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(Results of the 1996 Indiana Deer Survey for Ixodes scapularis)
Rocky Mountain Spotted Fever and Lyme Disease
Surveillance Program in Indiana
by Robert P. Pinger, Ph.D,.
Department of Physiology and Health Science
Ball State University
A total of 547 ticks was submitted for testing between January 1 and December 31, 1997. This total is well below last year’s total of last 841. While fewer specimens of Dermacentor variabilis, Amblyomma americanum and Dermacentor albipictus were received in 1997 than in 1996, more I. scapularis were received in 1997.
Species Composition
Seven species of ticks were received in 1997 (Table 1). The American dog tick, D. variabilis, again predominated, but constituted only 39% of all the ticks received (Figure 1).
Table 1. |
||
Species |
Number |
% |
|---|---|---|
Dermacentor variabilis |
214 |
39 |
Ixodes scapularis |
209 |
38 |
Amblyomma americanum |
105 |
19 |
Ixodes cookei |
5 |
0.9 |
Rhipicephalus sanguinius |
4 |
0.7 |
Dermacentor albipictus |
3 |
0.5 |
Amblyomma maculatum |
2 |
0.5 |
Unidentified ticks/non-ticks |
5 |
0.5 |
TOTAL |
547 |
|
Figure 1.
Ixodes scapularis, the blacklegged tick, ranked second; 209 specimens were received or collected by the lab. Only 105 specimens of A. americanum, the lone star tick, were received in 1997. These three species made up 95.5% of the total. Other species collected in 1997 were the woodchuck tick, Ixodes cookei (5), the brown dog tick, Rhipicephalus sanguinius (4), and the winter tick Dermacentor albipictus (3).
Geographic Distribution
Ticks were submitted from 60 Indiana counties, one more county than in 1996. Ten ticks were submitted from five other states: Kentucky (2), New Mexico (3), Tennessee (3), Virginia (1), and Wisconsin (1). The Indiana counties submitting the greatest number of ticks (and the number submitted from each) were: Newton (156), Franklin and Lawrence (40), Pulaski (27), Vanderburgh (25), and LaPorte (22). Thirty-two counties submitted no ticks in 1997. Except for Marion County, fewer ticks were submitted from counties in the center of the state than either northern or southern counties. Figure 2 is a map showing the distribution of ticks submitted by county.
Seasonal Distribution
The seasonal distribution for all ticks, by the date of collection, is presented in Table 2. There were two peaks in submissions, one in May-June, representing D. variabilis adults and A. americanum adults and nymphs, and one in October-November, representing primarily I. scapularis adults.
Table 2.
Monthly Distribution of Ticks
Submitted for Testing, Indiana 1997
Month |
Number Received |
January |
0 |
February |
1 |
March |
17 |
April |
39 |
May |
101 |
June |
110 |
July |
66 |
August |
21 |
September |
28 |
October |
87 |
November |
52 |
December |
25 |
TOTAL |
547 |
The seasonal distribution of ticks is more meaningful when viewed by species. Figures 3-6 depict the seasonal distributions of three species of public health importance (D. variabilis, A. americanum, and I. scapularis) based upon our records of submissions. As usual, D. variabilis populations were high in May and June, with the peak of adult activity in June (Figure 3).
Because of differences in the seasonal activity of adults and nymphs of A. americanum, these are displayed in two separate graphs (Figure 4 & 5). The peak activity of A. americanum adults occurred in June (Figure 4). Nymphs of A. americanum showed a bimodal seasonal distribution with two peaks: one in June, and a smaller one in September (Figure 5).
The peak for I. scapularis occurred in October again this year, but substantial numbers were also collected in September, November, and December (Figure 6). About three-quarters of the I. scapularis ticks (156/209) were once again collected at the Willow Slough Fish and Wildlife Area in Newton County.
Figure 3.
Figure 4.
Figure 5.
Figure 6.
Hosts
In Figures 7-9, host data are presented for A. americanum, D. variabilis, and I. scapularis. Approximately 88% of D. variabilis (Figure 7) and 87% of A. americanum (Figure 8) were collected from humans.
Forty-four percent of I. scapularis were collected from deer, 52% from dogs, and 4% (8 ticks) from humans (Figure 9).
Figure 7.
Figure 8.
Figure 9.
Testing
A total of 165 D. variabilis and 69 A. americanum were tested for spotted fever group (SFG) rickettsiae. Of these, only one D. variabilis and no A. americanum ticks were positive by the Gimenez screening test, and none was positive by immunofluorescence (FITC). A single I. scapularis tick that was submitted from a human host was tested for B. burgdorferi by polymerase chain reaction. This tick, sent from Vermillion County, was negative.
Human Cases of Tick-borne Diseases in Indiana, 1970-1997
Confirmed human cases of known tick-borne diseases in Indiana for 1970-1997 are presented in Table 3. Note that the 1997 data are provisional. As of February 19, 1998, one case of RMSF, 15 cases of Lyme disease (LD), and 2 cases of human monocytic ehrlichiosis (HME) had been confirmed for 1997.
