Combining Analytical Approaches and Multiple Sources of Information to Improve Interpretation of Diagnostic Test Results for Tuberculosis in Wild Meerkats

Abstract

Diagnostic tests are used to classify individual animals’ infection statuses. However, validating test performance in wild animals without gold standard tests is extremely challenging, and the issue is further complicated in chronic conditions where measured immune parameters vary over time. Here, we demonstrate the value of combining evidence from different diagnostic approaches to aid interpretation in the absence of gold standards, large sample sizes, and controlled environments. Over a two-year period, we sampled 268 free-living meerkats (Suricata suricatta) longitudinally for Mycobacterium suricattae (a causative agent of tuberculosis), using three ante-mortem diagnostic tests based on mycobacterial culture, and antigen-specific humoral and cell-mediated immune responses, interpreting results both independently and in combination. Post-mortem cultures confirmed M. suricattae infection in 22 animals, which had prior ante-mortem information, 59% (13/22) of which were test-positive on a parallel test interpretation (PTI) of the three ante-mortem diagnostic assays (95% confidence interval: 37–79%). A similar ability to detect infection, 65.7% (95% credible interval: 42.7–84.7%), was estimated using a Bayesian approach to examine PTI. Strong evidence was found for a near doubling of the hazard of death (Hazard Ratio 1.75, CI: 1.14–2.67, p = 0.01), associated with a positive PTI result, thus demonstrating that these test results are related to disease outcomes. For individual tests, small sample sizes led to wide confidence intervals, but replication of conclusions, using different methods, increased our confidence in these results. This study demonstrates that combining multiple methodologies to evaluate diagnostic tests in free-ranging wildlife populations can be a useful approach for exploiting such valuable datasets.

Two decades of tuberculosis surveillance reveal disease spread, high levels of exposure and mortality and marked variation in disease progression in wild meerkats

“…If individuals had records of suspected TB, that is, lumps or swelling with no alternative explanation, and progressed to develop clinical TB, the date of first putative TB signs was considered as onset of clinical TB. Clearance of clinical TB has not been recorded in meerkats, so we considered infections to be purely progressive with no return to prior states (Patterson et al., 2021). Within KMP, terminally ill individuals were euthanized to curb the spread of the disease (Duncan et al., 2021; Patterson et al., 2021), with infections being confirmed in post‐mortem examinations (Patterson et al., 2021).…”

“…We classified these individuals as having died of TB and included them in our data set of TB progression (see Table 2), as terminally ill individuals do not recover and are expected to die within a few days or weeks (Patterson et al, 2021). To be conservative in our interpretations, individuals displaying clinical signs at time of death but dying of other or unknown causes (e.g.…”

“…Individuals clinically ill with TB but dying of other causes are not included here. recorded in meerkats, so we considered infections to be purely progressive with no return to prior states (Patterson et al, 2021). Within KMP, terminally ill individuals were euthanized to curb the spread of the disease (Duncan et al, 2021;Patterson et al, 2021), with infections being confirmed in post-mortem examinations (Patterson et al, 2021).…”

Trait-Based Vaccination of Individual Meerkats (Suricata suricatta) against Tuberculosis Provides Evidence to Support Targeted Disease Control

“…Parallel test interpretation was used based upon previous analysis of the available diagnostic tests [ 41 ]. An individual was classified as test positive if it fulfilled one or more of the following criteria: (i) The IPRA result, being the difference in optical density between a peptide-stimulated and a control sample (OD PCHP-nil ), was greater than 0.038 [ 36 ]; (ii) The test line intensity was greater than 5.0 Reflective Light Units (RLU) using DPP serology [ 42 ]; or (iii) M. suricattae was cultured and confirmed by PCR from a tracheal lavage sample [ 35 ].…”

Climate change and tuberculosis drive non-adaptive shifts in the faecal microbiota of wild meerkats

“…1c;,30 . Once clinical disease manifests, individuals rapidly lose condition and generally reach terminal stages in approximately four to seven months 30,35 .…”