24 research outputs found
Vaccines against toxoplasma gondii : challenges and opportunities
Development of vaccines against Toxoplasma gondii infection in humans is of high priority, given the high burden of disease in some areas of the world like South America, and the lack of effective drugs with few adverse effects. Rodent models have been used in research on vaccines against T. gondii over the past decades. However, regardless of the vaccine construct, the vaccines have not been able to induce protective immunity when the organism is challenged with T. gondii, either directly or via a vector. Only a few live, attenuated T. gondii strains used for immunization have been able to confer protective immunity, which is measured by a lack of tissue cysts after challenge. Furthermore, challenge with low virulence strains, especially strains with genotype II, will probably be insufficient to provide protection against the more virulent T. gondii strains, such as those with genotypes I or II, or those genotypes from South America not belonging to genotype I, II or III. Future studies should use animal models besides rodents, and challenges should be performed with at least one genotype II T. gondii and one of the more virulent genotypes. Endpoints like maternal-foetal transmission and prevention of eye disease are important in addition to the traditional endpoint of survival or reduction in numbers of brain cysts after challenge
A new equation to predict the shear strength of recycled aggregate concrete Z push-off specimens
This article investigates the shear behaviour of Recycled Aggregate Concrete (RAC) Z push-off specimens. Fifteen specimens with different replacement levels of recycled concrete aggregate (RCA = 0 %, 25 %, 50 %, 75 % and 100 %) were tested. It is shown that a 100 % RCA replacement level reduces shear strength by 17.3 %. The shear behaviour of the specimens was further analysed using nonlinear finite element analysis (FEA). The results show that the shear strength results from the FEA and Digital Image Correlation measurements agree well (within 5 %) with the experimental results. This study proposes a new semi-empirical equation to calculate the shear strength of specimens with different RCA replacement levels. The new equation adopts a fracture mechanics approach, and it explicitly considers the shear slip deformation and crack opening. Compared to existing models, the new equation fits better the experimental data in this study, as well as test results from an extensive database obtained from the literature