Tuberculosis in Asian Elephants: Interpreting Screening Results in Context

Tuberculosis surveillance in elephants presents a fundamental diagnostic challenge: a test result is evidence, but it is not the diagnosis on its own. 

This distinction is particularly important in India, where Mycobacterium tuberculosis infection has been documented in both captive and free-ranging Asian elephants. 

A positive screening result answers only one part of the question 

A screening test may indicate that further investigation is warranted, but its interpretation depends on what the test was designed to detect. 

An evaluation of tuberculosis serodiagnostic tests in captive elephants in southern India found substantial variation in the estimated sensitivity and specificity of the assays assessed^[1]. The investigators used latent-class analysis because no perfect reference standard was available for determining infection status under the field conditions^[1]. 

The practical implication is clear: a positive screening result should not automatically be interpreted as confirmation of active tuberculosis. 

Similarly, a negative screening result should not be interpreted as absolute exclusion of infection, particularly when clinical findings or epidemiological circumstances raise concern. 

The next question should therefore be: 

What additional evidence is needed to understand what this result means for this elephant? 

Start with the elephant’s clinical and epidemiological context 

A screening result becomes more informative when considered alongside the individual animal’s circumstances. 

Relevant information may include: 

• Current clinical findings; 
• Previous tuberculosis test results; 
• Known or suspected contact with infected animals or people; 
• Duration and nature of human contact; 
• History of respiratory or systemic illness; 
• Findings from other elephants in the same facility; 
• Previous microbiological investigations. 

This approach is particularly important because M. tuberculosis has been documented in free-ranging Asian elephants in southern India. 

Cases from Karnataka have provided microbiological, molecular and pathological evidence of M. tuberculosis infection in wild elephants^[2],[3]. 

These reports demonstrate that tuberculosis surveillance is not relevant only to captive-elephant collections. 

However, the detection of M. tuberculosis in an elephant does not establish the direction of transmission in an individual case^[2],[3]. 

The human–elephant interface may be epidemiologically relevant, particularly where prolonged close contact occurs, but assumptions about source or direction of transmission require appropriate evidence. 

Understand what the screening method has been evaluated to do 

A 2024 Indian study evaluated a Dot ELISA for tuberculosis screening in Asian elephants using samples from animals classified as positive or negative based on available culture, PCR, serological and post-mortem findings^[4]. 

The value of such research extends beyond the performance of one assay. 

It highlights an essential question for every surveillance programme: 

What evidence was used to evaluate this test, and what does a positive or negative result actually represent? 

A screening test may contribute useful information about the likelihood of infection or exposure, but its interpretation should remain consistent with the test's intended purpose and the population in which it is being used. 

Avoid interpreting results in isolation 

A tuberculosis surveillance programme is stronger when individual results can be reviewed alongside previous findings and the broader epidemiological situation. 

Depending on the circumstances, interpretation may require consideration of: 

• The type of screening assay used; 
• Previous results from the same elephant; 
• Changes in clinical status; 
• Contact and exposure history; 
• Findings among other elephants or relevant human contacts; 
• Appropriate additional microbiological, molecular or pathological investigations when available. 

The purpose is not to create an unnecessarily complex testing pathway for every elephant. 

It is to avoid making major clinical, management or public-health decisions based on a screening result without understanding its limitations. 

A changing result requires interpretation, not assumption 

When results differ between testing occasions or methods, the discrepancy itself may provide useful information—but it does not automatically identify which result is correct. 

Differences may arise from variation in the biological response being measured, the diagnostic method, the timing of testing or other factors affecting interpretation. 

A changed result should therefore prompt a review of the elephant's clinical and epidemiological circumstances and, where appropriate, consideration of additional diagnostic evidence. 

The aim is to resolve uncertainty systematically rather than simply choosing the result that appears most convenient. 

Clinical takeaway 

Tuberculosis screening should be interpreted within a diagnostic and epidemiological framework, not as a binary exercise in which one positive result automatically means active disease. 

A useful assessment considers what the test measures, how the result has changed over time, the elephant's clinical status and its potential epidemiological exposures. 

This approach supports more responsible elephant management while avoiding both unnecessary assumptions about infection and false reassurance from an isolated negative result.

References:

1. Verma-Kumar S, Abraham D, Dendukuri N, Cheeran JV, Sukumar R, Balaji KN. Serodiagnosis of tuberculosis in Asian elephants (Elephas maximus) in Southern India: a latent class analysis. PLoS One. 2012;7(11):e49548. https://doi.org/10.1371/journal.pone.0049548
2. Zachariah A, Pandiyan J, Madhavilatha GK, et al. Mycobacterium tuberculosis in Wild Asian Elephants, Southern India. Emerg Infect Dis. 2017;23(3):504-506. https://doi.org/10.3201/eid2303.161741
3. Chandranaik BM, Shivashankar BP, Umashankar KS, et al. Mycobacterium tuberculosis Infection in Free-Roaming Wild Asian Elephant. Emerg Infect Dis. 2017;23(3):555-557. https://doi.org/10.3201/eid2303.161439
4. Abraham, D., Ravishankar, C., Deepa, P.M., Sumod, K., Bipin, K.C, Rajani, C.V. and Vijayakumar K. 2024. Evaluation of a Dot ELISA for tuberculosis screening in Asian elephants (Elephas maximus). J. Vet. Anim. Sci. 55(2):465-470. https://doi.org/10.51966/jvas.2024.55.2.465-470