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T J John

Publications and source records attributed to T J John.

At least 19 recordsLinked to original sources
PubMed2003

Comparison of different culture media and storage temperatures for the long-term preservation of Streptococcus pneumoniae in the tropics.

OBJECTIVE: The preservation of Streptococcus pneumoniae by standard freezing methods for subsequent tests--such as serotyping and antibiotic susceptibility--is not possible or is difficult in many developing countries because of the high cost of equipment, inadequate equipment maintenance, and irregular power supply. We evaluated alternative low-cost methods, by comparing different culture media and storage temperatures. METHODS: Clinical isolates of five capsular types (1, 5, 7, 19, and 23) of S. pneumoniae were preserved in rabbit blood, sheep blood, skimmed milk, or glycerol-chocolate broth, and stored at -20 degrees C or -70 degrees C. The cultures were also preserved by lyophilization or sand desiccation, followed by storage at room temperature and 4 degrees C. The viability of the preserved cultures was determined by making serial colony counts on day 0 and after 1 week, 4 weeks, 4 months and 16 months. The viability of cultures preserved by sand desiccation and storage at 4 degrees C was also determined every 6 months for up to 68 months. FINDINGS: Irrespective of the media used, cultures maintained at -20 degrees C became nonviable by the fourth month, while those maintained at -70 degrees C were still viable at 16 months. Cultures preserved by lyophilization or sand desiccation lost their viability by the fourth month when maintained at local room temperature (30-42 degrees C), but remained viable when stored at 4 degrees C for up to 68 months. CONCLUSIONS: Our results confirm that freezing at -70 degrees C, or lyophilization and storage at 4 degrees C are the ideal methods for the preservation of S. pneumoniae. In laboratories where lyophilization is not feasible, sand desiccation and storage at 4 degrees C offers an alternative low-cost method for the long-term preservation of S. pneumoniae.

Cell Culture Techniques↗
PubMed2001

Should health care workers in the tropics be immunized against varicella?

In tropical regions, chickenpox affects both adults and children. Therefore, healthcare workers in the tropics are vulnerable to hospital-acquired varicella infection and they may transmit infection to susceptible hospitalized individuals. Although the varicella vaccine is safe and effective, its cost is a deterrent to its use in routine immunization programmes. In order to assess whether vaccination of susceptible healthcare workers to prevent hospital-acquired transmission may be justified, we have documented the frequency of varicella among healthcare workers in our hospital. There were 96 admissions for varicella during the 1993-1997 period; staff and student nurses accounted for 76%. The peak season of admission was from February to April. The attack rate in staff and student nurses was 0.78 and 1.54 per 100 person-years, respectively. While community outbreaks of varicella occur in this region once in 4-5 years, hospital outbreaks of varicella occurred every year. This poses the risk of transmission to hospitalized patients, with serious consequences among immunocompromized individuals. Therefore, we recommend systematic selective vaccination of susceptible healthcare workers to break this cycle of annual varicella outbreaks among hospital personnel.

Chickenpox↗
PubMed2001

Anomalous observations on IPV and OPV vaccination.

Anomalies of vaccine performance are events or observations that go counter to the current paradigms on the properties of a vaccine. In the current paradigm, inactivated poliovirus vaccine (IPV) induces serum immunity to protect the individual from poliomyelitis, but not mucosal immunity to prevent subsequent wild poliovirus infection. Therefore, it is believed not to be suitable to interrupt virus transmission in polio-endemic tropical and developing countries, where poliovirus transmission is thought to be predominantly faecal-oral, unlike in countries with excellent sanitation, where it is predominantly respiratory. Oral poliovirus vaccine (OPV), because it is believed to mimic natural (wild) poliovirus infection and to induce serum and mucosal immunity, is considered ideal to interrupt virus transmission in countries with poor sanitation and endemic polio. Moreover, the vaccine viruses are shed in the stools and it is presumed to spread faeco-orally to unvaccinated children in the vicinity, thus increasing its effectiveness in the community. These paradigms on both vaccines may be seen in standard textbooks of virology and paediatrics. In reality, IPV induces very high mucosal immunity in a monkey model, lasting at least 12 months and providing complete protection against oral challenge with wild virus. In field trials, IPV has been found to have very high vaccine efficacy (VE) and to retard significantly wild-virus transmission in communities. OPV, requiring five to seven doses for individual protection, does not seem to induce effective mucosal immunity. Hence, 10-15 doses of OPV and near 100% vaccination coverage are necessary for interruption of virus transmission in countries with poor sanitation. In the monkey model, wild poliovirus infection did not offer any mucosal protection against a second infection, indicating that live virus infection is not the best way to induce mucosal immunity (unless repeated several times). The immunity induced by OPV has two arms, individual protection (by serum immunity) and mucosal protection from later infection by wild virus; these are dichotomous, as evidenced further by protected children participating in wild virus transmission in breakthrough outbreaks in communities well vaccinated with OPV. There is no evidence that polioviruses, wild or vaccine, spread faeco-orally to any meaningful extent. The median age of polio in India, in the pre-vaccine era, and even in recent years was 12-18 months. No other faeco-oral infection has such a low median age. Measles virus transmission is respiratory, and the median age of measles is over two years. Wild virus is shed faecally, but by the age when faecal microbes infect children, most of them are already immune to disease caused by polioviruses. As for vaccine viruses, even when heavy inocula are fed repeatedly, children may not always become infected. That exposure to the small amounts of virus through faecal contamination (unlike microbes that multiply in food) would infect them, is an unrealistic expectation. There are sufficient anomalies demanding our revision of the old paradigms. IPV is a better immunogen than OPV and is completely safe. During the interval between the cessation of wild virus transmission and the global stoppage of polio vaccination, it will be advantageous to use IPV, particularly combined with DPT vaccine, to provide individual protection, and herd effect to prevent spread in case of the introduction of wild polioviruses, whether unintentionally or otherwise, and to bolster the Expanded Programme on Immunisation.

