Brucellosis overview and Definition

      Brucellosis is a zoonotic  infection is caused by the bacterium genus Brucella. This infection is spread to the humans when the humans come into contact by the contaminated food materials by the bacteria. It also spreads to the humans by ingestion or direct contact with animals ,  or through aerosols by inhalation. The disease is an old one that has been known by various names, including Mediterranean fever, Malta fever, gastric remittent fever, and undulant fever.

The bacteria is an aerobic bacterium which lives intercellular and multiplies within the cells , the bacteria might cause abortion or sterility in the infected host.

 Incubation period: it takes more than 3 weeks.

Structure of Brucellosis


Brucella is an obligate intracellular aerobic bacteria. The brucella bacteria does not causes the spore formation.

Brucella are gram negative non spore forming cocco bacilli and also they lacks capsules or flagella and they are termed as non motile. They have a predominant lipopolysaccharide coating. They do not found to harbor plasmids.

The metabolism of the brucellae is mainly oxidative and they show little action on carbohydrates in conventional media. They are aerobes but some species require an atmosphere with added CO2(5-10 percent). Multiplication is slow at the optimum temperature of 37°C and enriched medium is needed to support adequate growth.



The bacterial causing this has 3 cycles which are acute , subacute and chronic. The four major bacteria causing brucellosis includes different Brucella species, i.e., Brucella suis (B. suis), Brucella melitensis (B. melitensis), Brucella abortus (B. abortus) and Brucella canis. Among these species, B. melitensis is the most contagious species, followed by B. abortus and B. suis.

These bacterial species lacks specific virulence causing factors such as genes encoding capsules, plasmids, pili or exotoxins, and because of factors that cause the bacteria to acquire resistance to phagocytes and increase the proliferation of phagocytic cells, they are relatively less known than other pathogenic bacteria.

Brucella bacteria prevents the bacteria from antibacterial cationic compounds and also aids the bacteria  to blocking the pathway for activation of the complement system. It has been studies that brucellosis is resistant to large number of substances  such as  peptides such as defensin NP-2, lactoferrin, cecropines lysozyme, bactenecin-derived peptides, defensin-like antibiotic polymyxin B, and also the lysosomal compounds produced from polymorphonuclear leukocytes.

By controlling the mechanism such as adenine and guanine system, the bacteria prevents the integration of the phagolysosomes, and the release of myeloperoxidase is also interfered and the action of tumour necrosis factor is lost giving rise to the increase in the pathogeniticity of the organisms and also resulting in causation of the disease.

And these brucella bacteria are very much intelligent and they knows the way to stay in the host immune system for prolonged period of time by causing severe complications. It forms a shield for itself  against the host immune system in certain ways such as stopping macrophage apoptosis, suppressing T1 specific immune responses and inhibiting TNF-α production. 

Brucella should prevent Th1 polarization in order to protect itself against the activation of macrophages and the production of cytotoxic T cells. Polarization of the immune system is carried out by the cytokines and macrophages. Therefore, stopping

out by the cytokines and macrophages. Therefore, stopping the expression of cytokines such as TNF is one of the methods of the pathogens to fight the immune system.

Brucellosis shows wide range of symptoms which might result in life threatening complication of the infected host

Routes of Transmission

Direct contact with the infected animals

Through inhalation of the spore

Ingestion of food materials of the bacterias

Clinical signs & symptoms




weight loss

 back pain





 and splenomegaly.

Bone involvement is the most commonly observed involvement in half of the people with brucellosis

Brucellosis might also results in endocarditis,myocarditis and also it results in inflammation of the

veins and arteries.

Differential Diagnosis

Direct Isolation and Identification

The isolation of the bacteria is considered as the gold standard treatment of diagnosis.

Culture examination:

There are several mediums available for the brucella which might include solid broth or biphasic forms of growing the bacteria. The biphasic forms of blood culture involves casteneda blood culture and hemoline performance blood cultute media

Lysis centrifugation:

 This is used to concentrate the lysis intracellular brucella species which are known to be found in the blood samples.

Blood Clot Culture:

These techniques are adviced in the area where the second blood sample cannot be collected. It is widely used because these culture is very simple, and also it reveals earlier results and it is test sensitive and the blood clot culture for brucellosis is done in areas where modern diagnostic aids are not available.

Automated techniques:

BACTEC (Becton Dickinson Diagnostic Systems), is used to find out the growth amd multiplication of the bacteria in the labelled CO2.

3.6. Serological Diagnostic Tests

The serological diagnosis of brucellosis commonly relies on the confirmation of the rising titters of Brucella-specific antibodies. This is the indirect proof of infection. Serological assays are used for the primary diagnosis of infection, as well as treatment follow-up (. Immunoglobulin (Ig) M isotype antibodies against the lipopolysaccharide (LPS) of Brucella spp. are the first immunoglobulins emerge after infection and are the predominant antibodies during the acute phase of the disease. The presence of specific IgM is considered suggestive of acute or recent infection.

Fluorescence Polarization Immunoassay:

It utilizes the molecular rotation and then detecting the antigen antibody interaction without the medium of separation. This test finds out the antigen antibody interaction.

Immunochromatographic Lateral Flow Assay:

Immunochromatographic lateral flow assay is a simplified version of the ELISA for the detection of Brucella-specific IgM and IgG antibodies . it helps in the identification of acute, persistent and relapsing infections. It might also aids in monitoring the treatment.

 Molecular Assays

Molecular assays can be performed on various clinical samples including serum, whole blood, cerebrospinal fluid (CSF), synovial or pleural fluid, urine, and even tissue specimens. The direct detection of brucella DNA  in patients suspected of brucellosis may be a challenge due to the small number of circulating bacteria in the blood, especially in chronic courses or after antibiotic therapy.

 Standard Polymerase Chain Reaction

PCR can be performed to amplify and detect Brucella DNA in clinical samples or pure cultures. Previously, Navarro et al. described several advantages of using serum samples for nucleic acid amplification . Several single-step PCR assays are developed to amplify and detect specific genomic sequences of the genus, species, or even biotypes of Brucella vary depending on the sets of primers, type of clinical sample, and presence of human genomic DNA


The prognosis is good and it purely depends upon the severity of organ damage and immune level of an individual.


  • Prevention is based on control measures at all stages of the food chain, from agricultural production on a farm, to processing, manufacturing and preparation of foods both commercially and domestically.
  • In countries without adequate sewage disposal systems, faeces and articles soiled with faeces may need to be disinfected before disposal.
  • Measures to reduce the prevalence of brucellosis in poultry include enhanced biosecurity to avoid transmission of brucellosis from the environment to the flock of birds on the farm. This control option is feasible only where birds are kept in closed housing conditions.
  • Good hygienic slaughtering practices reduce the contamination of carcasses by faeces, but will not guarantee the absence of brucellosis from meat and meat products. Training in hygienic food handling for abattoir workers and raw meat producers is essential to keep contamination to a minimum.

Prevention methods against infection in domestic kitchens are similar to those used against other foodborne bacterial diseases