[Emerging Infectious Diseases]
[Volume 4 No. 2 / April - June 1998]

Dispatches

Mycobacterium tuberculosis infection as a Zoonotic Disease: Transmission
between Humans and Elephants

Kathleen Michalak,* Connie Austin,† Sandy Diesel,* J. Maichle Bacon,* Phil
Zimmerman,‡ and Joel N. Maslow§
*McHenry County Department of Health, Woodstock, Illinois, USA; †Illinois
Department of Public Health, Springfield, Illinois, USA; ‡University of
Illinois, College of Medicine at Rockford, Rockford, Illinois, USA; and
§Boston University School of Medicine and the VA Medical Center, Boston,
Massachusetts, USA

  --------------------------------------------------
      Between 1994 and 1996, three elephants from an exotic animal
      farm in Illinois died of pulmonary disease due to Mycobacterium
      tuberculosis. In October 1996, a fourth living elephant was
      culture-positive for M. tuberculosis. Twenty-two handlers at
      the farm were screened for tuberculosis (TB); eleven had
      positive reactions to intradermal injection with purified
      protein derivative. One had smear-negative, culture-positive
      active TB. DNA fingerprint comparison by IS6110 and TBN12
      typing showed that the isolates from the four elephants and the
      handler with active TB were the same strain. This investigation
      indicates transmission of M. tuberculosis between humans and
      elephants.

Mycobacterium tuberculosis and M. bovis, related organisms of the M.
tuberculosis complex, infect a wide variety of mammalian species. M. bovis
is pathogenic for many animal species, especially bovidae, cervidae, and
occasionally carnivores. Human disease with M. bovis is well described and
historically was a common cause of tuberculosis (TB) transmitted by
infected dairy products. As a result of milk pasteurization and TB
eradication programs in most industrialized countries, zoonotic
transmission of M. bovis through domestic livestock is now rare. In
contrast, a similar eradication program has not been conducted for wild or
exotic animals, which therefore remain an uncommon source for M. bovis
exposure. Zoonotic transmission of M. bovis has been reported from seals,
rhinoceros, and elk (1-4).

M. tuberculosis, the most common species to cause TB, classically causes
disease in humans. Animal infection with M. tuberculosis, while uncommon,
has been described among species (e.g., birds, elephants, and other
mammals) with prolonged and close contact with humans (5-10). Transmission
of M. tuberculosis between animals and humans has not been reported. This
paper describes M. tuberculosis transmission from elephants to humans.

The Outbreak

In March 1996, five elephants from an exotic animal farm in Illinois were
in California as part of a circus act. One elephant (with chronic,
unexplained weight loss since October 1995) died under anesthesia on August
3, 1996, during a diagnostic dental work-up. Necropsy showed widespread
consolidation of lung tissue with caseous necrosis of the lungs and
mediastinal lymph nodes. Short, fat, relatively scant numbers of acid-fast
bacilli were observed in necropsy tissues. A presumptive diagnosis of M.
tuberculosis was made. The remaining four elephants were recalled to the
farm in Illinois. A second elephant died en route on August 6, 1996.
Necropsy revealed copious respiratory and trunk exudates and caseous
necrosis of the lung.

To determine the risk for and possibility of infection among the animal
trainers and caretakers, an epidemiologic investigation was initiated. The
remaining elephants in the herd and the elephant handlers and trainers who
were still traveling were recalled to the farm and examined for evidence of
M. tuberculosis infection. All elephants were empirically begun on
antituberculous therapy in early December 1996.

Epidemiologic Investigation

The exotic animal farm was visited on numerous occasions to evaluate the
type and degree of contact between elephants and employees. The farm,
located in a rural area and surrounded by barbed wire and trees, originally
housed 18 Asian and 2 African elephants. Thirteen elephants were tethered
on a chain in one large barn, four were housed in a separate large room
(two in a common stall), and a baby elephant was in a third room with 5-6
tigers. A separate barn housed approximately 80 tigers.

