Tuberculosis surveillance of elephants (Elephas maximus) in Nepal at the captive-wild interface

Abstract

A comprehensive elephant tuberculosis (TB) survey using culture and four serological screening tests was conducted in Nepal in response to concern raised by wildlife officials that TB could threaten wild populations of elephants, rhinos, and other susceptible species. Captive elephants come into close contact with wild animals during conservation and tourism activities inside Nepal's national parks. Private and government-owned male and female captive Asian elephants (Elephas maximus) were included in the study. The mean reported age was 38 years (range 5-60 years). A total of 289 samples from 120 elephants were collected for mycobacterial culture. Culture samples were processed at the National Tuberculosis Centre (NTC) in Nepal and the National Veterinary Services Laboratories (NVSL) in Ames, IA. Acid-fast organisms were observed in 11 and 21 samples processed at NTC and NVSL, respectively, and nontuberculous mycobacteria (NTMs) were isolated from six elephants. There were no isolations of Mycobacterium tuberculosis or Mycobacterium bovis. Blood samples were also collected from 115 of the elephants for serological testing using the Chembio ElephantTB STAT-PAK®, the Chembio MultiAntigen Print Immunoassay test, a multi-antigen ELISA, and an immunoblot assay. Culture and serological results were variable and required careful interpretation to develop criteria to assess TB risk. Elephants were assigned to one of four disease risk groups (high, moderate, low, and undetermined), and management recommendations for each group were made to government authorities. Serological results were prioritized in developing recommendations because of culture limitations and inconclusive culture results. This strategy was based on evidence for the early predictive value of serological tests and the urgent need expressed by wildlife authorities in Nepal to protect their captive elephants, mitigate TB at the captive-wild interface, and safeguard tourism.

Serum Health Biomarkers in African and Asian Elephants: Value Ranges and Clinical Values Indicative of the Immune Response

“…Elephants are also susceptible to infection with Mycobacterium tuberculosis , the same causative agent as that for human tuberculosis (TB). Around 10% of elephants currently residing in North America have tested positive for TB, with cases also identified in Europe [ 39 , 40 ], Australasia [ 41 ], Africa [ 42 , 43 ], and Asia [ 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. Although active disease can be detected via culturing trunk secretions, it is not possible to diagnose subclinical infection with current methodologies.…”

Fatal Tuberculosis in a Free-Ranging African Elephant and One Health Implications of Human Pathogens in Wildlife

“…For example, in the Malaysian peninsula, elephants had a seroprevalence of 20.4% and their handlers, tested with an interferon-gamma release assay, had a prevalence of 24.8% (33). Similarly, 13% of Nepal's and 15% of India's captive elephant populations were seropositive in recent surveys (35, 51, 54). High prevalence in these populations highlights the significant risk that humans present to captive and, potentially, free-ranging wildlife at interfaces.…”

“…Wildlife TB is recognized as a serious barrier to animal conservation efforts in South-East Asia (49). This threat to human, captive and free-ranging wildlife health is a growing concern globally (50), with the significance of this problem shown by the Government of Nepal's endorsement of The Nepal Elephant Tuberculosis Control and Management Action Plan (2011–2015) (51). Emerging diseases with potential to affect multiple species are of particular concern since wildlife may become reservoirs that impact domestic animal and human health, and biodiversity (52).…”

Diagnosis of tuberculosis in wildlife: a systematic review

“…In addition, the decontamination step prior to MTC culture can adversely affect the viability of mycobacteria, especially when the number of viable microorganisms is low, and it may, therefore, lead to false negative results in the culture [ 24 ]. In elephants, trunk wash culture is the officially recommended ante-mortem diagnostic test in USA [ 10 ], but the contamination by other pathogens is a major problem [ 48 ]. The Se of culture and isolation varies depending on the stage of the disease (latent or noticeable), the number and selection of tissues processed and on the sample quality [ 49 ].…”