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Hepatitis B vaccine is well established as very efficacious, but immune response to the vaccine is highly individual specific. A study involving fifty vaccinees was undertaken at the Hepatitis Laboratory, National Institute of Communicable Disease, Delhi. One ml (20 microgram) of Engerix B vaccine (recombinant yeast derived vaccine) was administered in the standard three dose schedule (0, 1 and 6 months). The sero-conversion of the vaccinees was 24%, 66%, 76% and 78% at 1 month, 6 months, 7 months, and 12 months respectively. There was no seroconversion in 22% of the vaccinees. Sero-conversion was assessed using Macro ELISA test (Ausab, Abbott Labs) for Anti HBs reactivity.

An ELISA assay based on mycobacterial antigen A60 (Anda, Biologicals France) was used to detect specific immunoglobulins (IgM, IgA and IgG) in 48 cases of adult neurotuberculosis (24 TBM; 24 Tuberculoma) and in 48 controls (24 diseased controls; 24 healthy controls). Serum was analysed in all the subjects whereas CSF was assayed only in TBM cases and diseased controls. The cut off values used for IgM, IgG and IgA in this study were 1.500 ODI (optical density index) at 1:100 dil, 250 units/ml and 150units/ml respectively in serum; and 1.500 ODI at 1:10 dil, 10 units/ml and 10 units/ml respectively in CSF. The mean titres of all three antibodies were found to be significantly higher in cases as compared to controls. In cases of TBM, in serum, the percentage positivity for IgM, IgG, IgA and combination of IgG or IgA were 41.67, 87.50 87.50 and 95.83 respectively. The corresponding figures in CSF were 62.50, 75.0, 66.67 and 79.16 for IgM, IgG, IgA and 'IgA or IgM' respectively. In tuberculoma cases, in serum, the figures were 37.50, 75.0, 75.0 and 83.33 respectively. Overall, a high sensitivity and specificity were obtained in cases of TBM (Serum: ST = 95.83%: SP = 87.50%; CSF ST = 79.16%. SP = 100%) and Tuberculoma cases (serum: ST = 83.33% SP = 87.50%) employing the combined antibody estimations.

To overcome limitations of the conventional laboratory tests for the diagnosis of tuberculosis, attempts have been made in the past to develop a good serodiagnostic test. Until the availability of ELISA results obtained with various immunological techniques were of limited use. Even with ELISA, early attempts to estimate specific antimycobacterial antibodies in the serum were based on the use of crude mycobacterial antigens resulting in a very high false positivity. Better results were obtained with purified antigens. Various purified and semipurified antigens which when used in the ELISA test for estimating antibodies in the serum and other body fluids in cases of tuberculosis have given encouraging results. These include a glycolipid antigen from Myc. bovis BCG (ST = 88%, SP = 96%), antigen '5' (ST = 72%, SP = 91%) and a 38 Kd protein antigen (ST = 83%). Estimation of various mycobacterial antigens in different clinical specimens has also been studied using ELISA technique. Encouraging results have been obtained with the detection of a 43 Kd antigen, Lipoarabinomannan antigen and antigen '5' in the serum, CSF and other body fluids of cases of tuberculosis (ST = 80-100%, SP = 93-100%). The serological tests by detecting specific mycobacterial antigens and antibodies can be of great help in diagnosing the smear negative tuberculosis as these are rapid, inexpensive and simple to perform.

The sensitivity and specificity of three serological tests viz. indirect immunofluorescent antibody test (IFAT), enzyme linked immunosorbent assay (ELISA) and counterimmunoelectrophoresis (CIEP) for the diagnosis of Indian kala-azar were evaluated. Of the 209 patients in whom Leishmania donovani parasite could be demonstrated in bone marrow, 207 (99.04 per cent) could be diagnosed with IFAT, 203 (96.6 per cent) with CIEP and 208 (99.5 per cent) with ELISA. None of these serological tests was positive in 40 healthy individuals and 10 patients each with tuberculosis, toxoplasmosis and malaria. In only one out of 10 patients with malaria ELISA alone gave false positive result. Of the 119 patients who had clinical features simulating kala-azar but were negative for Leishmania donovani in bone marrow and responded to treatment other than that for Indian Kala-azar, IFAT, CIEP and ELISA were false positive in three (2.5 per cent), nil and three (2.5 per cent) cases, respectively. The use of serodiagnostic tests like ELISA for mass screening and CIEP in less well equipped peripheral laboratories is suggested.

