Serial Interferon-Gamma Release Assay (IGRA) Testing to Monitor Treatment Responses in Cases of Feline Mycobacteriosis

The interferon-gamma release assay (IGRA) is used to diagnose cases of feline mycobacteriosis, but the use of serial testing to monitor treatment responses has not been evaluated in this species. From a population of cats that underwent IGRA testing for diagnostic investigation, individuals were identified with a pre- and end-of-treatment IGRA that passed control thresholds. The number of cats which reverted to negative at the end-of-treatment IGRA, changes in paired antigen-specific optical density (OD) values and differences in the pre-treatment antigen-specific OD values for those which underwent reversion were compared. Factors to explain reversion or recurrence of disease post-treatment were explored. Four of 18 cats (22%) reverted to negativity at the point of clinical resolution (p = 0.33), there was no difference in paired antigen-specific OD values (p ≥ 0.12), and cats that reverted did not have a lower baseline OD value (p = 0.63). No statistically significant factors were identified to predict reversion (p ≥ 0.08). Remaining positive at the end of treatment IGRA was not associated with recurrence of disease post-treatment (p = 0.34). Overall, these data suggest there is limited value in the use of the IGRA to monitor treatment responses in cats.