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Rocky Mountain Spotted Fever and Lyme Disease Surveillance Program in Indiana: Final Report, 1999 Robert R. Pinger, Ph.D. Department of Physiology and Health Science Ball State University Muncie, IN 47306-0510 Phone: (765) 285-5961

There were 957 ticks submitted for testing between January 1 and December 31, 1999. This total is greater than the total for any year since 1991. Mild Spring weather probably contributed to the increase in tick submissions in two ways: ticks became active earlier and people spent more time out-of-doors.

Six species of ticks were identified among the 957 ticks received in 1999 (Table 1). Forty-four percent (418) of these ticks were identified as the American dog tick, Dermacentor variabilis (Say). Thirty-four percent (329) were identified as the blacklegged tick (deer tick), Ixodes scapularis Say. The lone star tick, Amblyomma americanum (L.), made up just over 18% of the total. Together, these three species made up almost 96% of all the ticks received (Figure 1). The other species collected in 1999 (and the number of specimens received) were the winter tick, Dermacentor albipictus (Packard)(17), the woodchuck tick, Ixodes cookei Packard (9), the brown dog tick, Rhipicephalus sanguineus (Latreille) (7). There were six specimens that could not be identified because they were damaged.

Ticks were submitted from 65 of Indiana's 92 counties, six fewer counties than in 1998. Ticks were also submitted from five other states: Illinois (4), Kentucky (17), Ohio (1), Tennessee (1) and Virginia (1). The Indiana counties submitting the greatest number of ticks and the number submitted from each were: Newton (217), Porter (98), Franklin (37) and Lawrence (92), Bartholomew (34), Delaware (34), Lake (26) and Vanderburgh (26). Twenty-seven counties submitted no ticks in 1999. The distribution by county, of ticks submitted in 1999, is shown in Figure 2.

Figure 1.

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, representing D. variabilis adults and A. americanum adults and nymphs, and one in October, representing I. scapularis adults.

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 during April through July, with the peak of adult activity in May (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). In 1999, we received more A. americanum adults in April (Figure 4). More A. americanum nymphs were collected in May and June and there was a characteristic second, smaller peak in August (Figure 5).

Figure 4.

Figure 5.

The peak for I. scapularis occurred in October when we received 212 ticks, followed by November (45). The next highest month was April with 39 ticks (Figure 6). About 70% (231/329) of the I. scapularis ticks were sent to the Lab by Dave Spitznagle who picked them off his dog at the Willow Slough Fish and Wildlife Area in Newton County.

Figure 6.

In Figures 7-9, host data are presented for D. variabilis, A. americanum, and I. scapularis respectively. Approximately 90% of D. variabilis (Figure 7) and 97% of A. americanum (Figure 8) were collected from humans in 1999.

Figure 7.

Figure 8.

Seventy percent of I. scapularis were collected from dogs, about 25% from deer, and nearly 4% (10 ticks) from humans (Figure 9).

Figure 9.

A total of 310 D. variabilis and 74 A. americanum were tested for spotted fever group (SFG) rickettsiae. Of these, 34 D. variabilis ticks and one A. americanum tick were positive by the Gimenez screening test. Six of the D. variabilis, positive by Gimenez, were positive by immunofluorescence (FITC). The A. americanum tick was negative by FITC. Three I. scapularis ticks were tested for Lyme disease spirochetes by fluorescent antibody test; all were negative.

Confirmed human cases of known tick-borne diseases in Indiana for 1970-1999 are presented in Table 3. For 1999, 10 cases of RMSF, 13 cases of Lyme disease (LD), and 6 case of human monocytic ehrlichiosis (HME) have been confirmed. The asterisks (*) indicate that the 1999 figures are provisional.

Rocky Mountain spotted fever (RMSF). Dermacentor variabilis, the primary vector of RMSF, has been recorded from all 92 counties in Indiana. Since 1970, 220 confirmed cases of RMSF have been confirmed in Indiana. Although cases have been reported from 60 different counties, more cases have been reported from southern counties than from any other part of the State. Vanderburgh County has reported 45 cases in the past 30 years, far more than any other Indiana County, perhaps in part because it is recognized as a regional medical center for surrounding counties. A significant number of cases has also been confirmed in residents of the northern-most tier of counties, and the densely populated, Marion County (Indianapolis). The geographic distributions of the ten suspected, probable, and confirmed cases of RMSF for 1999 are shown in Figure 10. These data are provisional.

