Toxoplasma gondii

Gamble, Amandine, Ramos, Raül, Parra-Torres, Yaiza, Mercier, Aurélien, Galal, Lokman, Pearce-Duvet, Jessica, Villena, Isabelle, Montalvo, Tomás, González-Solís, Jacob, Hammouda, Abdessalem, Oro, Daniel, Selmi, Slaheddine & Boulinier, Thierry, 2019, Exposure of yellow-legged gulls to Toxoplasma gondii along the Western Mediterranean coasts: Tales from a sentinel, International Journal for Parasitology: Parasites and Wildlife 8, pp. 221-228 : 223

2.2. Anti-T. gondii antibody detection

Specific antibody levels were measured in yolk samples to infer the past exposure of breeding females to T. gondii using a commercially available indirect enzyme-linked immunosorbent assay (ELISA) designed to detect chicken IgY directed against the T. gondii p30 antigen (ID Screen ª Avian Toxoplasmosis Indirect, IDvet, France). This study is the first to investigate the detection of anti- T. gondii antibodies in gull egg yolk samples, and one of the few to investigate their detection in seabirds in general (Dubey, 2002 for a review). We thus included several validation procedures on a subset of samples in our laboratory analyses. Notably, as no gold standard is available for the detection of anti- T. gondii antibodies in wild birds, a second assay was run on a subset of samples (Enøe et al., 2000). The MAT was chosen as it is frequently used for T. gondii serosurveys, notably in wild birds (Cabezón et al., 2016; Sandström et al., 2013), although, to our knowledge, it has never been used on egg yolk samples before. Details are presented in the supplementary material (Appendix A). Overall, the ELISA was proven repeatable at a much higher level than the MAT at the sample scale (i.e., repeated analyses conducted on a given sample). At the nest scale (i.e., repeated sampling of eggs from a given nest), the detection probability was suitable. In addition, the ELISA and the MAT lead to the same prevalence of specific antibodies at the colony scale. These results are in line with previous studies suggesting that ELISA are generally suitable to detect anti- T. gondii antibodies in domestic and wild animals (e.g., Dubey et al., 2005; Gamble et al., 2005). Plasma samples from necropsied individuals were analysed by MAT with positivity threshold at dilution 1/20.