Prevalence and Demographic Risk Factors of Mycobacterium tuberculosis Infections in Captive Asian Elephants (Elephas maximus) Based on Serological Assays

Taweepoke Angkwanish; Hans J C M Vernooij; Anucha Sirimalaisuwan; Pattara Charernpan; Mirjam Nielen; Victor P M G Rutten

doi:10.3389/fvets.2021.713663

Prevalence and Demographic Risk Factors of Mycobacterium tuberculosis Infections in Captive Asian Elephants (Elephas maximus) Based on Serological Assays

Front Vet Sci. 2021 Nov 2:8:713663. doi: 10.3389/fvets.2021.713663. eCollection 2021.

Authors

Taweepoke Angkwanish^{1

2}, Hans J C M Vernooij³, Anucha Sirimalaisuwan⁴, Pattara Charernpan³, Mirjam Nielen⁵, Victor P M G Rutten^{1

6}

Affiliations

¹ Department Biomolecular Health Sciences, Division Infectious Diseases and Immunology, Section Immunology, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
² National Elephant Institute, Forest Industry Organization, Lampang, Thailand.
³ Department Population Health Sciences, Division Farm Animal Health, Faculty of Veterinary Medicine, Utrecht University, Utrecht, Netherlands.
⁴ Center of Excellence in Elephant and Wildlife Research, Faculty of Veterinary Medicine, Chiang Mai University, Chiang Mai, Thailand.
⁵ National Elephant Research and Health Services, Department of Livestock Development, Bangkok, Thailand.
⁶ Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Pretoria, South Africa.

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.

Keywords: Asian elephant; ELISA; TB Stat-Pak; latent class analysis; prevalence; risk factors; serology; tuberculosis.