November 18, 2021

NIOSH Recommends Controls to Protect Zoo Staff from Elephant-transmitted TB

A NIOSH Health Hazard Evaluation (HHE) report published in October (PDF) describes recommendations for preventing the transmission of tuberculosis (TB) bacteria from elephants to staff members of a zoological park. NIOSH began its investigation after eight employees who worked primarily in the elephant area tested positive for TB infection in September 2019. Testing in November that year confirmed that both elephants had TB.

TB is caused by Mycobacterium tuberculosis bacteria that most often infects the lungs in both humans and animals. A person or animal may not show disease symptoms for years after infection, a condition known as latent TB infection. Individuals with LBTI cannot spread the bacteria to others, but about one in 10 people with LBTI will go on to develop infectious, symptomatic TB disease in the future.

The eight employees who received positive TB blood test results were diagnosed with LBTI and treated with antibiotics. An additional keeper tested positive after the NIOSH team’s visit. All affected employees worked in the elephant barn at least occasionally.

A few months after the employees’ initial LBTI diagnoses, M. tuberculosis was isolated in cultures of trunk wash specimens taken from both animals. The zoo administration determined that the elephants were the probable source of infection.

TB in elephants, as in humans, can be treated with antibiotics. But due to concerns about noncompliance from the animals, the large amount of medication required, animal and human welfare, and antibiotic-resistant TB development, the lead zoo veterinarian, in consultation with zoo administration and local public health officials, initially determined not to treat the elephants. One elephant was later euthanized due to health issues unrelated to TB. The zoo then attempted to treat the remaining elephant, but treatment was discontinued due to the animal’s noncompliance and the severe side effects of treatment.

NIOSH’s team recommended that the zoo cease all nonessential tasks performed in the elephant barn and remove all nonessential items and personnel. NIOSH also recommended limiting the number of employees in the barn while the elephants were inside or while the area was being cleaned and limiting any dust or aerosol-generating task.

While the zoo had respiratory protection and TB surveillance programs, respiratory protection was not routinely worn before the employees’ diagnoses. When the NIOSH team visited in November 2019, employees wore personal protective equipment (PPE) including N95 respirators, gloves, and eye protection while working in the barn and during some tasks performed outside, but some employees did not use their PPE correctly, did not report having been trained in PPE use, or had facial hair that could have affected PPE fit.

Additionally, NIOSH recommended a redesign of the barn ventilation system, as a single air handling unit served both the area where the elephants were kept and the employees’ office space, and contaminated air was exhausted above the adjacent employee parking lot.

More information is available in NIOSH’s PDF of the HHE Report.