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Previous Infection (previous + infection)
Selected AbstractsComparison of a Stool Antigen Test and Serology for the Diagnosis of Helicobacter pylori Infection in Mass SurveyHELICOBACTER, Issue 2 2009Tadashi Shimoyama Abstract Background: Serum antibody to Helicobacter pylori is tested in mass screening for gastric cancer along with the level of serum pepsinogens (PG) I and II. Recently, stool antigen tests have been developed as a new non-invasive test. We examined H. pylori infection by both serology and stool antigen test in a mass survey and compared the results to estimate applicability of stool antigen test for mass survey. Methods: A total of 994 healthy adults who received mass survey in April 2005 were tested. There were 379 men and 615 women, and the mean age was 57.7 years old. Stool samples were used to measure a H. pylori- specific antigen by enzyme immunoassay. Serum samples were tested for the prevalence of IgG antibody to H. pylori, and the level of PGs I and II was also measured to determine the presence of atrophic gastritis. Results: Infection of H. pylori was defined as positive 61.4% and 56.4% by serology and stool antigen test, respectively. The concordance of both tests was not affected by gender and age of the subjects but difference was seen in subjects with atrophic gastritis. In particular, positivity of stool antigen test (81.8%) was significantly lower than that of serology (88.7%, p < .05) in 303 subjects with severe atrophic gastritis. Conclusions: Stool antigen test, which detects present but not previous infection of H. pylori, would be applicable to diagnose H. pylori infection in mass survey. Usefulness of stool antigen tests for the screening of gastric cancer should be examined. [source] Cross-strain protection reduces effectiveness of virally vectored fertility control: results from individual-based multistrain modelsJOURNAL OF APPLIED ECOLOGY, Issue 6 2007ANTHONY D. ARTHUR Summary 1Pest mammals have severe economic, environmental and social impacts throughout the world. Fertility control could reduce these impacts. Virally vectored immunocontraception (VVIC) has been proposed as an economic way to achieve this. However, the ability of an immunocontraceptive virus to control populations may be compromised if: (i) sufficient infected mice are not made infertile; (ii) the virus does not transmit at a sufficient rate; (iii) there is competition with field strains of virus; or (iv) its ability to induce infertility is altered by the presence of field strains. We tested this with stochastic, individual-based, disease,host models based on murine cytomegalovirus (MCMV) and house mice Mus musculus domesticus. 2Using field estimates of the MCMV transmission rate, immunocontraceptive MCMV (icMCMV) could prevent mouse populations from growing rapidly to damaging levels provided > 70% of mice infected with the virus became infertile. Successful control was possible even if engineering icMCMV reduced its transmission rate to c. 30% of the field-estimated value, but greater reductions in the transmission rate compromised successful control. 3Effective control was compromised if there was competition between icMCMV and field strains because of cross-immunity to infection or if previous infection with field strains blocked the development of infertility in mice subsequently infected with icMCMV. In these cases effectiveness was diminished, particularly if the transmission rate of icMCMV was reduced relative to field strains, or if close to 100% infertility of infected mice could not be achieved. If the blocking developed early after infection with field strains, doubling the transmission rate of icMCMV relative to field strains still could not produce successful control. 4Synthesis and applications. VVIC requires preliminary estimates of its efficacy to satisfy regulatory requirements before it can be released into the environment. Our models indicate that successful control of an outbreaking species using VVIC is possible if high levels of infertility can be achieved, but this is compromised by cross-strain protection and low transmission rates of engineered virus. Future research effort should focus on determining whether these compromising effects occur for specific engineered viruses and, if so, whether they can be overcome. [source] Regulation of immune responses to Strongyloides venezuelensis challenge after primary infection with different larvae dosesPARASITE IMMUNOLOGY, Issue 3 2010H. C. SCHILTER Summary Nematode infections are generally followed by high rates of reinfection, leading to elevated prevalence in endemic areas. Therefore, the effective control of nematode infections depends on understanding the induction and regulation of protective mechanisms. However, most experimental models for protective immune response against nematodes use high parasite exposure, not always reflecting what occurs naturally in human populations. In this study, we tested whether infecting mice with different Strongyloides venezuelensis larvae loads would affect protective responses against reinfection. Interestingly, we found that a previous infection with 10,500 larvae conferred high rate of protection against reinfection with S. venezuelensis in mice, by destroying large numbers of migrating larvae. However, low-dose priming did not abolish adult worm maturation, as detected in high-dose primed group. Results also indicated that a previous low-dose infection delayed the development of cellular infiltrate, while a high inoculum rapidly induced these inflammatory features. Cytokine production by splenocyte cultures of challenge