TB Screening of Employees

The animal handlers (trainers and caretakers) who had direct contact with
the elephants were administered purified protein derivative (PPD) skin
tests. Initial screening was performed in August 1996, with subsequent
screenings in December 1996 and March, June, and September of 1997. Testing
was performed by the McHenry County Department of Health, except in two
handlers who had subsequent skin tests performed elsewhere. As part of the
screening process, handlers were questioned about their risk factors for
TB, including previous bacillus Calmette-Guérin (BCG) vaccination.

Handlers were tested by the two-step method using 5 tuberculin units of PPD
(0.1 ml) by intradermal injection in the flexor surface of the forearm. A
positive result was defined as an induration of >5 mm. Handlers with
positive skin tests were evaluated by a TB health-care worker and had chest
radiographs taken. Sputum samples from any handler with a chest radiograph
consistent with TB were submitted to the Illinois Department of Public
Health Laboratory. Samples were examined by direct microscopy for acid-fast
organisms, stained with fluorochrome, and processed for culture by standard
methods.

Examination of Isolates

The human isolate and the four elephant isolates were sent to the National
Tuberculosis Genotyping and Surveillance Network at the Michigan Community
Public Health Agency for restriction fragment length polymorphism (RFLP)
analysis. Southern blots of Pvu II restricted whole chromosomal DNA,
resolved in 1% agarose gels, were probed with a DNA fragment corresponding
to the right side of IS6110 and detected by chemiluminescence (11). The
number and size of the hybridizing fragments for each isolate were compared
in the same gel. Isolates with identical RFLP patterns or with </= 2 band
differences were considered to represent the same strain. Additionally, Pvu
II digested DNA was similarly typed after probing with the repetitive
element TBN12.

Epidemiologic Findings

Elephant handlers worked in very close proximity with the elephants around
the clock, whereas tiger handlers had little direct contact with the
elephants. Most of the elephant handlers lived on the farm in a separate
section of the barn; four lived in trailers on the grounds. The handlers'
living quarters had a separate ventilation system from the elephants';
however, the doors between the two quarters were open for unknown periods.
Handlers indicated that they held social events in a building connected to
the elephant barn.

Necropsies of elephants were performed on the farm and were attended by a
number of elephant and tiger handlers (including the handler with the
active case). The necropsy of the elephant that died in 1994, also
performed on the farm, showed caseous necrosis of the lungs and pleural
exudates whose culture yielded M. tuberculosis.

In addition to the three elephants that died of M. tuberculosis infection,
a fourth living elephant was also infected with the mycobacterium; this
infection was diagnosed in late December 1996 from a trunk culture obtained
in October 1996. Subsequent cultures from this and the other animals have
been negative for mycobacteria. Another elephant from this farm died of M.
tuberculosis infection in 1981 (5), but contact between this elephant and
the present herd or any of the handlers could not be established.

Twenty-two handlers at the exotic animal farm had moderate to frequent
contact with the infected animals; 12 were elephant handlers and 10 were
tiger handlers. Initial PPD testing was performed for 14 handlers in August
1996, 2 in October 1996, and 5 in December 1996. One who was PPD-positive
in November 1995 reported receiving BCG more than 10 years before.

Eleven (50%) of 22 handlers were found PPD-positive as part of this
investigation. Eight of the 11 had positive PPD skin test results upon
initial testing, with a median induration of 12 mm (range, 10 to 19 mm).
Four of the eight were elephant handlers and four were tiger handlers. The
skin test reaction of three handlers converted from negative to positive
with a median induration of 12 mm (range, 8 to 15 mm). The three PPD
converters were initially tested in August 1996; one was positive upon
retesting in January 1997, and two tested positive in April 1997 (Table).

Eight of the 11 handlers reported that they had negative skin tests in the
past and had not received BCG. The other three reported some type of
reaction from a previous skin test in the past but did not know the
results. All three also reported receiving BCG more than 10 years before.
Eight of the 10 handlers with negative PPD skin tests had at least one
negative follow-up test at 3 months; two left the farm and did not receive
follow-up testing.

