The EG95 Antigen of Echinococcus spp. Contains Positively Selected Amino Acids, which May Influence Host Specificity and Vaccine Efficacy

Echinococcosis is a worldwide zoonotic parasitic disease of humans and various herbivorous domestic animals (intermediate hosts) transmitted by the contact with wild and domestic carnivores (definitive hosts), mainly foxes and dogs. Recently, a vaccine was developed showing high levels of protection against one parasite haplotype (G1) of Echinococcus granulosus, and its potential efficacy against distinct parasite variants or species is still unclear. Interestingly, the EG95 vaccine antigen is a secreted glycosylphosphatydilinositol (GPI)-anchored protein containing a fibronectin type III domain, which is ubiquitous in modular proteins involved in cell adhesion. EG95 is highly expressed in oncospheres, the parasite life cycle stage which actively invades the intermediate hosts. After amplifying and sequencing the complete CDS of 57 Echinococcus isolates belonging to 7 distinct species, we uncovered a large amount of genetic variability, which may influence protein folding. Two positively selected sites are outside the vaccine epitopes, but are predicted to alter protein conformation. Moreover, phylogenetic analyses indicate that EG95 isoform evolution is convergent with regard to the number of beta-sheets and alpha-helices. We conclude that having a variety of EG95 isoforms is adaptive for Echinococcus parasites, in terms of their ability to invade different hosts, and we propose that a mixture of isoforms could possibly maximize vaccine efficacy

Antibody responses and epitope specificities to the Taenia solium cysticercosis vaccines TSOL18 and TSOL45-1A

Taenia solium is a cestode parasite that causes cysticercosis in humans and pigs. This study examined the antibody responses in pigs immunized with the TSOL18 and TSOL45-1A recombinant vaccines against T. solium cysticercosis. Immunization with these proteins induced specific, complement-fixing antibodies against the recombinant antigens that are believed to be associated with vaccine-induced protection against T. solium infection. Sera from immunized pigs were used to define the linear B-cell epitopes of TSOL18 and TSOL45-1A. Prominent reactivity was revealed to one linear epitope on TSOL18 and two linear epitopes on TSOL45-1A. These, and oncosphere antigens from other taeniid cestodes, contain a protein sequence motif suggesting that they may show a tertiary structure similar to the fibronectin type III domain (FnIII). Comparison of the location of linear antigenic epitopes in TSOL18 and TSOL45-1A within the proposed FnIII structure to those within related cestode vaccine antigens reveals conservation in the positioning of the epitopes between oncosphere antigens from different taeniid species