Comparative stabilities of glutaraldehyde & heat inactivated pertussis vaccine components of adsorbed DPT vaccine with different preservatives.

The stability of pertussis component (glutaraldehyde or heat inactivated pertussis vaccine) of the adsorbed diphtheria-pertussis-tetanus (DPT) vaccine preserved in thiomersal or benzethonium chloride was studied at 4-8 degrees C and 35 degrees C for 30 days. The potency of pertussis component of adsorbed DPT vaccine preserved with benzethonium chloride was lower than that preserved with thiomersal. After the initial loss of potency of pertussis component in the benzethonium chloride during blending, the stability of potency of pertussis component at 4-8 degrees C and 35 degrees C for 30 days was similar for vaccines preserved with either benzethonium chloride or thiomersal. The stability of both types of pertussis components inactivated with glutaraldehyde or heat was also similar at both the temperatures for 30 days.

Increasing prevalence of high degree resistance amongst Salmonella to different antibiotics.

National Salmonella & Escherichia Centre situated at Central Research Institute, Kasauli receives Salmonella strains from all over the country. Eight hundred and fourteen Salmonella strains belonging to 14 serotypes received during 1986 were studied for antibiotic resistance and Minimum Inhibitory concentration (MIC) with regard to ampicillin (A), chloramphenicol (C), furazolidone (Fz) and gentamicin (G). Resistance to ampicillin was found to be highest (80%) and furazolidone the least (0.1%). Similarly a large number of strains (31%) had very high MIC values greater than 640 mcg per ml for chloramphenicol, whereas only 3.4% strains were found to have MIC values greater than 640 mcg per ml for gentamicin. The present findings have been discussed in the light of similar data published from this Centre earlier and from other sources in India.

Indirect haemagglutination test for the assay of antibodies against Japanese encephalitis viral antigen in human & animal sera.

The indirect haemagglutination (IHA) test was standardized for the assay of antibodies against Japanese encephalitis (JE) virus. Glutaraldehyde fixed sheep erythrocytes were sensitized with purified and concentrated JE vaccine (200-300% brain concentration). The JE vaccine made from Nakayama-NIH strain of JE virus was purified by protamine sulphate treatment and by ultracentrifugation in a sucrose gradient. The sensitized cells were quite stable in liquid as well as in lyophilized state both at -70 degrees C and 4-8 degrees C. These cells could be used for two years without much loss (4-8 times loss) in titre. The IHA test was as sensitive as the neutralization (N) test performed by plaque reduction method in chick embryo fibroblasts. The sensitivity of the test was influenced by the source of erythrocytes i.e., from the different sheep from which these were drawn. After standardization of the test, 16 human sera and 18 sera of immunized mice were assayed for antibodies against JE virus by N and IHA tests. There were no significant differences between titres of both human and mice sera determined by N and IHA tests (P greater than 0.05). The correlation coefficient between N and IHA titres for human sera was 0.60 (P less than 0.05) and for mice sera 0.82 (P less than 0.01). The IHA test has been found to be very simple, inexpensive, sensitive and reproducible.

Effect of different concentrations of diphtheria toxoid & aluminum phosphate on potency of diphtheria component in DPT vaccines.

An effort was made to determine the optimum concentration of diphtheria toxoid in combination with aluminum phosphate gel in DPT vaccines which may give a safe, potent and economical preparation. The effect of four different concentrations of aluminum phosphate and three different antigenic concentrations of diphtheria toxoid on potency of diphtheria component in DPT vaccine was assessed. A gradual increase in potency was seen with increase in toxoid concentration and a gradual decrease in potency with the increase in aluminum phosphate content. Vaccines made with minimum quantities of toxoid (30 Lf/ml) and aluminum phosphate (3 mg/ml) were found to be highly satisfactory. Vaccines prepared with high antigenic purity toxoid have better potency, as compared to those prepared with a relatively low antigenic purity toxoid.

Immune status of volunteers one year after administration of Japanese encephalitis vaccine produced in India.

The immune status of 40 volunteers who received the full course of Japanese encephalitis (JE) vaccine a year earlier and 15 individuals who had received only a booster dose at the same time, was studied by estimating the level of persistence of protective antibody in the sera. All the sera showed persistence of 100 per cent seroconversion rate. Individuals who had the full course of vaccination still had high levels of antibody (mean 2.8 Iog10); however there was a fall of 0.8 Iog10 from the post-booster level. Volunteers who had received only a booster dose, also showed persistence of high level of protective antibody (mean 2.4 Iog10), a drop of 0.9 Iog10 from the post-booster level. Neutralizing (N) antibody estimated using Dibrugarh (7812474) strain of JE virus also demonstrated persistence of high level of protective antibody against this virus (mean 2.4 Iog10). Persistence of high level of protective antibody against homologus and heterologus (Dibrugarh) virus strains and absence of vaccine related side-effects even one year after administration of JE vaccine produced in India, demonstrates the immunizing potency and safety of this new vaccine.

Evaluation of the new rapid rabies immunodiagnosis technique.

The rapid rabies enzyme immuno-diagnosis (RREID) kit was evaluated for its sensitivity and specificity in comparison to fluorescent antibody technique (FAT) and biological test (BT) for the diagnosis of rabies. While 93 per cent correlation was observed in case of fresh brain samples, 71 per cent correlation was noted with glycerol preserved samples, where RREID was more sensitive than FAT. RREID test can be employed for rapid diagnosis of rabies, when facilities for FAT are not available. However, to test, at one time, small number of specimens, the RREID kit needs to be modified.

Surveillance of salmonellae in India for drug resistance.

Out of 3001 salmonella received during 1984-85, 2985 strains were tested for antibiotic resistance and R-pattern transfer. Multidrug resistance was observed in 73% of diarrhoeal and 43% of non-diarrhoeal isolates. Antibiotic resistance markers were transferable in 46.6% of diarrhoeal and 41.1% of non-diarrhoeal isolates. Two out of 4 salmonella sero-types isolated for the first time in India during this period were multidrug resistant.

Correlation between mouse intracerebral potency & 50 per cent histamine sensitizing dose of pertussis vaccine.

A good correlation was observed between mouse intracerebral potency in terms of International Units and 50 per cent histamine sensitizing dose (HSD50) of various types of pertussis vaccine. The correlation was significant irrespective of the inactivating agent used for the preparation of pertussis vaccine. If the potency of the vaccine increased, the HSD50 decreased and vice versa showing a negative correlation between potency and HSD50. The relative histamine sensitizing (HS) activities of various types of pertussis vaccines in comparison to that of heat inactivated pertussis vaccine (HIPV) obtained in different experiments were very similar although the HSD50 values of same types of vaccines obtained in these experiments varied greatly. The conventional HIPV preparations having potency around 8 IU per 40 x 10(9) organisms had HSD50 values in the range of 1.0 to 2.2 x 10(8) organisms. The estimation of HSD50 of pertussis vaccine has been found to be a useful measure of the toxicity of the vaccine and also correlates well with the potency of the vaccine.

Characteristics of Escherichia coli isolates from infantile and childhood diarrhea.

Seventy-five strains of Escherichia coli from cases of infantile and childhood diarrhea were serogrouped and analysed in terms of hydrophobicity, mannose resistant haemagglutination and enterotoxigenicity. The strains were distributed over 21 serogroups of which 54.6% were hydrophobic, 37.3% were haemagglutinating and 66.5% were enterotoxigenic. EPEC strains were less than ETEC strains. LT producers were more than LTST or ST producers. MRHA activity was found to be well correlated with hydrophobicity.