The attack rates were approximately equal for the elephant and tiger
handlers. Of the 12 elephant handlers tested, 6 (50%) were PPD-positive
with two conversions documented in April 1997; of the 9 tiger handlers, 5
(56%) were PPD-positive, with one conversion documented in January 1997.
Overall, a very high rate (52%) of handlers tested positive.

All 12 handlers with positive PPDs (including the one with the known
positive PPD) received an evaluation and chest radiograph; one had
irregular nodules and interstitial changes in the right apex without
retraction of the lungs, consistent with active TB, but no cough, chest
pain, fever, night sweats, weight loss, or fatigue.

Three sputum samples were smear-negative for acid-fast bacilli, although
one yielded M. tuberculosis upon culture. Isoniazid (INH), rifampin,
pyrazinamide, and ethambutol treatment was initiated in September 1996, and
after 2 months, was reduced to INH and rifampin when the isolate showed no
resistance to antituberculous medications. Subsequent chest radiographs
revealed improvement or clearing of the initial lesions. Nine of the
remaining 11 PPD-positive handlers were prescribed INH prophylaxis; two
declined because of the risk for adverse reactions.

Table. TB PPDa skin test results of animal handlers, Aug
1996 – Sep 1997
--------------------------------------------------
                         Positive   Negative
--------------------------------------------------
Previously positive      1
Elephant handlers        4            6
Tiger handlers           4            4
Elephant handlers
(converted)              2
Tiger handlers
(converted)              1
Total                   12           10
--------------------------------------------------
(sup a)Tuberculin purified protein derivative.

Molecular Analysis of Elephant and Human Isolates

The sputum isolate from the handler with active TB was compared with the
isolates from the three animals that died and the living elephant whose
infection was diagnosed during the investigation. The isolates had
identical IS6110 RFLP pattern, differing by </= 2 bands (Figure 1).
Additionally, all isolates had the identical TBN12 RFLP pattern, except the
isolate from the elephant that died in August 1996, which demonstrated a
shift of one band (Figure 2).

Conclusions

Infection with M. tuberculosis or M. bovis has not been reported in
nondomesticated Asian or African elephants. M. tuberculosis infection in
domesticated elephants was first reported in 1875 by Garrod and has been
recognized in the ancient Ayurvedic literature (10); humans have been
considered the source of infection. A trainer with cavitary TB was
suspected as the source of infection (8) for one Asian elephant that died
of M. tuberculosis, although subsequent analysis showed the animal and
human isolates to be of two different phage types.

This report describes the first case of zoonotic M. tuberculosis
transmission. The epidemiologic investigation strongly suggests M.
tuberculosis transmission between humans and elephants, as evidenced by DNA
fingerprinting. RFLP analysis comparing Southern blots of chromosomal DNA
probed with IS6110 and TBN12 indicated that four elephant isolates had
identical patterns with the human isolate, differing by </= 2 bands. The
addition or loss of a single band has been demonstrated in other outbreak
settings, and the repetitive element that generates patterns has
characteristics of a mobile genetic element (11).

Eleven (50%) of 22 employees screened were skin-test positive, with no
difference between tiger and elephant handlers. This is a higher rate of
positives than documented in animal handlers exposed to M. bovis-infected
animals (3,4). Since the handlers had no accurate history of tuberculin
skin testing, it was not possible to determine when conversions took place.
The original source of infection for both elephants and humans is unknown.

The possible mechanisms of transmission include close contact while
handling and training elephants, cleaning the barn, participating in
elephant necropsies, and living in close proximity to the elephant barn.

Human-to-human transmission of TB is unlikely because the only handler with
active disease did not have cough. Of the three sputum samples initially
collected, two were smear- and culture-negative; the third had low numbers
of acid-fast bacilli manifested by a negative sputum smear, thus posing a
low infectivity risk to others. In contrast, the three elephants that died
had evidence of widespread pulmonary disease and, therefore, represented a
greater risk for dissemination.

