Tuberculosis at the human–animal interface: An emerging disease of elephants

Summary

Over the past 15 years, cases of infection with organisms of the Mycobacterium tuberculosis complex have been diagnosed among captive elephants in the United States and worldwide. Outbreak investigations have documented that among staff employed at facilities housing infected animals, skin test conversion to purified protein derivative have been documented. Clonal spread among animals in close contact and even inter-species spread between elephant and human has been documented. Detection of actively infected animals relies on samples obtained by trunk wash. Diagnosis has been augmented by the development of a multi-antigen serologic assay with excellent specificity and sensitivity. Treatment regimens are still in development with efficacy largely unknown due to a paucity of both premortem follow-up and necropsy data of treated animals. The epidemiology, diagnosis and treatment of tuberculosis in elephants require additional careful study of clinical data.

Introduction

Over the past 2 decades, tuberculosis (TB) has seen a resurgence initially associated with the epidemic of human immunodeficiency virus (HIV) infection and more recently with the emergence of multi-drug resistant (MDR) and extremely drug resistant (XDR) strains. Surprisingly overlooked in the fight against TB is the potential for transmission at the human–animal interface.¹ This interface includes not only domestic livestock such as cattle and buffalo but also non-human primates, elephants, and other species that interact with people in zoos, circuses, temples, and tourist facilities around the world and that represent potential reservoirs of both drug-susceptible and resistant strains of TB. In fact, the isolation of MDR-TB from an elephant in the United States (U.S.)²⁷ highlights what was heretofore a theoretical concern in the nation’s population of approximately 450 elephants.

While elephants are maintained in many zoos and circuses worldwide, Asia in particular hosts a large population of captive elephants including 3400–3600 in India alone.² Reports from India, Sri Lanka, and other Asian countries indicate that TB is not an unusual finding on post-mortem examination in captive elephants.3, 4 Moreover, unofficial reports from Asia and the U.S. indicate that some elephants with apparent active disease have been treated with short courses using single anti-mycobacterial drug regimens at doses that would be considered ineffective to achieve therapeutic serum levels creating the potential for drug resistance.

The pathogenesis of human TB has been studied for many centuries with the introduction of drug treatment in the 1940’s. In contrast, TB in elephants has been studied for only 14 years with limited, poorly funded research and reluctance to publish and/or share data.

While inter-species transmission of TB between elephants and humans has been described,¹ and public health evaluations have documented a risk for human exposure from infected elephants,1, 5, 6 the risk to animal handlers or to the general public of acquiring TB from non-humans is incompletely understood.