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Outbreak of Tick-Borne Tularemia -- South Dakota
Between May 30, and July 15, 1984, 20 definite and eight
probable
cases of tularemia were reported among residents of the adjoining
Lower Brule and Crow Creek Indian Reservations in central South
Dakota. All the patients were native Americans ranging in age from
2
years to 31 years (median 6 years). The attack rate for
reservation
residents 0-9 years of age was 2%; for those 10-19 years of age,
0.2%;
and for those 20 years and older, 0.2%. Sixteen of the patients
were
male. Twenty-two (79%) of the patients reported a tick bite, and
none
had contact with rabbits or dead animals or had eaten rabbit meat.
Most patients presented with fever, headache, and adenopathy.
All
the patients for whom a tick-bite location was known had been
bitten
on the head or neck. These patients presented with regional
adenopathy draining the area of the tick bite. All 28 patients had
either cervical, submandibular, occipital, or preauricular
adenopathy. Four patients also appeared to have enlarged parotid
glands and presented with a clinical picture that resembled mumps.
Seven patients had pharyngitis. Eight had a fourfold rise in serum
agglutination titer of 1:160 or greater to Francisella tularensis;
12
patients had a single convalescent titer of 1:160 or greater; and
eight with pending convalescent serology had compatible clinical
illnesses. Three lymph-node aspirates did not yield F. tularensis.
Twenty-six patients were treated with streptomycin; two, with
tetracycline. All responded to antimicrobial therapy.
Environmental investigation revealed few ticks on vegetation
near
the homes, but ticks were found on vegetation around the streams
and
rivers on the reservation. Forty-six (73%) of the 63 dogs that
were
examined on the two reservations were infested with ticks. Ticks
collected from both vegetation and dogs were identified as
Dermacentor
variabilis. These ticks, as well as three mud and three water
samples
from areas where children play on the reservation, were cultured
for
F. tularensis. Tick lots from eight (17%) of the 46 dogs were
positive. Mud and water samples were negative. Biochemical
analysis
of the F. tularensis isolates revealed that seven were type B, and
one
was type A.
Most families owned several dogs, and stray dogs were abundant
on
the reservations. It is likely that tularemia was seen
predominately
in children because of their increased exposure to ticks through
their
frequent contact with dogs and outdoor activities in tick-infested
areas.
Recommended prevention measures included continuing an
educational
program on tularemia for reservation residents, dusting dogs with
tick
powder (6% malathion), and cutting grass around the homes to
prevent
tick harborage.
Reported by P de la Cruz, MD, L Cummings, D Harmon, D Mosier, MS, P
Johannes, J Lawler, MS, F Pintz, MD, Aberdeen Area Indian Health
Svc,
K Senger, State Epidemiologist, T Dosch, South Dakota Dept of
Health;
Div of Bacterial Diseases, Div of Vector-Borne Viral Diseases,
Center
for Infectious Diseases, CDC. Editorial Note
Editorial Note: This outbreak is similar to two previously
reported
tick-borne outbreaks of tularemia in the United States. In 1966,
12
cases occurred on the Pine Ridge and Rosebud Indian Reservations in
South Dakota (1); in 1979, 12 cases occurred on the Crow Indian
Reservation in Montana (2). Infection in those two outbreaks also
occurred predominately among children, and the presentation was
mild
glandular or ulceroglandular tularemia. Adenopathy in the head and
neck areas, similar to the clinical picture in this outbreak, was
also
described in those outbreaks. In both prior outbreaks, D.
variabilis
was the tick vector, and F. tularensis was isolated from ticks.
Two subtypes of F. tularensis have been recognized (3). Type A
strains, which have been found only in North America, are more
virulent and cause illness that, without treatment, has a 5%-7%
mortality rate. Type B strains are less virulent. These strains
differ biochemically in that type A utilizes glycerol and is
citrulline ureidase positive (4). In this outbreak, seven of the
eight F. tularensis isolates from ticks were type B. Although no
human isolates were obtained, the mild clinical illness was
consistent
with disease caused by type B F. tularensis. Disease caused by
type B
strains have been most commonly associated with exposure to
contaminated water or aquatic animals, rather than insect vectors.
However, type B strains were also isolated from ticks in the 1979
outbreak in Montana (2).
Because glandular tularemia can be mild, as in the current
outbreak, and can mimic other illnesses such as pharyngitis or
mumps,
cases may be misdiagnosed. Physicians in areas endemic for
tularemia
should be aware of the manifestations of glandular tularemia so
that
cases can be identified and appropriately treated.
References
Saliba GS, Harmston FC, Diamond BE, Zymet CL, Goldenberg MI,
Chin
TDY. An outbreak of human tularemia associated with the
American
dog tick, Dermacentor variabilis. Am J Trop Med Hyg
1966;15:531-8.
Schmid GP, Kornblatt AN, Connors CA, et al. Clinically mild
tularemia associated with tick-borne Francisella tularensis. J
Infect Dis 1983;148:63-7.
Jellison W. Tularemia in North America, 1930-1974. Missoula,
Montana: University of Montana 1974.
Marchette NJ, Nicholes PS. Virulence and citrulline ureidase
activity of Pasteurella tularensis. J Bacteriol 1961;82:26-32.
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