Comparative evaluation of indirect fluorescent antibody test (IFAT) and Weil-Felix test (WFT) was carried out for detecting rickettsial antibodies in 102 patients with pyrexia of unknown origin (P.U.O.), 20 brucellosis cases and 20 normal healthy controls (N.H.C.). Of 102 sera of cases with P.U.O., antibodies against rickettsia could be detected in 11 (10.7 per cent) cases by IFAT and in 10 (9.8 per cent) cases by WFT, but amongst these 10 sera, antibodies could be detected only in six by IFAT. All 20 brucella positive sera were negative for rickettsia by IFAT but by WFT in 6 sera antibodies against rickettsia could be detected and 20 N.H.C. sera were negative by both the tests. Thus the advantages of IFAT over WFT in detecting antibodies against rickettsia in terms of sensitivity and specificity make it a more reliable test.

Intimate and prolong contact between man and animal facilitates the transmission of various communicable diseases between them. These diseases (zoonoses) are more prevalent in developing countries especially in the rural areas. These diseases virtually stunt the economic and social growth also. Lack of authentic data and awareness regarding the occurrence of these diseases and their true impact on public health have acted as major obstacles in instituting adequate and effective control measures. The information available regarding the current status of few important zoonoses in India is being presented in this paper.

One thousand and thirty-six serum samples obtained from women with bad obstetric history (BOH) were subjected to detection of toxoplasma antibody by indirect immunofluorescent antibody test (IFAT) using whole promastigotes of Rh strain of Toxoplasma gondii as antigen. Thirtyone (2.99 per cent) samples were found to be positive (titre greater than or equal to 1:64). Of these 31 patients' sera 27 (87.09 per cent) showed rising titre of antibody when second samples were drawn after 4 weeks. Two hundred serum samples from general population were also assayed and only 2 (1 per cent) were found to be having toxoplasma antibodies in titre of 1:64. The observations suggest low prevalence of toxoplasmosis in and around Delhi which is in consonance with the food habits of local people and their infrequent contact/association with cats.

Search for livelihood makes many people move from kala azar endemic areas to metropolitans like Delhi from where indigenous cases have not been reported. During 1986-1989, 211 laboratory confirmed kala azar cases were detected in Delhi. Of these 202 (95.73 per cent) were from Bihar and remaining nine (4.27 per cent) belonged to Uttar Pradesh. Younger age groups were affected more and maximum cases (54.02 per cent) were in the age group of 5-15 years. Male:female ratio was 2:1. Fever (100 per cent) along with mass in abdomen (99.05 per cent) were the major presenting complaints. Splenomegaly was seen in all the patients whereas hepatomegaly was a feature in 184 (87.20 per cent) cases. Response to sodium antimony gluconate (SAG) was variable and number of injections administered reached upto 80 in some (23) cases. All 37 patients responded to pentamidine after two full courses of SAG failed to bring about any clinical and parasitological cure.

The quest for the search of rapid, cheap, easy to perform and highly sensitive and specific tests has resulted into the introduction and application of various new tests for the diagnosis of bacterial meningitis. Most of these tests are based on immunological principles, viz. counter-immunoelectrophoresis, latex agglutination test, co-agglutination, radio-immunoassay, haemagglutination inhibition as well as study of immune profile of cerebrospinal fluid. Apart from these certain non-immunological tests viz. Limulus amoebecyte lysate test, gas liquid chromatography, nitroblue tetrazolium dye reduction test have also been evaluated to make the laboratory diagnosis of this important clinical entity rapid and more reliable. These tests have been discussed and their current status presented.

HDCS was given to 12 healthy volunteers in three different schedules. The levels of neutralising antibodies were determined by ELISA test. The antibodies could be detected on day 7 after vaccination. With 3 doses (D-0, D-15, D-30) satisfactory high level of neutralising antibodies could be detected in 3 out of 4 volunteers till 2 years. With 2 doses (D-0, D-15) similar levels could be observed only till day 270, and with single dose significant levels could be seen till day 30 only after which levels declined and no antibodies could be detected on day 270. Reactogenicity of the vaccine was nil as no major or minor side-effects were observed in any of the volunteer.

Rabies is responsible for a large extent of morbidity and mortality in human beings. However, the long incubation period of the disease allows the effective utilization of post exposure immunization. Till recently neural tissue vaccines were the mainstay of antirabic immunoprophylaxis. These vaccines are, associated with severe neuroparalytic complications. The recent introduction of human diploid cell vaccine and chick embro fibroblast vaccines have heralded a new era in antirabic vaccination because of their high immunogenicity and lack of major side effects.

Cellulose acetate precipitation (CAP) test for the detection of antibody against Entamoeba histolytica using the axenic antigen, was performed on the 127 serum samples obtained from patients with amoebic liver abscess (14), amoebic hepatitis (21), amoebic dysentry (11), amoebic colitis (31), other parasitic infestations (25) and normal individuals (25). The percent positivity was 100, 95.23, 90.9, 67.74 and 16 and 12 respectively whereas the corresponding figures for the indirect immunoflourescence (IFAT) test were 100, 100, 100, 74.19, 12 and 8 respectively. Although CAP is not as good a test as IFAT, yet it can be recommended for routine testing due to its sensitivity, speed of performance and applicability to a single serum sample.