Category Criteria
Level 1 Study quickly terminated by euthanasia, prior to any clinical signs of disease or distress.
Level 2 Comparative study; experimental groups given novel drugs or vaccines compared with positive ‘‘gold-standard’’ controls. Non-lethal infection with only transient mild symptomology. Probably lethal infections terminated before the onset of the most debilitating symptoms.
Level 3 Studies resulting in lasting deleterious effects on animal health and welfare, not alleviated by means of refinement.
Level 4 All studies having spontaneous death or ‘‘moribund’’ state as experimental endpoints and/or resulting in severe distress non-alleviated by means of refinement.
* It is adapted from Ref. 14.
Table 1: Severity classification of experimental studies on murine tuberculosis.*