Dec 15, 1983 - disease. In Ohio,353 RMSF cases, 16 of which were fatal, were reported to the State Health Department between 1964 and 1981. Although the ...
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/2e^>^e^-f "Reprinted from the JOURN^I "c T^ AMERICAN VETERINARY MEDICAL ASSOCIATION. Vol. 183, No. 12, Pages 1451.1453. (C) American Veterinary Medical Association, 1983. All Rights Reserved-
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Rocky Mountain spotted fever in an urban canine population Robert C. Smith, DVM,
MS: John C. Gordon, DVM, MPH; Scott W. Gordon, BA, MS; Robert N. Philip, MD
SUMMARY A survey for the prevalence of Rocky Mountain spotted fever antibodies in dogs from a well-defined endemic area in Columbus, Ohio (Franklin County), was conducted during the summer of 1981. Seventythree blood samples from dogs in this area were
tested by microimmunofiuorescence for antibodies to Rickettsia rickettsii and other rickettsial antigens. Thirty-three (45.2%) of these samples were positive for R rickettsii, with titers ranging from 1:8 to 1:2,048. For comparison, 137 blood samples from dogs at the Franklin County Dog Pound also were tested. One dog (0,7%) from the comparison group was seropositive to R rickettsii, with a 1:64 liter. The results indicated a nidus of this disease within the city of Columbus, Ohio.
ROCKY MOUNTAIN spotted fever (RMSF) is the most significant rickettsial disease in the United States in terms of number of cases as well as fatality rate.1"1 The causative agent of RMSF, Rickettsia rickettsii, is maintained in nature primarily in a cycle involving ticks and small mammals. The most common tick vector associated with RMSF in Ohio is Dermacentor variabilis, the American dog tick.5 The adult stage of this 3-host tick is active from mid-April through September, which corresponds to the period when most RMSF cases are diagnosed.6 Dogs, the preferred hosts of adult D variabilis, accidentally become involved in the disease cycle and when infected, probably do not pass the organism to man, arthropods, or other animals.7 However, dogs are an important means by which potentially infected ticks are From the Department of Veterinary Preventive Medicine (Smith, J. Gordon), College of Veterinary Medicine, The Ohio State University, Columbus, OH 43210; Vector Borne Disease Unit (S. Gordon), Ohio Department of Health, Columbus, Ohio; and Epidemiology Branch (Philip), Rocky Mountain Laboratory, NIAID, NIH, Hamilton, Mont. Send reprint requests to Dr. J. Gordon. Supported by grant from The Ohio State University Graduate School (22U31). The authors thank Harold Harlan for assistance in collecting survey material and DrJean Powers for statistical analysis,
JAVMA, Vol 183/ No. 12, December 15/ 1983
brought into contact with people, especially children. Although the primary route of exposure to RMSF is through a tick bite, in only 58% of 1,522 human cases studied between 1970 and 1974 could the person recall being bitten.8 Cases have been associated with deticking dogs, however, as tick feces and tick fluids can contain rickettsiae capable of penetrating the
conjunctivae and abraded skin.1 The name "Rocky Mountain spotted fever" is somewhat of a misnomer since more than 50% of all reported cases now occur in the south Atlantic states.9"11 However, the realization that RMSF is a national problem must be emphasized, as every state in the continental United States has reported the disease. In Ohio, 353 RMSF cases, 16 of which were fatal, were reported to the State Health Department between 1964 and 1981. Although the disease has been documented in 60 of the 88 counties, many cases have been associated with 3 widely separated foci of activity, located in northwestern (Lucas County), southwestern (Clermont County), and central (Franklin County) Ohio.12’13 A search of the Ohio Department of Health records revealed 37 cases of RMSF in Franklin County from 1966 through 1981. Of these cases, 12 were within the city of Columbus in an area known as the American Addition, and 16 other cases were within 2 miles of this location. The purpose of the study reported here was to determine the prevalence of antibodies to R rickettsii in dogs from the American Addition area of Columbus, Ohio.
Materials and Methods Description of the endemic study area-The American Addition consists of approximately 275 acres, located well within the confines of Columbus (Franklin County), Ohio, between the commercial area of downtown and suburban development that surrounds the business district of the city. As a result of development around it, the American Addition has become somewhat of an ecologic island within a city of approximately 1 million residents. To the east, a cemetery, landfill, and a swamp separate the Addition from neighboring residential areas. To the north and east of the Addition are residential areas, but an abandoned drive-in theater and a cemetery provide a barrier from these areas. To the south and west of the Addition lies the business area of downtown Columbus, but railroads and warehouses separate the Addition from this area (Fig 1). The American Addition has numerous vacant lots,
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Fig i-The American Addition, Columbus, Ohio. Dots indicate the locations of the households involved in the survey. Numbers represent the households with dogs from which blood samples were obtained. Circled numbers indicate dogs seropositive for R
they were tested for rickettsial antibodies by the indirect microimmunofluorescence (micro-lF) test.15 Antibodies were tested against rickettsial agent (antigen) groups that are categorized on the basis of clinical features and epidemiologic and antigen characteristics.16 Test antigens included strains representing spotted fever group (SFG) serotypes (.R rickettsii, strain; R akari, strain 29; R conorii, Malish; R rhipicephali, 3 to 7 2 6 strain; R montana, M/5 to 6 strain), typhus group serotypes (R prowazekii, Breini strain; R typhi, Wilmington, R Canada, 2678 strain), and 1 unclassified serotype, the 369-C agent (Sheephead 130 strain). Four ofthese serotypes (R rickettsii, R rhipicephali, R montana, and the 369-C agent) are known to infect D variabilis in the United States, but only 2 (R rickettsii and the 369-C agent) have thus far been detected in ticks collected in the American Addition (Ohio Department of Health laboratory reports). Fluorescein isothiocyanate-labeled goat anti-canine globulin" was the test conjugate. Statistical analyses-All data were compared by use of the chi-square test of significance, with Yates’ correction factor.
rickettsii.
Results
small wooded areas, and large open fields. A recent environmental survey conducted by the Columbus Board of Health indicated that many of the premises in the Addition were vacant lots and that 60% of all premises were overgrown with weeds and high grass." This situation has resulted in the creation of an optimal habitat for D vari-
Thirty-six households with a total of 73 dogs agreed to participate in’ the study. In all, 33 study dogs (45.8%) were seropositive toR rickettsii at a titer of 1:8 or greater (Table 1). This sample probably represented about 90% of the resident canine population of the American Addition. The number of dogs per household ranged from 1 to 8 (17 had a single dog; 11 had 2 dogs; 5 had 3 dogs; and 1 each had 4,7, and 8 dogs). Twenty-three of the 36 households had at least 1 seropositive dog (range, 1 to 3). There was no relation between sex of the study dogs and micro-lF test results. The comparison group consisted of 137 dogs from the Franklin County Dog Pound. Only one of these dogs (0.7%) was seropositive to R rickettsii, and that was at a titer of 1:64. The origin of that dog was uncertain, as it was apprehended near the pound and may have been abandoned there. These results indicate that R rickettsii antibodies in dogs from the American Addition were significantly more frequent (P