Lyme disease (LD). The first I. scapularis ticks collected in Indiana were removed from deer in northwestern counties in 1987 (Pinger and Glancy 1989). The first isolation of Borrelia burgdorferi (Johnson et al. 1984) from an Indiana tick was made in 1990 (Pinger et al. 1991). Since then, our laboratory has accumulated additional records of I. scapularis adults in Indiana through annual surveys of hunter-harvested deer and a state supported tick testing and surveillance program. For example, in 1998 deer were examined for ticks by more than 28 volunteers staffing 19 deer checking stations in 17 counties and tick mailers were sent to 360 official deer check stations. In summary, 226 ticks were recovered from 52 of 1,167 deer (4.5%) examined in 1998. The percentage of infested deer, 4.5%, was higher than the 1.8% of 1652 deer examined in 1997, the 1.6% of 1,049 deer examined in 1996, and the 1.5% of the 819 deer examined in 1995. Cumulative records reveal that at least one specimen of I. scapularis has now been collected from half (46) of Indiana’s 92 counties.

In 1993, we discovered the first established, B. burgdorferi-infected population of I. scapularis ticks in Jasper County, in northwestern Indiana (Pinger et al. 1996). As of July 1999, Borrelia burgdorferi-infected populations of I. scapularis have been found in four counties in northern Indiana, Newton, Jasper, Pulaski and Porter, and it is probable that populations exist in several of the adjacent counties too.

The first two cases of LD in Indiana were reported in 1983 (Pinger et al. 1989), but investigations of these two cases led neither to additional cases nor to the discovery of tick vectors. The third Indiana case, reported in 1985, led to the eventual discovery of the established population of I. scapularis in Jasper County described above (Pinger et al. 1996). During the period 1983-1999, 209 cases of LD have been reported from 59 of Indiana’s 92 counties (Indiana State Department of Health, unpublished records). In almost half of these counties, 26, just a single confirmed case has been reported. Figure 11 shows the distribution of the 13 probable and confirmed cases of Lyme disease for 1999. These data are provisional and additional cases are still under investigation.

Human monocytic ehrlichiosis (HME). In 1986, the known distribution of A. americanum in Indiana was limited to 12 counties in the southern part of the state with an occasional record from a northern county (Demaree 1986). There are now records of A. americanum from more than 50 counties, and the populations of this species in some southern counties are extremely high.

In 1994, HME was reported in Indiana for the first time and cases of HME have been confirmed in Indiana each year since (Table 3). As of December 31, 1999, 24 confirmed or probable cases of human HME had been reported (Table 3). The distribution of these cases, with several exceptions, closely follows the distribution of the A. americanum tick in Indiana (Figure 12).

We recently reported relatively high minimal infection rates with E. chaffeensis of pools of A. americanum ticks collected in 1995 in southern Indiana (Burket et al 1998). The average minimal infection rate observed at that time (4.9%) was somewhat higher than reported for Missouri (1.18%), North Carolina (1.15%), and Kentucky (3.57) (Anderson et al. 1993). To monitor the percentage and stability of E. chaffeensis-infected ticks in southern Indiana over time, pools of A. americanum ticks were screened for infection in southern Indiana again in 1997 (Steiner et al. 1999). The average minimum infection rate for all sites for 1997 was 1.6% lower than that of 4.9% previously observed for 1995.

To correlate the presence of infected ticks with the presence of exposed deer, which serve as a reservoir, dried blood samples collected from hunter-killed deer at 2 locations in southern Indiana were tested for E. chaffeensis-reactive antibodies using an indirect immunofluorescent assay. Antibodies were detected in 45 and 47% of 98 samples examined from the 2 stations. These data provide support to our previous report of a population of E. chaffeensis - infected A. americanum in southern Indiana and the high proportion of deer previously exposed to E. chaffeensis suggests a stable maintenance of E. chaffeensis in this tick-vertebrate zoonotic system (Steiner et al. 1999).

Each year we pay particular attention to the expanding distribution of I. scapularis, the tick that transmits Lyme disease. This tick carries the official common name "blacklegged tick," but it is sometimes called the deer tick or the Lyme disease tick. This year before we carried out the annual survey of hunter harvested deer, we had already received more than 300 specimens from 15 counties. We continue to receive large numbers of ticks from Dave Spitznagle at Willow Slough FWA in Newton County, and we made a special effort to collect ticks in Porter County. These activities are reflected in the distribution map below. The very large numbers of ticks from these counties does not obscure the fact that the blacklegged tick is spreading eastward and southward from these northwest counties (Figure 13).

