In vivo and in vitro models show unexpected degrees of virulence among Toxoplasma gondii type II and III isolates from sheep

Open Access

Abstract

15 páginas, 5 figuras, 2 tablas. ; Toxoplasma gondii is an important zoonotic agent with high genetic diversity, complex epidemiology, and variable clinical outcomes in animals and humans. In veterinary medicine, this apicomplexan parasite is considered one of the main infectious agents responsible for reproductive failure in small ruminants worldwide. The aim of this study was to phenotypically characterize 10 Spanish T. gondii isolates recently obtained from sheep in a normalized mouse model and in an ovine trophoblast cell line (AH-1) as infection target cells. The panel of isolates met selection criteria regarding such parameters as genetic diversity [types II (ToxoDB #1 and #3) and III (#2)], geographical location, and sample of origin (aborted foetal brain tissues or adult sheep myocardium). Evaluations of in vivo mortality, morbidity, parasite burden and histopathology were performed. Important variations between isolates were observed, although all isolates were classifed as "nonvirulent" (<30% cumulative mortality). The isolates TgShSp16 (#3) and TgShSp24 (#2) presented higher degrees of virulence. Signifcant diferences were found in terms of in vitro invasion rates and tachyzoite yield at 72 h post-inoculation (hpi) between TgShSp1 and TgShSp24 isolates, which exhibited the lowest and highest rates, respectively. The study of the CS3, ROP18 and ROP5 loci allelic profles revealed only type III alleles in ToxoDB #2 isolates and type II alleles in the #1 and #3 isolates included. We concluded that there are relevant intraand inter-genotype virulence diferences in Spanish T. gondii isolates, which could not be inferred by genetic charac‑terization using currently described molecular markers. ; This research was supported by projects funded by the Spanish Ministry of Science and Innovation (AGL2016-75935-C2-R) and the Community of Madrid (PLATESA2-CMP2018/BAA-4370). MF-E was funded by UCM-Santander/2017 pre-doctoral Grants. RC-B, EC-F, and LO-M are part of the TOXOSOURCES con‑ sortium supported by the funding from the European Union's Horizon 2020 Research and Innovation Programme under the Grant Agreement No 773830: One Health European Joint Programme.