Abstract:
To address putative TB statuses of elephants and to identify and quantify potential
demographic risk factors for TB, three ELISAs specific for different mycobacterial
antigens (ESAT6, CFP10, MPB83) and the TB Stat-Pak assay were used as surrogate
serological markers for TB infection in elephants. In view of the low number of animals
of which the infected status could be confirmed (4 out of 708) Latent Class Analyses of
TB serology test outcomes was used to predict the putative TB status of each of 708
elephants as positive (17.3%), inconclusive (48.7%), or negative (34%) when assessed
on a population basis. Correlation between test performance of the individual assays
was high between the ELISAs, but low with that of the TB Stat-Pak assay. Risk factors,
assessed based on cut off values for each of the ELISAs determined by ROC analysis,
included sex, BCS, age, working time, feed type, management system, camp size and
region. Old age elephants were more likely to show a positive TB serology test outcome,
than younger ones. Elephants working 7 h per day and the ones in good condition BCS
(7–11) were less likely to be positive in TB serology testing. In addition, fewer animals in
the large camp size (31–50 elephants) were found to be positive in ELISA tests, compared
to elephants in the other camp sizes. In this study, the North region had the lowest
percentages of elephants with positive TB test outcome, the West region and to a lesser
extend the other regions showed clearly higher percentages of positive animals. Even
though assays used in the present study have not been validated yet, results obtained
showed promise as diagnostic or screening tests. For the diagnosis of animals suspected
to be infected, the ELISA tests, once further optimized for the individual antigens, can be
used in parallel. For screening of complete camps for presence or absence of infection,
a single optimized ELISA test can be utilized.