infected mice demonstrated that low-dose priming had increased production of IL-4 and IFN-,, while high-dose induced IL-4 production but not IFN-,. Our data support the hypothesis that low-dose nematode infection does not induce a polarized type-2 immune response, allowing adult worm survival. [source] Evaluation of the immune response against Strongyloides venezuelensis in antigen-immunized or previously infected micePARASITE IMMUNOLOGY, Issue 3 2008A. FERNANDES Summary The present study was carried out to investigate the immune response against Strongyloides venezuelensis infection in Balb/c mice previously immunized with larva-antigens or primed with live-larvae. Our results indicate that all primed mice developed a strong protection against challenge infection that remained active for 45 days. In mice primed with live-larvae the challenge infection resulted in great reduction of migrating larvae and the worms were completely eliminated from the small intestine before maturation. The protection pattern did not alter when the primary infection was aborted by drug treatment. In these experimental groups, the challenge infection was accompanied by a type-2 predominant immune response, intense IgE and reactive IgG1 production, and granulocyte infiltration in skin, lungs and intestine. The challenge infection in antigen-immunized mice also resulted in great reduction of migrating larvae. However, the worms that reached the host intestine matured, produced eggs and were eliminated similarly to the ones from nonimmunized mice. Protective mechanisms after immunization with larva antigen were migrating larva-specific and associated with a strong and mixed Th1 and Th2 response, without tissue granulocyte infiltration. In conclusion, protective immunity induced by a previous infection or antigen-immunization are stage-specific and operate through different effector mechanisms. [source] A previous infection with Toxoplasma gondii does not protect against a challenge with Neospora caninum in pregnant sheepPARASITE IMMUNOLOGY, Issue 3 2001E.A. Innes Sheep immunized with Toxoplasma gondii (Toxovax®) prior to pregnancy were tested for their ability to withstand a challenge at 90 days gestation with 107 Neospora caninum (NC1) tachyzoites. The antibody responses in sheep following immunization with T. gondi were specific for T. gondii whereas peripheral blood mononuclear cells responded to both T. gondii and caninum antigen in vitro. This suggested that there was induction of crossreactive immune recognition in the sheep, at least at the cellular level. Following challenge of sheep at mid-gestation with N caninum, no febrile responses were recorded in the group of sheep which had previously received Toxovax® while significant febrile responses were recorded in the group of sheep which received N challenge alone. Antibody responses to N developed in all sheep following challenge and antibody responses to T,gondii were boosted in the group of sheep which had previously been immunized with Toxovax®. No antibodies to were observed in the sheep which received the challenge alone. Peripheral blood mononuclear cells from both groups of sheep responded to T.gondii N.caninum antigen invitro and interferon gamma was present in the cell-free supernatant from activated cells. However despite evidence of the induction of crossreactive immunity between T.gondii N.caninum this was not sufficient to prevent foetal death. The group of sheep which had received Toxovax® prior to pregnancy and the group of sheep which only received the N.caninum challenge experienced 100% foetal death compared with 0% in the unchallenged control group. Vaccination prior to pregnancy with Toxovax® did protect against foetal death following oral challenge at 90 days with 2000 oocysts which caused 100% foetal death in a control challenge group. [source] Markers of hepatitis B virus infection and immunity in Victoria, Australia, 1995 to 2005AUSTRALIAN AND NEW ZEALAND JOURNAL OF PUBLIC HEALTH, Issue 1 2010Benjamin Cowie Abstract Objective: Estimating the prevalence of chronic hepatitis B virus (HBV) infection in generally low-prevalence populations containing communities with a higher disease burden is difficult. This study was conducted to estimate the prevalence of serological markers of infection with, and immunity to, HBV in the Victorian population and to analyse trends in these estimates over time. Methods: A serological survey of 3,212 samples of convenience collected in the years 1995, 2000 and 2005 was conducted using a selection procedure designed to reduce selection bias. All samples were tested for hepatitis B surface and core antibodies; all core antibody positive samples (indicating previous infection) were then tested for the presence of hepatitis B surface antigen (HBsAg). Results: HBsAg prevalence was 1.1% (95%CI 0.8-1.6%) with significant differences observed by area of residence, age, gender and test year. Serological evidence of immunisation in infants and adolescents were lower than established estimates following the introduction of universal vaccination for these groups. Conclusions: This study emphasises the significant and growing problem of chronic HBV infection in Victoria and suggests lower than expected population immunity deriving from universal vaccination programs. Implications: Greater efforts are needed to formulate a comprehensive public health response to address this relatively neglected blood borne viral infection, the burden of which is very significant in some marginalised sections of our community. Increased attention to improving the universality of our immunisation programs is also needed. [source] | ||||||||||