Three handlers converted from negative to positive during the course of the
investigation; their relevant exposure is unknown. The source may have been
one elephant found antemortem to be culture-positive for M. tuberculosis,
although this animal did not return to the farm until November. Contact
with this animal is unlikely for handlers whose PPD tests converted in
December and unknown for the two handlers whose test results were positive
in April (the latter two had not been retested since August).

TB is transmitted through close prolonged contact with a person (or animal)
with active TB. The risk for TB transmission from an animal with a case of
active TB is higher for daily handlers than for persons with only brief
contact, e.g., members of the public viewing a performance or receiving
elephant rides. In this outbreak, screening of all persons who had (or
thought they had) contact with an elephant that died of M. tuberculosis
identified three PPD-positive cases but no cases of active TB (8). Because
the real risk for transmission to the general public was poorly understood,
this case received considerable media attention as well as mention in the
medical literature (7,12).

Veterinary practices should be initiated to reduce the risks for exposure
to animals infected with M. tuberculosis. No data are available on TB
incidence among domesticated elephants in the United States. An estimate
can be derived from a retrospective study of 379 zoo elephants of which
eight (2.3%) had M. tuberculosis infection (10).

Reliable diagnosis and prevention of TB in all domesticated and exhibited
animals is ideal. Short of this, possible ways to prevent and decrease
zoonotic spread of any mycobacterial infection (M. tuberculosis or M.
bovis) include 1) regular skin testing of handlers or keepers; 2) a high
index of suspicion of TB in elephants with unexplained weight loss, cough,
or rhinorrhea; 3) public health measures of contact tracing and
notification; and 4) active and effective treatment of infected personnel
and animals (13).

[fig 1]                              [fig 2]
Figure 1. IS6110 restriction         Figure 2. TBN12 restriction
fragment length polymorphism         fragment length polymorphism
results. Lane 1, elephant            results. Lane 1, elephant
isolate (died August 6, 1996);       isolate (died August 6, 1996);
Lane 2, elephant isolate (died       Lane 2, elephant isolate (died
1994); Lane 3, living elephant       1994); Lane 3, living elephant
trunk culture (October 1996);        trunk culture (October 1996);
Lane 4, elephant lung tissue         Lane 4, elephant lung tissue
isolate (died August 3, 1996);       isolate (died August 3, 1996);
Lane 5, elephant lymph node          Lane 5, elephant lymph node
tissue isolate (died August 3,       tissue isolate (died August 3,
1996); Lane 6, human sputum          1996); Lane 6, human sputum
isolate (September 1996).            isolate (September 1996).
Provided by State of Michigan        Provided by State of Michigan
Community Public Health Agency.      Community Public Health Agency.

Acknowledgments

We thank Stephen Dietrich and Laura Mosher, North Central Area TB-RFLP
Laboratory, Michigan Department of Public Health; George J. Dizikes, Chief
of Molecular Diagnostics, Illinois Department of Public Health, Division of
Laboratories; and Janet Payeur, National Veterinary Services Laboratory,
U.S. Department of Agriculture, MB Section. This research was supported in
part by the Centers for Disease Control and Prevention, National
Tuberculosis Genotyping and Surveillance Network cooperative agreement.

Kathleen Michalak is the Director of Nursing for McHenry County Department
of Health. She has worked to improve the use of community resources, and
improved service to client, providers, and the community as a whole.

Address for correspondence: Kathleen Michalak, McHenry County Department of
Health, 2200 N. Seminary Avenue, Woodstock, IL 60098, USA; fax:
815-338-7661.

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Emerging Infectious Diseases
National Center for Infectious Diseases
Centers for Disease Control and Prevention
Atlanta, GA

URL: http://www.cdc.gov/ncidod/EID/vol4no2/michalak.htm

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