleens of 5 patients with fatal cases in Malta. The disease gets its names from both its course (undulant) and location (Malta fever, Crimean fever). For Fourth- Year Medical Students Dr: Hussein Mohammed Jumaah CABM Mosul College of Medicine 28/11/2017

Microbiology and epidemiology Brucellosis is an enzootic infection (i.e. endemic in animals). Although six species of Brucella are known, only four are important to humans: B. melitensis (goats, sheep and camels). B. abortus (Cows, camels, cattle, buffalo). B. suis (pigs). B. canis (dogs). Brucellae are, gram- negative, non-motile, strict anaerobes, nonsporulating coccobacilli. Sensitive to sunlight, ionizing radiation. killed by boiling and pasteurization. Resistant to freezing and drying, facilitating airborne transmission to the respiratory tract and conjunctiva. Survive up to 2 months in soft cheese.

Portals of entry Brucellosis may be acquired by ingesting contaminated uncooked meat, milk, cheese, yoghurt and butter. Animal urine, manure particles through abraded skin and aerosols to the respiratory tract and conjunctiva. Inhaling 10 to100 organisms can cause disease. B. melitensis and B. suis have been developed as biological weapon (bioterrorism) . Person-to-person transmission is extremely rare, as is transfer of infection by blood or tissue donation. In a few cases, women have passed the disease to their infants during birth or through their breast milk. May also spread through sexual activity . Brucellae, along with leptspira, have the unique property of being able to penetrate through intact skin

Pathophysiology Brucellae are intracellular organisms that can survive for long periods within the reticulo-endothelial system invading both phagocytic and nonphagocytic cells avoiding the immune system. This explains the chronicity and the tendency to relapse even after adequate antimicrobial therapy and why brucellosis is a systemic disease and can involve almost every organ system. Lipopolysaccharide, a major component of the cell membrane, likely play a substantial role in intracellular survival.

Clinical features The disease may be Asymptomatic. Acute (< 2 months) Subacute (2-12 months) Chronic (> 1 year) incapacitating disease with severe complications. B. melitensis is associated with acute infection and causes the most severe disease, whereas the infections with other species are usually subacute and prolonged.

Clinical features The incubation period ,1week to several months Clinical features The incubation period ,1week to several months. Acute illness is characterised by a high swinging temperature, chills , rigors , sweating, lethargy, headache, and joint and muscle pains, and scrotal pain. Occasionally delirium, abdominal pain and constipation. Some authors consider malodorous perspiration pathognomonic. Fewer than 1% of patients die usually a consequence of cardiac involvement; rarely from severe neurologic disease. Brucellosis in pregnancy is associated with risk of spontaneous abortion, premature delivery, miscarriage, and intrauterine infection with fetal death. Brucellosis can be a cause of fever of unknown origin.

Localised infection

Localised infection which occurs in about 30%, more likely if diagnosis and treatment are delayed. Physical signs A palpable spleen, may lead to hypersplenism and thrombocytopenia. Enlarged lymph nodes. Diagnosis Laboratory tools for diagnosis of brucellosis include culture, serology, and polymerase chain reaction (PCR) . Culture: Definitive diagnosis depends on the isolation of brucellae from blood, CSF, BM, or joint fluid or from a tissue aspirate or biopsy sample, usually successful in 50–70%

Blood cultures are positive in 75–80% for melitensis and 50% of those caused by B. abortus. Bone marrow culture should not be used routinely but may increase the diagnostic yield, particularly if antibiotics have been given before specimens are taken. CSF culture in neurobrucellosis is positive in about 30%.The laboratory should be alerted to a suspected diagnosis of brucellosis.

Serology : May also aid diagnosis. Serum agglutination (standard tube agglutination (SAT)) ELISA (enzyme-linked immunosorbent assay) Rose Bengal agglutination Coombs test 2-mercaptoethanol agglutination (2-ME) SAT and ELISA are the most common serologic tests. Rose Bengal plate agglutination test is often used as a rapid screening test, with very high sensitivity (>99 percent), and fairly high specificity.

In endemic areas, a single high antibody titre of more than 1/320 or a fourfold rise in titre is needed to support a diagnosis of acute infection. The test takes several weeks to become positive, eventually detect 95% of acute infections. In acute infection, IgM antibodies appear early and are followed by IgG and IgA. As the disease progresses, IgM levels decline, and the avidity and subclass distribution of IgG and IgA change.

The 2-mercaptoethanol (2-ME) Treatment of serum with 2-mercaptoethanol destroy the inter-chain sulphydryl bonds of gamma globulins. IgM antibodies treated in this way lose their ability to agglutinate red cells while IgG antibodies do not. The test measures IgG antibodies only, and is a good marker to follow disease activity after initiation of therapy. A negative (IgG=chronic) 2ME test is strong evidence against a diagnosis of chronic brucellosis.

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, Vibrio cholera.  Positive serological tests results can persist long after recovery in treated individuals, so it is not always possible to distinguish serologically between active and past infection .

Prozone phenomenon is called as false SAT negativity seen due to because of the relative excess of antibodies (blocking antibodies) against antigens in the serum. In cases with clinical findings suggesting brucellosis with negative SAT, SAT must be diluted to titers 1/1280 or more in order to exclude false sero-negativity.

Polymerase chain reaction (PCR) . Has enormous potential to detect bacteremia, to predict relapse, and to exclude “chronic brucellosis.” This method is probably more sensitive and is certainly quicker than blood culture, and it does not carry the attendant biohazard risk posed by culture and now quite widely used.

Treatment of brucellosis Management Aminoglycosides show synergistic activity with tetracyclines against brucellae. Treatment regimens for different forms of brucellosis are outlined in the box

PROGNOSIS The rate of relapse following treatment is about 5 to 15 percent ,usually occurs within the first six months following completion of treatment. Relapse due to antibiotic resistance is rare. Relapse occurs in up to 30% of poorly compliant patients, which responds to a prolonged course of the same therapy used originally. Causes of relapse include inadequate choice of antibiotics, shortened treatment duration, lack of adherence, or localized foci of infection .

The general well-being and the body weight are more useful guides than serology. IgG antibody levels can remain in the diagnostic range for >2 years after successful treatment. Immunity is not solid; patients can be reinfected after repeated exposures. Fewer than 1% of patients die of brucellosis , usually a consequence of cardiac involvement; rarely, it results from severe neurologic disease.

PREVENTION Vaccines based on live attenuated Brucella strains, such as B. abortus strain, have been used in some countries to protect high-risk populations but have displayed only short-term efficacy and high reactogenicity. Subunit vaccines have been developed but are of uncertain value and not recommended at present.

The mainstay of veterinary prevention is a national commitment to testing and slaughter of infected herds/flocks , control of animal movement, and active immunization of animals. These measures are usually sufficient to control human disease as well. In their absence, pasteurization of all milk products before consumption is sufficient to prevent non-occupational animal-to-human transmission. All cases of brucellosis in animals and humans should be reported to the appropriate public health authorities.