CDC Investigation Pinpoints Elephant-to-Human TB Outbreak
Several employees at a Tennessee elephant refuge were infected in 2009, including some who had no close contact with the animals. Air flow tests indicated bacteria that were aerosolized during routine pressure washing of a quarantine barn entered an adjacent administrative building.
A newly published CDC study points out the need for strong infection control practices for workers who have close contact with elephants living in captivity. The authors explain what they found when the Tennessee Department of Health reported in 2009 that several employees of an elephant refuge not open to the general public had latent M. tuberculosis tests. The lead researcher was Dr. Rendi Murphree, Epidemic Intelligence Service Officer at CDC and a Vanderbilt University Visiting Scholar, and the study has been published in the March 2011 issue of CDC’s Emerging Infectious Diseases (Vol. 17, No. 3).
About 270 Asian elephants and about 220 African elephants live in captivity in North America, and about 12 percent of the Asian elephants and 2 percent of the African elephants are thought to be infected with M. tuberculosis, they report. The first reported outbreak of TB among elephants in North America occurred at an exotic animal farm in Illinois in 1996, and an investigation there confirmed four Asian elephants and 11 human caregivers were infected. As a result, since 1998, the USDA Animal Plant Health Inspection Service has required annual M. tuberculosis testing for all captive elephants in the United States.
Positive tests in March 2009 and July 2009 confirmed one elephant living in the Tennessee refuge’s quarantine area was infected. Its infection control practices were increased in October 2009. The authors report they found no human source of TB infection at the refuge. Employees working in the quarantine area in 2009 were significantly more likely than other employees to be infected, they determined.
The 2,700-acre refuge was established in 1995 to care for sick, old, or abused elephants that are transferred from private owners, zoos, and circuses. It received two female Asian elephants in 2004 with a history of active TB, with this transfer adhering to USDA-endorsed Guidelines for the Control of Tuberculosis in Elephants and an infection control plan. One of these elephants died of TB in 2005, while the other was treated with medication and released from isolation, the authors report. Eight more elephants arrived in 2006 from the same source, an exotic animal farm in Illinois; none was known to have active TB, but all were considered at high risk because they had been housed with M. tuberculosis culture-positive elephants.
"Our findings highlight the effects of gaps in scientific knowledge and provide new information on potential risk factors for zoonotic transmission of M. tuberculosis," the authors concluded. "First, in this outbreak the inability to accurately and expeditiously detect M. tuberculosis infection and disease in elephants contributed to unrecognized, and therefore uncontrolled, risk. Improved methods for diagnosis of M. tuberculosis infection in elephants are needed. Second, infection control practices were insufficient to protect employees, creating an argument for detailed evidence-based guidelines and a more comprehensive approach to implementation. Third, employees were largely unaware of the risk for zoonotic M. tuberculosis transmission and the need to use adequate respiratory protection. Because risk cannot be eliminated, a strong occupational health and training program is needed for employees who work in facilities that house elephants potentially exposed to M. tuberculosis." They recommend that facilities housing elephants try to reduce aerosol-generating practices and limit aerosol spread.
"The One Health movement argues for integrating human and veterinary medicine to defend the health and well-being of all animal species. This report provides a textbook illustration of this need," they continued. "Captive elephants have emerged as an unanticipated source of M. tuberculosis infection among humans and therefore must be integrated in our strategies to control and eliminate TB. Because of the gaps in scientific knowledge, the high prevalence of M. tuberculosis infection among elephants living in North America, and the insensitivity of diagnostic tests, a substantial need exists for focusing attention on infection control practices and occupational health programs specifically designed to reduce zoonotic M. tuberculosis transmission in the captive elephant industry."