Table 1.
Summary of non-lethal parameters for the assessment of in vivo virulence of Toxoplasma gondii strains (ordered by reliability and informativeness).
| Parameters evaluated | Sample to be tested | Method of evaluation | Information gathered/represented | Key references |
|---|---|---|---|---|
| Parasite load in tissues | Both parenchymatous and non- parenchymatous organs (brain-chronic phase, lungs-acute phase) | qPCR | Number of parasites/mg of tissue | Hill and Su, 2012; Fernández-Escobar et al., 2021; Salman et al., 2021 |
| Cystogenic capacity | Parenchymatous organs (brain) | Immunostaining | Number of tissue cysts/field-section | Masatani et al., 2020 |
| Direct counting in brain homogenates | Number of tissue cysts/mg of tissue or by whole organ | Wang and Sibley, 2020 | ||
| Morbidity and survival time | None | Animal monitoring by daily direct observation with clinical signs scoring* | Cumulative morbidity rate calculation, survival time | Fernández-Escobar et al., 2020 |
| Histological lesions | Both parenchymatous and non-parenchymatous organs (brain and striated muscle-chonic phase, lungs-acute phase) | H&E staining, IHC, light microscopy | Frequency and severity of the lesions Presence/absence of parasites. Scoring needs to be implemented | Chiebao et al., 2021; Fernández-Escobar et al., 2021 |
| Cytokines expression | Tissues (spleen, mesenteric lymph nodes) | mRNA expression by RT-qPCR | Cytokines profile (Fold change; Ct values) | Chiebao et al., 2021 |
| Serum | ELISA | Serum level | Araujo and Slifer, 2003 | |
| Haptoglobin levels in acute phase | Serum | Electroimmunoassay; ELISA | Serum level | Jensen et al., 1998; Jungersen et al., 1999; Jungersen et al., 2002 |
| Antibody levels (IgG) | Serum, plasma and whole blood | ELISA, IFAT, MAT | Serum level | Yang et al., 2021 |
| Behavioural changes | None | Image monitoring | Scoring needed | Bezerra et al., 2019 |
*Humane endpoints need to be set. IHC, immunohistochemistry.