Hunter-killed deer were examined for ticks by more than 50 volunteers at 26 deer checking stations in 21 counties. The results of this survey are available in a the report, Survey of Indiana Deer for Ixodes scapularis Ticks: 1999 Final Report. In summary, an additional 214 I. scapularis ticks not included on the map in Figure 13 were recovered from 75 of 1053 deer (7.1%) examined in 1999. This is the highest proportion of positive deer since 1994. Unlike the deer surveys in previous years, no I. scapularis ticks were collected on deer from Newton County in 1999. However, ticks were collected from deer killed in 16 Indiana counties including three new counties (Hamilton, Knox and Kosciusko) bringing the number of counties in which infested deer have been found since 1990 to 29. I. scapularis ticks were also found on humans from Elkhart and Sullivan Counties in 1999 bringing the total number new county records in 1999 to five, and the number of Indiana counties with at least one I. scapularis to 47 (Figure 14).

The number of ticks received in 1999 was the most ticks received since 1991. Six species were identified. Dermacentor variabilis made up 44% of the total. Ixodes scapularis made up 38%, and A. americanum made up 18% of the total. The seasonal distributions of the species of primary interest in this report were similar to those of previous years. Six D. variabilis ticks were positive for SFG rickettsiae. None of the I. scapularis were positive for B. burgdorferi. Ixodes scapularis ticks were discovered in five new counties this year bringing the total number of counties from which at least one I. scapularis tick has been collected to 47.

Differences remain between the Indiana counties reporting human LD cases and those with known, significant vector populations, a result perhaps of the rural nature of Newton, Jasper and Pulaski Counties. This situation may be changing. With the discovery of Borrelia burgdorferi-infected ticks in Porter County this year, greater human exposure to the Lyme disease agent, can be anticipated.

The Indiana State Department of Health and Ball State University sponsored this program. I thank Dr. Michael J. Sinsko for his support and encouragement and Fresia Steiner for her excellent laboratory work. Also, I thank my students Scott Miller and Julie Kratzman for their assistance in preparing this report. I also thank Cheryl Thomas of the Indiana State Department of Health who helped me reformat the final report and Brian Means, University Computing Services who helped me with the tick database.

I also thank Dr. James Pyle and Pam Rolfs 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 Don Van Meter, Associate Dean of the College of Sciences and Humanities for their support of this project.

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2. Burket, C.T., C. N. Vann, R. R. Pinger, C. L. Chatot, and F. E. Steiner. 1998. Minimum infection rate of Amblyomma americanum (Acari: Ixodidae) by Ehrlichia chaffeensis (Rickettsiales: Ehrlichieae) in southern Indiana. J. Med.Entomol. 35: 653-659.
3. Demaree, H.A. 1986. Tick of Indiana. Pittman-Robertson Bulletin No 16. Indiana Department of Natural Resources Indianapolis IN
4. Johnson, R. C., G. P. Schmid, F. W. Hyde, A. G. Steigerwalt, et al. 1984. Borrelia burgdorferi sp. Nov: Etiological agent of Lyme disease. Int. J. Syst. Bacteriol 34(4): 496-497.
5. Pinger, R. R. and T. Glancy. 1989. Ixodes dammini (Acari: Ixodidae) in Indiana. J. Med. Entomol. 26(2): 130-131.
6. Pinger, R. R., J. Holycross, J. Ryder, and M. Mummert. 1991. Collections of adult Ixodes dammini in Indiana, 1987-1990, and the isolation of Borrelia burgdorferi. J. Med. Entomol. 28(5): 745-749.
7. Pinger, R. R., L. Timmons, and K. Kerris. 1996. Spread of Ixodes scapularis (Acari: Ixodidae) in Indiana: collections of adults in 1991-1994 and description of a Borrelia burgdorferi-infected population. J. Med. Entomol. 33(5):852-855.
8. Pinger, R. R. 1999. Human cases of tick-borne diseases in Indiana, 1970-Indiana Epidemiology Newsletter. 7: 1-4
9. Steiner, F. E., R. R. Pinger, and C. N. Vann. 1999. Infection rates of Amblyomma americanum (Acari: Ixodidae) by Ehrlichia chaffeensis (Rickettsiales: Ehrlichieae) and prevalence of E. chaffeensis - reactive antibodies in white-tailed deer in southern Indiana. J. Med. Entomol. 36: 715- 719.

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