Understanding Mycobacterium tuberculosis complex in elephants through a One Health approach: a systematic review

Abstract

Background Mycobacterium tuberculosis complex (MTC) that causes the chronic infectious disease- tuberculosis (TB), often presents with a complicated epidemiological pattern where the transmission chain may include humans, domestic animals and wildlife, including elephants. TB has been reported globally in both captive and wild elephants. The One Health approach might be the most effective way of understanding the shared MTC infection dynamics in captive and wild animals like Asian elephants. This systematic review accumulates evidence on occurrence, transmission pathways, and preventive measures of TB in elephants from a One Health perspective. Results The prevalence of TB reported in elephant populations ranges from 0 to 23.33% and high prevalence’s are reported for elephants that are in close proximity to infected humans. The risk of elephant to human infection transmission increased significantly with exposure duration and contact with infected elephants. Some studies described the plausible TB transmission to captive elephants from other animals (wild and domestic), suggesting inter- and intra-species transmission. The results of this systematic review based on 27 relevant published works, suggest three overarching interrelated transmission pathways for M. tuberculosis infections in Asian elephants- i) humans and elephants, ii) other animals (wild or domestic) and elephants and iii) unclear sources of infection. Conclusions The progress made with new TB diagnostic tools provides multiple methods to choose from. However, lack of harmonization of TB testing in elephants and their human contacts remains a challenge to prevent TB in those animals. Routine TB screening among elephants and caretakers by setting up an occupational health program for early diagnosis of infection through combined efforts of public health, veterinary medicine, and occupational health experts is suggested. This implies the need for a One Health approach to elephant TB control. This review reveals the need for more research on Mycobacterium tuberculosis complex transmission pathways at the human-animal interface.

Genomic insights into anthropozoonotic tuberculosis in captive sun bears (Helarctos malayanus) and an Asiatic black bear (Ursus thibetanus) in Cambodia

“…Case E1’s history of living within a city household, along with disease onset so soon after arrival, suggests this bear was the index case in the Lineage 1 outbreak, and highlights the risk to bear sanctuaries receiving bears with a history of co-habiting with humans. Given the anthropozoonotic spread of TB in other species with human contact 17 , 20 , 42 , along with the high numbers of sun bears and Asiatic black bears held in captivity (legally and illegally) in high TB burden regions 56 – 60 , it is surprising this is the first report of incidental spill-over from humans to these species. Regardless, our findings confirm that both bear species are susceptible to human lineages of M. tuberculosis and should inform sanctuary disease screening strategies.…”

Elephant tourism: An analysis and recommendations for public health, safety, and animal welfare

“…TB among captive elephant populations is investigated using several methodologies, for example, blood serum sampling and lateral flow serological testing [112] and/or collection of material through trunk washing, culture, and PCR testing [113]. However, current methodologies are limited, and infection rates in populations are difficult to quantify conclusively [114,115]. One study, using blood serum sampling of approximately 600 captive Asian elephants found a positive TB prevalence rate of 16% [112], and another study, also using serology, found 23% in a captive population [22].…”

Short-read full-length 16S rRNA amplicon sequencing for characterisation of the respiratory bacteriome of captive and free-ranging African elephants (Loxodonta africana)

“…In addition, there are approximately 126 captive or managed African elephants reported in South Africa 4 . These elephant populations face further threats from infectious pathogens, such as elephant endotheliotropic herpesvirus (EEHV) 5 and tuberculosis (TB) 6 – 8 . The presence of disease in these populations can lead to detrimental consequences for the maintenance of a stable ecological niche 9 .…”