[  Production, Characterization and Applications for Toxoplasma gondii-Specific Polyclonal Chicken Egg Yolk Immunoglobulins BACKGROUND: Toxoplasma gondii may cause abortions, ocular and neurological disorders in warm-blood hosts. Immunized mammals are a wide source of hyperimmune sera used in different approaches, including diagnosis and the study of host-parasite interactions. Unfortunately, mammalian antibodies present limitations for its production, such as the necessity for animal bleeding, low yield, interference with rheumatoid factor, complement activation and affinity to Fc mammalian receptors. IgY antibodies avoid those limitations; therefore they could be an alternative to be applied in T. gondii model. METHODOLOGY/PRINCIPAL FINDINGS: In this study we immunized hens with soluble tachyzoite antigens of T. gondii (STAg) and purified egg yolk antibodies (IgY) by an inexpensive and simple method, with high yield and purity degree. IgY anti-STAg antibodies presented high avidity and were able to recognize a broad range of parasite antigens, although some marked differences were observed in reactivity profile between antibodies produced in immunized hens and mice. Interestingly, IgY antibodies against Neospora caninum and Eimeria spp. did not react to STAg. We also show that IgY antibodies were suitable to detect T. gondii forms in paraffin-embedded sections and culture cell monolayers. CONCLUSIONS/SIGNIFICANCE: Due to its cost-effectiveness, high production yield and varied range of possible applications, polyclonal IgY antibodies are useful tools for studies involving T. gondii. Toxoplasma gondii is a well-adapted parasite of warm-blooded hosts, including human and production animals. The parasite has distinct developmental stages, such as the fast-replicating tachyzoites that are present in the acute phase of infection, while the slow-replicating bradyzoites form tissue cysts in muscular and nervous tissues during the chronic phase of infection [1] [2] . Infection usually takes place after accidental ingestion of raw or undercooked meat containing tissue cysts, oocyst-contaminated food or water, and by transplacental passage of tachyzoites in active infection during the gestational period [3] [4] . Congenital infection may lead to neurological disorders, ocular disease and/or fetal death [5] . T. gondii is also a major cause of infectious abortion and induces clinical disease in production animals, especially goat, sheep and swine, elevating production costs and resulting in considerable impact on the livestock industry as well as the public health [6] .