Ans. is 'd' i.e., 2ME is used to detect IgA Brucella is a widespread zoonotic disease mainly seen in cattle sheep, goats, pigs and camels.Brucella is strictly a parasite of animals.No human to human transmission has been identified and infection in human occurs only by contact with infected animals or animal products.The disease in the man is known as Malta fever, Mediterranean fever or undulant fever.Transmission of BrucellaBrucella is a widespread zoonotic disease mainly seen in cattle, sheep, goats and pigs.Brucella is strictly a parasite of animalsNo human to human transmission has been identified and infection in human occurs by contact with infected animals or animal products.The possible means of acquisition of Brucella are:-Occupational exposure:Certain occupations are associated with high risk of exposure to brucellaThese include people who work with farm animals especially cattle sheep, goats and pigs: e.g. farmers, farm labourers, animal attendants, stockmen, shepherds sheep rearers, abattoirs.Persons involved in the processing of animal products may be at high risk of exposure to brucellosis. These include slaughter men, butchers, meat packers, processors of hides, skins and wool renderers and dairy workers.Infection may occur by inhalation, conjunctival contamination, accidental ingestion, skin contamination especially via cuts or abrasions.Food borne transmissionMain source of brucellosis for urban population, Ingestion of fresh milk or dairy products prepared from unheated milk is the main source of infection for most populations.Pasteurization of milk kilts brucella. Therefore unpasteurized milk or milk products may pose a particular risk.Infection from contaminated environment * Brucella species can survive for long periods in dust, dung, water, slurry, aborted fetuses, soil, meat and dairy products."Inhalational brucellosis may then result from exposure to contaminated dusty dried dung etc".(aerosol transmission)Contact infection may also result from contamination of skin or conjunctivae from soiled surfaces.Person to person transmission - Extremely rareDiagnosis of BrucellaUnequivocal diagnosis of Brucellosis requires isolation of the causative agent.Blood culture is the method of choice, it provides definitive diagnosisBut Brucella is a slow growing organisms and it requires prolonged period of incubation. In addition, failure to detect the pathogen is a frequent occurrence. The organism is isolated by culture methods in no more than 20% cases.Although in the last few years PCR based laboratory tests have been proposed but they cannot be considered a routine diagnostic method.These limitations make serology for antibody detection the most useful test for lab diagnosis:-Brucellosis may present clinically as acute or as chronic and of insidious onset.The serological results may differ depending on the clinical form and stage of the infection.IgM usually appears first followed by IgG.immunoglobulin M (IgM) antibody predominates for the first week of acute infection, after which the IgG antibody level starts to increase, reaches a peak after few weeks and predominates over the IgM antibody level until adequate therapy eliminates the infection.If adequate therapy is not done, the infection progresses to chronic state in which IgG level persists.Therapy only affects the IgG levelAdequate therapy reduces the IgG antibody level but not the IgM antibody level. If adequate therapy is not given, the infection may progress to a state of chronic brucellosis in which the serological activity is mainly due to IgG antibody.The routine brucella or the standard brucella agglutination test is the most frequently used type of serological test for the diagnosis of brucella.However it does not differentiate between, active and inactive disease because it does not differentiate between IgG and IgM agglutinins. The 2ME (2-MercaptoEthanol) agglutination test is most useful for differentiations active from inactive brucellosis. In this test the IgM immunoglobulin is inactivated by treating with 2-Mercaptoethanol (2ME) which breaks the disulfide bond and depolymerizes the IgM.The IgG immunoglobulin is resistant to depolymerization by 2 mercaptoethanol (2ME).The depolymerized IgM does not contribute to agglutination therefore the titre is primarily due to "ME resistant antibody (IgG)"The 2ME agglutination test is most useful for differentiating active from inactive brucellosis in persons having ill-defined complaint./ - The presence of 2ME resistant (IgG) brucella agglutinins indicates active disease in these patients.In addition 2ME agglutination test has been found to be superior to the routine agglutination test for determining the adequacy of antibiotic therapy.Adequate therapy reduces the IgG antibody level but not the IgM antibody level if adequate therapy is not given this infection may progress to a state of chronic brucellosis in which the serological activity is mainly due to IgG antibody.A fall in 2ME resistant IgG antibody titre indicates satisfactory response to therapy.