Animals↗
PubMed2000

Herd immunity and herd effect: new insights and definitions.

The term herd immunity has been used by various authors to conform to different definitions. Earlier this situation had been identified but not corrected. We propose that it should have precise meaning for which purpose a new definition is offered: "the proportion of subjects with immunity in a given population". This definition dissociates herd immunity from the indirect protection observed in the unimmunised segment of a population in which a large proportion is immunised, for which the term 'herd effect' is proposed. It is defined as: "the reduction of infection or disease in the unimmunised segment as a result of immunising a proportion of the population". Herd immunity can be measured by testing a sample of the population for the presence of the chosen immune parameter. Herd effect can be measured by quantifying the decline in incidence in the unimmunised segment of a population in which an immunisation programme is instituted. Herd immunity applies to immunisation or infection, human to human transmitted or otherwise. On the other hand, herd effect applies to immunisation or other health interventions which reduce the probability of transmission, confined to infections transmitted human to human, directly or via vector. The induced herd immunity of a given vaccine exhibits geographic variation as it depends upon coverage and efficacy of the vaccine, both of which can vary geographically. Herd effect is determined by herd immunity as well as the force of transmission of the corresponding infection. Clear understanding of these phenomena and their relationships will help improve the design of effective and efficient immunisation programmes aimed at control, elimination or eradication of vaccine preventable infectious diseases.

Adult↗
PubMed2000

Increase in plasma IL-10 levels and rapid loss of CD4+ T cells among HIV-infected individuals in south India.

Increased levels of immune activation among HIV patients from developing countries are believed to accelerate and/or enhance the shift to a Th2 cytokine environment, which in turn may result in a more rapid progression to AIDS. In support of this hypothesis, we present data from a cohort of 35 HIV+ individuals in southern India. Among asymptomatic individuals in this cohort, a dramatic increase in plasma interleukin (IL)-10 coincided with rapid decrease in CD4 counts and progression to AIDS. Serum IL-10 levels were significantly higher after 6 months of follow up (P=0.01), while CD4 counts declined at a rate of 280 cells/ul per year, roughly 3 times the rate of decline reported for HIV+ asymptomatic subjects in developed countries. Changes in serum IL-10 levels and CD4 counts fell short of statistically significant correlation (P=0.1). Among AIDS patients in this cohort, the mean period from diagnosis of AIDS to death was <5 months and is in agreement with an earlier report of rapid progression in India.

Acquired Immunodeficiency Syndrome↗
PubMed2000

Vaccinia reactive antibodies in a south Indian population.

The prevalence of vaccinia virus antibodies was determined in both urban and rural populations in southern India. The study sample consisted of 211 adults and 52 children. The antibody titre was measured in all sera by virus neutralisation and by indirect immunofluorescence assay (IFA). A small panel of sera was tested by Western blotting. There was no significant difference in detection rates between the tests. Generally, seropositivity correlated with a previous history of vaccination. All children were negative for vaccinia antibodies. Among adults overall, 54% had neutralising antibodies whereas 60% were positive for antibodies detected by IFA, however, the prevalence of vaccinia antibody by either method was significantly higher (P < 0.001) among rural subjects than in urban subjects. This higher antibody prevalence among the rural population could be due to exposure to other indigenous orthopoxviruses, possibly buffalopox.

Adult↗