A Trunkful of TB?
ABSTRACT & COMMENTARY
Synopsis: Wild, domesticated animals, including elephants, may pose a risk of mycobacterial infection in humans.
Source: Michalak K, et al. Mycobacterium tuberculosis as a zoonitic disease: Transmission between humans and elephants. Emerg Infect Dis http://www.cdc.gov/ncidod/EID/vol4no2/michalak.htm
Following the deaths of two circus elephants within one week of each other in August 1996 due to overwhelming pulmonary Mycobacterium tuberculosis (MTB) infection, the United States Department of Agriculture (USDA) now requires all elephants in the United States, as well as their handlers, to undergo regular screening for M. tuberculosis infection.
The elephants belonged to an exotic animal farm in Illinois and were travelling around the country giving rides to the public. MTB was initially suspected when the first elephant, who had a 10-month history of unexplained weight loss, died suddenly in California while undergoing a routine dental procedure. The second animal also died suddenly while en route home for evaluation. Necropsy of the animals revealed copious truncal and respiratory secretions, extensive pulmonary caseous necrosis, and pleural effusions.
An epidemiological investigation was launched. The farm originally housed 18 Asian and two African elephants, 13 of which lived in one large barn, which was in direct communication with a general social area and some of the handlers' housing-although there was a separate ventilation system. The elephant necropsies were apparently done on the farm and were attended by many of the handlers. Initial PPD skin tests were positive in eight of 22 handlers (36%), and three more converted their skin tests during the investigation (50% infection rate). One handler (who had attended the necropsy) had an abnormal chest radiograph; he proved to have smear-negative, culture-positive pulmonary tuberculosis.
Of the remaining elephants, a single live elephant had a positive mycobacterial culture of truncal secretions. Pulmonary MTB was also posthumously diagnosed in a fourth elephant who died in 1994. RFLP analysis demonstrated similarity between the isolates obtained from the four elephants and the handler, although the direction of the transmission could not be confirmed. Based on the presence of the organism in the elephants' truncal secretions, the USDA has recommended that screening cultures be obtained from this site. And, because you apparently cannot skin test an elephant, empiric antituberculous treatment was given to all of the elephants on the farm, although subsequent cultures remained negative.
COMMENT BY CAROL A. KEMPER, MD
Zoonotic transmission of M. bovis from animals to humans can occur with an extensive number of mammalian species, such as cattle, horses, deer, elk, buffalo, goats, swine, and bats; the greatest risk in these cases is posed by human contact with endemically infected wildlife species. For example, wild badgers have been implicated as a residual reservoir of infection for both humans and cattle in England and Wales, where eight patients younger than 30 years of age have been recently diagnosed with primary M. bovis infection (Hardie RM, Watson JM. Epidemiol Infect 1992;109:22-33).
On the other hand, zoonotic transmission of M. tuberculosis appears to be less common, and the direction of the transmission is not always clear. Nonetheless, exposure to both organisms remains a present-day occupational hazard for employees of zoos, nature parks, and abattoirs. A seal trainer developed pulmonary tuberculosis following the deaths of three seals in a marine park in Australia; molecular analysis confirmed the similarity of the mycobacterial isolates, although the direction of transmission could not be confirmed (Thompson PJ, et al. Am Rev Respir Dis 1993;147:164-167). Seven of 24 zookeepers converted their skin tests following exposure to a Southern white rhinoceros infected with M. bovis, but none developed clinical illness (Dalovisio JR, et al. Clin Infect Dis 1992;15:598-600).
Other animals, such as dogs, which live in close contact with humans, may be at greater risk for acquiring human infection than vice versa. In a survey of 15,272 canine necropsies in the Metropolitan New York area from 1962 to 1978, only eight (0.05%) cases of TB were identified (Si-Kwang Liu, et al. J Am Vet Med Assoc 1980;177:164-167). All eight dogs were symptomatic with anorexia, weight loss, lethargy, vomiting, and leukocytosis, and radiographic studies revealed pleural and pericardial effusions, ascites, and hepatomegaly. Given that each of the dogs had a history of close contact with a human known to have TB, the dogs most likely acquired their disease from their humans.
One of our local veterinarians became quite concerned about the possibility of zoonotic transmission of tuberculosis following her unsuccessful attempts at direct CPR on a client's favorite pet sailfin lizard (Inf Dis Alert 1995;14:119-120). Necropsy of the lizard subsequently revealed caseous necrosis involving numerous organs, including the lungs. Although mycobacterial cultures were negative, we were able to reassure her that lizards are probably too cold-blooded to support infection with MTB.
On the local scene, one of the elderly female elephants at the San Francisco Zoo is being treated for pulmonary TB. She recently made front page news because of continued gastrointestinal intolerance to rifampin requiring administration of the drug by rectal suppository. (How large is a rifampin suppository for an elephant?) As a result, she has developed very pink cheeks, a curiosity which does not go unnoticed by visiting children.
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