Figure

Figure. Location of study areas within the metropolitan area of Chicago, Illinois, USA, showing treatment and control sites. Insert indicates location of metropolitan Chicago counties where baits were placed.

We conducted this study in Cook and McHenry Counties, Illinois, within the Chicago metropolitan area, a landscape characterized as 45% developed, 12% forested and open, 31% agricultural, 10% vacant or wetland, and 2% water (11) (Figure). Our experiment was conducted throughout 6 study sites associated with 6 forest preserves, 3 each in Cook and McHenry Counties. In September and October 2012, we sampled sixty-three 200-m² quadrats across the 6 study sites. We sampled 8–16 quadrats per study site; the number of quadrats per site were related to the amount of forested habitat within each site (12). All fecal deposits were collected individually for analysis from each latrine within sampling quadrats (13). In contrast to previous studies (5,6), latrine substrates were not sterilized with a propane torch, nor were all latrines located and removed from the treatment sites. Similar to previous studies (5,6), we distributed anthelmintic baits monthly at 1.5 baits/hectare at each of the 3 randomly selected treatment sites for the duration (12 months) of the study. Baits were similar to oral rabies vaccine baits and consisted of a hollow fishmeal polymer food attractant (15 g, 33 mm × 32 mm × 21 mm) in which we placed 180 mg (base) of pyrantel pamoate mixed with marshmallow creme, which was sealed within the hollow chamber with paraffin wax. We distributed baits by hand along transects through forested portions of each site to achieve a relatively even distribution of 1.5/hectare. After 1 year of monthly bait distribution, we repeated latrine sampling in September and October 2013, using an equal sampling effort (sixty-three 200-m² quadrats) during surveys before and after treatment. All fecal samples were stored at –20°C until they were examined for B. procyonis eggs. We used centrifugal fecal flotation in Sheather sugar solution and microscopic examination to evaluate all samples for eggs (3). Each fecal sample was determined to be positive or negative, and prevalence (proportion positive) was determined for each year, site, and treatment type. We evaluated differences in prevalence by year, site, and treatment type using χ² analysis with a Fisher exact test. The Wheaton College Institutional Animal Care and Use committee approved this study.

We sampled 63 latrines (2.5 × 10⁻⁵/m²) in 2012, and 59 latrines (2.0 × 10⁻⁵/m²) in 2013. Latrine density did not differ between sampling years (F = 0.124, df = 1, p = 0.725). Pretreatment (2012) sampling of latrines resulted in 209 fecal samples, and a prevalence of 13% ± 4.56% across sites. The prevalence of B. procyonis roundworms did not differ between treatment (14% ± 6.91%) and control (12% ± 6.02%) sites before placement of anthelmintic baits (χ² = 0.368, d.f. = 1, p = 0.544) (Table). Posttreatment sampling of latrines resulted in 124 fecal samples, and a prevalence of 11% ± 5.28% across sites. Prevalence across sites did not differ between years (χ² = 0.44, d.f. = 1, p = 0.602) (Table); however, prevalence differed significantly between treatment (3% ± 3.94%) and control (21% ±1 1.07%) sites after treatment (χ² = 11.28, d.f. = 1, p<0.001) (Table).

Previous strategies to decrease prevalence of B. procyonis roundworms required removing all latrines and heat sterilizing latrine substrates (5,6). Wildlife managers in urban or suburban settings often do not have the resources to implement such a labor-intensive strategy. We found that a modified strategy that eliminates latrine removal and sterilization but retains the monthly distribution of baits effectively reduced environmental contamination with B. procyonis eggs.

Implementation of this anthelmintic baiting strategy in suburban green spaces might significantly reduce risk for exposure by humans who use green spaces for recreation or live in close proximity to forested areas (9). However, both material and distribution costs can be substantial when such management action is implemented at landscapes scales. This study shows that the monthly distribution of baits and subsequent consumption by raccoons would keep reinfections from reaching patency (32–38 days) (3). For initial disease control, it is recommended that intervals between consecutive bait distributions not exceed the prepatency period (14). Once prevalence is reduced, interbaiting intervals can be extended while reduced prevalence is maintained (14). Although we implemented labor-intensive hand baiting, implementation of bait stations (10) could maintain management efficacy while reducing labor required for bait distribution. Bait stations have been used successfully for oral rabies vaccination in raccoons (10) and may enable more targeted bait distribution in areas of high raccoon density. Our study demonstrated that anthelmintic baiting successfully reduced environmental contamination with B. procyonis eggs; prevalence among treatment sites decreased nearly 80% with 1 year of treatment; however, further study is needed to identify optimal long-term bait distribution frequencies and bait distribution strategies to make anthelmintic baiting a viable and sustainable management solution for B. procyonis control.