The geographic distributions of the five suspected, probable, and confirmed cases of RMSF for 1997 are shown in Figure 10. Only the Posey County case has been confirmed.
Figure 11 shows the distribution of the 15 confirmed cases of Lyme disease for 1997. Twenty-nine additional clinical cases of LD have been reported, some of which may eventually be confirmed. Thus, the final count could, indeed, end up being somewhat higher than 15.
Reports of clinical cases of Lyme disease were received from 30 Indiana counties in 1997 compared with 25 in 1996 and 23 in 1995. This suggests a growing recognition of LD among physicians and patients. However, the 15 confirmed cases reside in just ten counties.
Since 1994, when the first cases of human ehrlichiosis in Indiana were reported to the Indiana State Department of Health, a total of 17 cases have been confirmed from nine Indiana counties. Figure 12 shows the distribution of these 17 confirmed HME cases.
Table 3. |
|||
Year |
RMSF |
LD |
Ehrlichiosis |
|---|---|---|---|
1970 |
6 |
- |
- |
1971 |
9 |
- |
- |
1972 |
13 |
- |
- |
1973 |
6 |
- |
- |
1974 |
7 |
- |
- |
1975 |
5 |
- |
- |
1976 |
8 |
- |
- |
1977 |
15 |
- |
- |
1978 |
6 |
- |
- |
1979 |
7 |
- |
- |
1980 |
7 |
- |
- |
1981 |
6 |
- |
- |
1982 |
16 |
- |
- |
1983 |
16 |
2 |
- |
1984 |
7 |
0 |
- |
1985 |
4 |
1 |
- |
1986 |
0 |
0 |
- |
1987 |
3 |
4 |
- |
1988 |
4 |
3 |
- |
1989 |
1 |
4 |
- |
1990 |
7 |
15 |
- |
1991 |
13 |
17 |
- |
1992 |
4 |
19 |
- |
1993 |
1 |
32 |
5 |
1994 |
7 |
19 |
3 |
1995 |
7 |
16 |
7 |
1996 |
7 |
16 |
2 |
Lyme Disease Tick Surveillance in 1997
Hunter-killed deer were examined for ticks by more than 48 volunteers staffing 29 deer checking stations in 24 counties. The results of this survey are available in a separate report, Survey of Indiana Deer for Ixodes scapularis Ticks: 1997 Final Report.
In summary, 91 ticks were recovered from 30 of 1,652 deer (1.8%) examined in 1997, compared to 17 of 1,049 deer (1.6%) in 1996 and 12 of 819 deer (1.5%) in 1995. A total of 93 I. scapularis ticks were collected from deer in 1997 compared with 137 ticks in 1996 and only 18 ticks recorded in 1995. The vast majority of these ticks sent to us by Dave Spitznagle from Willow Slough Fish and Wildlife Area. Most of these were collected in October. During the 1997 deer survey, ticks were collected from deer killed in three counties for the first time (Boone, Knox, and Montgomery) bringing the number of counties in which infested deer have been found since 1990 to 22. I. scapularis ticks were also submitted from Vermillion and Randolph Counties in 1997 bringing the total number new county records in 1997 to five, and the number of Indiana counties with at least one I. scapularis to 37.
Conclusions
The number of ticks received in 1997 decreased slightly from that received in 1996. The proportion of ticks identified as D. variabilis this year (39%) increased from that in 1996 (33%), while the proportion of I. scapularis increased from 23% to 38%.
The seasonal distributions of the species of primary interest in this report were similar to those of previous years. Fewer I. scapularis were collected in 1997 than in 1996, but there were five new county records, bringing the total number of counties from which at least one specimen has been reported to 37.
The percentage of ticks that test positive for SFG rickettsiae remains small. None of the ticks examined in 1997 were positive for SFG rickettsiae.
There remains a disparity between the number of human LD cases reported by physicians and other health care providers and the number confirmed. While 46 cases were reported in 1997, only 15 have been confirmed as meeting the CDC case definition. While some additional cases may eventually be confirmed, many others may not. There are also four unconfirmed RMSF cases and one unconfirmed ehrlichiosis case on record for 1997.
Acknowledgments
This program was sponsored by the Indiana State Department of Health and Ball State University. I thank Dr. Michael J. Sinsko for his support and encouragement, and my students Debbie Bertram and Audra Cretsinger for their assistance in preparing this report. Thanks also go to Fresia Steiner for sharing her expertise.
I also thank Dr. James Pyle and Kathryn Pertler of Ball State’s Office of Academic Research and Sponsored Programs for their assistance with the Budget and Lola Miller of Ball State’s Contracts and Grants Office for her help with the project budget. Lastly, I thank Dr. Dale Hahn, chairman of the Department of Physiology and Health Science, Don VanMeter, Associate Dean of the college of Sciences and Humanities for their support of this project.
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